Experimental separation of resource quantity from temporal variability: seedling responses to water pulses

We tested the hypothesis that higher temporal variability in water supply will promote higher species richness of germinating and surviving seedlings using assemblages of 70 species of herbaceous plants from limestone pavement habitats. In a two-factor greenhouse experiment, doubling the total volume of water added led to greater germination (measured as number of germinated seeds and species) and establishment (survival and biomass) but the effects of temporal variability depended on the response variable considered. Low pulse frequencies of water addition with total volume added held constant resulted in greater temporal variability in soil moisture concentration that in turn promoted higher density and richness of germinated seedlings. Low pulse frequencies caused an eight-fold greater mortality in the low total volume treatment and biomass production to decline by one-third in the high total volume treatment. The effects of increasing temporal variability in water supply during recruitment stages can thus be opposite on different components of plant fitness and may also depend on total resource quantity. While greater species richness in more temporally variable soil moisture conditions was attributable to sampling effects rather than species-specific responses to the water treatments, species relative abundances did vary significantly with temporal variability. Changes in the amplitude or frequency of resource fluctuations may alter recruitment patterns, and could have severe and relatively rapid effects on community structure in unproductive ecosystems.Electronic Supplementary Material The French version of this article is available in the form of electronic supplementary material at.     

Effect of flooding and draw‐down disturbance on germination from a seashore meadow seed bank

Abstract. The objective of this study was to investigate the effects of flooding and draw‐down on the germination from the coastal grassland seed banks and to determine whether the effect of flooding varies between the delta and the seashore. Seed bank samples were collected from three shore transects in SW Finland, two on the shore of the Baltic Sea and one on the delta of River Kokemäenjoki. Samples were germinated in non‐flooded and flooded conditions for over a month, after which both treatments were maintained in non‐flooded conditions. A total of 9267 seedlings of 47 species germinated and mean density of seeds in the soil was ca. 84 000/m². Most of the seedlings were monocots (98%) and perennials (98%). Ca. 30–40% of the species found in the above‐ground vegetation had a seed bank including the majority of the most abundant species. The number of seeds and species richness increased as the organic layer became thicker. The organic layer was thicker in the seashore samples and the seed bank was significantly larger than in the delta. The flooding and draw‐down treatment significantly increased the number of germinating seedlings in the seashore and also increased species richness in two transects, one in the delta and the other in the seashore. Two species, Schoenoplectus tabernaemontani and Typha latifolia, had significantly higher germination in the flooded treatment than in the non‐flooded. Apparently, many species in these coastal grasslands have adapted to flood disturbance and for seeds of some species flooding may work as a positive signal, possibly breaking dormancy.     

Smoke and heat effects on soil seed bank germination for the re‐establishment of a native forest community in New South Wales

The effects of plant‐derived smoke and of heat on the emergence of seedlings from seeds were assessed. Seeds had been stored in forest topsoil used for mine site rehabilitation. The study was carried out in a dry sclerophyll, spotted gum (Corymbia maculata), forest community at the Mount Owen open‐cut coal mine in the Hunter Valley region of New South Wales. Samples of the surface 2.5 cm of topsoil were either exposed to cool smoke from eucalypt foliage for 60 min, heated to 80°C, or left untreated. Seedling emergence from the seed bank in this soil was then monitored in a glasshouse. Within the first month, smoke alone promoted a 4.3‐fold increase in the density of seedlings relative to control. There were 540 emergents per m² in the control and 2309 per m² in the smoke treated topsoil. Many annual and perennial herbs emerged but grasses responded most strongly to smoke. Germination in seven of the 20 grass species was promoted by smoke. Smoke promoted the germination of some introduced species as well as native species, and accelerated the rate at which seedlings emerged, although these differences sometimes declined with time. Heat also stimulated germination but smoke and heat stimuli appeared to be complementary in their promotion of seedling emergence from the topsoil seed bank. Each treatment increased the density of different species, enhanced the species richness of different components of the seed bank, and had different effects on the rate of emergence. The results suggest that increased seed germination in the field immediately following a moderate intensity fire may sometimes be the result of smoke stimulation and sometimes the result of heat stimulation of the soil seed bank. These findings may have important implications for minesite revegetation programs where topsoils are replaced after mining and rapid germination of seeds stored in these soils is required during short periods when conditions are favourable for germination.     

