Impact of microclimatic stressors on carbon dynamics in an agroecosystem in eastern Germany

Abstract Rising temperatures and shifting precipitation patterns can lead to altered water balances. This can increase the frequency of drought conditions, with strong implications for agricultural carbon uptake. Understanding the complex interplay between energy, water, and carbon fluxes and their coupling to vegetation is essential for characterizing carbon dynamics in agricultural ecosystems under ongoing climate change. This study investigates these interactions, focusing on how microclimatic conditions and soil water levels influence carbon dynamics in an irrigated apple tree orchard (agricultural region) in Germany during the growing seasons over the time period of March 2023 till November 2024. Using an eddy covariance flux tower installed over the apple trees, we quantified carbon fluxes, i.e. gross primary production (GPP) and ecosystem respiration (Reco), and examined the variability of GPP under varying climatic conditions. Energy- and water-limited regimes were characterized using the Ecosystem Limitation Index (ELI), and the impacts of a flash drought event on GPP were analyzed. The results showed that GPP was significantly influenced by vapor pressure deficit (VPD). Under energy-limited conditions, moderate levels of net radiation (Rn) and sufficient soil water content (SWC) enhanced GPP. In contrast, water-limited conditions, characterized by high Rn and VPD combined with low SWC, reduced GPP due to strong land-atmosphere coupling. During a flash drought event, the simultaneous occurrence of low SWC and high VPD depleted soil water availability, exacerbating plant water stress and further suppressing GPP. The findings revealed that irrigation could not fully mitigate these effects, highlighting the vulnerability of agricultural systems to extreme climatic stresses. This study underscores the critical role of SWC and VPD coupling in regulating carbon uptake during water-limited conditions. As flash droughts become more frequent with climate change, their impacts on carbon dynamics could significantly reduce the carbon uptake potential of agricultural ecosystems. Graphic abstract