Effekte von Diversität und Ressourcenverfügbarkeit auf der Plastizität funktioneller Eigenschaften von Pflanzen, pflanzliche Interaktionen und die Bestandsproduktivität
Zusammenfassung der Projektergebnisse
Complementarity in the acquisition and use of resources, which requires functional differences among species, has been suggested as a major driver for species coexistence and positive diversity-ecosystem functioning relationships. In this project, we investigated how the availability of light and nutrient availability known as key resources limiting plant growth in temperate grasslands affect (1) the expression of functional traits and functional differences among grassland species, and (2) plant diversity effects on productivity-related ecosystem processes. We established a field experiment with monocultures, two- and four-species mixtures based on a pool of eight common grassland species assigned to different functional groups (grasses vs. forbs) and varying in growth stature (small vs. tall). All species combinations had four replicates, which were exposed to different levels of resource availability combining the manipulation of light availability through shading and nutrient availability through fertilization. In addition, all species were grown as separate plant individuals in a pot experiment at different levels of light and nutrient availability. These experiments demonstrated that traits associated with allocation and resource uptake showed the strongest responses to resource availability. Due to varying magnitudes in the strength of trait variation among species assigned to different functional groups (grasses > forbs) and varying in growth statures (small-statured > tall-statured) trait-based ranking of species was not consistent across environments in many aboveground traits, while species ranking was more stable in belowground traits. Consequently, functional dissimilarity among species depended to some degree on resource availability, but the effects of intraspecific trait variation on functional diversity were small compared to functional differences between species. Although community-level aboveground biomass production did not increase with increasing mixture species richness of the experimental communities, mixtures produced on average more aboveground biomass than expected from their monocultures. These positive diversity effects on aboveground biomass production varied with resource availability and were stronger without fertilization. Small-statured species had generally lower relative yields than tall-statured species, while differences among functional groups in their relative yields depended on resource availability. The functional composition of the experimental communities had also stronger effects than species richness on belowground biomass production suggesting a greater potential for complementary use of belowground resources when species with different rooting patterns grow in combination. In summary, the results of our project show that it is important to consider the environmental context and the functional composition of plant communities to get a better mechanistic understanding of diversityecosystem functioning relationships.
