Jiang Qi, Lin Chengfang, Guo Runquan, Xiong Decheng, Yao Xiaodong, Wang Xiaohong, Chen Tingting, Jia Linqiao, Wu Dongmei, Fan Ailian, Chen Guangshui, Yang Yusheng
Fujian Sanming Forest Ecosystem National Observation and Research Station, School of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China.
Key Laboratory for Subtropical Mountain Ecology (Ministry of Science and Technology and Fujian Province Funded), School of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China.
Tree Physiol. 2023 Jan 5;43(1):31-46. doi: 10.1093/treephys/tpac103.
There is a knowledge gap in the effects of climate warming and nitrogen (N) deposition on root N absorption capacity, which limits our ability to predict how climate change alters the N cycling and its consequences for forest productivity especially in subtropical areas where soil N availability is already high. In order to explore the effects and mechanism of warming and the N deposition on root N absorption capacity of Chinese fir (Cunninghamia lanceolata), a subtropical arbuscular mycorrhizal conifer, the fine root 15NH4+ and 15NO3- uptake kinetics at a reference temperature of 20 °C were measured across different seasons in a factorial soil warming (ambient, +5 °C) × N addition (ambient, +40 kg N ha-1 yr-1) experiment. The results showed that (i) compared with the control, warming increased the maximal uptake rate of NH4+ (Vmax,20 °C-NH4+) in summer, while N addition enhanced it in spring and summer; compared with non-warming treatments, warming treatments increased the uptake rate of NO3- at a reference concentration of 100 μmol (V100,20 °C-NO3-) in spring. (ii) The analysis of covariance showed that Vmax,20 °C-NH4+ was positively correlated with root mycorrhizal colonization rate (MCR) and V100,20 °C-NO3- was positively correlated with specific root respiration rate (SRR), whereas no N uptake kinetic parameter was correlated with specific root length, root N and non-structural carbon concentrations. Thus, our results demonstrate that warming-increased root NH4+ uptake might be related to warming-increased MCR, whereas warming-increased root NO3- uptake might be related to warming-increased SRR. We conclude that root NH4+ and NO3- uptake capacity of subtropical Chinese fir can be elevated under warming and N deposition, which could improve plantation productivity and mitigate N leaching loss and soil acidification.
气候变暖和氮（N）沉降对根系氮吸收能力的影响存在知识空白，这限制了我们预测气候变化如何改变氮循环及其对森林生产力影响的能力，尤其是在土壤氮有效性已经很高的亚热带地区。为了探究变暖和氮沉降对亚热带丛枝菌根针叶树杉木根系氮吸收能力的影响及机制，在土壤增温（环境温度、+5℃）×施氮（环境水平、+40 kg N ha-1 yr-1）的析因实验中，测定了20℃参考温度下不同季节杉木细根对15NH4+和15NO3-的吸收动力学。结果表明：（i）与对照相比，增温提高了夏季NH4+的最大吸收速率（Vmax,20℃-NH4+），而施氮在春季和夏季提高了该速率；与未增温处理相比，增温处理提高了春季100 μmol参考浓度下NO3-的吸收速率（V100,20℃-NO3-）。（ii）协方差分析表明，Vmax,20℃-NH4+与根系菌根侵染率（MCR）呈正相关，V100,20℃-NO3-与比根呼吸速率（SRR）呈正相关，而没有氮吸收动力学参数与比根长、根系氮和非结构性碳浓度相关。因此，我们的结果表明，增温提高根系NH4+吸收可能与增温提高MCR有关，而增温提高根系NO3-吸收可能与增温提高SRR有关。我们得出结论，亚热带杉木根系对NH4+和NO3-的吸收能力在变暖和氮沉降条件下可以提高，这可能会提高人工林生产力并减轻氮淋失和土壤酸化。
