Linking Leaf Economic Traits With Forage Quality Across Temperate Grasslands Under Ambient and Drought Conditions

Increases in droughts may disrupt the life-supporting services of grasslands, including the forage provision for herbivores. However, less is known about drought impacts on forage quality (i.e., dynamics of the cell characteristics of leaves and stems of herbs). Leaf economic traits reflect drought effects on plant communities, but whether they can predict forage quality patterns under drought remains unclear. We assessed the effects of early- and late-season extreme droughts on (i) forage quality parameters [readily digestible, internal cellular constituents: protein, minerals, water-soluble carbohydrate (WSC); and non-readily digestible, cell wall components: neutral detergent fibre (NDF) and acid detergent fibre (ADF)]; (ii) community-weighted leaf traits [specific leaf area (cwmSLA) and leaf dry matter content (cwmLDMC)]; and (iii) leaf traits-quality parameters relationships across three grasslands over two growing seasons. Both early and late droughts decreased ash and ADF and increased WSC across sites, while early drought slightly reduced protein and NDF. Both droughts decreased cwmSLA and increased cwmLDMC across sites. Community-weighted leaf traits and forage quality parameters were unrelated under early ambient conditions, but their relationships under early-season drought imply that lower cwmSLA and higher cwmLDMC communities had higher forage quality (higher protein and less lignified fibre contents) than higher cwmSLA and lower cwmLDMC communities. Under late-season ambient or drought conditions, most relationships indicate that lower cwmSLA and cwmLDMC communities had higher forage quality (higher protein and ash, and more digestible fibre contents) than higher cwmSLA and cwmLDMC communities. Overall, forage quality was higher under late-season ambient conditions compared to the early season, and both drought types had limited negative effects on forage quality in the studied grasslands. Moreover, leaf traits can predict forage quality patterns and plants' adaptation under certain circumstances, including regular intra-seasonal dry periods and extreme drought conditions.