The effect of concentrated smoke products on the restoration of highly disturbed mineral sands in southeast Victoria

Summary Recent studies have recognized the potential of broad‐scale surface application of smoke compounds for enhancing germination from the soil seed‐bank in fire‐prone vegetation communities. Results suggest that smoke technology may play, in the future, a significant role in the restoration and management of areas supporting indigenous vegetation. An important step in the development of smoke‐based restoration tools is the conduct of in situ field trials in a range of geographical locations and environmental conditions. However, most of the published work on the effectiveness of smoke products in promoting seedbank germination has been conducted at sites in southwestern Australia. The present study examines the effect of commercially available smoke‐water products on the regeneration of a highly disturbed former mine‐site at the Royal Botanic Gardens Cranbourne, in southeastern Victoria. Various combinations of concentrated smoke products and topsoil harvested from a nearby heathy woodland community were applied to exposed, uniform mineral sands to test their effect on seedling density and species richness of regrowth. The trials showed that after 12 months a number of common, herbaceous species including Austrodanthonia setacea, Opercularia varia and Platysace heterophylla were recorded in significantly higher numbers in areas treated with a commercial smoke‐water. However, there was no overall improvement in the density of seedlings or the richness of species as a result of the application of the smoke products. Similarly, total seedling density and species richness were not affected by the addition of topsoil, either alone or in combination with smoke products.     

亚热带中山常绿阔叶林木本植物幼苗数量动态及其与生境的相关性

以百山祖自然保护区5 hm2永久样地150个幼苗监测站木本植物幼苗为研究对象,2008—2011年定期调查样方中幼苗的种类、数量、萌发、死亡等,探究亚热带中山常绿阔叶林幼苗种类组成、数量动态及其与生境的相关性。结果表明:1)百山祖样地在2008年至2011年出现的幼苗属于26科,40属,共53个物种,不同物种萌发时段有异;2)2009年样地幼苗存活比率为7.7%,2010年为-20.8%,2011年则是-0.3%,幼苗存活比率不高,种类和数量呈减少趋势;3)存活幼苗中有明显的优势物种,分别为光亮山矾(Symplocos lucida)、尖连蕊茶(Camellia cuspidata)、浙闽新木姜子(Neolitsea aurata var.undulatula)、尖叶菝葜(Smilax arisanensis)和短尾柯(Lithocarpus brevicaudatus),5个物种之和占幼苗总数比例50%;4)种子的萌发与生境有极显著的相关性,且与生境因子中水分关联最大;5)存活幼苗数与样站坡位、水分、落叶层厚度呈现显著相关性,水和光照是影响幼苗存活的主要因素。     

The effects of two abundant ant species on soil nutrients and seedling recruitment in Brazilian Atlantic Forest

Ants can influence soil fertility and the spatial distribution of seeds, with possible effects on seedling recruitment. The ant species Pachycondyla striata Fr. Smith, 1858 and Odontomachus chelifer (Latreille, 1802) co-occur in many forest areas in the Neotropics. We assessed soil fertility and seed bank structure in soil samples close and distant (control) from ant nests in forest fragments. We also assessed the richness and abundance of seedlings on nests and control sites. In soil samples from ant nests, the concentration of phosphorus and potassium were respectively 55.6% and 36% higher than in control sites. Aluminium was 11–15% lower in soil samples from ant nests. In the greenhouse, soils from ant nests had higher plant abundance and species richness, but the same species composition in comparison with control sites. Although more plants emerged from soil samples of O. chelifer nests, in the field, the density and richness of seedlings were similar for the two ant species studied. Seedlings in the nest sites were, on average, 1.8 times more abundant and 1.6 times richer in species than in control sites. Our results showed that ant species can play a key role in seedling recruitment in forest fragments, where other animals with equivalent and positive effects, such as mammals, are missing.     

