Efficiency of nitrogen and phosphorus cycling in paddy soils is directly driven by functional gene-microbe co-occurrence networks and indirectly controlled by soil physicochemical properties.

Rice productivity in karst regions is often constrained by low nitrogen (N) and phosphorus (P) use efficiency, yet the attributes associated with reduced nutrient cycling function in medium- and low-yield paddy fields remain unclear. We selected five representative paddy soil profiles in Qianxi City, Guizhou Province, comprising one high-yield field, one medium-yield field and three low-yield fields characterised by sandy soil, water deficit or waterlogging. These profiles contained 23 diagnostic horizons, yielding 23 composite soil samples for analyses of soil physicochemical properties, enzyme activities, metagenome-derived functional gene abundance and microbial community composition. Integrative analyses, including redundancy analysis, co-occurrence networks, random forest modelling and structural equation modelling (SEM), were used to evaluate attributes associated with nitrogen and phosphorus cycling functional potential. Across paddy field types, N- and P-cycling functional genes showed distinct abundance patterns. In the waterlogged low-yield field, the abundance value of nifH reached 525.33 reads, 5.3-fold higher than that in the high-yield field. Genes associated with organic P mineralisation and regulation, including phoD, phoU and ppnK, ranged from 608 to 2,480 reads across field types. Microbial taxonomic profiles associated with N- and P-cycling functions also differed among paddy fields. Available phosphorus showed the strongest association with P-cycling functional profiles (Mantel r = 0.72). SEM showed that gene-related variables were positively associated with integrated N and P cycling functional potential (path coefficient = 0.567, P < 0.01), whereas soil microbial variables were negatively associated with this potential (- 0.619, P < 0.01). These results identify attributes associated with nutrient cycling constraints in karst paddy fields and provide a basis for targeted nutrient management.