The dynamics of three shrub species in a fire-prone temperate savanna: the interplay between the seed bank, seed rain and fire regime

A model was developed to assess how the seed rain and fire regime affect seed bank dynamics and seedling establishment of three native shrub species (Acanthostyles buniifolius, Baccharis pingraea and Baccharis dracunculifolia) with different regeneration strategies, in temperate South American savanna. Seed bank and seed rain were quantified for each species under different fire regimes, and their relative roles in regeneration were evaluated. All species had short-term persistent seed banks and high annual variability in seed production. A high proportion of seeds deposited in the seed rain produced seedlings after fire; few entered the soil seed bank. Fire killed a high proportion of the seeds in the soil seed bank. Seedlings derived from the seed rain had a higher probability of surviving for 2 years than seedlings emerging from the soil seed bank. In the absence of fire, establishment depended on germination both from the seed rain and the soil seed bank, whereas with annual fire, establishment was primarily dependent on germination of seeds arriving in the annual seed rain, regardless of species’ regeneration strategies. These results help to explain changes in the vegetation of South American temperate savannas as a result of changes in fire regime and grazing management during the last 50 years. By revealing the crucial roles of the soil seed bank and seed rain in regeneration, this study provides vital information for the development of appropriate management practices to control populations of shrub species with different regeneration strategies in South American temperate savannas.     

Effect of temperature and light on seed germination of Erysimum naxense and Erysimum krendlii

Seed germination of two local Greek endemics was studied (Erysimum naxense, Erysimum krendlii). Seed viability was determined by using the tetrazolium method and germination was studied in synchronized cycles of five and four alternating temperatures [10/5 (for E. naxense only) and 15/10, 20/15, 25/20, and 30/25°C for both species, in cycles of 16 h day/8 h night], and in five light regimes (red, blue, green, white, and dark). Germination of E. naxense and E. krendlii seeds was determined daily for six and five weeks, respectively, with the data analyzed as viability adjusted accumulative seed germination at the end of each week. E. naxense’s seed viability was higher (90%) than that of E. krendlii (64%); seed germination (%) of both increased at low alternating temperatures (10/5°C, 15/10°C, 20/15°C). Germination of E. naxense seeds at low temperatures was light-independent, whereas at high temperatures it was increased with red light. Germination of E. krendlii seeds was inconsistently affected by light at the temperatures studied. Percentages of seed germination of both species were higher in experimental conditions similar to the ones of their natural habitats during autumn and/or spring (facilitated with Geographic Information Systems). These conclusions provide guidelines for species-specific propagation protocols and ex situ conservation.     

不同光照处理下青藏高原克隆植物黄帚橐吾(Ligulariavirgaurea)种子大小对其幼苗生长的影响

以高寒草甸克隆植物黄帚橐吾为实验材料,通过遮荫网模拟植被遮荫,研究种子大小与萌发及幼苗生长能力的关系和幼苗对光照条件的反应。结果表明：（1）在自然光照下,黄帚橐吾种子大小对种子萌发的影响显著,大种子的萌发率高于小种子。遮荫生境下,大、小种子萌发率有所降低,但遮荫对小种子萌发的影响比大种子显著。小种子的萌发率下降了近1/8,而大种子的萌发率仅下降了1/11。（2）黄帚橐吾种子大小对幼苗生物量积累影响显著,大种子幼苗总生物量（TB）大于小种子幼苗的。但生物量的分配与播种时间相关,播种后60 d,在自然光照条件下,大种子幼苗对根生物量的分配大于小种子幼苗,而对叶生物量的分配则正好相反。在遮荫环境中,大、小种子幼苗普遍对根的生物量分配增加,大种子幼苗根冠比（R/S）大于小种子幼苗。（3）黄帚橐吾种子大小对幼苗的生长也有明显影响。在自然光照下,小种子幼苗的相对生长速率（RGR）较大于大种子幼苗,但叶面积比率（LAR）、叶面积干质量比（SLA）、叶干质量（LWR）差别不明显。在遮荫条件下,幼苗的LAR、SLA、LWR显著增加,但大、小种子幼苗间差异不显著,幼苗的RGR减小,小种子幼苗的减小趋势大于大种子幼苗。     

