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weed seed germination temperature table

Abstract

Effects on seed germination characteristics of 17 tree species were investigated under elevated temperature and CO2. Seeds of 5 needle-leaf and 12 broad-leaf species were germinated under four conditions: 24°C + 400 μmol CO2 mol air –1 , 24°C + 750 μmol CO2 mol air –1 , 27°C + 400 μmol CO2 mol air –1 , and 27°C + 750 μmol CO2 mol air –1 . The elevated temperature and CO2 affected germination percent (GP) of 7 tree species seeds.GPs of Pinus densiflora, P. thunbergii, Betula ermanii, and Maackia amurensisseeds were affected by the elevated temperature, while only that of P.jezoensis seed was influenced by the elevated CO2. GPs of Malus baccata and Zelkova serrataseeds were influenced by both the elevated temperature and CO2. In addition, the elevated temperature and CO2also affected mean germination time (MGT) of 12 tree species seeds. Particularly, MGTs of P. thunbergii and Rhododendron tschonoskii seeds were influenced by both factors. In conclusion, elevated temperature and CO2 affected seed germination characteristics, which were reflected by significant differences among tree species. Specifically, these two factors exerted stronger influence on germination pattern such as MGT rather than seed germination percent.

1 Introduction

In Korea, the ambient air CO2 concentration is substantially higher than the global average. The average CO2 concentration for 2016 was recorded as 409.9 ppm, which was an increase of 39.2 ppm (10.6%) relative to the annual average of 370.7 ppm for 1999, and 6.6 ppm higher than the global average of 403.3 ppm for the same year as documented by World Meteorological Organization (WMO) [1]. The mean yearly temperature for South Korea in 2016 was 13.6°C, which was 0.6°C higher than the recent 10 years (2007-2016) and 1.1°C higher than the current climatological normal (1981-2010) [2]. Baseline scenarios, those without additional mitigation (RCP 8.5), result in an increase in the average temperature of the Korean Peninsula to 6.0 degrees at the end of the 21st century [3].

Climatic change, such as warming and alteration of precipitation regimes, is causing shifts in species distributions [3, 4] and phenologies [5]. These changes can also alter forest composition; for example, warming could increase the growth rate of established individuals or select for warm-adapted species. Population demographics of woody plants established within intact successional plant communities are likely to be constrained by factors that alter seed germination and seedling establishment, and ultimately, recruitment of individuals into the population [6,7,8].

Plant seed germination is a crucial stage in the life cycle of plants, and the successful establishment of plants largely depends on successful germination [9]. Generally, seed germination tends to be highly unpredictable over space and time.

However, climate has a large influence on plant recruitment [10,11,12]. For example, with shortening winters [13], seeds may remain partially dormant in spring and need an extended time to germinate [14]. The alteration of temperature and water supply due to global climate change could preclude, delay, or enhance regeneration from seeds [15].

Despite the considerable number of studies on the effects of climate change on plants [16], there have been few attempts to investigate its effect on plant regeneration [17]. Several environmental factors such as temperature, salinity, light, and soil moisture simultaneously influence seed germination [9, 18,19,20,21]. Among several factors, temperature has been considered as the most important. The variation in the optimal temperature for seed germination depends on the considered species, and for the majority of species, seed germination occurs over a wide range of temperatures [22]. This variation in the optimal temperature and the germination percent between species constitutes some adaptive strategies to harsh environmental conditions. It has been shown that temperatures above the thermal optimum often provoke an inhibition of germination and irreversible damage [9, 23].

In addition, plant regeneration from seed is largely governed by germinability and speed of germination. These components have received considerably less attention in CO2 research relative to studies of vegetative or reproductive output responses. Moreover, the limited literature has not been rigorously examined for generalizable patterns of responses and/or potential mechanisms. Marty and BassiriRad [24] presented a metaanalysis summarizing the results of studies that have addressed the parental and direct effects of enriched CO2 on seed germination success and germination percent. There is little empirical evidence that enriched CO2 can have a direct effect on a germinating seed, but similar to parental responses, this direct effect on germination is quite inconsistent [25,26,27,28,29].

A study on historical climate change period showed that woody plants migrate along with climatic zones, but its moving velocity is estimated to be 4–200 km per 100 years. Therefore, except for tree species with a high migration velocity, they will not be able to catch up with the migration of climatic zones and becomes at high risk of extinction due to climate change [30].

In Korea, summer is getting longer, while winter is getting shorter. This phenomenon unquestionably stems from climate change driven by global warming, and it affects seed germination and regeneration of woody plants. When seeds of woody plants germinate without enough dormancy time, they do not regenerate and finally die under unsuitable environmental conditions after germination.

Therefore, it is important to evaluate the effects of temperature and CO2 on vegetation, ecosystems, and certain tree species in order to secure a scientific basis for establishing actions to address adaptation and mitigation of climate change [31,32].

This is especially true considering that there are few studies in relation to seed germination of native tree species under the elevated temperature and CO2 concentration in Korea. Therefore, we evaluated the effects on seed germination characteristics of tree species under different temperatures and CO2 concentrations.

2 Materials and methods

2.1 Plant materials

Mature seeds of 17 forest tree species (5 needle-leaf and 12 broad-leaf tree species), which are major tree species in Korea, were collected from natural or artificial forests on October 2015 (Table 1) and stored in a refrigerator at -18°C before the experiments. The viability of seeds evaluated by tetrazolium (TZ) assay was as in Table 2. For breaking dormancy, the seeds were stratified at 4°C for 60 days or soaked in hot water (100°C) for 60 s followed by cold tap water for 1 day before imposing the temperature and CO2 treatments (Table 2).

Table 1

Seed collection sites and annual mean (minimum, maximum) temperature of 17 tree species

Scientific name Abbreviation Seed collection sites Annual mean temperature (°C) Remarks
1981-2010 2015
Chamaecyparis pisifera (Siebold & Zucc.) Endl. Cpi Yeosu 14.0 (11.3, 18.0) 15.3 (12.5, 18.6) Introduced
Larix kaempferi (Lamb.) Carriere Lka Chungju 11.2 (5.9, 17.7) 12.9 (7.5, 19.0) Introduced
Picea jezoensis (Siebold & Zucc.)Carriere Pje Mt. Jiri Not collected 8.5 (0.7, 14.0) Native
Pinus densiflora Siebold & Zucc. Pde Suwon 12.0 (7.5, 17.2) 13.6 (9.0, 19.1) Native
Pinus thunbergii Parl. Pth Yeosu 14.0 (11.3, 18.0) 15.3 (12.5, 18.6) Native
Albizia kalkora Prain Aka Mokpo 13.9 (10.3-18.6) 14.8 (11.5, 18.8) Native
Betula ermanii Cham. Ber Mt. Jiri Not collected 8.5 (0.7, 14.0) Native
Corylopsis gotoana var. coreana (Uyeki) T.Yamaz. Cgoc Suwon 12.0 (7.5, 17.2) 13.6 (9.0, 19.1) Native
Fraxinus rhynchophylla Hance Frh Suwon 12.0 (7.5, 17.2) 13.6 (9.0, 19.1) Native
Maackia amurensis Rupr. Mam Chungju 11.2 (5.9, 17.7) 12.9 (7.5, 19.0) Native
Malus baccata (L.) Borkh. Mba Suwon 12.0 (7.5, 17.2) 13.6 (9.0, 19.1) Native
Prunus padus L. Ppa Chungju 11.2 (5.9, 17.7) 12.9 (7.5, 19.0) Native
Rhododendron mucronulatum Turcz. Rmu Suwon 12.0 (7.5, 17.2) 13.6 (9.0, 19.1) Native
Rhododendron mucronulatum var. ciliatum Nakai Rmuc Mt. Jiri Not collected 8.5 (0.7, 14.0) Native
Rhododendron schlippenbachii Maxim. Rsc Suwon 12.0 (7.5, 17.2) 13.6 (9.0, 19.1) Native
Rhododendron tschonoskii Maxim. Rts Mt. Jiri Not collected 8.5 (0.7, 14.0) Native
Zelkova serrata (Thunb.) Makino Zse Imsil 11.2 (5.5, 18.0) 12.5 (7.0, 19.1) Native

