Plant traits and species interactions along gradients of N:P:K stoichiometry
Final Report Abstract
The goal of the research fellowship was to explore the relationships of plant responses (measured as plant trait responses) towards gradients of nitrogen (N), phosphorus (P) and potassium (K) availabilities in a comparative way, for both plant species grown in monocultures and in mixed communities. The motivation for the studies are higher nutrient input rates into natural ecosystems due to anthropogenically induced nutrient emissions with partly unknown consequences for biodiversity and community composition. N and P as crucial plant elements and regulatory factors for plant community structures have been widely studied. However, the role of K as limiting resource has yet to be explored, and yet there is no study investigating the role of K in direct comparison to N and P for plant growth and species composition. Relationships between nutrient availabilities and plant responses were investigated by conducting a greenhouse experiment, for which the results indicate that the pre-emption theory, a well-known theory in plant strategies, may be expanded to P- and K-availabilities, and not only to N-availabilities, as is the current state of knowledge. The study further shows that plant responses differ between the type of nutrient that is limiting and/or in abundance. So far a lot of studies encompass nutrients without differentiating between the specific type of nutrient (e.g. N, P or K). Our study shows for at least 12 measured plant traits distinct responses towards either type of nutrient and by that enlarge the body of scientific knowledge of plant responses and highlight the necessity to distinctively address and relate functional plant responses to distinct nutrients. The statistical analyses of this study are complete. A further goal of the research fellowship was to conduct meta-analysis between resource stoichiometry and plant tissue stoichiometry. This is done by two ongoing meta-analyses, both focusing on log-response ratios (LRRs) of biomass towards both a) LRR of tissue nutrient concentrations and LRR of tissue nutrient stock and b) resource N:P ratios and community N:P ratios of terrestrial, marine and aquatic primary producers. Results of LRR-biomass towards LRR-concentration and LRR-stocks indicate in part deviations from expectations derived from current scientific concepts, or in other words, responses of nutrient concentrations and stocks in plant tissue follow few ecological concepts and not multiple. As data distribution is in part not as expected (negative LRR-values) we are currently in the state of conducting further statistical analyses to elucidate possible reasons for data distribution and to further understand the underlying processes that drive the responses. Hence, the statistical analyses are yet incomplete. Results of the second meta-analysis confirm formulated hypotheses for terrestrial and marine plants, however, relationships are not as strong as expected. Responses of aquatic plants take an intermediate position between terrestrial and marine plants. A comparison of the data with another existing dataset of a grassland fertilisation study is still pending, so that the statistical analyses are in progress.
