Status: this preprint was under review for the journal BG but the revision was not accepted.
Wildfire effects on ecosystem nitrogen cycling in a Chinese boreal larch forest, revealed by 15N natural abundance
Weili Liu,Lin Qi,Yunting Fang,and Jian Yang
Abstract. Wildfire is reported to exert strong influences on N cycling, particularly during the early succession period immediately after burning (i.e., < 1 year). Previous studies have mainly focused on wildfires influences on inorganic N concentrations and N mineralization rates; but plant and soil 15N natural abundance (expressed by δ15N), as a spatial-temporal integrator of ecosystem N cycling, could provide a more comprehensive understanding of wildfire on various N cycling processes at a relatively broader time scale. In this study, we attempted to evaluate legacy effects of wildfire on nitrogen cycling using δ15N in a boreal forest of northeastern China, which is an important yet understudied ecosystem. We measured inorganic N concentrations (NH4+ and NO3−) and net N transformation rates (net ammonification, net nitrification, and net mineralization) of organic and mineral soil 4 years after a wildfire and compared with unburned area. We also measured δ15N of plant and soil samples in 4 and 5 years after the fire. We found that even 4 years after burning, wildfire still increased net mineralization and net ammonification in the organic soil and increased NH4+ and total inorganic N (TIN) concentrations in the mineral soil. Organic soil and foliar δ15N were significantly higher (by 2.2 ‰ and 7.4 ‰, respectively) in the burned area than the unburned area. Five years after fire, plant tissues such as foliar, branch, fine roots and moss in the burned area were increased significantly (by 1.7 ‰ to 6.4 ‰) greater than that in unburned area. The wildfire also significantly increased the δ15N of Oi, Oa+e and 0–10 cm mineral soil, but had no significant effects on deeper layer of mineral soil. These results indicate the wildfire had a strong legacy effect on N cycling. We suggest that the change of abiotic environment was the primary mechanism determining inorganic nitrogen transformation rates, and the NH3 volatilization might play a key role in severe N losses and thereby affect soil and plant 15N in this ecosystem.
Received: 14 Mar 2016 – Discussion started: 04 Apr 2016
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Wildfire is a major disturbance in boreal forest ecosystem and strongly affects ecosystem N cycling. We find that even 5 years after a wildfire, isotopic signatures of soil and plant N pools are still different from those in unburned areas in a Chinese boreal forest. Our results show persistent legacy effects in the form of increased N losses following wildfires. The fire-induced increases in NH3 volatilization may greatly contribute to the increased δ15N values in plant and soil.
Wildfire is a major disturbance in boreal forest ecosystem and strongly affects ecosystem N...
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