PNNL

Abstract

Temperature and precipitation simultaneously influence soil organic carbon (SOC) in agroecosystems. While their individual impacts have been extensively studied, their combined effects remain poorly understood at a regional scale. This study quantified the combined influence of temperature and precipitation on SOC in upland-crop fields of northern Jiangsu Province in eastern China. We used the DeNitrification-DeComposition (DNDC, version 9.5) model with the currently most detailed upland soil database in China. This 1:50,000 soil database contains 17,024 upland soil polygons that were generated using 983 upland soil profiles. Model simulations indicated that under a combined scenario of rising air temperature (T) of 2 °C and a simultaneous decrease (or increase) in precipitation (P) by 20%, the 3.93 Mha of upland soils in the study region sequestered 39.10 (or 37.39) Tg C from 2010-2039. The C sequestration from the combined effects of T and P on SOC was 2.40 (or 2.12) Tg C less, relative to the sum of the amount produced from the individual effect. Moreover, if the increase in T changed from 2 °C to 4 °C, with P still decreasing (or increasing) by 20%, the C sequestration further decreased by 1.2 (or 1.68) Tg C. Our analysis of the combined effects of T and P on SOC changes suggests that future warming and P change in this region may have a negative influence on SOC sequestration, despite the upland agroecosystems serve as a long-term sink for atmospheric CO2. Furthermore, SOC changes in different upland soil groups and administrative areas varied widely due to the heterogeneity in soil properties and fertilizer applications. This emphasizes the importance of detailed soil datasets and the need to adopt on-farm management practices to different soil groups and administrative areas under future climate change.