The response of soil microbial community to application of organic amendment to saline land

Abstract

Introduction: The salinization of coastal soils is a primary cause of global land degradation. The aim of this study was to evaluate the effect of organic amendment on the soil microbial community within a saline gradient.

Methods: The study was designed with five levels of electrical conductivity (EC): 0.33, 0.62, 1.13, 1.45 and 2.04 ds m^-1. By conducting indoor potted plant experiments, determine the effects of applying microbial organic fertilizer on the physicochemical properties of soil and the structure of soil microbial communities under different salinity concentrations.

Results: Compared with the control, higher OM content, total N, and higher crop biomass were observed in samples with organic amendment at the same salinity level. At the same salinity levels, the mean bacterial activity (AUC) and the mean number of substrates were higher than in the soil without organic amendment according to analyses by means of Biolog ECO MicroPlate. The results of canonical correspondence analysis indicate that after the application of organic amendments, the composition of loam and clay replaces soil pH, and aboveground biomass replaces root biomass as key indicators closely monitoring Community level physiological profiling (CLPP). In soil with the same salinity level, the application of microbial organic fertilizer led to an increase in the proportion of Actinobacteriota and a decrease in the proportion of Chloroflexi. In 0.3dS m-1 soil, the abundance of actinomycetes increased from 23% to 27% after application of microbial organic fertilizer, while the abundance of basidiomycetes decreased from 20% to 6%. In addition, after the application of microbial organic fertilizer, RB41, blastococcus and solirubrobacter significantly increased, while Melothermus and Herpetosiphon significantly decreased.

Discussion: This study provides a strong theoretical basis for using microbial organic fertilizers to improve saline-alkali soil.

Keywords: community level physiological profile; functional diversity; microbial community; organic remediation; salinity increase.

Figure 1

AUC of bacterial functional activity for different salinity levels, fertilizer types, and effects of the interaction between salinity and fertilizer status. (A) AUC of samples without organic amendment and (B) AUC of samples with organic amendment. Central points represent the means. Error bars represent 95% Tukey’s honestly significant differences. Different letters represent significant differences in AUC between salinity and fertilizer status.

Figure 2

Bacteria substrates used for (A) soil samples without organic amendment and (B) those with organic amendment. The middle points represent the means. Error bars represent 95% Tukey’s honestly significant differences. Different letters represent significant differences in AUC between salinity and fertilizer status.

Figure 3

Dynamics of the bacterial community under different fertilization treatments. (A) Relative abundances of the top 13 phyla. (B) Heatmap showing the relative abundances of the top 50 genera.

Figure 4

A canonical correspondence analysis (CCA) ordination plot of the bacterial substrate utilization patterns (CLPP) with soil and plant properties, including pH, total N content, organic matter (OM), bulk density, plant biomass, and the proportions of aggregates of all sizes. (A) The pattern without microbial fertilizer and (B) with microbial fertilizer. The substrate classes are indicated according to their site on a Biolog EcoPlate. A2: β-methyl-D-glucoside, A3: D-galactonic acid γ-lactone, A4: L-arginine, B1: pyruvic acid methyl ester, B2: D-xylose, B3: D-galacturonic acid, B4: L-asparagine, C1: Tween 40, C2: i-erythritol, C3: 2-hydroxy benzoic acid, C4: L-phenylalanine, D1: Tween 80, D2: D-mannitol, D3: 4-hydroxy, D4: L-serine, E1: α-cyclodextrin, E2: N-acetyl-D-glucosamine, E3: γ-hydroxybutyric acid, E4: L-threonine, F1: glycogen, F2: D-glucosaminic acid, F3: itaconic acid, F4: glycyl-L-glutamic acid, G1: D-cellobiose, G2: glucose-1-phosphate, G3: α-ketobutyric acid, G4: phenylethyl-amine, H1: α-D-lactose, H2: D,L-α-glycerol phosphate, H3: D-malic acid, H4: putrescine.