Effects of Temperature and Moisture on Soil Organic Matter Decomposition Along Elevation Gradients on the Changbai Mountains, Northeast China

Decomposition of soil organic matter (SOM) is of importance for CO2 exchange between soil and atmosphere and soil temperature and moisture are considered as two important factors controlling SOM decomposition. In this study, soil samples were collected at 5 elevations ranging from 753 to 2 357 m on the Changbai Mountains in Northeast China, and incubated under different temperatures (5, 10, 15, 20, 25, and 30 degrees C) and soil moisture levels (30%, 60%, and 90% of saturated soil moisture) to investigate the effects of both on SOM decomposition and its temperature sensitivity at different elevations. The results showed that incubation temperature (F = 1425.10, P < 0.001), soil moisture ( F = 1327.65, P < 0.001), and elevation ( F = 1937.54, P < 0.001) all had significant influences on the decomposition rate of SOM. The significant effect of the interaction of incubation temperature and soil moisture on the SOM decomposition rate was observed at all the 5 sampling elevations (P < 0.001). A two-factor model that used temperature and moisture as variables fitted the SOM decomposition rate well (P < 0.001) and could explain 80%-93% of the variation of SOM decomposition rate at the 5 elevations. Temperature sensitivity of SOM decomposition, expressed as the change of SOM decomposition rate in response to a 10 degrees C increase in temperature (Q(10)), was significantly different among the different elevations (P < 0.01), but no apparent trend with elevation was discernible. In addition, soil moisture and incubation temperature both had great impacts on the Q(10) value (P < 0.01), which increased significantly with increasing soil moisture or incubation temperature. Furthermore, the SOM decomposition rate was significantly related to soil total Gram-positive bacteria (R-2 = 0.33, P < 0.01) and total Gram-negative bacteria (R-2 = 0.58, P < 0.001). These findings highlight the importance of soil moisture to SOM decomposition and its Q(10) value, which needs to be emphasized under warming climate scenarios.