蚌湖湖滨带的土壤种子库特征

采用幼苗萌发法,在湿润和淹水两种水位萌发条件下,研究了蚌湖（鄱阳湖子湖）湖滨带5个水位梯度区的土壤种子库特征。结果表明,种子库中共萌发了33个物种,分属15科29属。物种组成以一年生草本为主,其中莎草科、禾本科、菊科、玄参科和水鳖科的物种数最多。不同水位区种子库的物种组成和幼苗密度差异不显著。种子库在两种水位条件下萌发的结果有显著差异,湿润条件下种子库萌发的物种以湿生和挺水植物为主,而在淹水条件下萌发的沉水植物种类和幼苗数量显著增多,其幼苗密度占总幼苗数的36％。t检验表明种子库在淹水条件下每个萌发盒中萌发的物种数（7．2±2．8）显著多于湿润条件（4．2±2．0）。     

Effects of Fire on Seedling Diversity and Plant Reproduction (Sexual vs. Vegetative) in Neotropical Savannas Differing in Tree Density

Little is known about the effects of fire on the structure and species composition of Neotropical savanna seedling communities. Such effects are critical for predicting long‐term changes in plant distribution patterns in these ecosystems. We quantified richness and density of seedlings within 144 plots of 1 m² located along a topographic gradient in long‐unburned (fire protected since 1983) and recently burned (September 2005) savannas in Brazil. These savannas differ in tree density and canopy cover. Sites along the gradient, however, did not differ in species composition prior to the fire. In recently burned savannas we also evaluated the contribution of vegetative reproduction relative to sexual reproduction by quantifying richness and density of root suckers. Finally, we tested seed tolerance to pulses of high temperatures—similar to those occurring during fires on the soil surface and below—of five dominant savanna tree species. Seedlings were more abundant and diverse in unburned than in burned savannas. Seedling species composition differed among unburned and burned savannas probably reflecting early differences in root: shoot biomass allocation patterns. In recently burned savannas, root suckers were more abundant and diverse than seedlings. Relatively long exposures (>10 min) of temperatures of 90 °C reduced seed germination in all studied species suggesting a negative effect of fire on germination of seeds located at or aboveground level. Because vegetative reproduction contributes more than sexual reproduction in burned environments, frequent fires are likely to cause major shifts in species composition of Neotropical savanna plant communities, favoring clonally produced recruits along tree density/topographic gradients.     

Seedling regeneration,environment and management in a semi‐deciduous African tropical rain forest

Questions: How is seedling regeneration of woody species of semi‐deciduous rain forests affected by (a) historical management for combinations of logging, arboricide treatment or no treatment, (b) forest community type and (c) environmental gradients of topography, light and soil nutrients? Location: Budongo Forest Reserve, Uganda. Methods: Seedling regeneration patterns of trees and shrubs in relation to environmental factors and historical management types were studied using 32 0.5‐ha plots laid out in transects along a topographic gradient. We compared seedling species diversity, composition and distribution patterns along topographic gradients and within types of historical management regimes and forest communities to test whether environmental factors contributed to differences in species composition of seedlings. Results: A total of 85 624 woody seedlings representing 237 species and 46 families were recorded in this rain forest. Cynometra alexandri C.H. Wright and Lasiodiscus mildbraedii Engl. had high seedling densities and were widely distributed throughout the plots. The most species‐rich families were Euphorbiaceae, Fabaceae, Rubiaceae, Meliaceae, Moraceae and Rutaceae. Only total seedling density was significantly different between sites with different historical management, with densities highest in logged, intermediate in logged/arboricided and lowest in the nature reserve. Forest communities differed significantly in terms of seedling diversity and density. Seedling composition differed significantly between transects and forest communities, but not between topographic positions or historical management types. Both Chao‐Jaccard and Chao‐Sørensen abundance‐based similarity estimators were relatively high in the plot, forest community and in terms of historical management levels, corroborating the lack of significant differences in species richness within these groups. The measured environmental variables explained 59.4% of variance in seedling species distributions, with the three most important being soil organic matter, total soil titanium and leaf area index (LAI). Total seedling density was positively correlated with LAI. Differences in diversity of >2.0 cm dbh plants (juveniles and adults) also explained variations in seedling species diversity. Conclusions: The seedling bank is the major route for regeneration in this semi‐deciduous tropical rain forest, with the wide distribution of many species suggesting that these species regenerate continuously. Seedling diversity, density and distribution are largely a function of adult diversity, historical management type and environmental gradients in factors such as soil nutrient content and LAI. The species richness of seedlings was higher in soils both rich in titanium and with low exchangeable cations, as well as in logged areas that were more open and had a low LAI.     

