Effect of nitrogen additions on root morphology and chemistry in a subtropical bamboo forest

Aims Plant roots play a critical role in ecosystem underground processes, and are potentially influenced by elevated atmospheric nitrogen (N) deposition. However, the effects of N deposition or long-term N additions on plant root properties in forest ecosystems are not well understood. The aim of this study is to explore how N deposition influences root morphology, biomass, and chemistry in a subtropical bamboo forest. Methods A field experiment was conducted with four N treatment levels (0, 50, 150, and 300 kg N ha(-1) year(-1), applied monthly) in a Pleioblastus amarus forest beginning in November 2007. After more than 7 years of N additions, P. amarus root samples were collected, and analyzed by an order-based classification approach. Results Nitrogen additions decreased specific root length (SRL) and specific root area (SRA) in orders (1 + 2), while the reverse was observed in order 3. The branch ratio (BR) of order (1 + 2): order 3 decreased by N additions. Root and rhizome biomass decreased in response to N additions. Nitrogen additions also decreased root tissue concentrations of N, P, K and Mn, and increased the concentration of Na and the ratios of C:N and N: P. Conclusions Our study indicated that the growth and quality of lower-order roots were inhibited by N additions, potentially leading to a slower underground C cycle. Order-based classification approach revealed more accurate information about roots response to N additions than diameter-based classification method. Chronic N deposition may have pronounced effects on soil environments, plant root traits, and underground C and nutrient cycles in bamboo forest ecosystems.