Microbial biomass and community structure in a sequence of soils with increasing fertility and changing land use

The microbial biomass and community structure of eight Chinese red soils wi th different fertility and land use history was investigated. Two community based microbiological measurements, namely, community level physiological profiling (CLPP) using Biolog sole C source utilization tests and phospholi pid fatty acid (PLFA) profiles, were used to investigate the microbial ecol ogy of these soils and to determine how land use alters microbial community structure. Microbial biomass-C and total PLFAs were closely correlated to organic carbon and total nitrogen, indicating that these soil microbial mea sures are potentially good indices of soil fertility in these highly weathe red soils. Metabolic quotients and C source utilization were not correlated with organic carbon or microbial biomass. Multivariate analysis of sole ca rbon source utilization patterns and PLFAs demonstrated that land use histo ry and plant cover type had a significant impact on microbial community str ucture. PLFAs showed these differences more than CLPP methods. Consequently , PLFA analysis was a better method for assessing broad-spectrum community differences and at the same time attempting to correlate changes with soil fertility. Soils from tea orchards were particularly distinctive in their C LPP. A modified CLPP method, using absorbance readings at 405 nm and differ ent culture media at pH values of 4.7 and 7.0, showed that the discriminati on obtained can be influenced by the culture conditions. This method was us ed to show that the distinctive microbial community structure in tea orchar d soils was not, however, due to differences in pH alone.