Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, QLD 4111, Australia; State Key Laboratory of Remote Sensing, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China.
Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, QLD 4111, Australia.
Environ Int. 2020 Jan;134:105209. doi: 10.1016/j.envint.2019.105209. Epub 2019 Oct 31.
Understanding the responses of local forests to the gradually rising atmospheric CO concentrations (c) and changing environment is critical for appropriate management activities. This work used tree ring width measures (i.e. basal areal increment, BAI) and carbon (C) and nitrogen (N) signals to explore the intrinsic water use efficiency (iWUE) and tree growth dynamics of three major tree species (Pinus massoniana, P.tabuliformis and Larix gmelinii) in the Miyun Reservae Basin (MRB) of Beijing. The results indicate that c was a primary contributor to tree growths, especially at the remote site where rising c accounted for 92% and 74% of BAI changes for P. tabuliformis and L. gmelinii, respectively. N deposition was found to have a positive effect on BAI at this site. The controlling effect of c on tree growth at the close-to-city site was smaller (52% and 44% of the contributions for P. tabuliformis and P. massoniana, respectively), while the negative influences of N deposition on BAI tends to be intensified. iWUE showed consistent increase during the entire growth period at all sites. Quadratic relationships between iWUE and BAI were observed, which indicated that the rising c stimulated photosynthesis, contributing to the initial BAI and iWUE increase. However, the intensified water stress resulting from reduced precipitation and increased temperature led to a reduction in tree stomatal conductance causing the subsequent increase in iWUE but decrease in BAI. Of the site- and species-related responses of tree growth to c, climatic and environmental changes in the MRB, the site-related variation dominated. The non-linear relationship between BAI and c combined with the quadratic relationship between BAI and iWUE indicate a decreased ability of forests to capture atmospheric CO once the CO tipping point has passed.
了解本地森林对逐渐升高的大气 CO 浓度（c）和不断变化的环境的响应对于适当的管理活动至关重要。本研究利用树木年轮宽度（即基面积增量，BAI）和碳（C）和氮（N）信号，探讨了北京密云水库流域（MRB）三种主要树种（马尾松、油松和落叶松）的内在水分利用效率（iWUE）和树木生长动态。结果表明，c 是树木生长的主要驱动因素，特别是在偏远地区，c 的上升分别解释了油松和落叶松 BAI 变化的 92%和 74%。研究发现，在该地区，N 沉降对 BAI 有积极影响。在靠近城市的地点，c 对树木生长的控制作用较小（分别为油松和马尾松的贡献的 52%和 44%），而 N 沉降对 BAI 的负面影响趋于加剧。在所有地点，iWUE 在整个生长期间均呈持续增加趋势。在所有地点，iWUE 与 BAI 之间存在二次关系，表明 c 的升高刺激了光合作用，有助于初始 BAI 和 iWUE 的增加。然而，降水减少和温度升高导致的水分胁迫加剧，导致树木气孔导度降低，从而导致随后的 iWUE 增加和 BAI 减少。在树木生长对 c 的站点和物种相关响应中，MRB 的气候和环境变化起主导作用。BAI 和 c 之间的非线性关系以及 BAI 和 iWUE 之间的二次关系表明，一旦 CO 转折点过去，森林吸收大气 CO 的能力就会下降。