Table 2

Initial viability, dormancy type, pretreatment method and substrates of 17 tree species seeds

Scientific name Viability (%) Dormancy Pretreatment Substrate References
Chamaecyparis pisifera (Siebold & Zucc.) Endl. 20 No NT petri dish [52]
Larix kaempferi (Lamb.) Carriere 86 Shallow CS petri dish [52]
Picea jezoensis (Siebold & Zucc.) Carriere 55 Shallow CS petri dish [52]
Pinus densiflora Siebold & Zucc. 70 No NT petri dish [52]
Pinus thunbergii Parl. 100 No NT petri dish [52]
Albizia kalkora Prain 30 Hard seedcoat SWC soil [63]
Betula ermanii Cham. 49 Shallow CS petri dish [52]
Corylopsis gotoana var. coreana (Uyeki) T.Yamaz. 66 Shallow CS soil [64]
Fraxinus rhynchophylla Hance 57 Embryo/Hard seedcoat CS soil [52]
Maackia amurensis Rupr. 25 No NT soil [65]
Malus baccata (L.) Borkh. 69 Embryo CS soil [52]
Prunus padus L. 46 Embryo/Hard seedcoat CS soil [52]
Rhododendron mucronulatum Turcz. 61 No NT petri dish [52]
Rhododendron mucronulatum var. ciliatum Nakai 81 No NT petri dish [52]
Rhododendron schlippenbachii Maxim. 75 No NT petri dish [52]
Rhododendron tschonoskii Maxim. 65 No NT petri dish [52]
Zelkova serrata (Thunb.) Makino 50 Embryo CS soil [66]

NT: non-pretreatment, CS: cold stratification at 4°C for 60 days, SWC: soaking in hot water (100°C) for 60 s and then cold tap water for 1 day, Soil = peat moss : perlite = 1 : 1

2.2 Experimental design

The seed trial was carried out in four walk-in chambers (3 × 3 × 1.8 m) that allowed controllable conditions corresponding to each treatment at the Department of Forest Genetic Resources in the National Institute of Forest Science (NIFoS), Suwon City, Gyeonggido, Korea.

The temperature and CO2 concentration in each chamber varied depending on the treatment: T1 as a control (24°C, ambient air CO2), T2 (27°C, ambient air CO2), T3 (24°C, enriched air CO2), and T4 (27°C, enriched air CO2). The temperature and CO2 concentration employed in the experiment were based on the annual mean temperature (24°C) during the growing season of May to September and annual mean CO2 level (400 μmol CO2 mol air –1 ) in Korea, and the projected temperature and CO2 level (27°C, 750 μmol CO2 mol air 1 ) at the end of the 21st century (2071–2100) according to the IPCC scenario [33]. The air in the chambers was circulated through charcoal filters and CO2 was mixed into the air stream. During the whole experimental period, the relative humidity was maintained at 68 ± 1% and illumination at a photon flux density of 400 μmol m –2 s –1 during a 16-h photoperiod.

2.3 Seed germination test

After pretreatments and stratifications, the seeds of the different treatments were left to germinate in the light/ dark (16 h/8 h a day) in a sand pot (1 cm depth from the soil surface) or in a 90 mm Petri dish with five replications. Each containing 50 seeds was evaluated for germination. The sand pots and Petri dishes were constantly rearranged to avoid positional bias once a week and the four chambers were switched once a month to reduce chamber effects on seed germination.

Seeds in the Petri dish were considered to have germinated once the radicle had protruded by 1 mm, and seeds in the soil pot were considered to have germinated when new stem tips were observed on the soil surface every day for 60 days after sowing.

Germination percent (GP) was determined using the following equation: GP = SG/TS × 100, where GP = percent germination, SG = seeds germinated, and TS = total seeds planted. Mean germination time (MGT) was calculated using the following formula: MGT = Σ(n × d)/N, where n = number of seeds germinated on each day, d = number of days from the beginning of test, and N = total number of seeds germinated at the termination of the experiment.

2.4 Statistical analysis

All data were statistically analyzed using analysis of variance of a completely randomized design. Means were compared using the Duncan multiple range test (DMRT) at the 5% level. Statistical analyses were conducted using SAS System for Windows, Version 8.01 (SAS Institute, USA).

3 Results

3.1 Germination Percent (GP)

The higher temperature and enriched CO2 had a positive or negative influence on GP of 17 tree seeds (Table 3, Figure 1). GP of two needle-leaf seeds (P. densiflora and P. thunbergii) and two broad-leaf seeds (B. ermanii and M. amurensis)were significantly affected by the higher temperature, and only the P. jezoensis seed was significantly changed by the enriched CO2 (p < 0.05). The changes of GP in response to the elevated temperature and CO2 were observed in two broad-leaf seeds (M. baccata and Z. serrata) of the 17 tree species.

Table 3

Effects of the elevated temperature and CO2 concentration on germination percent of seventeen tree species seeds

Scientific name F value
Temperature co2 Temperature × CO2
Chamaecyparis pisifera (Siebol & Zucc.) Endl. 0.15n.s. 2.02n.s. 0.02n.s.
Larix kaempferi (Lamb.) Carriere 0.21n.s. 1.24n.s. 0.52n.s.
Picea jezoensis (Siebold & Zucc.) Carriere 3.70n.s. 5.78 [*] 4.08n.s.
Pinus densiflora Siebold & Zucc. 5.20 [*] 4.11n.s. 0.58n.s.
Pinus thunbergii Parl. 26.53 [***] 0.89n.s. 2.32n.s.
Albizia kalkora Prain 0.20n.s. 3.59n.s. 1.83n.s.
Betula ermanii Cham. 7.67 [*] 0.28n.s. 2.94n.s.
Corylopsis gotoana var. coreana (Uyeki) T. Yamaz. 1.62n.s. 2.63n.s. 1.34n.s.
Fraxinus rhynchophylla Hance 4.63n.s 1.06n.s. 0.71n.s.
Maackia amurensis Rupr. 5.24 [*] 0.03n.s. 1.52n.s.
Malus baccata (L.) Borkh. 13.11 [**] 12.46 [**] 1.25n.s.
Prunus padus L. 2.05n.s. 2.05n.s. 4.82 [*]
Rhododendron mucronulatum Turcz. 2.23n.s. 0.10n.s. 0.92n.s.
Rhododendron mucronulatum var. ciliatum Nakai 0.35n.s. 0.04n.s. 0.04n.s.
Rhododendron schlippenbachii Maxim. 0.17n.s. 0.01n.s. 0.52n.s.
Rhododendron tschonoskii Maxim. 0.04n.s. 2.61n.s. 0.83n.s.
Zelkova serrata (Thunb.) Makino 47.06 [***] 11.76 [**] 8.30 [*]

