Abstract:

Pulse effects of precipitation cause soil organic matter to rapidly decompose and release CO₂ in a short period. The pulse effects of precipitation are important for ecosystem C cycling and soil C balance, although their spatial variation in forest soils and the underlying mechanisms remain unclear.

Soil samples (0–10 cm) from 22 typical forest ecosystems in eastern China were used, to investigate the effects of simulated pulse precipitation on soil microbial respiration rates (R_s). We simulated pulsed precipitation to reach 65% water-holding capacity, the R_s was measured on a minute scale for 48 h.

Precipitation pulses can cause a rapid 1.70–38.12-fold increase in the rate of mineralized decomposing organic matter. Maximum R_s (R_s-soil-max), cumulative R_s (A_Rs-soil) and the time taken to arrive at the maximal R_s (T_Rs-soil-max) were significant differences among different soil samples. Furthermore, the pulse effects in different climate zones were significantly different. R_s-soil-max (11.701 µg C g−1soil h−1) and A_Rs-soil (300.712 µg C g−1 soil) were the highest in the mid-temperate zone. Soil chemical properties (total C and, N, pH and oxidation–reduction potential) and soil fractions were strongly correlated with the pulse effects in forest soils, but soil microbes contributed less. Our findings demonstrated that the pulse effects increase forest soil carbon emissions in the short term at a regional scale, and identified the factors with the greatest influence on this change. These findings help guide future studies on the C cycles of forest ecosystems and regulating ecosystem C cycles.

Key words: soil respiration, carbon, mineralization, pulse effect, forest, spatial variation