Soil carbon mineralization in response to nitrogen enrichment in surface and subsurface layers in two land use types

PeerJ. 2019 Jul 8;7:e7130. doi: 10.7717/peerj.7130. eCollection 2019.

Abstract

Atmospheric nitrogen (N) deposition increases N availability in soils, with consequences affecting the decomposition of soil carbon (C). The impacts of increasing N availability on surface soil C dynamics are well studied. However, subsurface soils have been paid less attention although more than 50% soil C stock is present below this depth (below 20 cm). This study was designed to investigate the response of surface (0-20 cm) and subsurface (20-40 cm and 40-60 cm) C dynamics to 0 (0 kg N ha-1), low (70 kg N ha-1) and high (120 kg N ha-1) levels of N enrichment. The soils were sampled from a cropland and a grass lawn and incubated at 25 °C and 60% water holding capacity for 45 days. Results showed that N enrichment significantly decreased soil C mineralization (Rs) in all the three soil layers in the two studied sites (p < 0.05). The mineralization per unit soil organic carbon (SOC) increased with profile depth in both soils, indicating the higher decomposability of soil C down the soil profile. Moreover, high N level exhibited stronger suppression effect on Rs than low N level. Rs was significantly and positively correlated with microbial biomass carbon explaining 80% of variation in Rs. Overall; these results suggest that N enrichment may increase C sequestration both in surface and subsurface layers, by reducing C loss through mineralization.

Keywords: C sequestration; Land use types; Nitrogen enrichment; Soil c mineralization; Subsurface soil C.

Grant support

This research was funded by the Higher Education Commission (HEC, Pakistan) under grant No: 21-613/SRGP/R&D/HEC/2015 and National Key Research and Development Program of China (2017YFA0604300, 2018YFA0606500). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.