Effects of maternal salinity on salt tolerance during germination of Suaeda aegyptiaca,a facultative halophyte in the Arab Gulf desert

Suaeda aegyptiaca is a facultative halophyte found in saline and non‐saline habitats of the Arab Gulf desert, which produces small‐sized undispersible seeds. The interactive effects of maternal salinity and other environmental conditions, such as salinity, light and temperatures, that are prevailing during seed germination have received little attention for a facultative halophyte. This study tested the effects of maternal salinity on salt tolerance during seed germination of S. aegyptiaca under different light and temperature regimes. Seeds collected from both saline and non‐saline habitats of the United Arab Emirates (UAE) were germinated in 0, 50, 100, 200 and 400 mM NaCl, and incubated at 15/25°C, 20/30°C and 25/35°C in both 12‐h light/12‐h dark regimes and continuous darkness. Generally, seeds of the non‐saline habitat were 56% heavier and attained greater germination at the lower temperatures than seeds of the saline habitat. Seeds of the saline habitat germinated better in saline solutions at higher temperatures and in light. Germination was faster for seeds of the saline habitat than for seeds of non‐saline habitats. Germination recovery after transfer to distilled water was significantly greater for seeds from the non‐saline habitat, compared with seeds from saline habitats. Recovery was greater at lower and/or moderate temperatures, compared with at higher temperatures. Germination was significantly faster during recovery, compared with in the saline solutions. The study indicates that the maternal effect of salinity was confounded with the seed‐size effect and it cannot be conclusively confirmed.     

南亚热带森林24种乔木的种子萌发和幼苗生长

以膨胀珍珠岩为基质,在光和暗的条件下,对２４种南亚热带森林乔木的种子萌发和幼苗生长进行了研究。种子的形态和重量与种的演替阶段有关,种子的重量也与不同的种有关。不同种的萌发率差异较大,种子较大的种,萌发率较高。肉质果实的种子,开始萌发的时间较长。光和暗条件对萌发率和萌发速度无明显影响。幼苗高度和种子重量呈正相关,这一相关在光条件下比暗条件下更明显。暗条件明显地引起群落演替早期的树种的茎徒长,限制根的生长,而对演替后期种无显著的影响。幼苗地上部分和根系生物量的分配与种的演替阶段有关,也与不同的科有关。幼苗地上部分和根系生物量的分配也受光暗条件的影响,而不受种子重量的影响。根和叶的生物量分配和种在其群落演替阶段有关。幼苗的生物量与种子重量有显著的正相关。幼苗的相对生长率相差较大,在没有营养供应的生长基质中,以演替中间阶段的种的相对生长率较大。幼苗从种子的物质利用效率与种子重量呈负相关,而与种的演替阶段无明显的相关。     

Seed tolerance to predation: Evidence from the toxic seeds of the buckeye tree (Aesculus californica; Sapindaceae)

Tolerance, the capacity of plants to withstand attack by animals, as opposed to resistance, has been poorly examined in the context of seed predation. We investigated the role that the seed mass of the large-seeded endemic tree Aesculus californica plays as a tolerance trait to rodent attack by comparing, under greenhouse conditions, patterns of germination, and subsequent seedling growth, of seeds with a wide range of natural damage. Germination percentage was reduced by 50% and time to germination by 64% in attacked compared to intact seeds, and germination probability was negatively correlated with damage. Seedlings that emerged from intact seeds were taller and bore more leaves than those from damaged seeds. This species' large seed mass favors tolerance to damage because heavily damaged seeds are able to germinate and produce seedlings. This finding is significant given that seeds of this species are known to contain chemical compounds toxic to vertebrates, a resistance trait. We posit that this combination of tolerance and resistance traits might be a particularly effective antipredation strategy when seeds are exposed to a variety of vertebrate predators.     

