Stem photosynthesis (Pg) is an alternative and significant carbon source, playing a crucial role in plant survival under extreme environment. The main aims of this study were to quantify stem and leaf photosynthesis, find out the main drivers of Pg, and estimate the contributions of Pg to plant individual carbon balance of two dominant species Haloxylon ammodendron and Tamarix ramosissima in Gurbantunggut Desert. A Li-Cor 6400 portable photosynthesis system and a special chamber were used to measure leaf and stem photosynthesis. Ancillary measurements included leaf/stem functional trait (chlorophyll content, water content, leaf/stem area, carbon/nitrogen content, etc.) and environmental factors (air temperature and humidity, photosynthetically active radiation, soil temperature, and soil water content). Our results showed that Pg of H. ammodendron and T. ramosissima was 2.37 and 0.98 μmol·m-2·s-1, Pg refixation CO2 of stem respiration by 65%-76% and 57%-77% in H. ammodendron and T. ramosissima. Pg was influenced by photosynthetically active radiation, air temperature, soil temperature and water vapor deficit. Pg assimilation CO2 accounted for 8.2%-16.6% and 3.6%-8.3% of CO2 assimilation of H. ammodendron and T. ramosissima, respectively. The maximum value appeared at noon when temperature was high. There might be fundamental defects if we ignore the contribution of branch photosynthesis when predicting carbon process of desert ecosystem under the background of climate change.
荒漠植物长期演化过程中保留了枝干光合(Pg)的特性,枝干光合有效减少局部碳损失,且在维持植物正常生理代谢方面发挥重要作用。本研究以古尔班通古特沙漠南缘荒漠植物梭梭和多枝柽柳为对象,利用Li-Cor 6400便携式光合仪与特制叶室相结合监测枝干与叶片光合速率,同时辅以枝干/叶片功能性状(叶绿素含量、含水量、叶/枝面积、碳/氮含量等)与环境因子(空气温湿度、光合有效辐、土壤温度、含水量)的监测,量化两种荒漠植物的枝干光合,揭示枝干光合的主要影响因子,并评估其在植株个体水平上的贡献。结果表明: 梭梭和多枝柽柳枝干光合能够有效减少枝干呼吸所释放的CO2,梭梭Pg可达2.37 μmol·m-2·s-1,抵消枝干呼吸释放CO2的65%～76%;多枝柽柳Pg可达0.98 μmol·m-2·s-1,抵消枝干呼吸释放CO2的57%～77%。光合有效辐射、空气温度、土壤温度和饱和水汽压差是Pg的主要环境影响因子。梭梭和多枝柽柳的枝干光合所固定的CO2分别占植株二氧化碳吸收的8.2%～16.6%和3.6%～8.3%,且最大值出现在气温较高的正午。忽视枝干光合的贡献来预测未来气候变化背景下荒漠生态系统碳过程,可能存在根本性缺陷。.
Keywords: adapting strategy; desert plant; drought stress; stem photosynthesis.