Abstract
Denitrification is mediated by microbial, and physicochemical, processes leading to nitrogen loss via N2O and N2 emissions. Soil pH regulates the reduction of N2O to N2, however, it can also affect microbial community composition and functional potential. Here we simultaneously test the link between pH, community composition, and the N2O emission ratio (N2O/(NO + N2O + N2)) in 13 temperate pasture soils. Physicochemical analysis, gas kinetics, 16S rRNA amplicon sequencing, metagenomic and quantitative PCR (of denitrifier genes: nirS, nirK, nosZI and nosZII) analysis were carried out to characterize each soil. We found strong evidence linking pH to both N2O emission ratio and community changes. Soil pH was negatively associated with N2O emission ratio, while being positively associated with both community diversity and total denitrification gene (nir & nos) abundance. Abundance of nosZII was positively linked to pH, and negatively linked to N2O emissions. Our results confirm that pH imposes a general selective pressure on the entire community and that this results in changes in emission potential. Our data also support the general model that with increased microbial diversity efficiency increases, demonstrated in this study with lowered N2O emission ratio through more efficient conversion of N2O to N2.
Highlights
New Zealand soils) and decreasing N2O emission ratio (D)
Comparison of samples based on 16S rRNA community composition visualised with a non-metric multidimensional scaling (NMDS) plot, using a Bray-Curtis dissimilarity matrix, displayed a significant link to the N2O emission ratio and pH (Fig. 1E and Supplementary Fig. S3–S4)
Results support the role of native soil pH in shaping community composition and diversity
Summary
New Zealand soils) and decreasing N2O emission ratio (D). Microbial community dissimilarities of soils with different emission profiles as determined using NMDS (Bray-Curtis) ordination (E). Microbial studies that support the role of microbial diversity in controlling productivity[33,34], N cycling[35,36,37] and even N2O emissions[38] exist, these rely on single manipulated soils or small sample sizes. With increasing diversity there is increased redundancy and efficiency of ecosystem processes[39,40] This has been observed in other microbial studies[35,41], including those associated with N2O emissions[42]. In this study we aimed to link phenotypes (emission potential) to genotypes (functional potential and community composition) across 13 soils with varying pH (5.57–7.03) representing both Northern and Southern Hemisphere soils These soils were selected as they represent the normally observed pH range in agronomic grasslands (recommended pH optima = 6.2–6.5). We determined the microbial community composition and diversity of each soil and identified patterns linked to both changes in pH and emissions
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