Organic amendments enhance rhizosphere carbon stabilization in macroaggregates of saline-sodic soils by regulating...

Photosynthetic carbon plays a pivotal role in soil organic carbon (SOC) sequestration in agricultural soils. However, how organic amendments regulate photosynthetic carbon accumulation through multitrophic microbes at the aggregate scale, especially the core microbiota, remains unclear. Here, we conducted a¹³CO₂-labeled rhizo-box experiment on a saline-sodic soil with five treatments: no fertilizer (Ctrl), chemical fertilizer, pig manure (PM), milk vetch straw (MV), and vermicompost. The ¹³C-SOC in the MV and PM treatments was 2.4 and 1.4 times greater than that in the Ctrl, respectively. Compared with the Ctrl, organic amendments significantly increased ¹³C-macroaggregate-associated OC (¹³C-Macro-OC) by 122.4-615.8 % and ¹³C-mineral-associated OC (¹³C-MAOC) by 123.6-564.5 % in macroaggregates (> 0.25 mm). The ¹³C-Macro-OC was significantly positively correlated with biodiversity, the relative abundances of bacteria (mainly Acidobacteriota and Firmicutes) and fungi (mainly Ascomycota and Mucoromycota) in the keystone microbial cluster, network complexity, and the proportion of negative cross-trophic associations. Structural equation modeling revealed that the root trait-induced core microbiota, following organic amendments, affected photosynthetic carbon accumulation via ¹³C-MAOC in macroaggregates. In summary, our findings highlight the positive effects of milk vetch straw on SOC accumulation and provide a theoretical basis for the targeted regulation of SOC accumulation in saline-sodic soils through organic amendments.