Figure 1

Tree species responses on seed germination percent and mean germination time under the elevated temperature and CO2concentration

Effects of the elevated temperature and CO2 are described in Figure 2. Germination of Chamaecyparis pisifera and Larix kaempferi seeds was not affected at all by increased temperature and CO2 concentration. GP of P. jezoensis seed was the lowest under the higher temperature and the enriched CO2 (27°C + 750 μmol CO2 mol air –1 ) (p < 0.05) conditions. It was not affected by the elevated CO2 concentration under the ambient temperature (24°C) but was significantly lower under enriched CO2 and higher temperature (27°C). GP of P. densiflora seed was the lowest when both temperature and CO2 were elevated (27°C + 750 μmol CO2 mol air 1 ). The enriched CO2 influenced the reduction of GP, which was significantly higher at the elevated temperature (27°C) than at the ambient temperature (24°C) (p < 0.05). At the ambient CO2, the higher temperature (27°C) induced the lower GP, and the effect of temperature change was more clearly evident under the enhanced CO2. GP of P. thunbergii seed was higher at the ambient temperature (24°C) than at the higher temperature (27°C), and there was no effect under the different CO2 concentrations.

Figure 2

Seed germination percent (top) and mean germination time (bottom) of five needle-leaf tree species under the elevated temperature and CO2 concentration. All the values are mean of five replicates ± standard deviation (SD);the same letters are not significantly different at the 5% probability level by the Duncan’s multiple range tests.

Germination pattern of broad-leaf seeds was significantly different from those of needle-leaf seeds (p < 0.05) (Figure 3). GP of B. ermanii seed was higher under the higher temperature (27°C), whereas there was no effect by the enhanced CO2. The temperature effect on seed germination was clearer under the ambient CO2(400 μmol CO2 mol air –1 ) than the enriched CO2 (750 μmol CO2 mol air –1 ). GP of M. baccata seed was influenced by the change of both temperature and CO2 concentration (p < 0.05). Particularly, it was lower under the higher temperature (27°C) and was observed to be more significant under the elevated CO2 (750 μmol CO2 mol air –1 ). The GP of Z. serrata seed was highly sensitive to the changes of both temperature and CO2 concentration, and was significantly lower under the conditions of higher temperature and CO2 concentration.In particular, the effect of CO2 concentration was stronger at the ambient temperature (24°C) than at the elevated temperature (27°C).

Figure 3

Seed germination percent (top) and mean germination time (bottom) of twelve broad-leaf tree species under the elevated temperature and CO2 concentration. All the values are mean of five replicates ± standard deviation (SD); the same letters are not significantly different at the 5% probability level by the Duncan’s multiple range tests.

3.2 Mean Germination Time (MGT)

MGTs of three needle-leaf tree seeds (C. pisifera, P. densiflora and P. thunbergii) were significantly influenced by the change of temperature (p < 0.05). In particular, MGT of P. thunbergii seed was affected by the changes of both temperature and CO2 concentration (Table 4, Figure 1).

Table 4

Effects of the elevated temperature and CO2 concentration on mean germination time of seventeen tree species seeds

Scientific name F value
Temperature co2 Temperature x CO2
Chamaecyparis pisifera (Siebold & Zucc.) Endl. 14.80 [**] 0.06n.s. 2.78n.s.
Larix kaempferi (Lamb.) Carriere 4.39n.s. 3.61n.s. 2.59n.s.
Picea jezoensis (Siebold & Zucc.) Carriere 0.09n.s. 0.41n.s. 0.30n.s.
Pinus densiflora Siebold & Zucc. 10.28 [**] 1.53n.s. 1.82n.s.
Pinus thunbergii Parl. 54.90 [***] 19.84 [***] 0.58n.s.
Albizia kalkora Prain 1.71n.s. 0.84n.s. 2.23n.s.
Betula ermanii Cham. 1.67n.s. 1.09n.s. 2.76n.s.
Corylopsis gotoana var. coreana (Uyeki) T. Yamaz. 69.18 [***] 3.46n.s. 4.49n.s.
Fraxinus rhynchophylla Hance 0.00n.s. 5.11 [*] 0.16n.s.
Maackia amurensis Rupr. 18.48 [***] 1.54n.s. 6.27 [*]
Malus baccata (L.) Borkh. 0.54n.s. 8.83 [**] 10.44 [**]
Prunus padus L. 9.21 [*] 1.07n.s. 1.48n.s.
Rhododendron mucronulatum Turcz. 0.63n.s. 4.83 [*] 3.00n.s.
Rhododendron mucronulatum var. ciliatum Nakai 0.40n.s. 5.85 [*] 0.04n.s.
Rhododendron schlippenbachii Maxim. 1.42n.s. 35.55 [***] 8.62 [*]
Rhododendron tschonoskii Maxim. 7.84 [*] 59.27 [***] 9.92 [**]
Zelkova serrata (Thunb.) Makino 0.70n.s. 3.28n.s. 8.642 [**]

MGT of C. pisifera seed was lower under the higher temperature (27°C) regardless of CO2 concentration (Figure 2). In contrast, MGT of L. kaempferi seed was the highest under the higher temperature and enriched CO2 (27°C + 750 μmol CO2 mol air –1 ) conditions, and that of P densiflora seed was higher under the higher temperature (27°C) regardless of CO2 concentration (Figure 2). In addition, MGT of P. thunbergii seed was the lowest under the ambient temperature and CO2 (24°C + 400 μmol CO2 mol air –1 ) and the highest under the higher temperature and enriched CO2 (27°C + 750 μmol CO2 mol air –1 ) conditions

In the case of broad-leaf tree species, MGTs of Corylopsis gotoana var. coreana, Maackia amurensis and Prunus padus seeds were affected by the alteration of temperature, while those of Fraxinus rhynchophylla, Malus baccata, Rhododendron mucronulatum, R. mucronulatum var. ciliatum and R. schlippenbachii seed were influenced by the change of CO2 concentration (Table 4). On the other hand, MGT of R. tschonoskii seed was significantly affected by the change of both temperature and CO2 concentration. Meanwhile, MGTs of M. amurensis, M. baccata, R. schlippenbachii, R. tschonoskii and Z. serrataseeds responded to the interaction between temperature and CO2 concentration (Table 4).

