Precipitation reduction rather than nitrogen deposition promotes soil organic carbon sequestration by improving aggregate stability: Implications from 13C natural abundance.

Nitrogen (N) deposition and precipitation reduction shift soil organic carbon (SOC) turnover and can change the intensity of SOC stabilization pathways in the aggregate system. This study aimed to reveal the effect of 10 y of N access (50 kg N ha−1 yr−1 (N50)) and precipitation reduction (−30%, (PREC)) simulated in mixed temperate forest, with the predominance of Korean pine (Pinus koraiensis), on SOC stabilization pathways using a13C natural abundance approach. Control, N addition, PREC, and their interaction (PREC + N50) were carried out in a randomized complete block design with split plots. PREC increased SOC compared to the control because of the accumulation of coarse particulate organic matter (CPOM) and microbial residues by 12–147%. In contrast, bulk SOC was unaffected by N50 and PREC + N50; only a decrease in the C content in microaggregates occluded in macroaggregate fractions (−20%), and an increase in microbial residues of bulk soil was found. Based on the 13C natural abundance, C pathways were from microaggregates to macroaggregates and from CPOM to the mineral-associated organic matter in macroaggregates. The intensity of the C flows decreased in the PREC, with an increase of plant-derived C within aggregates in the CPOM. The intensity of the C flows increased in N50 and PREC + N50. These results suggested that precipitation reduction promoted plant-derived C accumulation through increasing aggregate stability; in contrast, under the N50 and PREC + N50, SOC increases through microbial residue accumulation. • Pathways of SOM formation under N deposition and rainfall decrease were clarified. • Rainfall reduction stimulated SOM accumulation by increasing aggregate stability. • Microbial residue accumulation enhanced SOM stability under N deposition. • The 13C natural abundance distinguished C flows in response to climate change. [ABSTRACT FROM AUTHOR]