Seed size effect on seedling growth under different light conditions in the clonal herb Ligularia virgaurea in Qinghai-Tibet Plateau

We studied the influence of seed size on germination, seedling growth and seedling responses to light in Ligularia virgaurea, a clonal herb native to the Qinghai-Tibet Plateau. (1) Under unshaded conditions, large seeds had significantly (P < 0.001) higher rates of germination than did small seeds. Both large and small seeds showed significantly reduced levels of germination under shaded conditions. The magnitude of this effect was greater for small seeds than for large seed. (2) Seedlings from large seeds had significantly higher rates of biomass accumulation (g · day⁻¹) than did seedlings from small seeds. The total biomass of seedlings from larger seeds is larger than that from smaller ones. And seedlings from large and small seeds also differed in biomass allocation. (3) Seedlings from small seeds have higher relative growth rates (RGR; g · g⁻¹ · day⁻¹) than do seedlings from large seeds under both shaded and unshaded conditions. In contrast, there was no significant difference in leaf area ratio (LAR), specific leaf area (SLA) or leaf weight ratio (LWR) between seedlings from small and large seeds. RGR, LAR, SLA and LWR were all significantly higher in seedlings grown under shaded conditions than under unshaded conditions.     

Effect of post-irradiation ageing on onion seeds

Seeds of onion (Allium cepa) cv. Ailsa Craig were exposed to various doses of gamma radiation (0, 10, 20, 40, 80 and 100 krad) and subjected to accelerated ageing (RH 100%, 42°C) for 12 h. Radiation doses significantly affected the percentage of normal seedlings, abnormality types (%) and seedling growth. Seed viability, conductivities of seed leachates, final germination (%), germination speed and time to reach 50% germination (T ₅₀) were not affected by the seed irradiation. Accelerated ageing after irradiation had significant influence on seed viability, conductivities of seed leachates, final germination (%) and percentage of normal seedlings. Germination speed, T ₅₀ and seedling growth were not affected by the accelerated ageing. However, all the parameters studied were significantly influenced by the interaction of radiation doses and accelerated ageing. Accelerated ageing generally enhanced the damaging effects of irradiation on seeds. Therefore, it was concluded that onion seeds should not be exposed to adverse environmental conditions after irradiation.     

Seeds photoblastism and its relationship with some plant traits in 136 cacti taxa

Seed germination triggered by light exposure (positive photoblastism) has been determined in quantitative studies for numerous plant families and species. For Cactaceae, positive photoblastism is thought to be associated with life form and seed mass, but this association has never been evaluated. To explore hypotheses on associations between seed mass, seed dispersal, seed dormancy, life form, taxa and plant height with Relative Light Germination (RLG) in Cactaceae, we evaluated the effect of light on seed germination of 136 taxa. The taxa studied are native to several countries: México, Chile, Argentina, Brazil, Perú, USA, and Venezuela. Seed traits contrasted with RLG were life form, seed mass, seed dispersal, seed dormancy, adult plant height and taxon. We found some differences between RLG among taxa; Cacteae, Pachycereeae and Trichocereeae had higher RLG than Notocacteae. RLG was lower for seeds from taller than for shorter taxa, and lower for taxa with heavier seeds than for taxa with lighter seeds. Dispersal syndrome groups varied with RLG. RLG did not differ between cylindrical and globose taxa. Trends found here were in agreement with expectations for small-seeded species to have a light requirement to germinate more often than large-seeded species. This is the first time that cactus height is related to photoblastism. It is possible that seeds from tall plants are larger and thus have the capacity to produce taller seedlings than those from small plants, and that seedlings from large seeds with more resources have the ability to emerge from greater soil depths than those from small seeds.     

