Abstract
Changing precipitation patterns could affect soil carbon (C) cycling in China’s forests. A throughfall reduction (TFR) experiment was conducted in a warm-temperate oak forest in central China to examine effects of reduced precipitation on total soil respiration (SR), heterotrophic soil respiration (HR), autotrophic soil respiration (AR), soil microbial biomass, and fine root biomass from 2013 to 2016. Rain-out shelters, excluding ~50% of throughfall, were applied between May and September, thereby simulating a ~30% reduction in annual precipitation. Although soil moisture was significantly reduced during TFR, microbial biomass and HR remained unaffected. SR, AR, as well as fine root biomass increased during TFR in a comparable dry year, but remained unaffected during all other years. Annual rates of SR, HR, and AR were all unaffected by TFR. Our results indicate that a mild, steady, reduction in growing season precipitation does not affect soil organic matter decomposition in the oak forest ecosystem studied. Low SR rates during a natural dry-spell indicate that SR can be significantly decreased under more severe drought than imposed by the TFR treatment. Our data suggest a low soil moisture threshold of about 10 vol% for SR in the studied soil.
Highlights
Northern and north-central China experienced a decrease in mean annual precipitation between 1960–20101 and growing season precipitation is expected to decrease further until 2035 in parts of central China[2]
In contradiction to our hypotheses, heterotrophic soil respiration (HR) and microbial biomass remained largely unaffected by throughfall reduction (TFR)
The increase in soil respiration (SR) resulted from a strong increase in autotrophic soil respiration (AR) at TFR plots, which was accompanied by significantly higher fine root biomass in the topsoil
Summary
Northern and north-central China experienced a decrease in mean annual precipitation between 1960–20101 and growing season precipitation is expected to decrease further until 2035 in parts of central China[2]. Covering major parts of central China and ~15% (15.5 × 106 ha) of total forest areas[3], Quercus forests represent the largest vegetation C stock (671 Tg), which accounts for ~18% of all forest vegetation C in China[4] It yet remains unclear how these important forest ecosystems are affected by decreasing precipitation. We hypothesized that (I) TFR significantly decreased SR; that (II) HR was primarily affected by TFR because topsoil and litter (both rich in labile C and hosting major parts of the decomposer community) were expected to dry most severely With this regard, we hypothesized that (III) soil microbial biomass in the topsoil declined during TFR. Fine root biomass was expected to decrease in topsoil as a matter of water shortage[27,28,29]
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