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Background and Aims Hydroperiod drives plant community composition in wetlands, resulting in distinct zonation patterns. Here, we explored the role of seed germination traits in shaping wetland community assembly along a hydroperiod gradient. Specifically, we tested the hypothesis that seeds of reed, mudflat, swamp, shallow- and deep-water communities only germinate under a specific set of environmental factors characterized by the community-specific optimal conditions for seedling survival and growth. Methods In a three-factorial experiment, we tested the seed germination response of 50 species typical for temperate wetlands of Europe to temperature fluctuations (constant vs. fluctuating temperature), illumination (light vs. darkness) and oxygen availability (aerobic vs. hypoxia). Phylogenetic principal component analysis, cluster analysis and phylogenetic linear regressions were used to confirm the community-specific seed germination niches. Key Results Our study revealed the presence of five distinct, community-specific seed germination niches that reflect adaptations made by the study communities to decreasing light intensity, temperature fluctuations and oxygen availability along the hydroperiod gradient. Light as a germination trigger was found to be important in mudflats, swamps and shallow water, whereas the seeds of reed and deep-water species were able to germinate in darkness. A fluctuating temperature is only required for seed germination in mudflat species. Germination of species in the communities at the higher end of the hydroperiod gradient (reed and mudflat) demonstrated a strict requirement for oxygen, whereas swamp, shallow- and deep-water species also germinated under hypoxia. Conclusions Our study supports the recent argument that the inclusion of seed germination traits in community ecology adds significant insights to community response to the abiotic and biotic environment. Furthermore, the close relationship between seed germination adaptations and community assembly could help reach a better understanding of the existing patterns of wetland plant distribution at local scales and wetland vegetation dynamics, as well as facilitate nature conservation measures and aquatic habitat restoration.

Background and Aims Although plant distribution patterns are well documented, our understanding of the ecophysiological mechanisms that control the geographical ranges of plant species remains poor. We used a largely ignored method, the performance of the male gametophyte in vitro, to assess whether the thermal range of pollen germination and tube growth controls species distribution ranges, in this case along an elevational gradient. Methods Using in vitro pollen germination experiments, we obtained cardinal temperatures (minimal, optimal and maximal) of pollen germination and pollen tube growth for 25 herbaceous species along a mean annual temperature gradient of about 5 A degrees C. These temperatures were correlated with temperatures of the sites where the species were collected. The presence of a phylogenetic signal in the data set as well as an effect of species flowering phenology were also estimated. Key Results and Conclusions We found a strong positive relationship between temperature conditions at our collection sites and the minimum temperature for both pollen germination and pollen tube growth. In addition, a significant correlation between maximum temperature of pollen tube growth and temperature of flowering month was apparent. We conclude that the restriction of pollen germination and growth by low temperatures is an important contributor to the climatic restriction of plant species distributions. Improved knowledge of this thermal precursor to seed production could, from a functional perspective, enhance our understanding of species distributions along climatic gradients and our ability to predict how anthropogenic climate change might affect plant community composition.

†Background and Aims Plant functional trait responses to processes such as grassland management have been analysed frequently; however, the scaling-up from individual traits to the outcomes of vegetation dynamics has seldom been tested. In this experiment, germination success was studied with respect to the relationships between grassland management (mowing and grazing), as well as abandonment, and two traits that are relevant for seedling recruitment: seed mass and germination season. On the basis of discussions in the literature and indirect trait analyses in our previous studies, the following hypotheses are proposed: (1) with respect to seed mass, mowing and grazing favour the germination of small seeds, whereas after abandonment the germination success of larger seeds is higher; and (2) with respect to germination season, mowing and grazing favour autumn-germinating seeds, whereas succession promotes spring-germinating seeds. †Methods The germination experiment took place in a semi-natural, dry grassland in north-east Germany. Seeds of eight herbaceous species that differ with respect to seed mass and germination season were sown in mown, grazed and abandoned plots. Germination success was documented during the following year. †Key Results and Conclusions Contrary to the hypothesis, germination of small seeds was not promoted by mowing or grazing and they germinated relatively more often than expected in the abandoned plots. A relationship between abandonment and gaps of bare soil below the vegetation cover that favour germination of small seeds was likely, but could not be proved statistically. It is possible that the small seeds suffered less from predation. Mowing favoured autumn germination, which could be explained by the removal of biomass in late summer. Contrary to our expectation, there was relatively more spring germination after grazing than after mowing, yet vegetation height was smallest in spring. Generally, germination season was found to be related to the temporal occurrence of favourable light conditions.

In arid environments many plant species are found associated with the canopies of woody perennials. Favourable conditions for establishment under canopies are likely to be associated with shade, but under canopies shade is distributed patchily and differs in quality. Diurnal temperature fluctuations and maximum temperatures could be reliable indicators of safe sites. Here, an examination is made as to whether canopy-associated species use temperature cues to germinate in shade patches, rather than matrix areas between trees.The study was carried out in arid southern Kalahari savannah (Republic of South Africa). Perennial and annual species associated with Acacia erioloba trees and matrix species were germinated at temperature regimes resembling shaded and unshaded conditions. Soil temperature was measured in the field.Germination of all fleshy-fruited perennial acacia-associated species and two annual acacia-associated species was inhibited by the temperature regime resembling unshaded conditions compared with at least one of the regimes resembling shaded conditions. Inhibition in perennials decreased with seed mass, probably reflecting that smaller seedlings are more vulnerable to drought. Germination of matrix species was not inhibited by the unshaded temperature regime and in several cases it increased germination compared with shaded temperature regimes or constant temperature. Using phylogenetically independent contrasts a significant positive relationship was found between canopy association and the germination at shade temperatures relative to unshaded temperatures.The data support the hypothesis that canopy species have developed mechanisms to prevent germination in open sun conditions. The results and data from the literature show that inhibition of germination at temperature regimes characteristic of open sun conditions can be found in fleshy-fruited species of widely divergent taxonomic groups. It is predicted that germination mechanisms to detect canopy shade based on temperature cues are widespread in species depending on nurse plants, especially bird-dispersed species.