Continuous-cropping-tolerant soybean cultivars alleviate continuous cropping obstacles by improving structure and function of rhizosphere microorganisms

Abstract

Introduction: Soybean continuous cropping will change soil microorganisms and cause continuous cropping obstacles, resulting in a significant yield decline. Different soybean cultivars have different tolerances to continuous cropping, but the relationship between continuous cropping tolerance and soil microorganisms is not clear.

Methods: Two soybean cultivars with different tolerances to continuous cropping were used to study the effects of continuous cropping on soil physical and chemical properties, nitrogen and phosphorus cyclic enzyme activities, rhizosphere soil microbial community and function.

Results: The results showed that the yield reduction rate of a continuous-cropping-tolerant cultivar (L14) was lower than that of a continuous-cropping-sensitive cultivar (L10) under continuous cropping. At R1 and R6 growth stages, soil nutrient content (NH₄ ⁺-N, NO₃ ^--N, AP, DOM, TK, and pH), nitrogen cycling enzyme (URE, NAG, LAP) activities, phosphorus cycling enzyme (ALP, NPA, ACP) activities, copy numbers of nitrogen functional genes (AOA, AOB, nirK, nirK) and phosphorus functional genes (phoA, phoB) in L14 were higher than those in L10. Soybean cultivar was an important factor affecting the structure and functional structure of bacterial community under continuous cropping. The relative abundances of Proteobacteria, Bacteroidota, Acidobacteriota and Verrucomicrobiota with L14 were significantly higher than those of L10. The complexity of the soil bacterial community co-occurrence network in L14 was higher than that in L10.

Discussion: The continuous-cropping-tolerant soybean cultivar recruited more beneficial bacteria, changed the structure and function of microbial community, improved soil nitrogen and phosphorus cycling, and reduced the impact of continuous cropping obstacles on grain yield.

Keywords: continuous cropping; enzyme activity; soil bacterial community; soil bacterial function; soil nutrient content; soybean.

Figure 1

LDA Effect Size (LEfSe) analysis of soil bacteria communities of soybean cultivars under continuous cropping. (A) is the R1 growth stage, (B) is the R6 growth stage. CL10T1, at the R1 growth stage, L10 under CC treatment; CL10T2, at the R6 growth stage, L10 under CC treatment; CL14T2, at the R6 growth stage, L14 under CC treatment.

Figure 2

Redundancy analysis (RDA) of soil properties and bacterial community (phylum level). (A) is the R1 growth stage, (B) is the R6 growth stage. RL10, L10 under CR treatment; RL14, L14 under CR treatment; CL10, L10 under CC treatment; CL14, L14 under CC treatment; FL10, L10 under CF treatment; FL14, L14 under CF treatment.

Figure 3

Relative abundance of functional bacteria in soil of soybean cultivars under crop rotation and continuous cropping. RL10T1, at the R1 growth stage, L10 under CR treatment; RL14T1, at the R1 growth stage, L14 under CR treatment; CL14T1, at the R1 growth stage, L14 under CC treatment; FL10T1, at the R1 growth stage, L10 under CF treatment; FL14T1, at the R1 growth stage, L14 under CF treatment; RL10T2, at the R6 growth stage, L10 under CR treatment; RL14T2, at the R6 growth stage, L14 under CR treatment; FL10T2, at the R6 growth stage, L10 under CF treatment; FL14T2, at the R6 growth stage, L14 under CF treatment.

Figure 4

Principal component analyses (PCA) of soil functional community of soybean cultivars under crop rotation and continuous cropping.

Figure 5

Redundancy analysis (RDA) of soil properties and bacterial functions. (A) is the R1 growth stage, (B) is the R6 growth stage.

Figure 6

Co-occurrence network analysis of bacterial community in soybean soil. (A) is L10 at the R1 growth stage, (B) is L14 at the R1 growth stage, (C) is L10 at the R6 growth stage, (D) is L14 at the R6 growth stage. Different nodes represent different genera, node size represents the degree of connection of the genus, and the same color represents the same phylum level. The thickness of the connection between nodes is positively correlated with the absolute value of correlation coefficient of species interaction. The size of the node is proportional to the relative abundance of the phylum. Connections indicate significant correlation (Screening conditions: Spearman’s ρ > 0.6, p < 0.05).