苦草繁殖生态学研究

通过太湖野外调查、室内培养、种子与块茎萌发及幼苗生长试验,对太湖苦草(Vallisneria natans)种群的繁殖生态特征进行了研究。结果显示:1)苦草分配于有性繁殖部分的生物量较无性的大,分别占总生物量的25.0%±13.8%和10.1%±7.0%。雌花数与座果率平均分别为22.9±13.8朵·株^-1和73.3%±17.9%。雄株可以产生11~33个佛焰苞,每个佛焰苞内平均含有364±38朵雄花,每个雄花产生的花粉为128~184粒。每个果实内种子丰富,多达150~360粒,估算太湖苦草种群立地种子量可达1.68×10⁴~1.01×10⁶个·m^-2。但每年种群主要来自地下块茎和匍匐茎,水深、风浪等可能是种子苗难以在湖泊中定植成功的主要因素。2)苦草的块茎数量较大,平均90~226个·m^-2,是种群发展的强大物质基础。3)温度、光照、基质及种子保存方式与时间长短对种子发芽率均有较大影响。10 ℃时种子发芽率较低,仅8.35%±1.89%;20 ℃时发芽率较高,为56.73%±6.42%;30 ℃时发芽率有所降低,为43.55%±4.34%。种子发芽对光照有一定要求,20 ℃、无光条件下,种子发芽率下降63.6%。在没有湖泥为基质的情况下,发芽率下降36.5%。此外,随干燥保存时间增加,种子发芽率下降。4)块茎发芽对光照需求不大,但温度对块茎的发芽率有较大影响,10 ℃时发芽率为20.3%±5.7%,20 ℃时较高,达90.2%±12.6%,30 ℃时发芽率降低至60.4%±7.6%。5)光照对幼苗生长有一定影响。有光照的幼苗伸长生长比无光条件下慢,但生物量积累较大,有光的苗生长速度平均为0.56~0.70 cm·d^-1,无光的为0.86~0.96 cm·d^-1。试验结果还显示,苦草的块茎苗初期的伸长生长主要依赖于基部的根茎生长。6)根据研究结果认为,在湖泊中恢复苦草种群应主要利用地下块茎,种子只适用于相对静止的浅水池塘种植。     

Seed Germination Ecology of Feather Lovegrass [Eragrostis tenella (L.) Beauv. Ex Roemer & J.A. Schultes]

Feather lovegrass [Eragrostis tenella (L.) Beauv. Ex Roemer & J.A. Schultes] is a C₄ grass weed that has the ability to grow in both lowland and upland conditions. Experiments were conducted in the laboratory and screenhouse to evaluate the effect of environmental factors on germination, emergence, and growth of this weed species. Germination in the light/dark regime was higher at alternating day/night temperatures of 30/20 °C (98%) than at 35/25 °C (83%) or 25/15 °C (62%). Germination was completely inhibited by darkness. The osmotic potential and sodium chloride concentrations required for 50% inhibition of maximum germination were -0.7 MPa and 76 mM, respectively. The highest seedling emergence (69%) was observed from the seeds sown on the soil surface and no seedlings emerged from seeds buried at depths of 0.5 cm or more. The use of residue as mulches significantly reduced the emergence and biomass of feather lovegrass seedlings. A residue amount of 0.5 t ha^-1 was needed to suppress 50% of the maximum seedlings. Because germination was strongly stimulated by light and seedling emergence was the highest for the seeds sown on the soil surface, feather lovegrass is likely to become a problematic weed in zero-till systems. The knowledge gained from this study could help in developing effective and sustainable weed management strategies.     

Life-history differentiation in Nymphoides coreana (Menyanthaceae) populations in aquatic habitats with different disturbance regimes in Japan

Different disturbance regimes in aquatic habitats may bring about life-history differentiation in aquatic plants. However, there is little information on this association. Adult longevity, seed size and mass, and seed-germination characteristics were surveyed for Nymphoides coreana populations, which grow in different types of aquatic habitats, to demonstrate life-history differentiation. Seed size and seed mass were significantly greater in paddy-field populations (disturbed habitats) than in irrigation-pond populations (stable habitats). Paddy-field populations were composed of annuals, whereas irrigation-pond populations contained perennials. Seed-germination characteristics were significantly different between paddy-field and irrigation-pond populations. The moist-chilling pretreatment period needed to release innate seeds from dormancy was significantly shorter in paddy-field populations than in irrigation-pond populations. The percentage of seeds that germinated was significantly higher under anaerobic conditions, irrespective of light, and under light aerobic conditions compared to dark aerobic conditions in paddy-field populations. Conversely, in irrigation-pond populations, the percentage of seeds that germinated was highest under light anaerobic conditions. These results show that the reaction norm of seed-germination characteristics was significantly broader in annual populations than in perennial populations. The occurrence of aquatic habitats with different disturbance regimes thus contributes to the maintenance of phenotypic diversity in N. coreana populations.     

