Plant identity and evenness affect yield and trace gas exchanges in forage mixtures

© 2015, Springer International Publishing Switzerland. Aims: We explore the potential effect of plant diversity on yield and greenhouse gas exchanges in forage mixtures, identifying potential co-benefits between functions. Methods: Using the biodiversity-ecosystem function (BEF) modelling framework (Connolly et al. 2013), we analyse results from a field experiment where the relative sown proportion of three forage species (a grass, a legume, and a non-legume forb) was varied to obtain a gradient in species proportions and evenness. The exchange rates of N2O, CH4, NH3 and CO2 were measured, together with forage yield and soil inorganic N content. We conducted gas measurements 4 years after sward establishment during the expected period of highest emissions. Results: Results support the hypothesis that emission rates are affected by plant diversity. Sown evenness was found to decrease N2O exchange rates, and some evidence was found for a similar negative effect on CH4. Plant composition affected gas exchanges, with legume monocultures showing the highest emission rates for all gases. Diversity also increased yield and modulated NO3− and NH4+ soil concentrations. Conclusions: The integrated analysis of yield and emission response to species diversity allows the identification of a range of species proportions for which both functions are optimized. Diversifying forage legume-based systems could contribute to mitigation while improving ecosystem productivity.