Subsoil Microbial Diversity and Stability in Rotational Cotton Systems

Katherine Polain,Oliver Knox,Brian Wilson,Lily Pereg

doi:10.3390/soilsystems4030044

Katherine Polain, Oliver Knox + Show 2 more

Open Access

https://doi.org/10.3390/soilsystems4030044

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Abstract

Microbial diversity has been well documented for the top 0–0.30 m of agricultural soils. However, spatio-temporal research into subsoil microbial diversity and the effects of agricultural management remains limited. Soil type may influence subsoil microbial diversity, particularly Vertosols. These soils lack distinct horizons and are known to facilitate the downward movement of organic matter, potentially supporting subsoil microbiota, removed from the crop root system (i.e., bulk soils). Our research used the MiSeq Illumina Platform to investigate microbial diversity down the profile of an agricultural Australian Vertosol to 1.0 m in bulk soils, as influenced by crop system (continuous cotton and cotton–maize) and sample time (pre- and in-crop samples collected over two seasons). Overall, both alpha- (Chao1, Gini–Simpson Diversity and Evenness indices) and beta-diversity (nMDS and Sørensen’s Index of Similarity) metrics indicated that both bacterial (16S) diversity and fungal (ITS) diversity decreased with increasing soil depth. The addition of a maize rotation did not significantly influence alpha-diversity metrics until 0.70–1.0 m depth in the soil, where bacterial diversity was significantly higher in this system, with beta-diversity measures indicating this is likely due to root system differences influencing dissolved organic carbon. Sample time did not significantly affect bacterial or fungal diversity over the two seasons, regardless of the crop type and status (i.e., crop in ground and post crop). The relatively stable subsoil fungal and overall microbial diversity in bulk soils over two crop seasons suggests that these microbiota have developed a tolerance to prolonged agricultural management.

Highlights

Soil microbiota mediate a range of functions within the soil environment, including the decomposition of organic matter (OM) and subsequent release and cycling of essential nutrients—carbon (C), nitrogen (N) and phosphorus (P)—into the terrestrial ecosystem [1,2,3,4,5,6]
The majority of agricultural soil microbial diversity studies have focused on the top 0–0.30 m, with exploration into subsoil (>0.3 m) limited and microbial diversity in rotational cotton systems cultivated in Vertosols non-existent
With both vertical and lateral soil movements facilitating the downward movement of organic matter, oxygen and water, with the potential to support microbial life beyond the top 0.3 m

Summary

Introduction

Soil microbiota mediate a range of functions within the soil environment, including the decomposition of organic matter (OM) and subsequent release and cycling of essential nutrients—carbon (C), nitrogen (N) and phosphorus (P)—into the terrestrial ecosystem [1,2,3,4,5,6] These mechanisms are vital to a healthy soil, but are key in managing and maintaining sustainable agricultural practice [7,8,9]. Microbiota are subject to disturbance from agricultural practice including minimum tillage, irrigation and crop rotations—all of which impose physical changes in the soil structure and nutrient availability [10]. The response of microbial communities, contributes to the overall stability of the soil system and soil health and productivity

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