Seed germination and seedling growth of Zostera marina L. (eelgrass) in the chesapeake bay

Seed germination and seedling growth of Zostera marina L. were monitored in the Chesapeake Bay in 1979 and 1980. Harvested seeds were placed in small acrylic tubes at several sites representing the salinity range of Z. marina distribution. Seed germination was observed first in late September and continued through May, with peaks in the fall and spring. The majority of seeds that germinated (66%) did so between December and March when water temperatures ranged from 0–10°C. There was no correlation between sites (different salinity regimes) and frequency of germination rates, indicating that salinity was not a major factor in the germination process in this study. Additional information on seed germination was available for seeds collected in 1977 and 1980 and subsequently monitored for germination at only one site. These data were similar to germination frequency recorded in 1979–1980.Seedling growth was measured from individuals collected from an existing Zostera marina bed. Seedlings were collected from November through May, at which time we could no longer distinguish seedlings from existing vegetative stock. Growth was characterized by the increased length of the primary shoot, number of leaves per shoot and numbers of shoots per plant. Seedling growth was slow during the winter months (water temperature ? 10°C) but rapidly increased in the spring (temperatures > 10°C). The size range of the harvested seedlings indicated that seed germination in the field probably occurred from October through April, corroborating evidence from the seed germination experiments.     

Cold stratification,light and high seed density enhance the germination of Ottelia alismoides

The effects of cold stratification, light and seed clustering in petri dish on Ottelia alismoides seed germination were investigated. The seeds required light and an extended cold period in order to germinate, but neither treatment alone was effective. Seed germination significantly increased with length of the 4 °C cold stratification period. Freshly collected seeds failed to germinate while a 5-month period at 4 °C yielded 29 ± 9% germination in the light, but none in the dark. Treatment with sodium nitroprusside, a nitric oxide source, failed to promote germination in the light or dark. Seeds of O. alismoides showed an unusual and significant positive response to aggregation. Germination in the light, after 5-month 4 °C cold stratification, was stimulated to almost five-fold in the dishes that were more densely sown with seed (20 seeds versus 200 seeds). Likewise, clustering seeds in dense aggregations stimulated germination significantly. Germination more than quadrupled with an increase from 1 to 50 seeds per cluster (200 seeds per dish), reaching a value of 72 ± 4%. Linear regression analysis shows the correlation between seed cluster density (no. per cluster) and germination rate (%) was highly significant (R² = 0.85, P = 0.000). The extended cold stratification requirement is probably an over-wintering device. The mechanism of the density-dependent stimulation is unclear.     

Seed germination patterns in green dragon (Arisaema dracontium,Araceae)

Arisaema dracontium (green dragon) is a perennial herb that is widely distributed in eastern North America. However, in Canada, at the northern edge of its distribution, the species is designated as “vulnerable” with respect to conservation status. In natural populations, seedlings are uncommon; the present study was undertaken in order to characterize seed and seedling properties in green dragon. Seeds were sampled from five sites, ranging from Ontario at the northern limit of the distribution range, to Louisiana in the south. Seed germinability ranged from 25 to 55%, depending upon source. Experiments indicated that neither the hard seed coat nor a water-soluble exudate from the seed was responsible for inducing or maintaining dormancy. Patterns of seed germination appear to reflect general climatic conditions at the sites where seeds had originated. Cold stratification at 3°C produced significantly greater relative germinability in all seed collections except the most southerly one, from Baton Rouge. These seeds also had a slower overall speed of germination. In contrast, germination of seeds from the most northerly site was promoted by cold stratification and occurred over a relatively brief period. Germination in alternating light and dark conditions decreased the speed of germination compared to germination in the dark, however exposure to light changed the phenology of germination by promoting development of adventitious roots and primary leaves in these seedlings.     

