Effect of Microbial Carbon, Nitrogen, and Phosphorus Stoichiometry on Soil Carbon Fractions under a Black Locust Forest within the Central Loess Plateau of China.

Microbial C/N/P stoichiometry ratios are of interest because of important ecosystem fluxes of C, N and P, such as mineralization and immobilization, and they can help to characterize the cycling of soil elements, especially regarding soil C sequestration. However, it is not clear how soil microbial C/N/P stoichiometry influences C cycling. In this study, the concentrations of microbial biomass C, microbial biomass N, microbial biomass P, and soil C fractions were measured in 45-, 40- and 25-yr-old black locust (Robinia pseudoacacia L.) forest soils and a sloped cropland. The results showed that soil organic C (SOC) concentrations or stocks and the percentage increment of the SOC stocks were highest under 45-yr-old black locust (RP45a). The concentrations of each C fraction in the black locust forest soils (45a, 40a and 25a) were higher than that of sloped cropland in the 0- to 30-cm soil profile. The concentrations of microbial C, N and P in RP45a were also higher by an average of 29.6 to 232.9, 9.2 to 17.9, and 0.6 to 1.1 mg kg-1, respectively, compared with the same concentrations in sloped cropland at the 0- to 30-cm soil depth. Redundancy analysis indicated that soil C fractions, especially for particulate organic C (53-2000 and >2000 mm), were significantly correlated with the microbial C/P and N/P ratios and the "best" model selection indicated that the microbial N/P and C/P ratios significantly changed with soil C fractions with regard to stand age and soil depth in the black locust forests. Therefore, the present study demonstrated that C fractions respond to microbial C, N and P stoichiometry after farmland-to-forest conversion and hence have the potential to affect C storage in the loess hilly region. [ABSTRACT FROM AUTHOR]