Improved grasslands dominate many parts of Europe, where they sustain livestock farming - a major but fragile component of the agricultural economy. Climate change will inevitably lead to changes in agroecosystem functioning. Against a backdrop of increasing atmospheric CO2, ground-level O3 and temperature, the UK and many areas of the world have recently witnessed unprecedented extreme weather patterns impacting on the capacity of agricultural grasslands to deliver a range of ecosystem services (e.g. food security, carbon and water storage, biodiversity). To future-proof the ecological, socioeconomic and cultural aspects of agricultural landscapes, land users will need to adapt management practices to meet this challenge. Critically, we need to develop regimes which provide resistance to more than one stress (multi-stress resilience). Focusing on flooding, drought and ozone pollution extremes, this project aims to provide benchmark information on grassland responses to individual stresses, quantify tipping points for regime shifts, after which pasture productivity, quality and soil function are irretrievably damaged, and establish fundamental relationships between shifts in above- and below-ground diversity and function. To achieve this, intact sample mesocosms were taken from a typical UK grazed grassland and stressed for varying lengths of time, replicating extreme weather events. Measurements were designed to reveal whether there is a gradual deterioration in ability to recover with increasing exposure to stress, or whether there is a move to a new irreversibly different steady state.
Results/Conclusions
The results from this year-long experiment generally indicate a severe decline in grassland forage production and soil quality after four to eight weeks of continuous drought, or just two weeks of continuous flooding. Total above- and below-ground biomass were significantly lower after prolonged drought and flooding, with no signs of healthy recovery after floods. Earthworm abundance was very low compared to the unstressed controls within two weeks of both drought and flooding, with their complete eradication, with no recovery, after longer periods of stress. Persistent flooding led to a significant release of greenhouse gasses (CH4 and N2O). Examination of microbial community structure showed diverging taxonomic communities within the soil for each extreme stress. Overall, the effects of severe stress from climate extremes was shown to have a significant effect on the provision of ecosystem services, the points at which the damages become irreversible being crucial in planning for land users, as well as developing new means to reduce their impact.