MGT of C. gotoana var. coreana seed was the highest under ambient temperature and enriched CO2 (24°C + 750 μmol CO2 mol air 1 ) and the lowest under the higher temperature (27°C) regardless of CO2 concentration (Figure 3). MGT of M. amurensis seed was more sensitive to temperature change than to CO2 change, and it was the highest under higher temperature and ambient CO2 (27°C + 400 μmol CO2 mol air 1 ). MGT of M. baccata seed was the highest under ambient temperature and enriched CO2 (24°C + 750 μmol CO2 mol air 1 ) and that of P. padus seed was the lowest under the higher temperature and ambient CO2 (27°C + 400 μmol CO2 mol air- 1 ) conditions. MGT of R. mucronulatum seed was the lowest under the higher temperature and ambient CO2 (27°C + 400 μmol CO2 mol air 1 ) conditions, but the highest under higher temperature and enriched CO2 (27°C + 750 μmol CO2 mol air –1 ). MGTs of R. schlippenbachii and R. tschonoskii seeds were also the lowest in the higher temperature and the ambient CO2 (27°C + 400 μmol CO2 mol air –1 ) conditions and the highest under higher temperature and enhanced CO2 (27°C + 750 μmol CO2 mol air –1 ). Lastly, the MGT of Z. serrata seed was the lowest under the higher temperature and enriched CO2 (27°C + 750 μmol CO2 mol air –1 ) conditions.

4 Discussion

Each individual species has a base and ceiling temperature that represents the extremes at which germination can occur. Below and above these extremes no germination can occur [34]. If climate change results in temperatures that exceed the ceiling for a species, then that species will not be able to germinate; thus, affecting its survivability.

In our study, seed germination of 6 species were affected by the higher ambient temperature (Figure 1), and GP of 5 tree seeds, except for B. ermanii, was reduced at the higher temperature. In addition, elevated temperature affected MGTs of 7 species of 17 tree seeds. MGTs of P. densiflora, P. thunbergii, and M. amurensis seed were higher under the higher temperature, but MGTs of C. pisifera, C. gotoana var. coreana and P. padus seed were lower under the higher temperature.

Several researchers have shown that the optimal temperature for germination and seedling growth depends on the species [35, 36]. Generally, temperature plants germinate between 0°C and 35°C whereas tropical plants germinate between 10°C to 45°C. Within the species, optimal temperature varies significantly between the genotypes [37], and high temperature tolerance of seed contributes to the attributes of the species [38].

Our findings also showed a variety of species responses to the increase in temperature, as was the case in previous studies. This means that the optimum temperature range for seed germination in 17 species is different. This is due to the different seed shapes (seed size and weight) and physiological characteristics found in each species.

In our results, three species (P. densiflora, P. thunbergii and M. amurensis) seeds that showed lower GP had higher MGT at the higher temperature (Figure 2), which means delayed seed germination at the higher temperature. In particular, seeds of Pinus species were highly sensitive to higher temperature and lost their germinability due to decay under the higher temperature. In an accelerated aging test of Pinus seeds, high temperature accelerated pine seed aging [39]. This suggests that the failure to germinate was more likely a consequence of seed mortality rather than of delayed or aborted germination. It is generally known that the higher the temperature, exposure to any temperature beyond the optimum range for germination can negatively affect seed germination, as in the above three species [34].

Germination substrate can also affect seed germination. In our study, the seeds of M. baccata and Z. serrata germinated in sand decreased in GP at higher temperatures (Figure 3). Many studies have shown that seeds germinated in the soil have seen a decrease in germination percent at higher temperatures [40]. Several factors under high soil temperature are considered key to germination reduction: maximum temperature attained [41, 42], soil moisture and seed water content [43], seed structure, anatomy and morphology (e.g. size, seed coat) [44], and seed dormancy dynamics [41]. However, the relative importance of any individual factor is difficult to assess, and maximum temperature and heat duration are considered foremost to seed germination reduction [45]. Much of the literature assumes an inverse relationship between temperature and duration [46]. The long term exposure of the seeds at higher temperatures, as shown in our experiments, may be the main cause of the decline in seed germination.

As shown above, high temperature has a detrimental effect on seed germination causing thermos-inhibition [47], and temperature causing thermo-dormant changes varies with the genotype [48]. In general, high temperatures reinforce dormancy or may even induce it [49]. A drastic change in temperature will also have a significant effect on germination due to the temperature dependence of hormones and enzymes. If the temperature window is breached, then these enzymes may become inactive [50].

However, unlike the above results, high temperatures sometimes break internal dormancy and stimulate germination [51]. In our study, B. ermanii seeds have increased their GP at high temperature (Figure 3). This is also due to the different temperature ranges of optimum germination for Betula species. Birch seeds such as B. ermanii require relatively high temperatures to germinate. The optimal germination temperature range for birch seeds is 30°C for 8 hours and 20°C for 16 hours [52]. Further, several reasons have been given for the enhancement of seed germination by high temperature. Among these are fracturing of hard seed coats, stimulation of seed embryos, and desiccation of seed coats [53].

High temperatures also increase the speed of germination [34]. This is because high temperatures can speed up the chemical reaction in seed germination [54]. In our results, the lower MGT of C. gotoana var. coreana and P. padus seeds with impermeable hard seed coat were more pronounced at the elevated temperature (Figure 3). However, germination speed can differ according to species, soil structures, sowing methods and especially temperature and soil moisture rations [54].

CO2 has been shown to stimulate the germination of various seeds at relatively high concentration [55]. Doubling the CO2 concentration resulted in an increase in the speed and final percent of germination, for Medicago sativa, Amaranthus hybridus and Chenopodium album [25].

Unlike the above results, in our study, an increase in CO2 concentrations did not contribute positively to seed germination. CO2 enrichment affected seed GPs of only three species (M. baccata, Z. serrata, and P. jezoensis) out of 17 tree species (Figure 1). Seed germination of the three species was significantly lower under CO2 enrichment (Figure 2). As such, the effects of seed germination on CO2 changes appear to vary from species to species. Corbineau and Côme [56] were suggested that CO2 does not always have a beneficial effect on seed germination. Several reports mention that at high concentration it inhibits the germination of some seeds. In addition, Omer and Horyath [57] suggested that increased CO2 concentration does not significantly affect the seed germination of many plants, but could cause variations in seed germination patterns as a result of our study.

CO2 enhancement significantly influenced the seed MGTs of 7 tree species, and seeds of 6 tree species, except F. rhynchophylla, showed significantly higher MGT under CO2 enhancement (Figure 3). Similar to the results of our study, previous studies have shown that elevated CO2 concentration can have different influences on seed germination and emergence among different species [25]. In particular, our studies show that F. rhynchophylla seed has a positive effect of a reduction in the MGT from high CO2 unlike other species, but it is not easy to find the cause. However, these species were germinated in the soil unlike other species, and they had different types of dormancy.

In addition, the effect of CO2 concentration on seed germination may even differ among genotypes of the same species, and there is a strong interaction between genotype and treatment. This means that genetic variation for a selective response to changes in CO2 concentration may be present in natural populations [26].

Although the germination response to CO2 has been suggested to be generally positive because of an enhancement in ethylene production due to CO2 [58], many studies have shown contradictory results, similar to our study results [59]. Summing up, the effect of CO2 enrichment on seed germination is very different among different species, and their effects may be positive [60], neutral [61], or negative [26], with a strong dependence on the species studied [62]. No significant interaction was observed between CO2 and temperature on the germination response [25], and this was also re-confirmed in our study.

