Drought intensity alters productivity, carbon allocation, and plant nitrogen uptake in fast versus slow grassland communities

Grasslands face more frequent and extreme droughts, yet their responses to increasing drought intensity are poorly understood. Increasing drought intensity likely triggers abrupt shifts (thresholds) in grassland ecosystem functioning which can implicate recovery trajectories.
Here, we determined how drought intensity affects plant productivity, and plant-soil carbon (C) and nitrogen (N) cycling. We exposed model grassland plant communities with contrasting resource acquisition strategies (a fast- vs a slow-strategy plant community), to a gradient of drought intensity. The drought gradient ranged from well-watered to severely water-limited conditions. We identified thresholds of plant community productivity (above-ground biomass) at peak drought and two months after re-wetting, and measured net ecosystem exchange and ecosystem respiration of carbon throughout the drought and recovery phases. At peak drought and one week after re-wetting, we traced recently acquired C from plants to the ..., Experimental set-up
An outdoor mesocosm experiment was established at the Botanical Garden, University of Innsbruck, Austria (47°16'04.1\"N 11°22'46.3\"E), which included five sets of mesocosms (7 L plastic pots, 21 cm Ø, 25 cm height, n = 210). Two sets were destructively harvested throughout the experiment at: peak drought (set 1), early recovery (set 2), and the final three sets were used for non-destructive measurements throughout the experiment and to monitor recovery (sets 3-5). The drought treatment followed a gradient design, which optimizes the use of experimental units to determine thresholds and non-linear responses (Kreyling et al., 2018). We created the drought intensity gradient by determining the soil water content (SWC, gwater gfresh soil-1) at field capacity and then established a gradient of increasing drought intensity (increasing soil water deficit compared to field capacity, SWD) ranging from well-watered controls (20% SWD) to no water added in the drought period (98%...,