Seedling establishment after endozoochory in disturbed and undisturbed grasslands

Local plant community composition and structure may be largely influenced by germination and seedling establishment from seeds dispersed in animal dung, through seed input, gap creation and nutrient enrichment. With an experimental approach we assessed (1) what the effect is of dung deposition on the number of seedlings in the plant community 3 months and 1 year after dung deposition, (2) what the effect is of this seedling establishment on the local plant community characteristics such as species richness and (3) if this effect interacts with large-scale soil disturbance which removes the close canopy, such as sod-cutting. Viable seeds of monocotylous species were abundantly present in the dung, and dung deposition led to a higher number of monocotylous seedlings after 3 months. However, this effect was no longer significant after 1 year. Moreover, the proportion of viable monocotylous seeds that effectively established in the field after 3 months was less than 5%. A lower number of viable seeds of the less-dominant dicotylous species was dispersed in the dung but they had a higher cover and species richness after 1 year. This resulted in an increased total small-scale species richness and diversity after dung deposition through a decreasing dominance of monocotylous species. Sod-cutting had a pronounced effect on seedling emergence: viable seeds dispersed by dung had a higher probability of successful establishment when the dung was deposited in large gaps. This indicates that an increase of safe sites associated with disturbance strengthens the effects of seed dispersal and gap creation by dung deposition.     

Can atmospheric input of nitrogen affect seed bank dynamics in habitats of conservation interest? The case of dune slacks

Questions: Does the increased atmospheric deposition of nitrogen, which can have major effects on the established vegetation of nutrient‐poor habitats, also impact germination from the soil seed bank? Location: Coastal dune slacks at Newborough Warren, Wales, UK. Methods: The effects of nitrogen addition (15 kg.ha^‐1.a^‐1) on seed germination from the soil seed bank were investigated using the seedling emergence method between September 2004 and February 2005. Results: More seedlings emerged from fertilised samples than unfertilised controls. Most species showed enhanced germination after fertilisation with nitrogen, with seedling numbers statistically significantly greater in nitrogen addition samples in a quarter of species abundant enough for analysis. Species that responded positively to fertilisation were species with low Ellenberg indicator values indicative of infertile sites. Conclusions: Most species showed increased germination after fertilisation with nitrogen, including early successional species normally growing in nutrient‐poor conditions. This suggests that the increased atmospheric deposition of nitrogen probably not only impacts on established vegetation, but also has the potential to alter seed bank dynamics.     

Effects of smoke,heat and charred wood on the germination of dormant soil‐stored seeds from a Eucalyptus baxteri heathy‐woodland in Victoria,SE Australia

The effects of dry heat, wet heat, charred wood and smoke on the germination of dormant soil‐stored seeds from a Eucalyptus woodland in western Victoria were tested by using a glasshouse seed‐bank germination experiment. Seedling density, species richness and species composition were compared between replicated treated and control samples. A total of 5922 seedlings, comprising 59 plant species, was recorded from the soil samples over a period of 150 days. While a few species dominated (including Centrolepis strigosa, Wahlenbergia gracilenta and Ixodia achillaeoides), 26 species were represented by fewer than five seedlings and 18 species were restricted to single treatment types. With the exception of charred wood, all treatments led to a significant increase in seed germination relative to the control. The highest number of germinants was obtained for the smoke treatment, with a mean (± SE) of 12 547 ± 449 seedlings m^–2. Heat treatments yielded intermediate densities, with means (± SE) varying between 7445 ± 234 and 9133 ± 445 seedlings m^–2. In comparison with the estimates of seed‐bank sizes from other fire‐prone ecosystems, these densities are high. Species richness differed significantly among treatments. Highest mean richness was recorded in the smoke treatment and lowest for the control and charred wood treatments. There were significant differences in seed‐bank species composition between treatment types based on analysis of similarity (Anosim) using Bray–Curtis similarity. While heat was a specific requirement for triggering germination in hard‐seeded species (e.g. Fabaceae), smoke was the most effective trigger for species from a broad range of other families. The potentially confounding effect of physical and chemical mechanisms of germination stimulation in heated bulk soil samples is raised as an issue requiring further investigation in relation to the role of smoke as a germination trigger.     

