Stoichiometry controls asymbiotic nitrogen fixation and its response to nitrogen inputs in a nitrogen‐saturated forest

作者：Mianhai Zheng, Wei Zhang, Yiqi Luo, Dejun Li, Senhao Wang, Juan Huang, X. L. Lu, Jiangming Mo · 发表于：Ecology · 年份：2018 · DOI：10.1002/ecy.2416 · 被引用次数：53 · 研究领域：Soil Carbon and Nitrogen Dynamics、Legume Nitrogen Fixing Symbiosis、Peatlands and Wetlands Ecology

Abstract Lowland tropical forests with chronic nitrogen (N) deposition and/or abundant N‐fixing organisms are commonly rich in N relative to other nutrients. The tropical N richness introduces a paradoxical relationship in which many tropical forests sustain high rates of asymbiotic N fixation despite the soil N richness and the higher energy cost of N fixation than of soil N uptake. However, the mechanism underlying this phenomenon remains unclear. Our study aims to test this phenomenon and examine potential mechanisms of nutrient concentrations vs. substrate stoichiometry in regulating N fixation using multiple linear regression models. We hypothesized that the rates of asymbiotic N fixation would be low in an N‐rich forest under N deposition and substrate stoichiometry would explain the variation in N fixation better than nutrient concentrations. We conducted a chronic N‐addition experiment in an N‐saturated tropical forest in southern China and measured the N fixation rates, carbon (C), N, and phosphorus (P) concentrations, and stoichiometry in different substrates (soil, forest floor, mosses, and canopy leaves). Total N fixation rates were high (10.35–12.43 kg N·ha −1 ·yr −1 ) in this N‐saturated forest because of the high substrate C:N and N:P stoichiometry (which explained 13–52% of the variation in N fixation, P < 0.037) rather than substrate nutrient concentrations ( P > 0.05). Atmospheric N deposition (34–50 kg N·ha −1 ·yr −1 ) failed to down‐regulate asymbiot...