Ramial chipped wood amendment drives shifts in soil microbial carbon and phosphorus cycling networks across a depth gradient

Soil regeneration depends on microbial processes driving nutrient cycling and organic matter retention. Ramial chipped wood (RCW), a carbon-rich organic amendment, stimulates microbial activity and may promote short-term soil restoration. This study evaluated the effects of RCW on microbial function, focusing on fungal community structure and genes involved in carbon (C) and phosphorus (P) cycling. A field experiment was conducted with tomato ( Solanum lycopersicum ) under Mediterranean conditions, comparing surface (0–20 cm) and subsurface (20–25 cm) soils treated with low and high RCW doses (RCW-LD, RCW-HD), compost (CMP) and nitrogen-rich organic pellets as control (CTL), representing standard fertilisation practices. RCW-HD enhanced microbial metabolic capacity, particularly in response to amino acids, sugars, and organic P sources. This response was more pronounced in the subsurface, where RCW also improved microbial access to P pools. Functional gene profile showed that RCW-HD enhanced pathways involved in lignin and lignocellulose degradation (e.g. katG, MAN, glcD ), and organic P mobilisation and transport (e.g. phoD, ugpC ). In contrast, CMP soils showed a higher abundance of genes linked to methanogenesis (e.g. hdrC2, mttC ) and P starvation responses ( phoB ). Fungal community shifted under RCW, favouring saprotrophic and symbiotic taxa associated with wood decomposition (e.g. Thermothelomyces thermophilus, Linnemannia elongata ). These findings underscore the potential of RCW to promote functional microbial homeostasis and support its use as a regenerative amendment in organic Mediterranean farming systems. • Ramial chipped wood (RCW) enhances microbial metabolic capacity one year after application. • RCW promotes degradation of recalcitrant carbon and organic phosphorus mineralisation. • Lignocellulose degradation and phosphorus acquisition genes are upregulated by RCW. • RCW promotes saprotrophic fungi (e.g. Linnemannia elongata ) aiding nutrient cycling. • Nitrogen-rich amendments favours Fusarium solani relative abundance over complex amendments.