Nitrogen deposition drives the intricate changes of fine root traits

Increase in nitrogen (N) deposition will cause changes of root morphological and functional traits, thus deeply affecting ecosystem carbon (C) and N cycles. However, the influence of N deposition to root traits under different climatic conditions, and with different N deposition rate and durations were still unclear. Here, a meta-analysis was conducted to evaluate the effects of simulated increase in N deposition on 11 root traits under different conditions. In general, N addition significantly increased root/shoot ratio, fine root diameter, total root biomass, fine root production, fine root turnover rate, root respiration, fine root N concentration, while decreased fine root C/N at the global scale. Under N addition, the increased extents of fine root biomass and total root biomass were significantly greater in grassland ecosystems, while the increased extent of fine root turnover was greater in forests. N addition significantly increased fine root production in snow climate zone where forests with ectomycorrhizae. A pattern may be inferred that with increases in mean annual temperature (MAT) and mean annual precipitation (MAP), N addition decreased fine root N concentration and fine root C/N, while increased fine root turnover at the high-MAT and high-MAP areas. In addition, it may be ascertained that fine roots became shorter in the low-rate and short-term N addition experiments, while roots became longer in the high-rate and long-term N addition experiments. Our study indicates that increase in N deposition will cause intricate changes of root traits due to the diversity of climatic conditions and the uncertainty of increase rate and duration of N deposition in future.