Species ecological strategy and soil phosphorus supply interactively affect plant biomass and phosphorus concentration

Background and aim: Excess soil phosphorus often constrains ecological restoration of degraded semi-natural grasslands in Western-Europe. Slow-growing species, often target for restoration, are at a disadvantage because they are outcompeted by fast-growing species. Gaining insight into the responses of plant species and communities to soil phosphorus availability will help understanding restoration trajectories of grassland ecosystems. Methods: We set up a pot experiment using twenty grassland species with contrasting growth forms (i.e. grasses versus forbs) and nutrient use strategies (i.e. acquisitive versus conservative nutrient use). We quantified the nutrient use strategy of a species based on the stress-tolerance value of the CSR framework (StrateFy, Pierce et al. 2017). We grew these species as monocultures and in mixtures along a soil phosphorus gradient and measured the aboveground biomass and plant phosphorus concentrations. Results: We found plant phosphorus to increase with soil phosphorus supply, but observed no biomass response. Forbs had higher plant phosphorus concentrations compared to grasses both in monocultures and mixtures. The species’ nutrient use strategy had contrasting effects on plant tissue phosphorus concentrations, depending on the amount of phosphorus supply (interaction effect) and the biomass of the vegetation (dilution effect). Species with conservative nutrient use strategies survived and even thrived in under excess soil phosphorus availability. Conclusion: Our findings contribute to the knowledge required for successfull ecological restoration of species-rich grasslands. Adopting a trait-based approach enabled us to link findings from comparative ecological studies with insights from (eco)physiological research