Stoichiometric characteristics of soil microbial biomass carbon, nitrogen, and phosphorus under different postfire regeneration forest types in the Greater Khingan Mountains, China.

To investigate the responses of soil microbe-mediated carbon (C), nitrogen (N), and phosphorus (P) across different regeneration forests following severe fire disturbance in cold-temperate region, and to clarify the characteristics of microbial nutrient cycling and resource limitation in post fire soils, we selected five typical forest types (34 years post the Black Dragon Fire in the northern Greater Khingan Mountains): Larix gmelinii plantation, L. gmelinii and Betula platyphylla mixed plantation, Pinus sylvestris var. mongolica plantation, P. sylvestris var. mongolica and B. platyphylla mixed plantation, naturally regenerated forest of L. gmelinii. We measured soil microbial biomass C (MBC), N (MBN), and P (MBP) contents, and analyzed their stoichiometric ratios, microbial quotients, and soil-microbe stoichiometric imbalances. The results showed that there were significant differences in soil microbial biomass and stoichiometric ratios among the five forest types. Naturally regenerated forest of L. gmelinii had the lowest soil MBC (455.79 mg·kg-1) and MBN (25.93 mg·kg-1) contents, while the P. sylvestris var. mongolica plantation had the lowest soil MBP content (9.81 mg·kg-1). The naturally regenerated forest of L. gmelinii exhibited the highest MBC:MBN (17.77) and the lowest MBC:MBP (28.11) and MBN:MBP (1.59). Across all postfire regeneration stands, soil MBC:MBN ranged from 10 to 18, indicating fungi dominated soil microbial community. The MBN:MBP was consistently below 6.9, suggesting that soil metabolism was likely limited by nitrogen. The soil microbial quotients in the monocultures and mixed plantations were generally higher than those in the naturally regenerated forest. The soil microbial quotient of C was significantly higher in P. sylvestris var. mongolica plantation (monoculture: 2.0%; mixed plantation: 2.3%) than in L. gmelinii stands (monoculture: 1.4%; mixed plantation: 1.1%). The soil-microbe C:N stoichiometric imbalance was greatest in the L. gmelinii plantation (1.87) and smallest in the P. sylvestris var. mongolica and B. platyphylla mixed plantation (0.77). Both C:P and N:P stoichiometric imbalance were the lowest in the P. sylvestris var. mongolica plantation (0.80 and 0.72, respectively). For post fire forest management in the Greater Khingan Mountains, we recommended monoculture and mixed plantation regeneration to increase soil microbial biomass and enhance C-N-P turnover potential. Regarding tree species, regenerated forests dominated by P. sylvestris var. mongolica were beneficial to overall soil resources.