[Changes of soil microbial phospholipid fatty acid in soil profile under different land use types].

We elucidated the changes of soil microbial biomass and community structure in soil profiles under four typical land use types (farmland, grassland, Betula platyphylla secondary forest and Larix principis-rupprechtii plantation)and across five soil layers (0-10, 10-20, 20-30, 30-40, 40-50 cm) in the northern mountainous region of Hebei Province. We measured soil microbial biomass by phospholipid fatty acid (PLFA) method, and investigated the effects of land use and soil depth on soil microbial biomass and community structure by variance analysis, correlation analysis and redundancy analysis. The results showed that soil water content, bulk density, and organic carbon content of farmland differed significantly from other land use types. The content of PLFA in farmland was significantly lower than that in other land use types. The Gram-positive bacteria/Gram-negative bacteria (G⁺/G^-) in farmland were higher, and the nutrient stress was greater. With the increase of soil depth, soil water content, organic carbon, total nitrogen, total phosphorus and microbial biomass of the four land use types showed a decreasing trend. In grassland, secondary forest and plantation, G⁺/G^- was larger in deep soil than top soil. Except for grassland, the bacteria/fungi was smaller in deep soil than top soil. Correlation analysis and redundancy analysis showed that soil bulk density, natural water content and organic carbon were the main environmental factors affecting microbial communities in the four land use types. Our results would provide theoretical basis for the optimization of land use structure in the northern mountainous region of Hebei Province.