Data from: Depth-dependent mechanisms regulate accumulation of plant- and microbial-derived residues under long-term nitrogen addition in a semiarid grassland

Plant- and microbial-derived residues constitute the primary sources of
soil organic carbon (SOC) in grassland ecosystems. However, their
differential responses to chronic nitrogen (N) enrichment and the
depth-dependent mechanisms governing their accumulation remain poorly
characterized, particularly for water-limited grassland systems. Based on
a 13-year field experiment in a semiarid grassland, we quantified the
effects of long-term N addition on the accumulation of plant- (lignin
phenols) and microbial-derived (amino sugars) residues. We found that N
addition significantly increased lignin phenol content and its
contribution to SOC in the topsoil, whereas lignin phenols exhibited a
hump-shaped response peaking under moderate N levels in the subsoil. Amino
sugar concentrations and their relative contribution to SOC increased in
both soil layers under N addition, but declined at the highest N input.
The dominant factors regulating residue accumulation varied with soil
depth: in the topsoil, microbial K-/r-traits and community composition
primarily explained lignin phenol and amino sugar dynamics, while in the
subsoil, mineral-associated protection and microbial composition were the
key drivers. These findings underscore the depth-dependent nature of SOC
formation pathways and highlight the importance of incorporating both
plant- and microbial-derived residues into Earth System Models to improve
projections of carbon-climate feedback under changing nitrogen regimes.