Annual yields of multispecies grassland mesocosms outperformed monocultures across a drought gradient due to complementarity effects and rapid recovery

Background: More frequent and severe drought events due to climate change pose a major challenge for sustainable forage production in managed grasslands. This study investigated whether multispecies grassland communities can provide greater resistance to and/or recovery from drought compared to monoculture communities. Methods: Mesocosms of Lolium perenne L., Cichorium intybus L., Trifolium repens L. and Trifolium pratense L. were established as monocultures, and a four-species mixture. A drought gradient with five levels of water supply ranging from a mild to a severe treatment was applied for 10 weeks, in each of 2 years. Shoot biomass was harvested to assess drought resistance, drought recovery and annual yields. Root mass density and specific root length were measured in Year 2. Results: Across the drought gradient, four-species communities had significantly larger annual yields than each of the four monocultures, indicating transgressive overyielding. This was despite relatively low drought resistance for four-species communities compared with L. perenne and C. intybus monocultures. Recovery of yields following drought was high for all communities. Conclusions: Multispecies swards with complementary traits can provide a viable adaptation option across a wide range of drought severities. Application of a stress gradient methodology allowed a more detailed understanding of stress responses.