Open AccessDynamics of Organic Matter of Soil Profiles with Different Vegetation Conditions from the Chinese Loess Plateau: δ13C and δ15N Approaches
Author(s) -
Longbo Li,
Xiaodan Wang,
Ping Zhang,
Yao-Qiang Zhu,
Mingchun Ren,
Da-Wei Cai
Publication year - 2020
Publication title -
iop conference series. earth and environmental science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.179
H-Index - 26
eISSN - 1755-1307
pISSN - 1755-1315
DOI - 10.1088/1755-1315/570/2/022008
Subject(s) - topsoil , soil carbon , soil organic matter , litter , environmental science , vegetation (pathology) , biogeochemical cycle , organic matter , soil science , agronomy , soil water , chemistry , environmental chemistry , biology , medicine , organic chemistry , pathology
To understand the biogeochemical processes associated with soil organic matter (SOM) decomposition, we analyzed the SOM contents, the δ 13 C and δ 15 N values of the dominant species foliage, litter and SOM from soil samples for five soil profiles with different vegetation conditions in the Loess Plateau, Northwestern China. Results showed that the amounts of soil organic carbon (SOC) and total nitrogen (TN) mainly concentrated on the surface soil and differentiated according to the vegetation conditions in the following order: broad-leaved forest > coniferous woodland > shrub forest > grassland > wasteland. SOC and TN contents decreased with depth and varied in the ranges of 1.1–31.2 g/kg and 0.3–3.7 g/kg, respectively. Compared with the other regions, the 13 C and 15 N were enriched and the δ 13 C and δ 15 N values of topsoil SOM respectively increased in the ranges of 0.5%o–3.2%o and 0.7%o–4.6%o during litter degradation to SOM on the surface soil, which was controlled by SOM turnover rates. This result indicates that the effect of isotopic fractionation was obvious during the transformation of SOM from plant debris to SOM in topsoil, which resulted in great increments of SOM δ 13 C and δ 15 N. Litter inputs lowered the surface soil δ 13 C and δ 15 N values while decomposition increased δ 13 C and δ 15 N values in deeper soil. Foliage and litter inputs averaged 1.0% and 1.3% δ 15 N and -28.3% and -27.0% δ 13 C, respectively. The five soil profiles with different vegetation conditions had similar characteristics in variations of SOM δ 13 C and δ 15 N and increased with depth, respectively. However, the patterns of δ 13 C in our sites were less pronounced than the patterns of δ 15 N primarily because the discrimination against 13 C during organic matter decomposition is weaker than the discrimination against 15 N. Except for the shrub profiles, significant correlations were found between the two stable isotopes, 15 N and 13 C. Combined with information on SOM contents, the variations of the isotopic values of SOM showed a mixing process of litter inputs between different soil profiles. Two controls of soil isotopic compositions were established: new litter inputs and overall isotopic fractionation during decomposition. In conclusion, the overall isotopic fractionation during decomposition left residual soil N and C enriched in 15 N and 13 C, explaining the high δ 15 N and δ 13 C values observed in deeper soil.