Divergent Accumulation of Microbial Residues and Amino Sugars in Loess Soil after Six Years of Different Inorganic Nitrogen Enrichment Scenarios

Dominic Kwadwo Anning,Chunhong Zhang,Philip Ghanney,Qirong Shen,Huizhen Qiu,Delei Deng,Zhilong Li

doi:10.3390/app11135788

Dominic Kwadwo Anning, Chunhong Zhang + Show 5 more

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https://doi.org/10.3390/app11135788

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Abstract

Amino sugars are key microbial biomarkers for determining the contribution of microbial residues in soil organic matter (SOM). However, it remains largely unclear as to what extent inorganic nitrogen (N) fertilization can lead to the significant degradation of SOM in alkaline agricultural soils. A six-year field experiment was conducted from 2013 to 2018 to evaluate the effects of chronic N enrichment on microbial residues, amino sugars, and soil biochemical properties under four nitrogen (urea, 46% N) fertilization scenarios: 0 (no-N, control), 75 (low-N), 225 (medium-N), and 375 (high-N) kg N ha−1. The results showed that chronic N enrichment stimulated microbial residues and amino sugar accumulation over time. The medium-N treatment increased the concentration of muramic acid (15.77%), glucosamine (13.55%), galactosamine (18.84%), bacterial residues (16.88%), fungal residues (11.31%), and total microbial residues (12.57%) compared to the control in 2018; however, these concentrations were comparable to the high-N treatment concentrations. The ratio of glucosamine to galactosamine and of glucosamine to muramic acid decreased over time due to a larger increase in bacterial residues as compared to fungal residues. Microbial biomass, soil organic carbon, and aboveground plant biomass positively correlated with microbial residues and amino sugar components. Chronic N enrichment improved the soil biochemical properties and aboveground plant biomass, which stimulated microbial residues and amino sugar accumulation over time.

Highlights

Amino sugars (AS) are important constituents of microbial cell walls in soil, and their accretion influences the contribution of microbial residues to soil organic matter (SOM)stability [1]
Chronic N enrichment significantly affected the concentration of amino sugar components in the soil (Figure 1)
Galactosamine content was significantly affected by N enrichment from 2016 and 2018 (Figure 1b)

Summary

Introduction

Amino sugars (AS) are important constituents of microbial cell walls in soil, and their accretion influences the contribution of microbial residues to soil organic matter (SOM)stability [1]. Amino sugars (AS) are important constituents of microbial cell walls in soil, and their accretion influences the contribution of microbial residues to soil organic matter (SOM). More than 90% of AS are found in dead cells [2], with the characteristic function of quantifying microbial residues, which is not a surrogate for animate microbial activity and biomass [3]. Soil microbes use amino sugars as an alternative nitrogen (N) source in the absence of N due to their nutrient-dependent bioavailability. AS serves as a stable nitrogen pool in soils with high N content or as a labile nitrogen pool in N-limited soils [4], and they contribute significantly to bioavailable organic nitrogen in the soil [5]. Amino sugars account for about 5.0% to 12.0% of soil organic nitrogen [6,7], and

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