The role of water depth and soil temperature in determining initial composition of prairie wetland coenoclines

In this study, we examined the effects of water depth and temperature on seedling recruitment from a prairie wetland seed bank. We collected seed-bank samples from natural and restored prairie pothole wetlands in northwestern Iowa and combined them into a single sample. We examined seedling recruitment from this seed-bank sample in an experimental study using a factorial design of 4 temperature treatments (5° night and 15° day to 20° night and 30° day) and 3 water-depth treatments (0, 2, and 7 cm).Principal Components Analysis showed that both water depth and temperature had significant effects on the composition of the seedling community as measured by changes in relative stem density and biomass. Water depth had its strongest effects on stem density while temperature had its strongest effects on biomass.For the 22 most common species, stem density varied with water depth for 95% of the species and with temperature for 50% of the species. Most species with water depth responses had lower stem counts as water depth increased, and for the majority of species with temperature responses stem density increased with temperature.Total, annual, and perennial species richness was negatively correlated with water depth. Total and annual species richness was positively correlated to temperature, while perennial species richness was unresponsive to temperature. In addition, species found at low elevations as adults emerged at higher rates in the deep water treatments while species that occurred at higher elevations as adults had their highest emergence rates in the low water treatments.Our results suggest that differences in environmental conditions along coenoclines can affect the initial distribution of species emerging from the soil seed bank. Water depth sorted seedlings according to their adult water-depth tolerances, and temperature determined the proportion of annuals in the seedling community.     

Species richness and evenness respond in a different manner to propagule density in developing prairie microcosm communities

Diversity has two basic components: richness, or number of species in a given area, and evenness, or how relative abundance or biomass is distributed among species. Previously, we found that richness and evenness can be negatively related across plant communities and that evenness can account for more variation in Shannon’s diversity index (H′) than richness, which suggests that relationships among diversity components can be complex. Non-positive relationships between evenness and richness could arise due to the effects of migration rate or local species interactions, and relationships could vary depending on how these two processes structure local communities. Here we test whether diversity components are equally or differentially affected over time by changes in seed density (and associated effects on established plant density and competition) in greenhouse communities during the very early stages of community establishment. In our greenhouse experiment, we seeded prairie microcosms filled with bare field soil at three densities with draws from a mix of 22 grass and forb species to test if increased competition intensity or seedling density would affect the relationships among diversity components during early community establishment. Increased seed density treatments caused diversity components to respond in a different manner and to have different relationships with time. Richness increased linearly with seed density early in the experiment when seedling emergence was high, but was unrelated to density later in the experiment. Evenness decreased log-linearly with seed densities on all sampling dates due to a greater dominance by Rudbeckia hirta with higher densities. Early in the experiment, diversity indices weakly reflected differences in richness, but later, after the competitive effects of Rudbeckia hirta became more intense, diversity indices more strongly reflected differences in evenness. This suggests that species evenness and diversity indices do not always positively covary with richness. Based on these results, we suggest that evenness and richness can be influenced by different processes, with richness being more influenced by the number of emerging seedlings and evenness more by species interactions like competition. These results suggest that both diversity components should be measured in plant diversity studies whenever it is possible.     

Relationships of marsh seed banks to vegetation patterns along environmental gradients

• 1 The relationship of the seed bank to the vegetation of a freshwater marsh was studied along gradients of water depth and soil organic matter content. Characters examined included standing crop, seedling density, and species composition, distribution and richness.
• 2 The seed bank differed from the vegetation in that only nine of twenty-seven species were present in both, abundant seed-bank species were uncommon as adults, and adults showed different distributions along a gradient of soil organic matter content whereas their seeds were most abundant in soils with high organic matter.
• 3 The seed bank resembled the vegetation in that separate multivariate analyses of the communities revealed that variation in the species composition of each was significantly correlated with water depth and soil organic matter content. Further, species richness in both communities decreased with water depth and increased with soil organic matter content. Lastly, the standing crop of the vegetation and the number of seedlings both decreased with water depth and increased with soil organic matter.
• 4 Consideration of spatial patterns and environmental gradients revealed more similarities between vegetation and seed banks than were obtained by comparing species lists. The results suggest that artificial stimulation of seed bank germination for management purposes will not produce vegetation changes as large as those suggested by differences in species lists.

