Application of high carbon amendments stabilizes soil microbial community composition and improves microbial recovery after a late spring drought during winter wheat cultivation

Abstract High-carbon amendments (HCAs) are increasingly recognized as important tools in agriculture for reducing nutrient losses, such as nitrate leaching resulting from nitrification. However, most studies have not considered the influence of climate change as a confounding factor. In this study, we took advantage of an extreme drought lasting over eight weeks in late spring 2023 in Southern Germany. We examined the effects of wheat straw application as an HCA, implemented in late autumn 2022, within a field trial of an oilseed rape–winter wheat rotation. Using a molecular barcoding approach, we analyzed bacterial and archaeal communities in soil samples collected six, nine, eleven, and twelve months after HCA application during the wheat-growing season. HCA application had a positive effect on the thousand-kernel weight and stabilized microbial community composition, as indicated by a greater shared core microbiome across all sampling time points. Members of the phyla Acidobacteriota (e.g., Vicinamibacteraceae , Blastocatellaceae ) and Bacteroidota ( Chitinophagaceae ), known degraders of complex organic materials, benefited from HCA addition. In contrast, bacteria typically associated with the winter wheat rhizosphere, such as Arthrobacter and Bradyrhizobium , were not affected, suggesting that HCAs exerted a greater impact on the bulk soil microbiome than on the rhizosphere. Overall, HCA implementation enhanced the stability of the soil microbiome during drought and promoted faster recovery afterward, highlighting an additional ecological benefit of these amendments.