Characteristics of dissolved organic matter and bacterial community structure in rhizosphere soil of long-term cover crops in apple orchards

Background and aims

Soil microorganisms and dissolved organic matter (DOM) play a prominent role in soil carbon and nutrient cycles. However, the relationship between rhizosphere DOM components and bacterial communities in different cover crops remains unclear. This study accordingly details the relationships between soil DOM and microorganisms in cover crops within apple orchards on the Loess Plateau.

Methods

We selected three cover crops, Gramineae orchardgrass (OG), legume crown vetch (CV), and white clover (WC), to study the bacterial community composition, DOM content and components, and their associations in both rhizosphere and bulk soils.

Results

The available nutrients content in rhizosphere soil was higher than that in bulk soil. The rhizosphere DOM was primarily composed of protein-like substances. The humic-like component predominated in Gramineae treatment, whereas the protein-like component dominated in legume treatment. The rhizosphere bacterial α-diversity decreased compared with that in bulk soil. Network analysis indicated that the relationship between DOM components and bacterial communities in rhizosphere soil was more complex than that in bulk soil, with negative associations being predominant. Moreover, Gramineae cover crops reinforced the association between bacterial community composition and DOM components compared to legume.

Conclusions

Cover crop species significantly affect the relationship between the rhizosphere soil DOM components and bacterial communities, exhibiting a closer relationship under Gramineae cover crop. This study enhances our understanding of the ecological processes through which cover crops regulate bacterial communities and strengthen the interactions with DOM, providing new insights for assessing soil quality in apple orchards.