Key Laboratory of Forest Ecology and Environment, State Forestry Administration of China, Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing, 100091, China.
Environ Sci Pollut Res Int. 2018 Jan;25(3):2112-2120. doi: 10.1007/s11356-017-0584-z. Epub 2017 Nov 6.
Numerous studies have demonstrated the negative effects of elevated O on leaf photosynthesis. Within trees, a portion of respired CO is assimilated by woody tissue photosynthesis, but its response to elevated O remains unclear. Saplings of two evergreen tree species, EuCahetus dunnii Maiden (E. dunnii) and Osmanthus fragrans (Thunb.) Lour. (O. fragrans), were exposed to non-filtered air (NF), 100 nmol mol O air (E1) and 150 nmol mol O air (E2) in open-top chambers from May 5 to September 5, 2016 (8 h a day; 7 days a week) in subtropical China. In this study, O fumigation significantly reduced leaf net photosynthesis rate in both two tree species on most measurements. However, compared with leaf net photosynthesis rate, woody tissue gross photosynthesis rate showed less negative response to O fumigation and was even stimulated to increase. Refixation rate reflects the utilization efficiency of the respired CO by woody tissue photosynthesis. During the experiment period, E1 and E2 both increased refixation rate in O. fragrans compared with NF. Whereas for E. dunnii, E1 increased refixation rate until 81 days after starting of fumigation and then decreased it, and E2 decreased it all the time. Refixation rate had a significant positive correlation with woody tissue chlorophyll contents, indicating that the response of refixation rate to elevated O may relate to chlorophyll contents. All these suggested that under O fumigation, when atmospheric CO uptake and fixation by leaf is limited, woody tissue photosynthesis can contribute more to the total carbon assimilation in trees. The findings help to understand the significance of woody tissue photosynthesis under elevated O conditions.
大量研究表明，O 浓度升高对叶片光合作用有负面影响。在树木内部，一部分呼吸释放的 CO 通过木质组织光合作用被同化，但它对 O 浓度升高的响应仍不清楚。2016 年 5 月 5 日至 9 月 5 日，亚热带中国的开顶式气室中，两种常绿树种的幼树，蓝果树（EuCahetus dunnii Maiden）和桂花（Osmanthus fragrans）（Thunb.）Lour.（O. fragrans）分别暴露于未过滤空气（NF）、100 nmol mol O 空气（E1）和 150 nmol mol O 空气（E2）中，每天 8 小时（每周 7 天）。在这项研究中，O 熏蒸在大多数测量中显著降低了两种树种的叶片净光合速率。然而，与叶片净光合速率相比，木质组织总光合速率对 O 熏蒸的负面响应较小，甚至受到刺激而增加。再固定率反映了木质组织光合作用对呼吸释放的 CO 的利用效率。在实验期间，与 NF 相比，E1 和 E2 均增加了桂花的再固定率。而对于蓝果树，E1 在熏蒸开始后 81 天增加了再固定率，然后降低了再固定率，E2 则一直降低。再固定率与木质组织叶绿素含量呈显著正相关，表明再固定率对 O 浓度升高的响应可能与叶绿素含量有关。所有这些都表明，在 O 熏蒸下，当叶片大气 CO 吸收和固定受到限制时，木质组织光合作用可以为树木的总碳同化做出更大的贡献。这些发现有助于理解在 O 浓度升高条件下木质组织光合作用的意义。
