Comparative Microbial Nitrogen Functional Gene Abundances in the Topsoil vs. Subsoil of Three Grassland Habitats in Northern China.

Yuqing Liu,Jinbo Zhang,Jun Zhao,Hui Cheng,Guohua Liu,Huanxin Ding,Xiaojuan Feng,Teng Wen,Qiaodong Chi,Zucong Cai

doi:10.3389/fpls.2021.792002

Abstract

The microbial groups of nitrogen fixers, ammonia oxidizers, and denitrifiers play vital roles in driving the nitrogen cycle in grassland ecosystems. However, the understanding of the abundance and distribution of these functional microorganisms as well as their driving factors were limited mainly to topsoil. In this study, the abundances of nitrogen functional genes (NFGs) involved in nitrogen fixation (nifH), ammonia oxidation (amoA), and denitrification (nirK, nirS, and nosZ) were investigated in both topsoil (0–10 cm, soil layer with concentrated root) and subsoil (30–40 cm, soil layer with spare root) of three grassland habitats in northern China. The abundance of NFGs decreased with soil depth except for the archaeal amoA gene and the distribution of nifH, archaeal amoA, nirK, and nirS gene was significantly impacted by grassland habitats. Moreover, the distribution of NFGs was more responsive to the vertical difference than horizontal spatial heterogeneity. Redundancy analysis revealed that the distribution pattern of overall NFGs was regulated by grassland habitats, and these regulations were more obvious in the subsoil than in the topsoil. Variance partitioning analysis further indicated that soil resource supply (e.g., organic matter) may control the vertical distribution of NFGs. Taken together, the findings in this study could fundamentally improve our understanding of the distribution of N cycling-associated microorganisms across a vertical scale, which would be useful for predicting the soil N availability and guiding the soil N management in grassland ecosystems.

Highlights

Nitrogen (N) cycling is considered a vital biogeochemical cycle on Earth as it controls the availability of nitrogenous nutrients and biological productivity in natural ecosystems (Vitousek and Howarth, 1991; Nelson et al, 2016)
Soil N cycle serves as an important component of the global N cycle, and the transformation among various N forms is largely accomplished by the enzymes encoded by several N functional genes (NFGs) harbored in diverse soil microbes (Robertson and Groffman, 2007; Hu et al, 2015)
Nitrification is a two-step process linking the reduced and oxidized forms of N, in which ammonia oxidation is thought to be a rate-limiting step and mediated by the ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) with the monooxygenase encoded by the gene amoA (Prosser and Nicol, 2008; Levy-Booth et al, 2014)

Summary

INTRODUCTION

Nitrogen (N) cycling is considered a vital biogeochemical cycle on Earth as it controls the availability of nitrogenous nutrients and biological productivity in natural ecosystems (Vitousek and Howarth, 1991; Nelson et al, 2016). It is believed that environmental factors, such as altitude, longitude, and latitude, usually covary with the changes in the geographical distance (Fierer and Jackson, 2006; Griffiths et al, 2011; Jia et al, 2017) Such horizontal differences are often characterized by heterogeneity of soil type, climate, vegetation, etc., and, pronouncedly shape the distribution of microorganisms (Zhang et al, 2006; Hu et al, 2014; Chen et al, 2018). Root vertical distribution could impact the microbial populations between soil depths mainly by providing different quantity and type of organic carbons and nutrients within a soil profile via root exudates and/or root litter decomposition (Peng et al, 2017; Shi et al, 2018). We hypothesized that the major driving factors shifted from topsoil to subsoil, and we expected that soil resources prevailed over soil edaphic parameters in driving the variation of N-cycling microbes residing in the subsoil

MATERIALS AND METHODS

DISCUSSION

CONCLUSION