Abstract
Soil drainage and phosphorus (P) availability are considered indicators of management intensity in pasture-based agriculture supporting livestock. However, microbial adaptations to P-availability according to soil drainage class are rarely investigated. We hypothesized that well-drained grasslands with high P-availability will sustain a distinctive soil microbiota when compared to poorly-drained grasslands with low-P availability. The relationship between soil drainage, plant available P and grassland microbial communities was evaluated among well-drained sites with high- or low-P and poorly-drained sites with high- or low-P, using fingerprinting, next-generation sequencing and quantitative PCR. Bacterial community structures were primarily affected by drainage as well as significantly separated between a combination of drainage and P availability i.e. low-P and poorly drained versus high-P and well drained. Abundance of the bacterial phylum Actinobacteria was significantly higher in well-drained high-P soils while Firmicutes were more abundant in well-drained low-P soils. Soil fungal communities responded to both drainage status and plant available P. Fungal phyla such as Basidiomycota responded strongly towards availability of P, while Glomeromycota were most abundant in poorly drained low-P soils. The diversity of the alkaline phosphatase gene phoD responded more clearly to drainage than availability of P. Of the other environmental factors, soil pH significantly affected the bacterial and fungal communities structure analyzed. This study suggests that while bacteria and fungi are affected by a combination of soil drainage and P availability in Irish grassland soils, drainage has a more profound influence on bacterial communities than P availability.
Highlights
Grasslands cover 40% of the world’s surface and represent Ireland’s most important resource in pasture-based systems [1]
Differ ences in inorganic P (Pi) were consistent with the plant available P status, with high-P soils showing significant increases in Pi, with highest concentration in the WHP soils
Real world farming scenarios across Ireland were selected for this study instead of manipulated trials to ensure that findings related to drainage and P availability are representative and robust
Summary
Grasslands cover 40% of the world’s surface and represent Ireland’s most important resource in pasture-based systems [1]. In countries with temperate climates, grass production is widely affected by soil drainage [2]. Drained soils can sustain grazing livestock and machinery for most of the year and they are highly suited for grass produc tion [3]. Poorly-drained soils are characterized by long pe riods of water saturation that negatively impacts the ability to maximize grazing or cutting, reducing overall grass productivity as well as the length of the grazing season [4]. The bacterial commu nity composition changes, albeit without necessarily affecting associated functions in relation to nitrogen cycling [2,6]. Little is yet known about the impacts of soil drainage in grassland microbial communities in relation to phosphorous (P) cycling
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