Soil Responses to Mineral Nitrogen and Carbon-Bearing Amendments in Moso Bamboo Forests: A Meta-Analysis

Moso bamboo (Phyllostachys edulis) plantations in subtropical China are intensively fertilized, yet it remains unclear how soil responses differ between mineral nitrogen and carbon-bearing amendments, and how far they depend on the nitrogen application rate. This meta-analysis of 69 articles covered four fertilization regimes (N, nitrogen alone; NPK, balanced mineral fertilizer; N+OM, nitrogen with organic carbon; B, biochar alone). We found that soil pH and organic carbon (SOC) responded in opposite directions to nitrogen alone and to the carbon-bearing amendments. Nitrogen alone acidified the soil (−5.3%) and reduced SOC (−11.4%), whereas B and N+OM raised pH (+9.5%, +3.4%) and SOC (+14.0%, +28.7%); NPK also raised SOC (+17.9%) but slightly lowered pH (−1.7%). The mineral regimes increased nitrate (+72.9% under N) but not total nitrogen, which rose only under N+OM (+33.3%). Microbial biomass carbon (MBC) increased under N, NPK and N+OM (+9.8% to +20.6%), whereas enzyme activities were largely unchanged. Nitrogen alone increased cumulative nitrous oxide emission (+18.7%) and reduced methane uptake (−15.5%), whereas N+OM lowered the nitrous oxide emission rate (−5.9%) and increased methane uptake (+9.0%). Each additional 100 kg N ha−1 yr−1 raised MBC by 1.9% and ammonium nitrogen by 4.7% without altering SOC, although most of the application rates tested were below 100 kg N ha−1 yr−1. Within this range, adding an exogenous carbon source to nitrogen may limit soil acidification and SOC depletion.