Spatial-temporal variation of soil organic matter decomposition potential in China

Soil organic matter decomposition is an essential process of the ecosystem biogeochemical cycle. However, the comprehension of soil organic matter decomposition mechanisms at a large-scale level remains relatively inadequate, especially due to the high variability in organic matter quality, which poses challenges for standardized analysis of decomposition. Therefore, in this study, standardized cotton strips (to represent cellulose) and wooden sticks (to represent lignin) were used to conduct field research on the decomposition potential of soil organic matter, comparing the mass loss of these standardized materials across 23 sites situated in different climate types in China. After 6 months of incubation, the decomposition rate of both substrates displayed an increasing trend from north to south and a decreasing trend from east to west, driven by variations in temperature and precipitation at a large scale. However, the decomposition pattern of wooden sticks along the latitude exhibited a reversal during summer, with a positive correlation between mass loss per unit temperature and latitude, possibly attributable to reduced constraints on decomposer activity at high latitudes in summer. These results suggest that the decomposition ability of decomposers is more powerful at high latitudes compared with the decomposers at low latitudes. Random forest analysis showed that decomposers, soil conditions and climate had significant effects on the decomposition of standardized organic matter at the large-scale. Notably, as decomposition progressed, the relative influence of the decomposers on the cotton strips mass loss significantly increased, while for wooden sticks, the relative influence of climate significantly increased. In summary, this study provides crucial evidence for the spatial characteristics and temporal dynamics of soil organic matter decomposition in large-scale patterns.