Multivariate and scale-dependent controls of deep soil carbon after afforestation in a typical loess-covered region

Ruifeng Li; Xuanhua Zhang; Wangjia Ji; Xiaoling He; Zhi Li

doi:10.1016/j.jenvman.2024.120998

Multivariate and scale-dependent controls of deep soil carbon after afforestation in a typical loess-covered region

J Environ Manage. 2024 Apr 26:359:120998. doi: 10.1016/j.jenvman.2024.120998. Online ahead of print.

Authors

Ruifeng Li¹, Xuanhua Zhang¹, Wangjia Ji¹, Xiaoling He², Zhi Li³

Affiliations

¹ State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, College of Natural Resources and Environment, Northwest A&F University, Yangling, 712100, Shaanxi, China.
² State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, College of Natural Resources and Environment, Northwest A&F University, Yangling, 712100, Shaanxi, China. Electronic address: xiaolinghe@nwafu.edu.cn.
³ State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, College of Natural Resources and Environment, Northwest A&F University, Yangling, 712100, Shaanxi, China. Electronic address: lizhibox@nwafu.edu.cn.

PMID: 38677232
DOI: 10.1016/j.jenvman.2024.120998

Abstract

Afforestation is beneficial to improving soil carbon pools. However, due to the lack of deep databases, the variations in soil carbon and the combined effects of multiple factors after afforestation have yet to be adequately explored in >1 m deep soils, especially in areas with deep-rooted plants and thick vadose zones. This study examined the multivariate controls of soil organic carbon (SOC) and inorganic carbon (SIC) in 0-18 m deep under farmland, grassland, willow, and poplar in loess deposits. The novelty of this study is that the factors concurrently affecting deep soil carbon were investigated by multiwavelet coherence and structural equation models. On average, the SOC density (53.1 ± 5.0 kg m^-2) was only 12% of SIC density (425.4 ± 13.8 kg m^-2), with depth-dependent variations under different land use types. In the soil profiles, the variations in SOC were more obvious in the 0-6 m layer, while SIC variations were mainly observed in the 6-12 m layer. Compared with farmland (SOC: 17.0 kg m^-2; SIC: 122.9 kg m^-2), the plantation of deciduous poplar (SOC: 28.5 kg m^-2; SIC: 144.2 kg m^-2) increased the SOC and SIC density within the 0-6 m layer (p < 0.05), but grassland and evergreen willow impacted SOC and SIC density insignificantly. The wavelet coherence analysis showed that, at the large scale (>4 m), SOC and SIC intensities were affected by total nitrogen-magnetic susceptibility and magnetic susceptibility-water content, respectively. The structural equation model further identified that SOC density was directly controlled by total nitrogen (path coefficient = 0.64) and indirectly affected by magnetic susceptibility (path coefficient = 0.36). Further, SOC stimulated the SIC deposition by improving water conservation and electrical conductivity. This study provides new insights into afforestation-induced deep carbon cycles, which have crucial implications for forest management and enhancing ecosystem sustainability in arid regions.

Keywords: Land use conversion; Loess plateau; Soil carbon sequestration; Structural equation model; Wavelet coherence.