Responses of Soil Organic Carbon Decomposition and Temperature Sensitivity to N and P Fertilization in Different Soil Aggregates in a Subtropical Forest

Soil organic carbon (SOC) decomposition, a key process controlling the carbon (C) loss from terrestrial soils to the atmosphere, varies with soil aggregate size and is influenced by increasing nitrogen (N) and phosphorus (P) inputs from anthropogenic activities. However, how increasing N and P affects SOC decomposition and its temperature sensitivity (Q(10)) in soil aggregates remains unclear. Thus, we collected soils from a subtropical Cunninghamia lanceolata forest receiving N and P addition for 8 years to explore the interactive effects of N and P fertilization on SOC decomposition and its Q(10) in mega-aggregates (>2 mm, MeA), macroaggregates (0.25-2.0 mm, MaA), and microaggregates (<0.25 mm, MiA). Results showed that aggregate size has a huge influence on SOC decomposition and its Q(10). Specifically, SOC decomposition in MiA is 49.2% and 26.0% higher than MeA and MaA, respectively. Moreover, the averaged Q(10) values were 2.29, 2.26 and 1.83 in MeA, MaA and MiA. SOC decomposition significantly increased by 39.4% in MaA and 23.7% in MiA with N fertilization, but P fertilization had less impact. However, P fertilization increased Q(10) by 46.7% in MeA and 46.6% in MaA. Furthermore, we found P fertilization changed the influences of N fertilization on SOC decomposition in MaA and MiA but had no effect on responses of Q(10) to N fertilization. Overall, our findings suggested that there were differences in SOC decomposition and Q(10) among aggregates, and fertilization treatment had an impact on them. Our results highlighted the significance of considering differences in SOC decomposition and its response to climate warming and nutrient input among different aggregates in the prediction of SOC dynamics and its feedback to environmental changes in terrestrial ecosystems under climate warming scenarios.