古尔班通古特沙漠白梭梭枝干光合及其影响因素

Abstract

植物枝干光合（P_g）固定其自身呼吸所释放的CO₂，有效减少植物向大气的CO₂排放量。以古尔班通古特沙漠优势木本植物白梭梭（Haloxylon persicum）为研究对象，利用LI-COR 6400便携式光合仪与特制光合叶室（P-Chamber）相结合，观测白梭梭叶片、不同径级枝干的光响应及光合日变化特征；同时监测环境因子（大气温湿度、光合有效辐射、土壤温度及含水量等）与叶片/枝干性状指标（叶绿素含量、含水量、干物质含量、碳/氮含量等），揭示叶片/枝干光合的主要影响因子；采用破坏性取样，量化个体水平上叶片与枝干的总表面积，阐明枝干光合对植株个体碳平衡的贡献。研究结果显示：（1）白梭梭叶片叶绿素含量是枝干叶绿素含量的12-16倍，各径级枝干叶绿素含量差异不显著；（2）枝干光饱和点低于叶片，枝干不同径级（由粗至细），暗呼吸速率和枝干光合逐渐减小；（3）光合有效辐射、土壤含水量和空气温湿度是影响叶片光合的主要因子，对枝干光合无显著影响；（4）枝干光合可以固定其自身呼吸产生CO₂的73%，最高可达90%，枝干光合固定CO₂约占个体水平固碳量的15.4%。研究结果表明，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，并且在估算枝干呼吸时，需要考虑枝干是否存在光合作用，以提高枝干呼吸的准确性。;Stem photosynthesis reassimilates CO₂ that released from their own respiration, which effectively reduces the CO₂ efflux to the atmosphere. In this study, Haloxylon persicum, the dominant woody plant in Gurbantunggut Desert, was selected as the research object. A portable LI-6400 photosynthesis system combined with P-Chamber was used to observe the light response and diurnal photosynthetic characteristics of leaves and stems. The environmental factors, including temperature and humidity, photosynthetically active radiation, soil temperature and water content, and leaf or stem traits (chlorophyll content, water content, dry matter content, carbon or nitrogen content, etc.) were monitored to reveal the main influencing factors of leaf or stem photosynthesis. The destructive sampling was used to quantify the total surface area of leaves and stems to clarify the contribution of stem photosynthesis to individual carbon balance. The results showed that:(1) the chlorophyll content of the leaves was 12-16 times than that of stems in H. persicum, and there was no significant difference in chlorophyll content among different diameter stems. (2) The light saturation point of the stems was lower than that of the leaves, and the dark respiration rate and photosynthesis of different diameter classes (from coarse to fine) of stems gradually decreased. (3) The photosynthetic effective radiation, soil moisture and air temperature and humidity were the main factors affecting leaf photosynthesis, but had no significant effect on stem photosynthesis. There was a strong correlation between stem photosynthesis and stem. (4) Stem photosynthesis fixed 73% of CO₂ produced by its own respiration, and the highest rate reached 90%, photosynthetic CO₂ fixation in stems accounted for about 15.4% of individual level carbon fixation. The results of this study show that there may be a fundamental defect in ignoring the contribution of stem photosynthesis to predict the carbon process of desert ecosystem under the background of future climate change. When estimating the stem respiration, it is necessary to consider whether there is stem photosynthesis to improve the accuracy of branch respiration.