Resilience and resistance of ecosystem functional response to a precipitation pulse in a semi‐arid grassland

Abstract

Summary In water‐limited ecosystems, discrete precipitation events trigger brief but important episodes of biological activity. Differential responses of above‐ and below‐ground biota to precipitation may constrain biogeochemical transformations at the ecosystem scale. We quantified short‐term dynamics of whole ecosystem response to 39 mm irrigation events (precipitation pulses) during June 2002 and 2003 using plant physiological and ecosystem gas‐exchange measurements as state variables in a principal components analysis (PCA). Experimental plots consisted of either native (Heteropogon contortus L.) or non‐native (Eragrostis lehmanniana Nees) bunchgrasses planted in monoculture on two distinct geomorphic surfaces in a semi‐arid grassland. For 15 days, treatments followed similar, non‐linear trajectories through state variable space with measurement periods forming distinct clusters; PCA axes 1 and 2 combined to explain 80.7% of the variation during both 2002 and 2003. During both years, bunchgrass species interacted with soil type such that there was a reduction in ecosystem functional resistance in plots planted with the non‐native bunchgrass species on the fine‐textured clay geomorphic surface. System‐level hysteresis, emerging as a result of independent responses of photosynthesis, respiration and evapotranspiration to precipitation, indicated the potential for alternative functional states. Quantifying the frequency and duration of ecosystem alternative functional states in response to individual precipitation events within a season will provide insights into the controls of species, soils and climate on ecosystem carbon and water cycles.