Soil organic and inorganic carbon and stable carbon isotopes in the Yanqi Basin of northwestern China

Abstract

Summary Soil organic carbon (SOC) and soil inorganic carbon (SIC) are important reservoirs of carbon in terrestrial ecosystems. Assessments of both SOC and SIC are lacking in arid regions. We carried out a survey in central Xinjiang, the Yanqi Basin, to evaluate the dynamics of SOC and SIC. Twenty‐one soil profiles were sampled from three land types: desert, shrub and agricultural soils. We determined SOC and SIC and the stable carbon isotope compositions (δ13C). Our data showed a decrease with depth for SOC in all soil profiles but an increase for SIC except in the desert soils. Both SOC and SIC stocks (over the 0–30‐cm depth) were least in the desert soils (1.0 ± 0.3 and 4.0 ± 0.8 kg C m−2 for SOC and SIC, respectively) but greatest in the agricultural soils (4.6 ± 0.6 and 11.0 ± 2.0 kg C m−2 for SOC and SIC, respectively). Total soil carbon stocks at 0–100 cm were 11.6 ± 4.8, 45.1 ± 10.4 and 51.2 ± 5.6 kg C m−2 in the desert soils, shrub soils and agricultural soils, respectively. On average, SIC accounted for more than 80% of the total carbon in this region. There were no significant differences in δ13C of SOC between land‐use types. In contrast, the δ13C of SIC was different: desert soils (−0.6‰) > shrub soils (−2.2‰) > agricultural soils (−3.4‰). The depleted 13C in SIC in the agricultural soils indicates enhancement of pedogenic carbonate by cropping. Our study suggests that converting shrub land to agricultural land in arid regions may lead to an increase not only in SOC stock, but also in SIC stock.

Dynamics of soil organic and inorganic carbon in the cropland of upper Yellow River Delta, China

“…reported slightly higher value of 7.7 kg C m −2 in the cropland of the Loess Plateau23. Our estimate was also significantly lower than the previously reported value of 8.38 kg C m −2 in the cropland of Hebei, the North China Plain24, the value of ~9.0 kg C m −2 in the regions of Yanqi15 and Urumqi8, Xinjing province, and that of 11.4 kg C m −2 in the Xilin River Basin, the Inner Mongolia13. The differences in SOC stock among different regions were probably due to the climate condition (such as temperature and precipitation) and land management (e.g., cropping system, fertilization and organic amendments)2225.…”

“…There were some studies of SIC dynamics in north China, which were mainly conducted in the Loess Plateau1011, the Inner Mongolia1213 and near the deserts of Xinjiang province1415. Recent analyses have shown that SIC content is largely related to land use type.…”

“…Recent analyses have shown that SIC content is largely related to land use type. For example, Wang, et al 15. reported that SIC stock was much higher in cropland than in the native lands of Yanqi Basin.…”

Soil CO2 Uptake in Deserts and Its Implications to the Groundwater Environment

“…Although soil CO2 uptake in deserts has been investigated in many previous studies, its potential influences on the groundwater environment remain unaddressed [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. This is partially due to the lack of a simple method for the separation and quantification of such CO2 uptake.…”

“…It has been widely recognized that the overall magnitude of CO2 dissolution beneath deserts and its contributions to the ecosystem carbon balance can be huge [30][31][32][33][34][35][36][37][38][39], but its effect on the local environment are seldom reported. As a first attempt to analyze the implications of the soil CO2 uptake to the groundwater environment, the present study simply assumes that the absorbed CO2 has been largely dissolved in the soil-groundwater system beneath the deserts.…”