Organic C and N mineralization as affected by dissolved organic matter in paddy soils of subtropical China

In this study, dynamics of dissolved organic matter (DOM) and mineralization of soil organic C and N in subtropical China were investigated. Paddy and upland soils were derived from Tertiary sandstone, Quaternary red clay and river alluvium with low, middle, and high levels of soil fertility. Dissolved organic carbon contents (DOC) varied from 3.8 to 68.7 mg/kg and dissolved organic nitrogen contents (DON) ranged from 2.9 to 18.3 mg/kg, respectively, during the experimental period. Both DOC and DON increased with increasing soil fertility. The content of DOM was characterized by strong seasonal fluctuation in soils, and seasonal patterns showed the maximum value in Nov and the minimum in July. The contribution of DOM to mineralization of C and N was significantly affected by soil types and seasons. DOM removal significantly decreased the cumulative organic C mineralization in soils derived from Tertiary sandstone and River alluvium (by 1.6%–20.3% with an average of 7.1%), while it did not significantly change those in soils derived from Quaternary red clay. Similarly, the cumulative mineralization of N in paddy soils after DOM removal decreased by 6.7%–27.3% over seasons. In this study, DOM played an important role in soil C and N mineralization in subtropical China. It appears that contribution of DOM to minerilization of C and N in paddy soils was possibly related to DOM content and composition.