Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil

Soil moisture affects microbial decay of SOM and rhizosphere respiration (RR) in temperate forest soils, but isolating the response of soil respiration (SR) to summer drought and subsequent wetting is difficult because moisture changes are often con-founded with temperature variation. We distinguished between temperature and moist-ure effects by simulation of prolonged soil droughts in a mixed deciduous forest at the Harvard Forest, Massachusetts. Roofs constructed over triplicate 5 5m2 plots excluded throughfall water during the summers of 2001 (168mm) and 2002 (344mm), while adjacent control plots received ambient throughfall and the same natural temperature regime. In 2003, throughfall was not excluded to assess the response of SR under natural weather conditions after two prolonged summer droughts. Throughfall exclusion sig-nificantly decreased mean SR rate by 53mgCm2 h1 over 84 days in 2001, and by 68mgCm2 h1 over 126 days in 2002, representing 10–30 % of annual SR in this forest and 35–75 % of annual net ecosystem exchange (NEE) of C. The differences in SR were best explained by differences in gravimetric water content in the Oi horizon (r25 0.69