Differential structure and function of phosphorus-mineralizing microbial communities in organic and upper mineral soil horizons across a temperate rainforest chronosequence.

Microbial community structure and function were assessed in the organic and upper mineral soil across a ~4000-year dune-based chronosequence at Big Bay, New Zealand, where total P declined and the proportional contribution of organic soil in the profile increased with time. We hypothesized that the organic and mineral soils would show divergent community evolution over time with a greater dependency on the functionality of phosphatase genes in the organic soil layer as it developed. The structure of bacterial, fungal, and phosphatase-harbouring communities was examined in both horizons across 3 dunes using amplicon sequencing, network analysis, and qPCR. The soils showed a decline in pH and total phosphorus (P) over time with an increase in phosphatase activity. The organic horizon had a wider diversity of Class A (phoN/phoC) and phoD-harbouring communities and a more complex microbiome, with hub taxa that correlated with P. Bacterial diversity declined in both horizons over time, with enrichment of Planctomycetes and Acidobacteria. More complex fungal communities were evident in the youngest dune, transitioning to a dominance of Ascomycota in both soil horizons. Higher phosphatase activity in older dunes was driven by less diverse P-mineralizing communities, especially in the organic horizon.

Soil microbial communities influencing organic phosphorus mineralization in a coastal dune chronosequence in New Zealand.

The Haast chronosequence in New Zealand is an ∼6500-year dune formation series, characterized by rapid podzol development, phosphorus (P) depletion and a decline in aboveground biomass. We examined bacterial and fungal community composition within mineral soil fractions using amplicon-based high-throughput sequencing (Illumina MiSeq). We targeted bacterial non-specific acid (class A, phoN/phoC) and alkaline (phoD) phosphomonoesterase genes and quantified specific genes and transcripts using real-time PCR. Soil bacterial diversity was greatest after 4000 years of ecosystem development and associated with an increased richness of phylotypes and a significant decline in previously dominant taxa (Firmicutes and Proteobacteria). Soil fungal communities transitioned from predominantly Basidiomycota to Ascomycota along the chronosequence and were most diverse in 290- to 392-year-old soils, coinciding with maximum tree basal area and organic P accumulation. The Bacteria:Fungi ratio decreased amid a competitive and interconnected soil community as determined by network analysis. Overall, soil microbial communities were associated with soil changes and declining P throughout pedogenesis and ecosystem succession. We identified an increased dependence on organic P mineralization, as found by the profiled acid phosphatase genes, soil acid phosphatase activity and function inference from predicted metagenomes (PICRUSt2).