Integrating Ecological Stoichiometry to Understand Nutrient Limitation and Potential for Competition in Mixed Pasture Assemblages

Much is known about growth and nutrient uptake traits and ecological stoichiometry in natural systems. However, these concepts have been comparatively understudied in agricultural systems despite their potential to infer nutrient limitation and interspecific resource competition. This study established a model mixed pasture system to assess tissue C:N and C:P stoichiometry and aboveground biomass (AGB) in a grass (Phalaris aquatica) and legume (Trifolium vesiculosum) under factorial inputs of high and low nitrogen (N) and phosphorus (P), in monoculture and mixture. Due to inherent trait diversity, we expected grass and legume growth, shoot vs root stoichiometry and N:P homeostasis to differ in response to nutrient limitation and between monoculture and mixture. Grass AGB was greater with N addition and in mixture, and legume AGB was decreased by N but increased by P, more so in mixture. Nutrient limitation in grass was determined via a strong coupling of growth with shoot stoichiometry, by which AGB decreased and C:N increased under N limitation. Legume growth was not correlated with tissue stoichiometry, but potential for growth limitation by N and P was detected via increased shoot C:N under low N and P, and C:P under low P. Legume shoot N:P was more homeostatic than grass, and grass shoot N:P homeostasis was greater in mixtures than in monocultures. Integrating ecological stoichiometry alongside trait-based ecology is a useful tool for predicting how fertiliser management may affect nutrient balance and species dominance in mixed pasture agroecosystems.