Long-Term Land Use Affects Phosphorus Speciation and the Composition of Phosphorus Cycling Genes in Agricultural Soils.

Jin Liu,Corey W Liu,Michael Schellenberg,Jianjun Yang,Yongfeng Hu,Kerry Laforge,Chantal Hamel,Luke D Bainard,Julien Tremblay,Barbara J Cade-Menun

doi:10.3389/fmicb.2018.01643

Abstract

Agriculturally-driven land transformation is increasing globally. Improving phosphorus (P) use efficiency to sustain optimum productivity in diverse ecosystems, based on knowledge of soil P dynamics, is also globally important in light of potential shortages of rock phosphate to manufacture P fertilizer. We investigated P chemical speciation and P cycling with solution 31P nuclear magnetic resonance, P K-edge X-ray absorption near-edge structure spectroscopy, phosphatase activity assays, and shotgun metagenomics in soil samples from long-term agricultural fields containing four different land-use types (native and tame grasslands, annual croplands, and roadside ditches). Across these land use types, native and tame grasslands showed high accumulation of organic P, principally orthophosphate monoesters, and high acid phosphomonoesterase activity but the lowest abundance of P cycling genes. The proportion of inositol hexaphosphates (IHP), especially the neo-IHP stereoisomer that likely originates from microbes rather than plants, was significantly increased in native grasslands than croplands. Annual croplands had the largest variances of soil P composition, and the highest potential capacity for P cycling processes based on the abundance of genes coding for P cycling processes. In contrast, roadside soils had the highest soil Olsen-P concentrations, lowest organic P, and highest tricalcium phosphate concentrations, which were likely facilitated by the neutral pH and high exchangeable Ca of these soils. Redundancy analysis demonstrated that IHP by NMR, potential phosphatase activity, Olsen-P, and pH were important P chemistry predictors of the P cycling bacterial community and functional gene composition. Combining chemical and metagenomics results provides important insights into soil P processes and dynamics in different land-use ecosystems.

Highlights

Driven by the increasing demand for agricultural production, land-use change has been widespread globally over the last several decades (Guillaume et al, 2015)
Among the investigated land uses, there were no significant differences in soil pH, total P, total C, organic C, total N, Mehlichextractable P, Al, Fe, and Ca (Table 1)
The highest Olsen-P concentration was observed in roadside soils (12.5 mg kg−1), which was significantly higher than native grasslands (3.8 mg kg−1) and annual croplands (5.6 mg kg−1, Table 1)

Summary

Introduction

Driven by the increasing demand for agricultural production, land-use change has been widespread globally over the last several decades (Guillaume et al, 2015). The global effects of land-use change contribute to global changes in nutrient cycling and dynamics (Houghton, 1994). This is especially significant for phosphorus (P), which often limits the productivity and sustainability of agriculture, requiring fertilization. P loss from agriculture can have a negative effect on the aquatic environment This is expected to continue even if P fertilization is reduced due to the large amount of residual P accumulated in agricultural soils through time in many regions (Garcia-Montiel et al, 2000; Sharpley et al, 2013; Stutter et al, 2015). Efficient P use is a priority when replacing natural ecosystems with managed ecosystems (Stutter et al, 2015)

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