Samples from rhizosphere and bulk soils were used immediately
after harvest for community-level physiological profiling
(CLPP) with Biolog EcoPlates™ (Biolog, California, USA). For each
sample, 1 g of soil was dissolved in 10 ml 0.01 M phosphate buffer
(pH ¼ 7.2), and after thorough shaking, the solution was further
diluted 1:20. After settling of remaining particles, 120 ml was
dispensed into each well of all 31 carbon sources (3 replicates per
plate). The plates were incubated in the dark at 25 C, and absorbance
at 590 nm of all wells per plate was measured twice every
24 h using a FLUOstar® Omega plate reader, with the final measurement
taking place after 94 h. Absorbance data were used to
calculate the average well color density (AWCD), richness (R) with
threshold equal to 0.25, and Shannon-Weaver index (H) per treatment.
Absorbance values per carbon source were also used separately
in subsequent statistical analyses.