In conclusion, increased temperature and CO2 had a direct effect on seed germination characteristics, but the direct effect of the increase in CO2 on seed germination was relatively minor. Also, two factors exerted stronger influences on germination pattern (such as MGT) rather than seed GP of woody plants. On the other hand, the germination effects of seeds from changes in temperature and CO2 concentration varied greatly depending on the species. Various factors appear to be involved in the interspecific differences, including seed morphological structure, dormancy type, germination substrate, and optimum germination temperatures. These results indicate that if the increase in temperature has negative effects total germination and germination speed, persistence of individual species will be altered and the distribution of species could change. Similarly, if increasing temperatures have a differential positive effect on germination of some species, then these species will promote their fitness and also change their distribution. This has incredible ecological and economic effects for the local ecosystems and surrounding areas. However, more accurate and more data is needed to predict the species distribution changes due to temperature and CO2 changes. In other words, additional research should be continued in order to more accurately interpret the effects of seed germination on species, considering various factors including natural conditions.

Acknowledgements

This study was supported by the Dong-A University research fund.

Conflict of interest: Authors state no conflict of interest

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© 2018 Du Hyun Kim, Sim Hee Han

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Cranberry Germination and Emergence Response to Environmental Factors and Seeding Depth

Cranberry (Vaccinium macrocarpon Ait.) cultivars are clonally propagated. Germination of cranberry seeds produces off-type varieties that are generally characterized by lower fruit productivity and higher vegetative vigor. Over time, the productivity of cranberry beds decreases as off-type frequency increases over time. Improved knowledge of cranberry germination biology would facilitate the use of targeted agronomic practices to reduce the emergence and growth of less productive off-types. The influences of light, temperature regime, pH, and water potential on cranberry seed germination were assessed in a growth chamber, whereas the effect of seeding depth on seedling emergence was evaluated in a greenhouse. Seeds stratified for 6 months at 3 °C were used for these experiments. Cranberry germination was influenced by light quality, with maximum germination reaching 95% after 15 minutes of exposure to red light but decreasing to 89% under far-red light. However, light was not required for inducing germination. Cranberry seeds germinated over a range of alternating diurnal/nocturnal temperatures between 5 and 30 °C, with an average maximum germination of 97% occurring for diurnal temperatures of 20 to 25 °C. The length of emerged seedlings was reduced by an average of 75% for pH 6 to 8 compared with pH 3 to 5. Seedlings that emerged at pH greater than 5 showed increasing chlorotic and necrotic injuries and were not considered viable at pH 7 or 8. Germination at 15 °C was reduced when seeds were subjected to water stress as low as −0.2 MPa, and no germination occurred below −0.4 MPa. Seeds incubated at 25 °C were more tolerant to water stress, with at least 70% maximum germination for osmotic potential (ψS) −0.6 MPa or greater. The average seedling emergence was 91% for seeds left on the soil surface or buried at a maximum depth of 1 cm; however, it was null at a burying depth of 4 cm. These results indicate that germination of cranberry seeds in cultivated beds in the northeastern United States likely occurs during the summer months, when temperatures are optimal and the moisture requirement is supported by irrigation. However, timely application of residual herbicide or sanding (a traditional cranberry agronomic practice) of open areas in cranberry beds could help prevent seed germination and reduce minimizing the onset of off-type varieties.

Abstract

Cranberry (Vaccinium macrocarpon Ait.) cultivars are clonally propagated. Germination of cranberry seeds produces off-type varieties that are generally characterized by lower fruit productivity and higher vegetative vigor. Over time, the productivity of cranberry beds decreases as off-type frequency increases over time. Improved knowledge of cranberry germination biology would facilitate the use of targeted agronomic practices to reduce the emergence and growth of less productive off-types. The influences of light, temperature regime, pH, and water potential on cranberry seed germination were assessed in a growth chamber, whereas the effect of seeding depth on seedling emergence was evaluated in a greenhouse. Seeds stratified for 6 months at 3 °C were used for these experiments. Cranberry germination was influenced by light quality, with maximum germination reaching 95% after 15 minutes of exposure to red light but decreasing to 89% under far-red light. However, light was not required for inducing germination. Cranberry seeds germinated over a range of alternating diurnal/nocturnal temperatures between 5 and 30 °C, with an average maximum germination of 97% occurring for diurnal temperatures of 20 to 25 °C. The length of emerged seedlings was reduced by an average of 75% for pH 6 to 8 compared with pH 3 to 5. Seedlings that emerged at pH greater than 5 showed increasing chlorotic and necrotic injuries and were not considered viable at pH 7 or 8. Germination at 15 °C was reduced when seeds were subjected to water stress as low as −0.2 MPa, and no germination occurred below −0.4 MPa. Seeds incubated at 25 °C were more tolerant to water stress, with at least 70% maximum germination for osmotic potential (ψS) −0.6 MPa or greater. The average seedling emergence was 91% for seeds left on the soil surface or buried at a maximum depth of 1 cm; however, it was null at a burying depth of 4 cm. These results indicate that germination of cranberry seeds in cultivated beds in the northeastern United States likely occurs during the summer months, when temperatures are optimal and the moisture requirement is supported by irrigation. However, timely application of residual herbicide or sanding (a traditional cranberry agronomic practice) of open areas in cranberry beds could help prevent seed germination and reduce minimizing the onset of off-type varieties.

Cranberry (Vaccinium macrocarpon Ait.) is a low-growing, woody, perennial vine native to eastern North America that grows in moist acidic soils with variable organic matter content. In New Jersey, large-fruited cranberry is a common native species in wet, sandy, peaty bogs, and along the edges of streams in the Pine Barrens (Beckwith, 1922). Cranberry distribution ranges from Newfoundland to Minnesota in the west and Delaware in the south, with populations also present at higher elevations in the Appalachian Mountains of North Carolina and Tennessee (Vander Kloet, 1988). Cranberry domestication from selected wild plants and cultivation began in the early 1800s in Massachusetts and New Jersey (Eck, 1990). Cranberry is now commercially cultivated in the United States, Canada, and Chile, which produced 53% (359,110 t), 26% (172,440 t), and 21% (141,338 t) of the global cranberry production, respectively, in 2019 (FAOSTAT, 2019). In 2019, Wisconsin was the highest cranberry-producing state in the United States (202,791 t) followed by Massachusetts (90,839 t), Oregon (23,854 t), New Jersey (20,279 t), and Washington (6433 t) (Cranberry Marketing Committee, 2019).

Cranberry propagates asexually from stolons that spread over the ground and rapidly form a dense mat, and sexually by seed (Eck, 1990). Seeds are produced through outcrossing by native pollinators or European honeybee (Apis mellifera L.), or through self-pollination (Marucci and Filmer, 1964; Sarracino and Vorsa, 1991). Historically, growers cultivated cranberries from wild selections that were clonally maintained and propagated (Eck, 1990). Genetic improvement since the 1950s has been conducted either by crossing wild selections to produce first-generation hybrids or by crossing first-generation hybrids with elite wild selections (Eck, 1990; Fajardo et al., 2013). Hybrid cultivars currently grown by growers are considered to have higher levels of heterozygosity than cultivars selected from wild populations (Bruederle et al., 1996). Maintaining heterozygosity may be advantageous for improving cranberry tolerance to abiotic stresses, therefore contributing to a higher fruit yielding capacity (Davenport and Vorsa, 1999; Ortiz and Vorsa, 1998). Commercial cranberry beds are generally maintained for long periods of time, often surpassing 20 years. This longevity provides opportunities for seeds contained in rotten or unharvested fruit to germinate and become established, thereby increasing the genetic heterogeneity of cranberry plantings over time. Using random amplified polymorphic DNA (RAPD) markers, Novy et al. (1996) observed high genetic heterogeneity and identified 15 genetic profiles in 12 Washington ‘McFarlin’ beds, including four associated with low-producing cranberry beds and not corresponding to the true ‘McFarlin’ profile. Reduced pollen viability, mean seed/berry, and fruit set indicated that these divergent genotypes were less fertile. It was hypothesized that genotypes with reduced fertility would be more vegetatively competitive and preferentially selected when stolons were collected for establishing new cranberry beds, thus contributing to yield reduction in beds contaminated with these genotypes (Novy et al., 1996; Polashock and Vorsa, 2002; Vorsa and Johnson-Cicalese, 2012).