     

咸海湖泊退缩对岸边土壤真菌和植物内生真菌的影响研究

[目的] 研究咸海岸边不同暴露时期土壤带的土壤真菌和植物内生真菌群落构成及其对湖泊干涸的响应。[方法] 从咸海湖岸远端（土壤带的暴露时间最长）到湖岸近端（土壤带的暴露时间最短）的不同土壤带采集土壤样品,对其进行地球化学和矿物学分析。同时也采集各土壤带的土壤样品和优势植物,通过ITS基因高通量测序方法分析土壤真菌和植物内生真菌群落构成,进而探讨其如何响应湖泊干涸（如盐度升高、矿物组分变化、植物种类丰富度变化等）过程。[结果] 持续暴露的咸海湖床从湖泊远岸到湖泊近岸形成了一个连续的盐度梯度：E48（暴露于1970年之前,总可溶解盐0.5±0.5 g/L）;E38（暴露于1980年之前,总可溶解盐0.4±0.2 g/L）;E28（暴露于1990年之前,总可溶解盐23.3±2.1 g/L）;E18（暴露于2000年之前,总可溶解盐23.7±7.5 g/L）;E9（暴露于2009年之前,总可溶解盐71.3±6.1 g/L）;E1（暴露于2017年之前,总可溶解盐62.9±10.7 g/L）和E0（2018年湖岸线附近沉积物样品,总可溶解盐69.9±8.3 g/L）。咸海岸边不同土壤带分布着不同的植物：梭梭（Haloxylon ammodendron）在E48和E38区域中占优势地位;滨藜（Chenopodium album）在E28、E18和E9区域占优势;而在E1和E0区域无可见植物物种分布。另外,咸海岸边不同土壤带的主要矿物成分也存在差异：粘土矿物和蒸发岩的含量从咸海湖岸远端到湖岸近端逐渐增加,而碳酸盐矿物含量逐渐减少。咸海岸边不同土壤带土壤样品优势真菌类群（>5%）为散囊菌纲（Eurotiomycetes）、粪壳菌纲（Sordariomycetes）、锤舌菌纲（Leotiomycetes）、座囊菌纲（Dothideomycetes）、黑粉菌亚门（Ustilaginomycotina）和伞菌纲（Agaricomycetes）,且按植物种类丰富度进行聚类。而植物样品优势真菌类群为未知真菌门类（>97.8%）,且按植物种类进行聚类。线性回归结果显示,咸海岸边不同土壤带土壤样品真菌群落差异性与暴露时间距离具有显著相关（R²=0.32,P<0.05）,而与总可溶解盐差异则无明显相关性。而植物内生真菌群落差异性与暴露时间距离/总可溶解盐差异之间均无显著相关。Mantel检验结果显示,咸海岸边不同土壤带土壤真菌群落与植物种类丰富度和矿物成分组成（如白云石、方解石、微斜长石和石膏）呈显著相关（P<0.05）,其中植物种类丰富度和方解石含量的相关性系数最大;植物内生真菌群落与方解石含量之间呈显著相关（P<0.05）。[结论] 咸海岸边不同暴露时期土壤带的土壤真菌和植物内生真菌种群结构具有时空差异,与植物种类丰富度和特定矿物组成相关,而与总可溶解盐无显著相关。     

Germination and Seedling Responses of Subalpine Plants to Different Soil Substrates

In this study we explored the regeneration niche of 18 alpine plant species by testing the germination responses and seedling growth to soil mixtures made with gypsum, ophiolite, and quartzite, and a control soil. We analyzed different phases of germination: time of radicle emergence, germination duration, and germination percentage, and thereafter seedling performance measured using seedling biomasses. Species were grouped as acidophilous, basophilous and neutrophilous according to their Ellenberg indicator values. Seeds were germinated on each soil mixture in a greenhouse, and then seedlings were selected and transplanted outdoors to grow for one season at 2,050 m a.s.l. The time of radicle emergence, length of germination, final germination percentage, seedling biomass and specific leaf area (SLA) varied according to the soil mixtures depending on the pH group. There were some consistencies between the Ellenberg groups, which were built for adult plant species, and the way these seedlings responded to a particular soil mixture. For instance, the group of species predominantly occurring in basic soils during their adult life (basophilous) had the highest germination percentage and the shortest emergence time on the soil mixture composed of gypsum, but a low germination percentage and the smallest seedling biomass on the other two soil mixtures. In addition, the decrease in SLA for seedlings of the basophilous group when they were cultivated on acidic soil (especially quartzite) seems to indicate a weaker functioning of the plants. Our results highlight, first, the significance of the regeneration niche in the establishment of plants in a given soil environment, especially by emphasizing the links between germination and soil chemistry, and secondly, the consideration that different germination phases add more information about the plant community assemblage with respect to the soil environment.     

