Effect of six years of nitrogen additions on soil chemistry in a subtropical <Emphasis Type="Italic">Pleioblastus amarus</Emphasis> forest,Southwest China

Soil chemistry influences plant health and carbon storage in forest ecosystems. Increasing nitrogen (N) deposition has potential effect on soil chemistry. We studied N deposition effects on soil chemistry in subtropical Pleioblastus amarus bamboo forest ecosystems. An experiment with four N treatment levels (0, 50, 150, and 300 kg N ha^?1 a^?1, applied monthly, expressed as CK, LN, MN, HN, respectively) in three replicates. After 6 years of N additions, soil base cations, acid-forming cations, exchangeable acidity (EA), organic carbon fractions and nitrogen components were measured in all four seasons. The mean soil pH values in CK, LN, MN and HN were 4.71, 4.62, 4.71, and 4.40, respectively, with a significant difference between CK and HN. Nitrogen additions significantly increased soil exchangeable Al³⁺, EA, and Al/Ca, and exchangeable Al³⁺ in HN increased by 70% compared to CK. Soil base cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺) did not respond to N additions. Nitrogen treatments significantly increased soil NO₃^?–N but had little effect on soil total nitrogen, particulate organic nitrogen, or NH₄⁺–N. Nitrogen additions did not affect soil total organic carbon, extractable dissolved organic carbon, incorporated organic carbon, or particulate organic carbon. This study suggests that increasing N deposition could increase soil NO₃^?–N, reduce soil pH, and increase mobilization of Al³⁺. These changes induced by N deposition can impede root grow and function, further may influence soil carbon storage and nutrient cycles in the future.