Cascading regulation from soil microbial resource limitation to crop physiology by carbon-based materials for tobacco growth in continuous cropping obstacle soil

Microbial resource limitation, as a risky obstacle in continuous cropping systems for sustainable production, can be relieved by carbon-based materials (CBMs). However, the mechanisms by which CBMs of differing bioavailability influence microbial resource limitations and subsequent crop performance remain unclear. To assess this issue, four CBMs with low (i.e., biochar, BC; carbon nanosol, CN) and high (i.e., polypeptide, PO; chitosanm, CS) bioavailability were applied in continuous cropping soils of tobacco. Results showed that low-CBMs reduced the oxidative-/osmotic-pressure of tobacco more effectively and increased plant height and leaf area by 11.2–23.7 %, while high-CBMs only improved root development without positive effects on aboveground part. PLS-PM modeling indicated that these effects were directly mediated by cascade regulation of “underground resource limitation - aboveground physiological processes”, and indirectly affected by dissolved organic matter (DOM) chemodiversity and core bacteria. Specifically, low-CBMs increased phenolic DOM and enriched P-activating bacteria, which lowered microbial P limitation by enhancing P mobilization and uptake, thereby increasing microbial biomass P and optimizing the C:P ratio. Moreover, low-CBMs relieved C limitation by enriching microbiomes associated with recalcitrant-C decomposition. Accordingly, the synthesis of leaf-/root-TP and osmotic substances increased, leading to reduced malondialdehyde/ oxyradical and enhanced photosynthesis. Inversely, although high-CBMs recruited N-fixing taxa to relieve N limitation, the increased hydrotropic DOMs (e.g., aliphatic, and polysaccharide) aggravated P limitation by elevating the available C:P ratio. This imbalance further impaired chlorophyll a-dominated photosynthesis, intensified oxidative damage, and depressed leaf-TP accumulation. Collectively, the findings contribute to resolving resource limitations for crop growth through balancing microbial functional requirements with C supply, highlighting the effectiveness of low-CBMs.