Turning Up the Heat: More Persistent Precipitation Regimes Weaken the Micro‐Climate Buffering Capacity of Forage Grasses During a Hot Summer

Developing climate-proof forage grasslands does not only require developing plant communities that are soil drought resistant, but also adept at buffering elevated atmospheric temperatures to minimize heat stress for plant and soil. Previous studies indicate that the emerging trend towards rainfall regimes with longer dry and wet spells negatively affects forage grass performance (i.e., greater physiological plant stress and yield loss) in Western Europe. We conducted a 120-day open-air experiment testing whether a hot summer (+3°C for the first 60 days) exacerbates the negative effects of increased persistence in precipitation regimes (PR) (3 vs. 30 days consecutive wet/dry) on the performance of four distinct forage varieties (Dactylis glomerata, Festuca arundinacea, Lolium perenne (tetraploid) and Lolium perenne (diploid)) across two soils differing in management history (permanent vs. temporary grasslands). Our results indicate that climate warming indeed worsens negative effects of more persistent PR on forage grass productivity and physiological plant stress by inducing more extreme soil drought and elevated micro-climatic temperatures, but permanent grassland soils with elevated organic carbon can buffer yields. Moreover, higher yielding varieties are more proficient at buffering soil surface and canopy temperatures and maintaining plant greenness and stomatal opening under water shortage and elevated temperatures (Dactylis and Festuca) were impacted less than those which could not (both Lolium cultivars). These results indicate that not only differences in resource-extraction traits but also the ability of a species to buffer its surrounding microclimatic conditions shapes its response to future climate change. Given the indirect positive effects such temperature-buffering traits may have on soil functioning (e.g., reduced soil respiration during heat waves limiting carbon loss), we argue that managers should also incorporate such traits when developing climate-proof forage grasslands.