Characterizing rhizosphere microbial communities in long-term monoculture tea orchards by fatty acid profiles and substrate utilization

An experiment was conducted at the Tie Guanyin tea orchards with continuous cropping histories for 1, 10, and 20 years in China to investigate the effects of long-term monoculture of tea bushes on rhizospheric soil micro-environment. Community-level physiological profiles (CLPP) combined with phospholipid fatty acid (PLFA) approaches were employed to quantify soil microbial potential activity and community structure. Results show that the invertase, urease, phosphomonoesterase, and catalase activities in the 20-year soils significantly decreased by 43.63%, 67.12%, 48.28%, and 34.00%, respectively, compared with those in the 10-year soils. The CLPP analysis indicates a significant decrease of 27.86% and 16.98% in the average well color development and richness index, respectively, in the 20-year soils compared with the 10-year soils. Long-term monoculture tended to result in higher utilization of phenolic compounds and carboxylic acids than other substrates in the 10- and 20-year soils. PLFA analysis reveals that the total PLFA concentrations ranged from 13.68 nmol g−1 to 62.47 nmol g−1, which were significantly higher in the 1- and 10-year soils than in the 20-year and control soils. Stress indicators (i.e., saturated/monosaturated fatty acids) significantly increased in the 10- and 20-year soils than in the 1-year soils. Redundancy analysis indicates that the soil organic carbon and available phosphorus had high correlations with the variation in soil microbial community composition. Therefore, the long-term monoculture of tea bushes led to significant decreases in soil enzymatic activities, microbial metabolic activity, and microbial biomass in the 20-year tea orchards.