Effects of tillage and fertilization on physiological profiles of soil microbial communities

The present work evaluated the ability of a rapid physiological profiling method to determine the long term effects of alternative tillage practices (no till vs. chisel plow) and nitrogen fertilization on soil microbial activity. Community respiratory response (i.e., O2 consumption) to carbon and mineral nutrient (N and P) amendments was examined in soil samples (Typic Argiudoll) from a tillage and N-fertilization trial. O2 consumption was assessed under control conditions (no C-substrate added) and in response to the addition (50 μg ml−1) of five carbon sources: acetate, asparagine, coumaric acid, mannose, carboxy-methyl cellulose (CMC). The effect of nutrient limitation on microbial activity was assessed by the single or combined addition of N and P (5.3 μg ml−1 N and 0.6 μg ml−1 P as (NH4)2SO4 or K2HPO4, respectively). High throughput analysis was enabled by automated monitoring of an O2-quenched fluorophore immobilized in a gel added to microtiter plates. Basal (i.e., control) respiration caused a 15-25% increase in the maximum peak of fluorescence (Fmax) while amendments caused 30-450% increases across all soils with response to CMC < mannose < acetate = asparagine < coumaric acid. Chisel plowing significantly increased basal respiration and response to all substrates except CMC. Fertilization had a more variable effect, with basal respiration and response to asparagine and CMC unaffected, acetate and mannose use stimulated, and coumaric acid use inhibited. Basal respiration and use of all the substrates except asparagine were N-limited as evidenced by the significant increase in Fmax with addition of N or N + P to the assay. General P limitation was not consistently observed except in the case of coumaric acid use. However, the effects of nutrient addition in the plate varied depending on the fertilization treatment. Overall, the O2-based CLPP approach was effective for detecting soil management effects on overall microbial activity as well as shifts in functional groups and bioavailability of soil N and P.

► The effect of tillage and fertilization on soil microbial physiological profiling was evaluated. ► Chisel increased basal respiration and response to most substrates; fertilization was variable. ► The addition of N or N + P to the assay stimulated microbial activity, evidencing soil N-limitation. ► Evidence of P limitation was not consistent; secondary limitation seems to occur by N-fertilization. ► O2-based CLPP detected soil management effects on overall microbial activity and soil N and P bioavailability.