Combined experimental drought and nitrogen loading: the role of species dependent leaf level control of carbon and water exchange in a temperate grassland
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Combined experimental drought and nitrogen loading: the role of species dependent leaf level control of carbon and water exchange in a temperate grassland
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Nitrogen (N) loading and extreme drought were found to strongly alter biomass production, species composition, carbon and water fluxes of temperate grasslands. Such changes at the community level are often attributed to species and functional group‐specific responses in phenology and/or physiology. In a multifactorial field experiment, we studied the responses of three abundant grassland species (forb Centaurea jacea, grasses Arrhenatherum elatius and Dactylis glomerata) to N loading and extreme drought, focusing on responses in carbon and water relations at the leaf level. We analyzed 1) changes in bulk leaf N (uptake efficiency of additional N), 2) adaptation of plant water status (leaf water potential) and 3) the impact on leaf carbon and water fluxes. We observed more efficient N utilization in both grasses compared to C. jacea. Naturally occurring summer drought impacted the plant water status of all species significantly while extreme drought treatment only affected water status additionally during and after summer drought. C. jacea was able to maintain much lower leaf water potentials compared to grasses during drought. Despite these clear species‐specific responses to N loading and drought in bulk, species were able to maintain homeostasis of leaf carbon and water fluxes. Thus, strong declines in the (community) carbon sequestration observed at this site during the (natural) summer drought were not related to leaf physiological responses in assimilation but driven by phenological adaptions of the species community: The drought sensitive grasses, even though exhibiting a higher N uptake efficiency, responded with a shortened life cycle to severe summer drought.