Effects of elevated CO2 and nitrogen addition on organic carbon and aggregates in soil planted with different rice cultivars

Elevated CO2 and nitrogen addition can increase rice yield and stimulate rice to absorb more nutrients from the soil. The aim of this study was to investigate how soil organic carbon and aggregates change under such high-output conditions. Rice cultivars IIY 084 and WYJ 21 (strong and weak response to elevated CO2, respectively) were planted in free-air CO2 enrichment (FACE) platforms. Treatments included: 1) elevated CO2 without nitrogen addition (EC); 2) nitrogen addition and ambient CO2 (EN); 3) combined elevated CO2 and nitrogen addition (ECEN); and 4): ambient CO2 without N addition (CK). Soil organic carbon (SOC), readily-oxidizable organic carbon (ROC) and soil aggregate components were measured. Treatment EC increased SOC and ROC, while EN decreased SOC and ROC compared to CK in soil under either rice cultivar. EC and EN decreased the percentage of large macroaggregates (LM) and the mean weight diameter (MWD) of aggregates compared to CK in ‘WYJ 21’ soil, while they increased LM and MWD in ‘IIY 084’ soil. ECEN increased LM and MWD compared to CK in soil under either rice cultivar. High productivity of ‘IIY 084’ through long-term cultivation under current N fertilization in future climatic conditions of elevated CO2 could be achieved due to increased soil aggregate stability and SOC.