The importance of off-types as an endogenous source of genetic diversity has been emphasized by studies investigating the impact of cranberry fairy ring (Thanatophytum sp.) disease on crop losses and cultivar homogeneity (Oudemans et al., 2008; Polashock and Oudemans, 2006). Higher fruit morphological diversity was noted in areas recovering from fairy ring disease than in healthy areas with ‘Ben Lear’ cranberry beds. This was correlated with greater genotypic diversity within areas affected by fairy ring, with an average of seven haplotypes compared to an average of two haplotypes in healthy areas (Oudemans et al., 2008). Cranberry seedlings recolonizing open areas where vines were killed by fairy ring disease may originate from a soil seed bank. The proportion of off-types with more vigorous vegetative development and reduced yield potential will increase and contribute to long-term decline of the productivity of cranberry beds (Oudemans et al., 2008).

Because cranberry cultivars are traditionally propagated vegatatively to ensure the preservation of genetic characteristics and rapid fruit set (Vorsa and Johnson-Cicalese, 2012), few studies have investigated the effects of biotic and abiotic factors on seed germination. Devlin and Karczmarczyk (1977) assessed the influence of light intensity, abscisic acid (ABA), and gibberellic acid (GA) on cranberry seed dormancy; they demonstrated that cranberry seeds are photoblastic and will germinate if exposed to sufficient light, whereas GA will promote seed germination under dark conditions. Paglietta (1977) indicated that premoistened seeds germinate 2 to 3 d quicker than dry seeds, whereas Demoranville (1974) reported that a temperature of at least 22 °C was required for >90% cranberry seed germination.

We hypothesize that openings in the cranberry canopy may induce changes in the local environmental conditions that may be favorable to the germination of cranberry seeds from the seedbank. A better understanding of cranberry germination in relation to environmental conditions may help provide cranberry growers with practical information about minimizing the onset of off-type varieties in renovated cranberry beds or in open areas that result from damage to the cranberry canopy. Therefore, the objectives of this research were to explore the effects of light, temperature regime, solution pH, water stress, and seeding depth under controlled conditions on cranberry seed germination.

Materials and Methods

Growth chamber and greenhouse studies were conducted at the Rutgers University P.E. Marucci Center for Blueberry and Cranberry Research in Chatsworth, NJ, in 2019 and 2020. Ripe berries were collected from the ground after harvest in a commercial ‘Ben Lear’ bed (Chatsworth, NJ) on 25 and 26 Oct. 2018. Seeds for the different experiments were obtained after gently crushing the berries. Seeds were washed and sieved under tap water flow for 10 min to remove remaining fragments of the endocarp and dried in open air at room temperature (24 °C) for 5 d. Then, seeds were placed in paper bags and stratified at 3 °C for 6 months under complete darkness in a controlled environmental chamber. Cranberry seed viability was 95 ± 3% based on the results of a 1% (weight/volume) tetrazolium chloride test conducted for 150 seeds before performing experiments (Association of Official Seed Analysts, 2010). Seed surface disinfection was conducted in a laminar flow hood by rinsing seeds in a 70% (v/v) ethanol solution for 1 min, dipping them in a mixed solution of sodium hypochlorite (1.06%) and a nonionic surfactant (Tween 20 at 0.1%) for 10 min, and rinsing them three consecutive times with sterilized distilled water. Germination of stratified cranberry seeds in response to light quality, temperature, pH, and water potential was evaluated in 10-cm diameter petri dishes with 25 seeds per replication. Seeds were placed on two sheets of filter paper (Whatman #1) moistened with 8 mL of treatment solution. Then, petri dishes were wrapped with a single layer of parafilm (Bemis Company, Neenah, WI) around the circumference to reduce evaporation. The number of germinated seeds was monitored daily for 21 d, and then every 3 d until there were no newly germinated seeds for 7 d. Cumulative germination for each rating date was calculated as the total number of germinated seeds divided by the total number of seeds in the treatment.

Lighting conditions.

The light requirement and effect of light quality on cranberry seed germination were assessed using a growth chamber fitted with red (R) (650- to 670-nm waveband) and far-red (FR) (720- to 740-nm waveband) light-emitting diode (LED) lamps. Artificial light treatments included 15 min of R light, FR light, R light immediately followed by 15 min of FR light, and FR light immediately followed by 15 min of R light. Light irradiance values to which the seeds were exposed during the treatment were 2 W⋅m −2 and 13 W⋅m −2 for R and FR light, respectively. After artificial light treatments, petri dishes were wrapped in two layers of aluminum foil to prevent further exposure to light and incubated at 25 °C. Other treatments included seeds maintained in full darkness as well as exposure to natural light. Seed exposed to natural light were placed on a bench in a greenhouse maintained at 24 °C.

Temperature regime.

Four temperature regimes were selected to represent typical seasonal variations in New Jersey. Regimes of 5 and 15 °C, 10 and 20 °C, 15 and 25 °C, and 20 and 30 °C corresponded to mean daily low and high temperatures for the months of April, May, June, and July, respectively, in Indian Mills, NJ (Robinson, 2020). Low temperatures were maintained for 8 h under complete darkness, whereas high temperatures were maintained for 16 h under multicolor LED lights set to deliver irradiance of 15 W⋅m −2 .

Solution pH.

Cranberry seed germination was evaluated for pH values ranging from 3 to 8. Buffer solutions were prepared using the procedure described for hairy beggarticks (Bidens pilosa L.) (Reddy and Singh, 1992). A 0.1-M potassium hydrogen phthalate buffer solution was adjusted to pH 3 and 4 with 0.1 N hydrochloric acid (HCl) and to pH 5 with 0.1 N sodium hydroxide (NaOH). A 0.1-M solution of potassium phosphate monobasic was adjusted with 0.1 N NaOH to obtain solution pH values of 6 and 7. A 25-m m solution of sodium tetraborate anhydrous was adjusted with 0.1 N HCl to obtain buffer solution with a pH value of 8. The pH value of the solutions was tested with a pH meter calibrated with standardized buffers before the filter paper (Whatman #1) was moistened with the prepared solutions. Seeds were incubated at 25 °C and subjected to an 8-h dark/16-h light photoperiod with multicolor LEDs set to deliver a photosynthetically active radiation (PAR) flux density of 70 μmol⋅m −2 ⋅s −1 . Seed germination was evaluated daily until no new germination occurred for 7 d. Additionally, measurements of the seedling radicle and shoot length as well as ratings of the shoot coloration and development of rootlets along the radicle were collected from all emerged seedlings at the end of the incubation period. Shoot coloration was rated using the following scale of 0 to 4: 0 = healthy green epicotyl and reddish radicle; 1 = muddy green epicotyl and brown radicle; 2 = yellow–green epicotyl and yellow–brown radicle; 3 = white epicotyl and yellow radicle; and 4 = brown epicotyl and black radicle.

