Post-drought rewetting triggers substantial K release and shifts in leaf stoichiometry in managed and abandoned mountain grasslands

Abstract

When soil is rewetted after drought, typically a transient pulse of mineralization and other microbial processes occur. This “Birch effect” translates into a temporarily elevated soil carbon dioxide efflux (SCE) and may alter nutrient availability. While rewetting effects on SCE have been frequently studied, effects on soil nutrient supply have rarely been considered despite potential relevance for plant nutrition during post-drought recovery. We investigated the magnitude of the post-drought rewetting effect on SCE, ion exchange membrane-derived soil nutrient supply rates and leaf stoichiometry in a drought experiment in the Austrian Alps. We conducted the experiment on a managed grassland (MG) and a nearby abandoned grassland (AG). Under drought, soil moisture depleted faster at MG than at AG. Upon rewetting, the SCE pulse was significantly larger at MG than at AG, whereas N, P and K supplies were more strongly stimulated at AG. A large, transient rewetting effect on soil K supply (MG: +363 ± 132%; AG: +821 ± 195%) was reflected in elevated K in leaves of Leontodon hispidus. Rewetting can alter post-drought nutrient availability in mountain grasslands, with particularly pronounced effects on soil K supply.