Soil & Water Res., 2022, 17(4):211-221 | DOI: 10.17221/29/2022-SWR

Changes in soil organic carbon and its fractions under grassland reclamation in alpine-cold soils, ChinaOriginal Paper

Tong-Hui Wu¹, Yu-Fu Hu^*,1, Yan-Yan Zhang^2,3, Xiang-Yang Shu¹, Ze-Peng Yang¹, Wei Zhou¹, Cheng-Yi Huang⁴, Jie Li¹, Zhi Li¹, Jia He¹, Ying Yu¹

¹ College of Resources, Sichuan Agricultural University, Chengdu, P.R. China

² Department of Natural Resource Sciences, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

³ Department of Chemistry, Université de Montréal, Montréal, Canada

⁴ College of Environmental Sciences, Sichuan Agricultural University, Chengdu, P.R. China *Corresponding author. huyufu@sicau.edu.cn

Grasslands are the main land use types in China, but their reclamation into croplands can influence the terrestrial carbon and, consequently, impact the global carbon balance. The long-term reclamation of alpine-cold grasslands to croplands are expected to decrease the soil organic carbon (SOC) and its fractions. Here, we conducted an in situ systematic study to measure the SOC and its fraction in soils sampled in an alpine-cold grassland with a gradient of cultivation history from 0 to 40 years. The SOC and its fractions significantly decreased after reclamation (P < 0.05), and the changes in the 0-20 cm soil layer were the greatest among the three sampling depths. After 40 years of reclamation, the SOC content and storage at 0-20 cm decreased by 74 and 60%, respectively. The decreases in the soil labile carbon fractions were more rapid and apparent than the SOC, especially the particular organic carbon (POC), which decreased by 82%. The soil humus carbon fractions also decreased, particularly the humic acid carbon (HAC), which decreased by 81%. The reduction rates of SOC and its fractions gradually decreased with an increase in the cultivation history. Besides, the ratios of the optical densities or absorbances of humic acid (HA) and fulvic acid (FA) solutions at 465 and 665 nm (E₄/E₆ ratios) and the hue coefficient (Δlog K values), which is the logarithm disparity between the 400 and 600 nm absorbance of the HA (FA) substance, in the solution gradually decreased, indicating that the quality of the soil humus decreased. The reclamation significantly decreased the SOC and its fractions in the alpine-cold soils, which should not be underestimated in the impact on the terrestrial carbon cycles and balance in the long run.

Keywords: land use change; Qinghai-Tibet Plateau; soil carbon; soil humus carbon; soil labile carbon

Published: November 2, 2022  Show citation