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Response of soil carbon to nitrogen and water addition differs between labile and recalcitrant fractions: Evidence from multi–year data and different soil depths in a semi-arid steppe
- Wang, Ruzhen, Dijkstra, Feike A., Liu, Heyong, Yin, Jinfei, Wang, Xue, Feng, Xue, Xu, Zhuwen, Jiang, Yong
- Catena 2019 v.172 pp. 857-865
- arid lands, carbon nitrogen ratio, carbon sequestration, clay fraction, field experimentation, lignin, models, nitrogen, nitrogen content, silt, soil depth, soil organic carbon, stable isotopes, steppes
- We examined the effect of nitrogen and water addition on soil carbon pool dynamics in a semi–arid grassland field experiment. Soils were sampled over a four–year period at different soil depths and analyzed for total soil organic carbon (SOC), oxidizable C (OxC), lignin and total nitrogen (TN) in bulk soil and the silt and clay fraction (<53 μm). We found that water but not N addition increased SOC (by 18.1%), OxC (by 12.2%), and TN (by 15.1%) in bulk soil. In contrast, SOC, OxC, and TN in the silt and clay fraction showed no change in response to both N and water addition. Both N and water addition showed no effect on total lignin concentration in soils. A more enriched 13C and lower C:N ratio in the silt and clay fraction indicated enhanced microbially processed C of relatively greater stability in this fraction compared to the bulk soil. Water addition promoted soil C sequestration by enhancing C input from plant materials as evidenced from more depleted soil δ13C compared to the ambient precipitation. We suggest that the increase in OxC was likely one of the main drivers of the larger SOC concentration with higher water inputs. Soil C fractions in subsoils were also affected by exogenous resource inputs in a similar way as surface soils. Future modeling work on soil C sequestration should consider the relative contribution of OxC and mineral–associated C to SOC changes.