Soil aggregation and aggregate-associated organic carbon under typical natural halophyte communities in arid saline areas of Northwest China

Information on the effects of halophyte communities on soil organic carbon (SOC) is useful for sequestrating C in arid regions. In this study, we identified four typical natural halophyte communities in the Manasi River Basin in Xinjiang Province, Northeast China, namely, Karelinia caspia (Pall.) Less., Bassia dasyphylla (Fisch. et C. A. Mey.) Kuntze, Haloxylon ammodendron (C. A. Mey.) Bunge, and Tamarix ramosissima Lour. We compared soil aggregation and aggregated-associated SOC under these communities. The aggregate fraction of 0.053-0.25 mm accounted for 47%-75% of the total soil mass, significantly more than the > 0.25 and < 0.053 mm fractions, under all the halophyte communities. Significant differences in soil aggregate size distribution were observed among the plant communities, with the H. ammodendron and B. dasyphylla communities showing the highest proportions of > 0.25 mm aggregates (13.3%-43.8%) and T. ramosissima community having more < 0.053 mm aggregates (14.1%-27.2%). Aggregate-associated SOC concentrations were generally the highest in the > 0.25 mm fraction, followed by the < 0.053 mm fraction, and were the lowest in the 0.053-0.25 mm fraction; however, because of their large mass, 0.25-0.053 mm aggregates contributed significantly more to the total SOC. Total SOC concentrations (0-60 cm depth) decreased in the order of H. ammodendron (5.7 g kg) > T. ramosissima (4.9 g kg) > K. caspia (4.2 g kg) > B. dasyphylla (3.4 g kg). The H. ammodendron community had the highest total SOC and aggregate-associated SOC, which was primarily because aggregate-associated SOC content at the 0-10 and 10-20 cm depths under this community were higher than those under other plant communities. The H. ammodendron community could be beneficial for increasing SOC in saline soils in the arid region.