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Scientia Silvae Sinicae ›› 2021, Vol. 57 ›› Issue (1): 1-11.doi: 10.11707/j.1001-7488.20210101

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Effects of Long-Term Nitrogen Application on Soil Respiration and Its Components in Warm-Temperate Forest of Pinus tabulaeformis

Lu Yang1,2,Jinsong Wang2,Bo Zhao1,Xiuhai Zhao1,*   

  1. 1. Research Center of Forest Management Engineering of National Forestry and Grassland Administration, Beijing Forestry University Beijing 100083
    2. Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences Beijing 100101
  • Received:2019-10-28 Online:2021-01-01 Published:2021-03-10
  • Contact: Xiuhai Zhao

Abstract:

Objective: The objective was to explore the differences of soil respiration and its components among different levels of nitrogen addition of the natural forest of Pinus tabulaeformis under long-term nitrogen enrichment, to reveal the main influencing factors of the changes in the respiration of soil components, and to provide a scientific basis for evaluating the effect of long-term nitrogen application on soil respiration in regional forests. Method: We conducted a 10-year nitrogen addition experiment (2009-2018) in a P. tabulaeformis forest in Taiyue Mountain, Shanxi Province, with four levels of nitrogen addition including control (CK, 0 kg N·hm-2 a-1), low nitrogen (LN, 50 kg N·hm-2 a-1), medium nitrogen (100 kg N·hm-2a-1), and high nitrogen (HN, 150 kg N·hm-2 a-1). Soil respiration and its components were measured monthly in growing seasons from 2016-2018. Result: Mean annual soil respiration rate was significantly decreased by 21.9%, 27.3%, and 29.1%; and mean annual heterotrophic respiration rate was significantly reduced by 21.8%, 36.6%, 31.4% under LN, MN and HN, respectively, compared with the control. Long-term nitrogen addition had no significant effect on soil autotrophic respiration rate. Meanwhile, soil pH and soil microbial biomass carbon were significantly decreased by 0.07, 0.37, 0.78 units and 11.3%, 14.5%, 14.7% under LN, MN and HN, respectively relative to the control. However, soil organic carbon, total nitrogen and fine root biomass were not altered by nitrogen enrichment. There was a significant linear relationship between heterotrophic respiration and soil microbial biomass carbon; autotrophic respiration also exhibited a significant linear correlation with fine root biomass. The long-term nitrogen addition significantly increased temperature sensitivity(Q10) of soil autotrophic respiration (CK=2.19, LN=2.90, MN=2.86, HN=2.34), but decreased the Q10 values of soil heterotrophic respiration (CK=2.72, LN=2.23, MN=2.12, HN=2.27). Soil respiration were not correlated with soil moisture (P>0.05). In addition, two-factor models combining soil temperature and soil moisture explained 28.7%-42.0% (P < 0.05) and 64.9%-78.1% (P < 0.001) of the autotrophic respiration and heterotrophic respiration, respectively. Conclusion: Long-term nitrogen addition reduced soil respiration by the nitrogen-induced decrease in the heterotrophic respiration, but had no significant effect on autotrophic respiration rate. In addition, changes in respiratory substrates were the main factors for the inconsistent effects of chronic nitrogen application on the Q10 values of autotrophic and heterotrophic respiration. Our study highlights that fine root biomass and respiration substrate should be incorporated into future models when accurately predicting chronic nitrogen addition effect on soil respiration and its components.

Key words: long-term nitrogen addition, Pinus tabulaeformis natural forest, autotrophic respiration, heterotrophic respiration, temperature sensitivity

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