Summary1. While plant competition for light has received considerable attention, the facilitative effect that shading can have on plants and the role of species-specific adaptations in mediating this phenomenon are still poorly understood. Evidence is accumulating, however, that positive interactions can play as important a role in community structuring as has been shown for competition. 2. We examined interspecific variation in growth responses to shade using 46 temperate grassland species grown for 10 weeks in a common garden under identical soil conditions but at different levels of shading. The importance of morphological plasticity and habitat preference as species traits determining the net effect of shading on plant growth was tested. 3. Moderate shade (50% daylight) had, on average, a net facilitative effect on plant mass. Plant growth in the 25% daylight treatment was not significantly different from that in full daylight, and it was only when 90% of natural light was made unavailable that shaded plants attained a significantly lower dry mass than plants in full daylight. 4. Species that exhibited the most pronounced reduction in specific leaf area and increased allocation to roots in full compared with 50% daylight were least facilitated by shading. This finding supports the hypothesis that morphological plasticity is an important trait determining the strength of facilitative interactions. 5. The growth response to shade was also dependent on species' ecological optima, with species characteristic of nutrient-poor or dry habitats most facilitated by shade. Greater growth enhancement by shade in grassland stress-tolerant plants is surprising because such species frequently occupy unproductive vegetation with little shade and should therefore be adapted to high irradiance. This result calls into question the notion that a positive effect of shade on growth always reflects stress amelioration. 6. Synthesis. Our study demonstrates a widespread ability of plant species to decouple growth from resource availability and challenges our understanding of the processes determining plant productivity.

Several theoretical considerations imply that high shoot morphological plasticity could increase competition symmetry and favour plant coexistence. We tested whether mean plasticity across co-occurring species is a key trait for explaining ramet density and species richness in herbaceous vegetation. We used three data sets to test the hypotheses: (a) experimentally achieved estimates of plasticity to light availability for 35 herbaceous species; (b) richness, ramet density and canopy architecture data from 17 herbaceous communities; (c) species richness data from a 5-year permanent-plot study in a calcareous grassland. In herbaceous communities containing species with relatively higher shoot plasticity, ramet density was significantly higher. Consequently, relatively more species were growing per unit area-a greater proportion of the community species pool was represented on 1 m(2). In the permanent plot study species-richness was higher in those 40 x 40 cm quadrats where species with high shoot plasticity prevailed-there was a positive regression of richness on the mean plasticity of species. This relationship was highly significant in five consecutive years. Our results suggest that shoot plasticity to light availability is evidently one of the key traits in processes that alter the density of co-existing plants and, therefore, species diversity in herbaceous communities.

Little is known about the consequences of phenotypic plasticity in co-existing species for plant community structure. However, it has been proposed that the potential of plants to exhibit plastic responses to light availability could be a key factor determining the capability of individuals to co-exist at small scales. Our previous research demonstrated that morphological plasticity to light was positively related to small-scale species richness in a temperate grassland. However, it remained unclear whether this relationship was solely due to a higher shoot density in plastic assemblages, or whether diversity was directly related to the morphological plasticity of the co-inhabitants. We used two data sets to clarify this relationship: experimentally acquired estimates of plasticity to light availability for 45 herbaceous plant species, and species richness and ramet density data from a 2-year permanent plot study in a semi-natural calcareous grassland. There was little ramet mortality observed in the permanent plot study indicating that the link between plasticity and richness does not operate through reduced mortality in more morphologically plastic assemblages. The local density of ramets explained most of variation in small-scale richness, but there was also a significant direct density-independent effect of mean shoot plasticity on richness, showing that plasticity to light directly enhances the small-scale co-existence of species.

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Aim The occurrence, relative richness and abundance of N‐fixing plants are the main features of the N‐fixing potential of vascular plant communities. We aimed to unveil how climate, biome type and land management regime affect the N‐fixing potential of vegetation. Since the world is witnessing an invincible transition of all those environmental factors during the last century, we examined the global growth trends of N‐fixers throughout recent history. Location Global. Taxon Vascular plant species. Materials and Methods We conducted a meta‐analysis of publicly available vegetation data from 290 communities. Combined with the species' N‐fixation capability, we examined the occurrence, abundance and richness of N‐fixing vascular species across varying climate conditions, land use regimes and potential habitat types. Results There are relatively more N‐fixing vascular plants in warmer and drier climatic conditions. Management of communities by cutting woody plants, grazing and mowing hay increases the number and abundance of N‐fixing species. The effect of management is pronounced in wet conditions, where a dense canopy would otherwise emerge. As a result, semi‐natural grasslands exhibit higher N‐fixer occurrence than natural grasslands and non‐tropical forests, cessation of management results in a temporary increase in the abundance of N‐fixers. Repeated observations of sites indicated that the global occurrence of N‐fixers increased slightly in managed communities from 1906 to 2018, but there were no other temporal trends. Main conclusions The overall number of N‐fixers in plant communities is low. The occurrence, relative richness and abundance of N‐fixing species are higher in sparse vegetation in dry climates and in extensive management where biomass is removed from communities. A probable explanation is the high light availability in dry vegetation and due to biomass removal, which provides a competitive advantage to light‐demanding N‐fixers. A lack of consistent temporal trends suggests that global change is not yet an active driver of N‐fixing potential in plant communities.