The microbial PLFA composition as affected by pH in an arable soil

The influence of soil pH on the phospholipid fatty acid (PLFA) composition of the microbial community was investigated along the Hoosfield acid strip, Rothamsted Research, UK – a uniform pH gradient between pH 8.3 and 4.5. The influence of soil pH on the total concentration of PLFAs was not significant, while biomass estimated using substrate induced respiration decreased by about 25%. However, the PLFA composition clearly changed along the soil pH gradient. About 40% of the variation in PLFA composition along the gradient was explained by a first principal component, and the sample scores were highly correlated to pH (R2 = 0.97). Many PLFAs responded to pH similarly in the Hoosfield arable soil compared with previous assessments in forest soils, including, e.g. monounsaturated PLFAs 16:1ω5, 16:1ω7c and 18:1ω7, which increased in relative concentrations with pH, and i16:0 and cy19:0, both of which decreased with pH. Some PLFAs responded differently to pH between the soil types, e.g. br18:0. We conclude that soil pH has a profound influence on the microbial PLFA composition, which must be considered in all applications of this method to detect changes in the microbial community.