Warming prevents the elevated CO₂‐induced reduction in available soil nitrogen in a temperate, perennial grassland

Abstract

Abstract Rising atmospheric carbon dioxide concentration ([CO 2 ]) has the potential to stimulate ecosystem productivity and sink strength, reducing the effects of carbon (C) emissions on climate. In terrestrial ecosystems, increasing [CO 2 ] can reduce soil nitrogen (N) availability to plants, preventing the stimulation of ecosystem C assimilation; a process known as progressive N limitation. Using ion exchange membranes to assess the availability of dissolved organic N, ammonium and nitrate, we found that CO 2 enrichment in an Australian, temperate, perennial grassland did not increase plant productivity, but did reduce soil N availability, mostly by reducing nitrate availability. Importantly, the addition of 2 °C warming prevented this effect while warming without CO 2 enrichment did not significantly affect N availability. These findings indicate that warming could play an important role in the impact of [CO 2 ] on ecosystem N cycling, potentially overturning CO 2 ‐induced effects in some ecosystems.