生态位限制和物种库限制对湖滨湿地植物群落分布格局的影响

研究了物种库限制与生态位限制在湖滨湿地植物分布格局形成过程中的相对重要性。在龙感湖湖滨湿地具有明显水位梯度的湿生植 物区、挺水植物区和沉水植物区采集种子库土样, 采用幼苗萌发法确定了不同水位区种子库的物种成分;并将不同水位区的种子库土样分别置于0、25和50cm3个水位下萌发和生长, 45和90d后比较不同取样区种子库在不同水位处理下所建立的植物群落的异同。结果表明, 不同取样区的种子库物种成分有显著差异, 沿水深梯度呈现明显的带状分布格局。水位处理实验表明, 0cm水位条件下的群落主要由湿生植物和挺水植物组成, 而25和50cm水位下只有沉水植物, 表明不同功能群的物种对水深有不同的耐受力, 生态位限制是决定湿地植物分布格局的关键因子。同时, 挺水植物区的种子库置于沉水条件下, 以及沉水植物区的种子库置于0cm水位下都只能形成极为简单的植物群落, 表明物种库限制对湿地植物群落的形成同样具有显著影响。研究表明, 湿地植物的群落构成与分布格局是由生态位限制和物种库限制共同决定的, 两者的相对重要性可能取决于水体的稳定性。     

Heat shock increases the reliability of a temperate calcareous grassland seed bank study

Reliable assessment of the density and species richness of the viable seeds in the soil is essential to estimate the probability of successful restoration of a particular plant community. Since temperate calcareous grasslands contain several thermophilous species typical of fire prone habitats, heat shock can be expected to break dormancy of target species for calcareous grassland restoration. We tested the effect of heat shock on the estimated density and species richness of seeds in soil samples. Heat shock treatments between 70 and 110°C resulted in both a higher estimated seed density and estimated species richness, in particular of specialist calcareous grassland species. Moreover, 25 species germinated exclusively from the heat-treated samples. This indicates that several species would have been missed by handling soil seed bank samples following the standard germination protocol, resulting in an underestimation of the restoration potential.     

The role of the soil seed and seedling bank in the regeneration of diverse plant communities in the subtropical Ailao Mountains,Southwest China

We compared species composition and diversity of the soil seed and seedling banks in three secondary vegetation types (shrubland, Populus bonatii forest, Lithocarpus regrowth forest) and a primary old-growth forest in the subtropical Ailao Mountains of southwestern China to clarify the importance of seed and seedling banks for forest dynamics. The average species richness was the highest in soil samples from the shrubland (26.80 ± 1.98), and the lowest from the primary forest (9.93 ± 0.50). The density of germinable tree seeds increased from the secondary vegetation to the primary forest, and the density of shrub, forb, and graminoid seeds decreased significantly. The most abundant seedlings recorded in soil samples were light-demanding species in the shrubland and Populus bonatii forest. For ground flora, the number of shrub seedlings strongly decreased with the increase in stand age, and shade-tolerant tree seedlings tended to increase. The species similarity between the seed bank and the aboveground vegetation in all sites was low (Sørensen’s index = 0.11–0.33), however, the shrubland had higher similarity compared with the other three plant communities. In the primary forest, light-demanding woody species dominated in soil seed banks, while shade-tolerant species dominated in the overstory and the forest floor. In the primary forest, seedlings of dominant tree species were rare in the understory, and no seeds of the dominant species were found in the soil. Results indicated that the early stages of vegetation recovery should take into account the possibility of recovering soil seed bank processes. However, colonization and establishment of tree seedlings will be difficult once a primary forest is destroyed.