CO2 absorption of sandy soil induced by rainfall pulses in a desert ecosystem

Abstract

Soil CO2 flux is strongly influenced by precipitation in many ecosystem types, yet knowledge of the effects of precipitation on soil CO2 flux in semi-arid desert ecosystems remains insufficient, particularly for sandy soils. To address this, we investigated the response of sandy soil CO2 flux to rainfall pulses in a desert ecosystem in northern China during August-September 2011. Significant changes (P<0.05) were found in diel patterns of soil CO2 flux induced by small (2.1mm), moderate (12.4mm) and large (19.7mm) precipitation events. Further analysis indicated that rainfall pulses modified the response of soil CO2 flux to soil temperature, including hysteresis between soil CO2 flux and soil temperature, with Fs higher when Ts was increasing than when Ts was decreasing, and the linear relationship between them. Moreover, our results showed that rainfall could result in absorption of atmospheric CO2 by soil, possibly owing to mass flow of CO2 induced by a gradient of gas pressure between atmosphere and soil. After each precipitation event, soil CO2 flux recovered exponentially to pre-rainfall levels with time, with the recovery times exhibiting a positive correlation with precipitation amount. On the basis of the amounts of precipitation that occurred at our site during the measurement period (August-September), the accumulated rain-induced carbon absorption evaluated for rainy days was 1.068gCm-2; this corresponds approximately to 0.5-2.1% of the net primary production of a typical desert ecosystem. Thus, our results suggest that rainfall pulses can strongly influence carbon fluxes in desert ecosystems.