茶树树冠整体的光合能力是决定茶树生产力的主要因素。本文研究了10龄龙井43投产茶园茶树树冠表层（受光率100%）、中层（受光率50%~70%）、下层（受光率0%~15%）叶片的光合作用特性、生理生态指标的特点及其相互关系。结果表明,从树冠表层至下层叶片接受到的光合有效辐射显著降低,但空气CO2浓度以树冠下层最高;叶片比叶重、单位面积全氮和全碳含量、叶绿素含量均以表层显著高于下层,而以重量为基础的全氮和全碳含量没有表现出明显的冠层分布差异;表层和中层叶片的光响应曲线表现为典型的Farquhar模型,但下层叶片无类似特征;光饱和速率、气孔导度、蒸腾速率均以表层叶片最高、下层叶片最低,但胞间CO2浓度以下层叶片最高;表层和中层叶片光合氮效率差异不大,但显著高于下部叶片。这表明,冠层下部叶片光合作用速率下降的主要原因是光照强度减弱使光合系统活性和羧化效率明显降低,而气孔导度的下降可能不是主要影响因素。因此,如何采取科学的栽培技术,进而调节树冠叶片分布以提高茶树群体光合能力值得深入研究。
The canopy photosynthetic capacity is one of the dominant factors determining the productivity of tea plants. The photosynthetic traits, physiological and ecological factors as well as their interactions of 10-year old tea plant (Longjing 43 cultivar) at surface, middle, low positions in the canopy receiving 100%, 50%~70%, 0%~15% photosynthetically active radiation (PAR) were investigated in this paper. The received PAR decreased sharply from the surface to low canopy, while CO2 concentration was the highest at low canopy. There were magnificent decreases of leaf mass area ratio (LMA), total nitrogen (NA), total carbon (CA), chlorophyll contents based on leaf area from the surface to low canopy. However, the contents of total N and C were not significantly different among positions in tea plant when calculated based on leaf mass. Leaves at the surface and middle positions, but not low canopy showed typical light response curves fitting well to the Farquhar model. The light-saturated photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) also decreased markedly from surface canopy to low canopy, while concentration of intercellular CO2 (Ci) was the highest at low canopy. Photosynthetic nitrogen use efficiency (PNUE) of surface canopy and middle canopy were significantly higher than that of low canopy. The overall results suggested that the decreased Pn within the leaves of tea plant from surface to low canopy was mainly related to the reduced capacity of photosystem and carboxylation efficiency caused by decreased light intensity instead of low Gs. More research is needed to illustrate the optimum canopy structure shaped by rational agronomical management which could improve the canopy photosynthetic capacity of tea plants.
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