TY - JOUR
T1 - Stoichiometry controls asymbiotic nitrogen fixation and its response to nitrogen inputs in a nitrogen-saturated forest
AU - Zheng, Mianhai
AU - Zhang, Wei
AU - Luo, Yiqi
AU - Li, Dejun
AU - Wang, Senhao
AU - Huang, Juan
AU - Lu, Xiankai
AU - Mo, Jiangming
N1 - Funding Information:
We appreciated three anonymous reviewers and the editor for their constructive comments on the manuscript. This study was financially supported by the National Natural Science Foundation of China (31770523, 41731176, and 41473112) and National Postdoctoral Program for Innovative Talents (BX20180312). The authors declare no conflict of interests.
Publisher Copyright:
© 2018 by the Ecological Society of America
PY - 2018/9
Y1 - 2018/9
N2 - 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 asymbiotic N fixation in this forest possibly because the N deposition rate was insufficient to inhibit N fixation or N deposition maintained high N fixation rates by increasing C sequestration in the substrates. Our N-addition experiment showed the insensitivity of N fixation in all the tested substrates to low N addition (50 kg N·ha−1·yr−1); however, medium and high N addition (100–150 kg N·ha−1·yr−1) stimulated the moss and foliar N fixation because of the increases in substrate C:N stoichiometry (which explained 30–34% of the variation in N fixation, P < 0.001). Overall, our results emphasize the importance of substrate (particularly mosses and foliage) stoichiometry as a driver of asymbiotic N fixation and sustained N richness in lowland tropical forests.
AB - 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 asymbiotic N fixation in this forest possibly because the N deposition rate was insufficient to inhibit N fixation or N deposition maintained high N fixation rates by increasing C sequestration in the substrates. Our N-addition experiment showed the insensitivity of N fixation in all the tested substrates to low N addition (50 kg N·ha−1·yr−1); however, medium and high N addition (100–150 kg N·ha−1·yr−1) stimulated the moss and foliar N fixation because of the increases in substrate C:N stoichiometry (which explained 30–34% of the variation in N fixation, P < 0.001). Overall, our results emphasize the importance of substrate (particularly mosses and foliage) stoichiometry as a driver of asymbiotic N fixation and sustained N richness in lowland tropical forests.
KW - asymbiotic nitrogen fixation
KW - leaky nitrostat model
KW - nitrogen deposition
KW - nitrogen-saturated forest
KW - nutrient concentrations
KW - substrate stoichiometry
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U2 - 10.1002/ecy.2416
DO - 10.1002/ecy.2416
M3 - Article
C2 - 29893021
AN - SCOPUS:85051062795
SN - 0012-9658
VL - 99
SP - 2037
EP - 2046
JO - Ecology
JF - Ecology
IS - 9
ER -