Effects of management and temperature anomalies on grassland CO2 fluxes using a long-term eddy covariance dataset

Temperature anomalies, such as heatwaves and cold spells, are becoming increasingly common, posing significant challenges to ecosystem functioning and carbon sequestration. While temperature anomalies have been shown to influence broad-scale carbon flux patterns, their fine-scale effects, particularly in conjunction with agricultural management, remain poorly understood. This study investigates the impact of air temperature (Tair) anomalies on CO₂ fluxes in an upland mesic grassland under two grazing management regimes: low cattle grazing intensity and high cattle grazing intensity and fertilisation. Using 18 years (2003–2021) of CO₂ flux and climate data, we assessed gross primary productivity (GPP) and ecosystem respiration (Reco) responses to temperature anomalies, including cold, warm, extreme cold, and extreme warm conditions. The study site experienced an average of 40 anomalous temperature days per year, including ~10 days of extreme events. CO₂ fluxes were most affected by temperature anomalies during the early growing season, with the strongest increases in GPP and Reco observed in spring. Warm anomalies generally enhanced CO₂ fluxes in spring but suppressed them in summer and autumn, particularly under extreme warm conditions lasting more than six days. This suppression likely reflects the exceedance of a temperature stress threshold (~20°C). Management intensity modulated these responses. High-intensity grazing and fertilisation increased the sensitivity of CO₂ fluxes to warm anomalies, whereas low-intensity grazing appeared to buffer fluxes against temperature-induced stress. Cold anomalies promoted asynchrony between patterns of grassland carbon uptake and release, adding further complexity to temperature–flux relationships. Our findings emphasize the importance of management × climate interactions in shaping CO₂ flux responses. Low-intensity management regimes may enhance ecosystem resilience to warming in cool temperate grasslands, providing a potential adaptation strategy under climate change. This study highlights the importance of long-term, field-based research to refine our understanding of how grasslands can maintain their carbon sink capacity amidst increasing temperature extremes.