Effects of plant-derived dissolved organic matter (DOM) on soil CO2 and N2O emissions and soil carbon and nitrogen sequestrations

Dissolved organic matter (DOM) in soils play an essential role in soil physical, chemical and biological processes, but little information is available on the biodegradability of plant-derived DOM and its effect on soil carbon and nitrogen sequestration in field soils. The objectives of this study were to investigate the impacts of crop residue-derived DOM on soil CO2 and N2O emissions, as well as soil carbon and nitrogen sequestration by adding water extracts of maize stalk (i.e., plant-derived DOM) to soils. In this study, wheat was grown in pots under field conditions with treated soils, the soils treatments were: plant-derived DOM (PDOM), urea nitrogen (N), PDOM + urea nitrogen (PDOM + N), as well as a control with no additions to soil (CK). Adding plant-derived DOM to soil increased soil CO2 and N2O emissions (P < 0.05). During the wheat growing season, the cumulative CO2-C emission from CK, PDOM, N and PDOM + N was 107 ± 1, 157 ± 7, 136 ± 2 and 149 ± 6 g C m−2, respectively. Meanwhile, the cumulative N2O-N emission from CK, PDOM, N and PDOM + N was 188 ± 8, 256 ± 5, 239 ± 10 and 258 ± 7 mg N m−2, respectively. Compared with N treatment, DOM addition had little effect on soil N sequestration, but it accelerated the decomposition of native soil organic carbon (SOC) and caused a net loss of SOC. The soil C sequestration decreased about 151 ± 67 and 51 ± 45 g C m−2 in PDOM and PDOM + N treatments, respectively. The increased microbial biomass and root biomass were responsible for the greater CO2 emission in DOM-amended soils. Negative correlation between dissolved organic carbon (DOC) content and N2O flux suggested that the release of N2O was dependent on the supply of DOC. These results indicated that the supply of plant-derived DOM exacerbated soil CO2 and N2O emissions and reduced soil C sequestration. Therefore, agricultural management practices that increase the stability of highly soluble C inputs and/or retard the decomposition of crop residues should be adopted to decrease soil greenhouse gas emission and increase soil C sequestration.