Soil soluble organic carbon and nitrogen pools under mono- and mixed species forest ecosystems in subtropical China

Purpose The objective of the present study was to assess the differences in soil total C and N, microbial biomass C and N, soil soluble organic C and N among eight mono- and mixed species forest ecosystems (18-year-old restoration) in subtropical China. Materials and methods Soil samples were taken at the 0-10 and 10-20-cm depths from each of the eight forest ecosystems: Masson pine (CP1); Pitch pine (CP2); mixed Slash pine and Sweetgum (CBMP1); mixed Slash pine and Camphortree (CBMP2); mixed Masson pine, Sweetgum, and Chinese Gugertree (CBMP3); mixed Sweetgum and Chinese Gugertree (BMP); Chinese Gugertree (BP1); and Sweetgum (BP2). Soil soluble organic C and N pools were measured using hot water and KCl extraction methods. Microbial biomass C (MBC) and N (MBN) were measured by fumigation-extraction method. Soil total C and N were determined using an isotope ratio mass spectrometer. Results and discussion Concentrations of soil soluble organic N (SON) extracted by KCl solution (35.1-116.9 and 11.2-78.2 mg kg(-1)) were greater than those by hot water (20.7-72.8 and 8.4-30.6 mg kg(-1)) in the 0-10 and 10-20-cm soils, while concentrations of soluble organic C (SOC) extracted by KCl solution were lower than those extracted by hot water in the 0-10 cm. Soil soluble C and N pools extracted by both hot water and KCl solution and the MBC and MBN were greatest under the broadleaf forest ecosystems, followed by the mixed conifer-broadleaf forest ecosystems, and then the conifer forest ecosystems. Conclusions Different restored forest ecosystems had significant impacts on soil SOC and SON, and MBC and MBN. The broadleaf forest ecosystems could be a better choice for the restoration of red soil chemical and biological prosperities than the conifer-broadleaf forest ecosystem and coniferous forest ecosystems. A further study is necessary to sample over seasons in order to understand whether the significant impacts on soil properties are related to the sample time. In addition, soil microbial community composition and microbial activity should be measured in such studies to understand mechanisms involved in the dynamics of soil SOC and SON pools.