Regulation of Soil Microbial Community Structure and Biomass to Mitigate Soil Greenhouse Gas Emission

Abstract

Sustainable reduction of fertilization with technology acquisition for improving soil quality and realizing green food production is a major strategic demand for global agricultural production. Introducing legume (LCCs) and/or non-legume cover crops (NLCCs) during the fallow period before planting main crops such as wheat and corn increases surface coverage, retains soil moisture content, and absorbs excess mineral nutrients, thus reducing pollution. In addition, the cover crops (CCs) supplement the soil nutrients upon decomposition and have a green manure effect. Compared to the traditional bare land, the introduction of CCs systems has multiple ecological benefits, such as improving soil structure, promoting nutrient cycling, improving soil fertility and microbial activity, controlling soil erosion, and inhibiting weed growth, pests, and diseases. The residual decomposition process of cultivated crops after being pressed into the soil will directly change the soil carbon (C) and nitrogen (N) cycle and greenhouse gas emissions (GHGs), and thus affect the soil microbial activities. This key ecological process determines the realization of various ecological and environmental benefits of the cultivated system. Understanding the mechanism of these ecological environmental benefits provides a scientific basis for the restoration and promotion of cultivated crops in dry farming areas of the world. These findings provide an important contribution for understanding the mutual interrelationships and the research in this area, as well as increasing the use of CCs in the soil for better soil fertility, GHGs mitigation, and improving soil microbial community structure. This literature review studies the effects of crop biomass and quality on soil GHGs emissions, microbial biomass, and community structure of the crop cultivation system, aiming to clarify crop cultivation in theory.

Keywords: cover crop management practices; cover crops; decomposition; greenhouse gas emission; soil microbial community structure.

FIGURE 1

Schematic diagram of CCs growing, termination methods, and their relationship with soil microbes and GHG emissions.

FIGURE 2

Schematic relationship of residues incorporation, decomposition, nutrient immobilization, and mineralization through soil microbes.

FIGURE 3

Percent changes of AMF, fungi, F:B, bacteria, Gram-positive bacteria (G P bacteria), Gram-negative bacteria (G N bacteria), Gram positive: Gram negative bacteria (Gp:Gn), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), MBC:MBN, and total phospholipid fatty acid analysis (PLFA) in cover crop (CC) treatments over control (Ncc).

FIGURE 4

Principal coordinates analysis (PCoA) of microbial communities based on weighted UniFrac distances across soil horizons and among the different experimental treatments (Nx: conventional N fertilization; N0: no N fertilization; CC: presence of cover crops; No-CC: bare soil conditions). (Copied with permission from Alahmad et al., 2019, copyright (2018) John Wiley & Sons, Inc).

FIGURE 5

Results of the hierarchical clustering of bacterial species composition and used C-sources. (A) Heat-map of C-source groups and species clusters based on their values in the cross-table of the BGCoIA. (B) Relative importance of the clusters across soil depths and among treatments (Nx: conventional N fertilization; N0: no N fertilization; CC: presence of cover crops; No_CC: bare soil conditions). (C) Distribution of the main bacterial phyla among clusters. (D) Projection of the clusters and their constitutive species in the diagram defined by the first two BGCoIA axes. Only the name of the most characteristic species for each cluster is reported. (E) Projection of the groups and their constitutive C sources in the diagram defined by the first two BGCoIA axes. (Copied with permission from Alahmad et al., 2019, copyright (2018) John Wiley & Sons, Inc).

FIGURE 6

Distance-based redundancy analysis (db-RDA) plot showing the relationship of abiotic soil factors and plant functional group identities to community composition of AMF (A), archaea (B), and fungi (D). Community composition of protists (C) could not be explained by any of the factors measured; therefore, a non-metric multidimensional scaling (NMDS) of the community is shown instead. The plant functional groups tested were grasses (G; green), legumes (L; red), small herbs (SH; yellow), and tall herbs (TH; blue). The ordination is based on Bray–Curtis distance. With forward selection, factors were chosen that significantly (P_adj < 0.05) contributed to the model. In each window, the percentage of explained variation is shown. (Adapted from Dassen et al., 2017 under the terms of the Creative Commons Attribution License 4.0).

FIGURE 7

(A,B) Examples of cover cropping termination methods (incorporation, mulching, and removing), and the concept of cover crop residues biomass and soil microbes interaction.