Water potential and temperature.

Solutions of water potentials of −0.1, −0.2, −0.4, −0.6, −0.8, and −1.0 MPa were prepared by dissolving 7.6 to 28.7 g of polyethylene glycol (PEG-8000) in 100 mL of deionized water (Michel, 1983). The PEG concentrations were corrected for incubation temperature. A control treatment with deionized water alone (0.0 MPa) was also included. Seeds were incubated at either 15 or 25 °C and subjected to an 8-h dark/16-h light photoperiod with multicolor LEDs set to provide a PAR flux density of 70 μmol⋅m −2 ⋅s −1 . Seeds not germinated after 50 d were removed, rinsed for 3 min with tap water, and placed for 2 min in deionized water. Then, seeds were placed in petri dishes containing two layers of filter paper (Whatman #1) and moistened with 8 mL of distilled water. Seed germination was assessed daily over a 30-d period.

Seeding depth.

The effect of seeding depth on cranberry seedling emergence was determined on a greenhouse bench and using 0.3-L plastic containers. Depths of 0, 0.5, 1, 2, 3, and 4 cm from the base of the pot ring were marked inside. Then, pots were filled to the mark with a sterilized 1:1 (v/v) mix of sphagnum peatmoss (Sun Gro Horticulture Distribution Inc., Agawam, MA) and pre-sieved Woodmansie sand (coarse-loamy, siliceous, semiactive, mesic Typic Hapludults) obtained from a local gravel pit. The organic matter content (3.9%) and pH (4.4) of the potting mix were adjusted to be representative of typical New Jersey cranberry soils based on a soil analysis conducted over multiple years in local commercial cranberry beds by Ocean Spray (Middleborough, MA). Then, 25 seeds were equidistantly placed on the soil surface at the required depth before being covered with the same soil mix. Two high-pressure sodium 2000 K lamps were equidistantly placed above the bench to provide a 16-h light period with a PAR flux density of 640 μmol⋅m −2 ⋅s −1 followed by an 8-h dark period. Greenhouse temperature was maintained at 24 °C during the duration of the experiments. All pots were initially sub-irrigated to bring soil to field capacity and later surface-irrigated twice per day with a garden spray hose to provide adequate soil moisture for emerging seedlings. Seed germination was evaluated daily until no new germination occurred for 7 d.

Statistical analysis.

In Eq. [1], y is considered the percentage of cumulative germination after x days after planting (DAP), y0 is the intercept on the y axis (≤0), a is the maximum cumulative germination or emergence percentage, b is a mathematical parameter controlling the shape and steepness of the germination or emergence curve, and c represents the time (DAP) required to reach 50% of the final cumulative germination or emergence (t50). As recommended by Soltani et al. (2015), t50 was used instead of the mean germination time (MGT) for the postmodeling analysis of variance (ANOVA).

Gmax, LAG, Rs, and t50 data computed for each experiment were subjected to an ANOVA using SAS software (version 9.4; SAS Institute, Cary, NC) and PROC GLIMMIX. A similar analysis was also conducted using seedling measurement data collected for the solution pH experiment. Before the analysis, the percent values were arcsine-transformed and seedling growth data were subjected to a logarithm transformation to achieve normality assumptions. All data were subsequently back-transformed for presentation purposes. Lighting conditions, temperature regime, water potential, pH, and seeding depth were considered fixed variables, and replications, experimental runs, and their interaction were considered random effects (Grafen and Hails, 2002). The treatment × run interaction was not significant; therefore, data were pooled across experimental runs. Mean comparisons were performed using Tukey’s honestly significant difference test at a 5% level of significance.

Results and Discussion

Lighting conditions.

The light treatment significantly affected cranberry germination, with an average Gmax of 95% under natural light or when seeds were exposed to R light, but it decreased to 89% for seeds exposed to FR light (Table 1). However, Gmax and Rs remained statistically comparable for seeds incubated under continuous darkness or exposed to natural light. Germination occurred faster for seeds exposed to R light (18.9 seeds per day) than for seeds exposed to FR light (15.2 seeds per day). LAG was not significantly affected by light treatments, whereas t50 occurred significantly earlier for seeds exposed to FR light followed by R light (7.7 d) compared with darkness (9.4 d). Overall, these results suggest that FR light may partially inhibit cranberry seed germination, whereas natural light or dark conditions only affect the rapidity of seed germination.

Effect of lighting conditions on the maximum germination (Gmax), daily germination rate (Rs), time of germination onset (LAG), and time required for 50% of viable cranberry seeds to germinate (t50).

In agreement with observations of other species (Benvenuti et al., 2001; Leon and Owen, 2003), the stratification of cranberry seeds in this study for 6 months at 3 °C may have contributed to the loss of dormancy, with 94% germination recorded in darkness. Previous work demonstrated that seeds from freshly harvested cranberries remained dormant under dark conditions at 25 °C, but that 69% germinated 20 d after being treated with 500 ppm GA (Devlin and Karczmarczyk, 1977). Therefore, in the absence of treatments enhancing seed germination, cranberry seeds are photoblastic (i.e., require light to germinate) (Devlin and Karczmarczyk, 1975). R light promotes the germination of photoblastic seeds (Benech-Arnold et al., 2000), and nonstratified seeds of European blueberry (Vaccinium myrtillus L.) incubated at 25 °C have been shown to require at least 18 h of R light irradiation daily for 9 d to reach 90% germination (Giba et al., 1995). Although stratification before the experiment probably broke cranberry seed dormancy, a higher germination rate was still noted for seeds exposed to R light. Conversely, FR light treatment for 15 min caused lower germination when applied alone or after irradiation with R light, indicating that phytochrome is involved in the germination process of cranberry seeds. Similarly, a gradual decrease in European blueberry germination was noted with increasing FR irradiation time, and germination of European blueberry seeds exposed to R light for 3 d decreased by 50% when irradiated with 5 min of FR light, thus supporting the view that phytochrome is responsible for the light-induced germination of European blueberry seeds (Giba et al., 1995). The results of FR light on cranberry seed germination imply that the germination of cranberry seeds could be partially inhibited in cranberry beds characterized by dense vine canopy, as noted for various sedge (Carex spp.) species for which germination was inhibited in wetlands with a dense leaf canopy and a low R:FR ratio (Kettenring, 2006; Schütz, 1997). This supports the hypothesis that areas of cranberry beds where the crop canopy is thin or has disappeared (e.g., caused by fairy ring disease) may provide light conditions that will stimulate the germination of cranberry seeds from the soil seed bank. However, this may also depend on how long cranberry seeds can remain viable until environment conditions become suitable for inducing germination.

Temperature regime.