Seed germination of Agave species as influenced by substrate water potential

Background

Plants of Agave spp. perform Crassulacean acid metabolism (CAM) and are highly drought-tolerant, but little is known concerning seed germination under low water availability. The aim of this study was to assess the effect of substrate water potential (Ψ_W) on seed germination and contrast hydrotime parameters of seven valuable and commercially-important Agave species from different geographical distributions and climatic regions of Mexico. Our hypothesis was that seed germination of Agave species is not affected by low water availability independently of seed biomass and the climate of their distribution area.

Results

Seed germination (at 25°C and in the dark) between 85 and 100% for all species occurred within 80–180 h at -0.03 MPa and 250–430 h at -1.0 MPa. Seed germination at -1.5 MPa declined to less than 50% (p < 0.05) for A. asperrima and A. cupreata but did not change significantly for A. americana var. marginata, A. lechuguilla and A. striata, although they showed the lowest mean base water potential (-2.01 to -2.64 MPa). Seed germination of 40% Agave species, from arid and semi-arid climates in this study, was not affected by the lower Ψ_W.

Conclusion

Germination of seeds of Agave species is moderately affected by low water availability, is partially dependent of their ecological distribution, and is independent of seed mass.     

Hoary cress (Cardaria draba (L.) Desv.) seed germination ecology,longevity and seedling emergence

The effects of gibberellic acid (GA₃), potassium nitrate (KNO₃), prechilling, temperature, salt stress and osmotic potential on seed germination and sowing depth on seedling emergence and burial depth on seed viability of hoary cress (Cardaria draba (L.) Desv.), were studied in a series of laboratory, glasshouse and outdoor experiments. The optimal temperature for hoary cress seed germination was 20°C, both in light/dark and darkness regimes. Seed germination of hoary cress at 400 ppm concentration of GA₃ in a light/dark regime was maximal. Potassium nitrate concentrations increased the percentage of germination in comparison with the control treatment. Increasing the duration of dry prechilling to 30 and 45 days promoted the seed germination of hoary cress. Germination of hoary cress markedly decreased as salt and drought stress increased. Seed germination of hoary cress occurred at a range of pH from 3 to 11. Seedling emergence significantly decreased as planting depth increased. Total seed viability decreased with increasing burial depth. The maximum increase in mortality occurred in seeds that were buried at 5‐cm depth.     

Understanding the potential effects of water regime and salinity on recruitment of Melaleuca ericifolia Sm.

Although many emergent wetland plants may readily tolerate rapid changes in flooding and drying under freshwater conditions, their tolerance to dynamic water regimes may be compromised by salinity. Melaleuca-dominated woodlands occur naturally in Australia, south-east Asia and New Caledonia. Coastal wetlands dominated by Swamp paperbark (Melaleuca ericifolia) (Myrtaceae), native to south-east Australia, are commonly degraded as a consequence of altered water regime and salinity. This study simulates the release of M. ericifolia seeds from the aerial canopy under a range of water regime and salinity scenarios to determine conditions limiting sexual recruitment. Plant growth and survival were examined following seed release under two static water regimes (moist and flooded sediment) and two dynamic water regimes (simulated drawdown—“flooded-moist” and simulated re-flooding—“moist-flooded”). All water regimes, excluding the continuously flooded regime, were examined at three salinities: 0.1 dS m⁻¹ (fresh), 8 dS m⁻¹ and 16 dS m⁻¹, over a 50-day period commencing 44 days after the seeds were sown. The flooded treatment was examined at 0.1 dS m⁻¹ only, to confirm that flooding prohibits establishment of M. ericifolia. Seed and seedlings were positively buoyant and establishment was limited to moist soil. Flotation of seedlings in the flooded-moist treatment, however, did not inhibit subsequent establishment upon moist soil, even at the highest salinity of 16 dS m⁻¹. Growth, but not survival, was reduced by salinities of 8 dS m⁻¹ and 16 dS m⁻¹ in the moist treatment. Flotation of seedlings in saline water in the flooded-moist treatment did not reduce growth or survival compared with fresh water. Survival of seedlings in the moist-flooded treatment was lower in the freshwater and 16 dS m⁻¹ treatment compared with the moist treatment, but not at 8 dS m⁻¹. These findings suggest that water regime influences establishment of young M. ericifolia plants more strongly than does salinity, at least up to ∼1/3 seawater and in the short term (<2 months). Seedlings are likely to establish during a drawdown where the soil is exposed at salinities of ≤16 dS m⁻¹. In contrast, premature re-flooding of seedlings, even with fresh water, will compromise survival.     

