Li Renshan, Yu Dan, Zhang Yankuan, Han Jianming, Zhang Weidong, Yang Qingpeng, Gessler Arthur, Li Mai-He, Xu Ming, Guan Xin, Chen Longchi, Wang Qingkui, Wang Silong
Huitong Experimental Station of Forest Ecology, CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Shenyang 110016, China; Life Science Department, Luoyang Normal University, Luoyang 471934, China.
Life Science Department, Luoyang Normal University, Luoyang 471934, China.
Sci Total Environ. 2022 Sep 20;840:156537. doi: 10.1016/j.scitotenv.2022.156537. Epub 2022 Jun 6.
Plant carbon (C) assimilation is expected to nonlinearly increase with continuously increasing nitrogen (N) deposition, causing a N saturation threshold for productivity. However, the response of plant productivity to N deposition rates and further the N saturation threshold still await comprehensive quantization for forest ecosystem. Here, we tested the effect of N addition on aboveground net primary productivity (ANPP) of three-year old Chinese fir (Cunninghamia lanceolata) trees by adding N at 0, 5.6, 11.2, 22.4, and 44.8 g N m yr for 2.5 years. The N saturation threshold was estimated based on a quadratic-plus-plateau model. Results showed that ANPP transitioned from an increasing stage with increasing N addition rate to a plateaued stage at an N rate of 16.3 g N m yr. The response of ANPP to N addition rates was well explained by the net photosynthetic rates of needles. Results from the dual isotope measurement [simultaneous determination of needle stable carbon (δC) and oxygen (δO) isotopes] indicated that the photosynthetic capacity, rather than the stomatal conductance, mediated the response of photosynthesis and ANPP of the young Chinese fir trees to N addition. Accordingly, the amount of needle N partitioning to water-soluble fraction, which is associated with the photosynthetic capacity, also responded to N enrichment with a nonlinear increase. Our study will contribute to a more accurate prediction on the influence of N deposition on C cycles in Chinese fir plantations.
随着氮沉降持续增加，植物碳同化作用预计将呈非线性增长，从而导致生产力出现氮饱和阈值。然而，森林生态系统中植物生产力对氮沉降速率的响应以及氮饱和阈值仍有待全面量化。在此，我们通过以0、5.6、11.2、22.4和44.8克氮每平方米每年的速率添加氮，持续2.5年，测试了添加氮对三年生杉木（Cunninghamia lanceolata）地上净初级生产力（ANPP）的影响。基于二次加平台模型估算了氮饱和阈值。结果表明，ANPP从随着氮添加速率增加的增长阶段转变为在16.3克氮每平方米每年的氮添加速率下的稳定阶段。针叶的净光合速率很好地解释了ANPP对氮添加速率的响应。双同位素测量结果[同时测定针叶稳定碳（δC）和氧（δO）同位素]表明，光合能力而非气孔导度介导了幼龄杉木光合作用和ANPP对氮添加的响应。因此，与光合能力相关的分配到水溶性部分的针叶氮含量也随着氮富集呈非线性增加而做出响应。我们的研究将有助于更准确地预测氮沉降对杉木人工林碳循环的影响。
