Microbial genetic and enzymatic responses to an anthropogenic phosphorus gradient within a subtropical peatland

Abstract

Many of the world's peatlands are subject to agricultural runoff, which may impact fundamental biogeochemical processes by altering the concentrations of limiting nutrients. In this study, the distribution of specific microbial genes associated with phosphorus (P) and nitrogen (N) metabolism was compared with potential enzyme activities related to P and N acquisition at five stations along a nutrient gradient in soils of Water Conservation Area 2A (WCA-2A) of the Florida Everglades, USA. Quantitative PCR was used to compare the relative concentrations of genes encoding alkaline phosphatases (phoX and phoD) with those encoding dinitrogenase reductase (nifH). Combined phosphatase and phosphodiesterase (EP) activities were compared with leucine aminopeptidase activities (EN), yielding a measure of potential microbial investment in P acquisition relative to N acquisition. The significant inverse relationship observed between bicarbonate extractable organic P concentrations and ratios of gene copy numbers of phoX:nifH (p=0.049, R2=0.77), and phoD:nifH (p=0.043, R2=0.79), combined with the significant inverse relationship between total P and EP/EN (p=0.021, R2=0.87), suggest that there is a greater community selection towards P acquisition relative to N acquisition as bicarbonate extractable organic P and total P decrease, suggesting a shift from P limitation to N limitation along the transect. The total number of unique genes detected by the functional microarray GeoChip 3.0 was greatest in an intermediate site, suggesting that the alleviation of nutrient limitation yielded increased functional diversity. The general agreement between genetic and enzymatic data suggests that assessing microbial nutrient demands with molecular techniques is feasible, although future work is needed to apply genetic information as indicators of nutrient enrichment.