Diverse biological communities promote SOM molecular diversity and compositional transformations during natural fallow stage in paddy fields

Abstract

Abstract Monoculture cultivation patterns in agro-ecosystems only provide less varied soil organic matter (SOM) molecules of plant origin. Whether and how the natural fallow stage between cultivation seasons facilitates the restoration of SOM molecular diversity and mitigates the adverse impacts of constant cropping pattern is elusive. Here, we utilized FT-ICR-MS, UHPLC-MS/MS, and high-throughput sequencing to investigate the biological change processes in SOM molecular composition under cultivation and fallow status in a long-farmed paddy field. Our study showed that SOM molecular diversity increased by 45.70%–85.36% in fallow stage compared to rice cultivation season. SOM molecular diversity was positively correlated with bacterial diversity and root exudate molecular diversity, and negatively correlated with fungal diversity. Notably, root exudate molecular diversity accounted for 48.48% of the variation in SOM molecular diversity. The increased SOM molecular diversity in fallow stage was attributed more to the diverse plant-produced molecules than the microbe-consumed molecules. Plant species turnover resulted in the conversion of root exudate components to Organoheterocyclic compounds and Organic acids/derivatives from rice planting stage to fallow stage. Recruited microbes were dominated by Basidiomycita, Ascomycota, Acidobacteria, Chloroflexi and Proteobacteria, resulting in the transformation from carbohydrates, lipid-like SOM molecules to lipid-like and lignin-like SOM molecules. Both field and microcosm experiments confirmed that root exudates are the main source of SOM molecules, and are influenced by the soil microbial community. This study provides solid evidence that fallow status in agro-ecosystems provides explosion of biodiversity and counteracts the negative effects of long-term monoculture cultivation on SOM diversity. Graphical Abstract

Keywords

• Soil organic matter molecular diversity
• Biodiversity
• FT-ICR-MS
• Root exudate molecules
• Winter fallow