Effects of Contemporary Land Use Types and Conversions from Wetland to Paddy Field or Dry Land on Soil Organic Carbon Fractions

Abstract

Soil organic carbon (SOC) concentration is closely related to soil quality and climate change. The objectives of this study were to estimate the effects of contemporary land use on SOC concentrations at 0-20 cm depths, and to investigate the dynamics of SOC in paddy-field soil and dry-land soil after their conversion from natural wetlands (20 and 30 years ago). We investigated the dissolved organic carbon (DOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), and other soil properties (i.e., moisture content, bulk density, pH, clay, sand, silt, available phosphorous, light fraction nitrogen, and heavy fraction nitrogen) in natural wetlands, constructed wetlands, fishponds, paddy fields, and soybean fields. The results indicated that the content of DOC increased 17% in constructed wetland and decreased 39% in fishponds, and the content of HFOC in constructed wetland and fishponds increased 50% and 8%, respectively, compared with that in natural wetlands at 0-20 cm. After the conversion of a wetland, the content of HFOC increased 72% in the paddy fields and decreased 62% in the dry land, while the content of DOC and LFOC decreased in both types. In the paddy fields, LFOC and HFOC content in the topmost 0.2 m of the soil layer was significantly higher compared to the layer below (from 0.2 to 0.6 m), and there were no significant differences observed in the dry land. The findings suggest that the paddy fields can sequester organic carbon through the accumulation of HFOC. However, the HFOC content decreased 22% after 10 years of cultivation with the decrease of clay content, indicating that paddy fields need to favor clay accumulation for the purpose of enhancing carbon sequestration in the paddy fields.

Land use conversion impacts on the stability of soil organic carbon in Qinghai Lake using 13C NMR and C cycle‐related enzyme activities

“…The SOC and labile organic C had the strongest effects on the variability of soil enzyme activities by RDA (Figure 4). Supporting evidence, after wetland conversion, the DOC content decreased in paddy fields and dryland (Zhao et al, 2020). Wang et al (2013) showed that BGL and NAG decreased after conversion from native wetland to soybean cropland in a chronosequence over 24 years, and soil enzyme activities were highly correlated with DOC (r = 0.59, p = 0.01 for NAG; r = 0.89, p < 0.001 for BGL).…”

Effects of different farmland utilization types on soil organic carbon in China: A meta‐analysis

“…There was a significant difference in SOC content between PF and DL, with DL showing an overall 37.1% lower SOC content than PF (Table 2). Several mechanisms may explain the higher SOC in PF (Chen et al, 2021; Kögel‐Knabner et al, 2010; H. Zhang et al, 2016; Zhao et al, 2020): (1) straw return is a common practice in paddy lands in China, with the result of a higher amount of organic matter in the soil; (2) the higher SOC content in PF could be linked to the lower decomposition rate of organic material in flooding condition; (3) generally higher contents of Fe oxyhydrates in PF, which can facilitate soil C sequestration through the large surface area. Although no significant difference was found between PF and VF, VF had an overall 7.5% lower SOC than PF.…”

“…Several mechanisms may explain the higher SOC in PF (Chen et al, 2021;Kögel-Knabner et al, 2010;H. Zhang et al, 2016;Zhao et al, 2020): (1) straw return is a common practice in paddy lands in China, with the result of a higher amount of organic matter in the soil;…”

“…Gao et al (2019) reported that total SOC was higher in paddy fields [PFs] than in dry land [DL], orange grove, and woodland under different land utilization types. The large biomass production, straw return practice, and flooding condition in rice fields led to an increase in the amount of organic matter and a lower decomposition rate, resulting in carbon accumulation (Chen et al, 2021; Zhao et al, 2020). Different types of land use alter surface plant cover, soil carbon stocks, and soil respiration, which in turn affect the local soil carbon balance and the global carbon cycle (Jiang et al, 2015; Li et al, 2022; Lima et al, 2020).…”

Export of Dissolved Organic Carbon from the Source Region of Yangtze River in the Tibetan Plateau

“…Anthropogenic activities play a substantial role in the transport of riverine DOC, e.g., acid deposition, nitrogen deposition, and agricultural activities [27][28][29][30]. In particular, land use and cover change, fire, and forest species greatly affect the variation of SOCs, which further alter the riverine DOC amount [31][32][33][34].…”