Seed germination and seedling growth in the arrow bamboo <Emphasis Type="Italic">Fargesia qinlingensis</Emphasis>

Improving natural regeneration of bamboos after they die following mass flowering is critical for conservation of giant pandas. However, little is known about factors that affect seed germination and seedling growth of bamboos. We studied seed germination and seedling growth in Fargesia qinlingensis, which mass flowered in a giant panda habitat in the Qinling Mountains of China in early 2000, in laboratory and greenhouse conditions. Seed germination rate was tested under light and dark conditions 5 and 12 months after seed collection. Germination rate displayed no significant difference under light or dark conditions 5 months after seed collection, but was significantly greater in the dark than under light 12 months after seed collection, suggesting light inhibition of seed germination. A 2×2 factorial design was conducted to test the effects of nitrogen (N fertilization and non-N fertilization) and light [full sun and shade (i.e., 14% full sun)] on seedling growth and biomass allocation. N fertilization significantly increased seedling growth, resulting in greater seedling height, more branches, more leaves, greater stem biomass, and greater leaf biomass. Seedlings under 14% full sun conditions had a significantly lower percentage of biomass allocated to the stem. The root/shoot ratio was significantly greater in non-N/shade than non-N/full sun, while there was no significant difference in this ratio between N/shade and N/full sun, suggesting that nitrogen fertilization compensated for the effect of shade on biomass allocation. Our results suggest that N fertilization could be employed in restoration of F. qinlingensis stands after die-off following mass flowering.     

Effects of increased nitrogen deposition and precipitation on seed and seedling production of Potentilla tanacetifolia in a temperate steppe ecosystem

Background

The responses of plant seeds and seedlings to changing atmospheric nitrogen (N) deposition and precipitation regimes determine plant population dynamics and community composition under global change.

Methodology/Principal Findings

In a temperate steppe in northern China, seeds of P. tanacetifolia were collected from a field-based experiment with N addition and increased precipitation to measure changes in their traits (production, mass, germination). Seedlings germinated from those seeds were grown in a greenhouse to examine the effects of improved N and water availability in maternal and offspring environments on seedling growth. Maternal N-addition stimulated seed production, but it suppressed seed mass, germination rate and seedling biomass of P. tanacetifolia. Maternal N-addition also enhanced responses of seedlings to N and water addition in the offspring environment. Maternal increased-precipitation stimulated seed production, but it had no effect on seed mass and germination rate. Maternal increased-precipitation enhanced seedling growth when grown under similar conditions, whereas seedling responses to offspring N- and water-addition were suppressed by maternal increased-precipitation. Both offspring N-addition and increased-precipitation stimulated growth of seedlings germinated from seeds collected from the maternal control environment without either N or water addition. Our observations indicate that both maternal and offspring environments can influence seedling growth of P. tanacetifolia with consequent impacts on the future population dynamics of this species in the study area.

Conclusion/Significance

The findings highlight the importance of the maternal effects on seed and seedling production as well as responses of offspring to changing environmental drivers in mechanistic understanding and projecting of plant population dynamics under global change.