Soil moisture and ecosystem function responses of desert grassland varying in vegetative cover to a saturating precipitation pulse

Abstract

ABSTRACTA critical linkage between hydrological and ecological processes is plant cover, yet the ecosystem‐level responses of aridland systems of varying plant cover to extreme precipitation events, predicted to increase in the future, have not been well studied. We tracked volumetric soil water (θ15 cm) across the entire summer monsoon season, and ecosystem evapotranspiration (ET), net ecosystem carbon dioxide exchange (NEE), ecosystem respiration (Reco), gross ecosystem photosynthesis (GEP), and leaf‐level net carbon assimilation (Anet) and stomatal conductance to water vapour (gs) for 30 days in high‐cover (ca. 50%) and low‐cover (ca. 23%) plots in response to a runoff generating experimental rainfall. For 35 days following the pulse, θ15 cm was 2·5% higher in high‐cover plots compared to low‐cover values, with identical soil drying rates between cover conditions. After θ15 cm converged to similar values between cover conditions, dry‐down rates were longer in low‐cover plots. ET and gs did not differ between plots. For 7 days after the pulse, slower Anet development in some grass species compared to rapid development by the canopy dominant, Lehmann's lovegrass, may have resulted in similar GEP between low‐ and high‐cover plots. After this, GEP and Reco were higher and increased in parallel in high‐cover plots. In low‐cover plots, Reco levelled at + 21 days, resulting in similar NEE to high‐cover plots, even though GEP was lower. These findings suggest that low biomass in low‐cover areas may constrain Reco and lead to more evenly distributed productivity across semiarid grasslands following large, infrequent precipitation events. Published in 2011. This article is a US Government work and is in the public domain in the USA.