Is elemental stoichiometry (C, N, P) of soil and soil microbial biomass influenced by management modes and soil depth in agro-pastoral transitional zone of northern China?

Purpose Soil and soil microbial biomass carbon (C), nitrogen (N), and phosphorus (P) are the most common elements and key macronutrients that play an important role in assessing soil ecosystem functions degradation and restoration mechanism. However, the effects of interactions of soil depth and management modes on them remain elusive. Here, we compared changes in soil C, N, and P contents and their stoichiometry properties along soil profile to evaluate the effects of interactions. Materials and methods In this paper, we first choose three grassland with different management modes on adjacent grassland areas in the traditional agro-pastoral transitional zone of northern China (APTZNC), including grazing grassland (GG), enclosed grassland (EG), and abandoned cropland (AC). These grasslands have been differently managed since 2000. Then, we set up an experiment using soil samples with different depths (0–10, 10–20, 20–30, and 30–40 cm) were collected from three different types of grassland to evaluate the effects interactions of soil depth and grassland management modes on soil and soil microbial biomass C, N, and P stoichiometry. Results and discussion Key findings were that (1) concentrations of C, N, and P all decreased deeper within the soil layer, while C:N, C:P, and N:P showed no similar varying trends; (2) the concentrations of C, N, and microbial biomass N (MBN) were the highest in GG, while the concentrations of P, microbial biomass C (MBC) and microbial biomass P (MBP) were the highest in EG; (3) the C:N ratio in APTZNC was relatively high than that in the Chinese and global scales, while the N:P ratio in APTZNC was lower; (4) soil C, N, and P were correlated with MBN, while they were not correlated with MBP, soil MBC:MBN and MBC:MBP were correlated with C:N and C:P, while soil MBN:MBP was not correlated with N:P. Conclusions The vertical distribution of soil and soil microbial biomass C, N, and P are consistent, but the stoichiometric ratios of C, N, and P have strong stability. The grassland conversion changed the input of nutrients and affected the storage of soil microbial biomass. Soil was restricted by N in APTZNC. MBP is more reliable than MBN in evaluating soil fertility.