Effect of long-term plant biomass management on phosphatase-producing bacterial populations in soils under temperate grassland

Organic forms of phosphorus (P) account for over half of the total P present in most soils and make a significant contribution to P cycling and plant nutrition through the actions of various plant and microbial phosphatase enzymes. However, not much is known about the bacterial communities harbouring phosphatase genes, either in composition, abundance, or transcriptional activity. Thus a grassland trial was selected that was undergoing long-term management of plant biomass removal/retention. Treatment plots were sampled after 22 years to examine the impact of prolonged nutrient depletion on bacterial communities helping to mediate organic P turnover. Total bacteria, total fungi, alkaline phosphatase (phoD) and the three classes (A, B, C) of non-specific acid phosphatases (NSAPs) were quantified and amplicons of the phoD and NSAP genes were sequenced. Of the genes quantified, class B (CBAP) genes were positively impacted by biomass removal (p < 0.01). Phosphatase gene transcripts generally appeared to increase in the biomass removed plots, but perhaps only weakly differentiated at this one time point. In the removed plots, we identified the class A (CAAP) community as the most significantly differentiated (p < 0.05). This difference was found strongly at the level of the operational taxonomic unit, indicating that changes in composition are reflective of the biomass management. Several key differentiating bacteria were found, many of which shared a closest known identity to Stenotrophomonas spp. Further, Mantel tests also revealed strong associations of NSAP communities CAAP and CCAP to measures of soil biogeochemistry. The findings of this study further support the importance of microbial mediated P cycling and in the contribution of under-studied P cycling enzymes such as bacterial acid phosphatases.