The Gmax was statistically similar for the 20/10 °C and 25/15 °C day/night temperature regimes, with an average germination rate of 97% (Table 2). The Gmax declined to 63% and 81% with 5/15 °C and 30/20 °C day/night temperature regimes, respectively. Rs was not statistically different for the 20/10 °C and 25/15 °C day/night temperature regimes, with an average of 9.5 germinating seeds per day, but it increased to 24.6 seeds per day with the 30/20 °C regime. LAG was delayed by 10.5 d, 9 d, and 3.5 d for the 15/5 °C, 20/10 °C, and 25/15 °C regimes, respectively, in comparison with the 30/20 °C regime, for which seed germination was initiated 3.3 d after the start of the experiment. Time to 50% germination (t50) was 5.9 d for the 30/20 °C regime, and it significantly increased by 5 d for the 25/15 °C regime and by an average of 13 d for the 15/5 °C and 20/10 °C regimes.

Effects of day/night temperature regime (TR) on maximum germination (Gmax), daily germination rate (Rs), time of germination onset (LAG), and time required for 50% of viable cranberry seeds to germinate (t50).

The reduced Gmax at 15 or 30 °C indicated that the optimal temperature range for cranberry seed germination is 20 to 25 °C, which is in agreement with previous research reporting a temperature of 22 °C to obtain a minimum of 90% cranberry germination (Demoranville, 1974). The lower Gmax at low temperatures suggests that cranberry germination occurs during the spring and summer months of the growing season, but it may slow in July and August, when daily air and soil surface maximum temperatures frequently exceed 30 °C (Robinson, 2020). These results may also suggest that cranberry seed germination is more likely to occur at or near the soil surface, where temperature fluctuates more than it does at deeper depths. Similar optimal seed germination temperatures have been reported for other Vaccinium spp. Baskin at al. (2000) reported 82% and 73% average germination rates for nonstratified seeds of European blueberry and lingonberry (Vaccinium vitis-idaea L.), respectively, with a 25/15 °C alternating temperature regime, whereas the maximum germination was only 12% for both species with a 15/5 °C regime. Nin et al. (2017) obtained 82% and 83% germination of European blueberry seeds at constant temperatures of 22.5 and 25 °C, but only 10% at 15 °C. Ranwala and Naylor (2004) suggested that germination of European blueberry occurs above the threshold of 15 °C but sharply decreases beyond 23 °C. Cranberry may have a similar range of optimal germination temperatures because the data indicate reduced germination when the day temperature exceeds 25 °C. However, the decrease is not sharp, suggesting that cranberry germination will likely occur at higher temperatures. European blueberry and lingonberry grow at higher latitudes or elevations than American cranberry (Tirmenstein, 1990, 1991), and they may have lower tolerance to high temperature. Further evaluations of germination at higher temperature regimes are warranted to provide valuable information regarding the upper temperature germination threshold for cranberry.

Solution pH.

Rapidity of cranberry seed germination was affected by the solution pH, with LAG indicating that the first seeds germinated an average of 2.5 d earlier at pH 3 than at pH 7 or 8, and t50 occurring 4 d later at pH 7 than at pH 3 (Table 3). However, the average Gmax was 92% and unaffected by solution pH, whereas the Rs was 28.5 germinating seeds per day for pH 3 to 5 and declined to 20.8 germinating seeds per day for pH 6 to 8. Based on these results, cranberry germinates faster under acidic conditions, but it can also germinate near neutral or basic pH. The development of new shoots and roots following germination was investigated to assess the viability of the seedlings under different pH conditions. The radicle plus shoot length significantly increased as pH decreased, ranging from 2.5 mm at pH 8 to 16.4 mm at pH 4 (Fig. 1). At pH 6 to 8, the radicle plus shoot length was less than 4 mm, and none of the seedlings produced leaves or rootlets; however, at pH 3 to 5, the leaf and rootlet production rates ranged from 62% to 80% and 78% to 96%, respectively (data not shown). Seedlings grown at pH 3 to 5 had green to dark green epicotyl and reddish radicle and were considered healthy (Fig. 2A–C). Conversely, at pH higher than 6, seedlings were not considered viable, with white to brown epicotyl and brown to black radicle (Fig. 2D–F). These results suggest that cranberry germination may occur over a broad pH range, but that elongation of the seedlings only occurs under acidic conditions, corresponding to the soil pH deemed optimal for adequate growth of this crop (Eck, 1990). Similarly, Stanienė and Stanytė (2007) reported that clonally propagated and hydroponically grown cranberry can tolerate alkaline pH when grown in vitro, but that the plants will die or show very weak growth when transferred to soils with pH higher than 6.45.

Weed seed germination temperature table

Grass seed will germinate at a wide variety of temperatures; the optimum temperatures for germination are in the table below. The temperatures listed are air temperatures which would be almost identical to that in on the surface of the soil barring radiation effects.

Realize though that optimum temperature for seed germination can vary depending on seed age, cultivar, etc. Also, the optimum germination temperature of certain species may not involve a specific temperature but a rhythmic alternation of temperatures. Additionally, the maximum and minimum temperatures for seed germination are poorly defined because of the extreme slowness of germination, especially for the minimums.

Most of our cool season grasses can germinate almost throughout the summer, so there are many other factors control the success of seeding. Poor irrigation, diseases like damping off, and weed pressure are the most common causes of seeding failures.

Optimum Temperatures for Seed Germination

Turfgrass Species Optimum temperatures for seed germination
(degrees F)
Creeping Bentgrass 59–86°
Annual Bluegrass 68–86°
Kentucky Bluegrass 59–86°
Rough Bluegrass 68–86°
Tall Fescue 68–86°
Red Fescue 59–77°
Sheep fescue 59–77°
Chewings Fescue 69–77°
Perennial Ryegrass 68–86°
Intermediate Ryegrass 45° +

Contact your sales rep for more information about our Field of Dreams, Greenskeeper and Legend grass seed mixtures.

Pennmulch Seed Accelerator with Starter Fertilizer

  • A unique pelleted seeding mulch with starter fertilizer (equivalent of 10-20-5)
  • For establishing new turf
  • Water absorbing polymer to retain moisture essential for germination.
  • Tackifier to hold seed in place even on significant slopes.
  • Unlike straw it is 100% weed seed free and breaks down overtime requiring no raking or clean up

Lambert Peat Moss (OMRI Listed)

Lambert Peat Moss is an excellent soil amendment because of its capacity to retain water, aerate the soil and it is completely natural. It is certified by OMRI for organic production. Lambert Peat Moss helps retain moisture, aerate soil, and provide organic matter for gardens and flower beds.

Upcoming Events

NEMF – Northeast Municipal Foresters

Date: March 18, 2021
Time: 10:00am-12:00pm
Virtual Zoom Meeting
Title: GIS Dashboards & Story Maps
Speakers: Steve Lane & Lindsay Darling

Communication within forestry departments and to the greater public is incredibly important for an efficient forestry program. ESRI, the most commonly used GIS software company for public and private users, has created a suite of online tools that can streamline that process. These tools are often compatible with existing software that forestry departments use. We will demo a few of those products, outline some ways that they could be used by foresters, and give some tips on how to create your own online stories and dashboards. This presentation will not be overly technical and is open to all people interested in how trees and GIS can work together to create valuable public outreach tool.