格木人工林不同冠层光合特征

Photosynthetic characteristics in different canopy positions of an Erythrophleum fordii plantation

评价格木Erythrophleum fordii人工林不同冠层分枝的光合能力,为格木人工林修枝提供光合生理基础。以9年生格木-马尾松Pinus massoniana混交人工林为研究对象,观测格木人工林不同冠层叶片的光响应曲线、二氧化碳响应曲线及光合因子的日变化。结果表明:格木人工林不同冠层叶片的光合初始斜率(α)和最大净光合速率(Pmax)的大小顺序相同,依次为冠层C>冠层B>冠层A,而暗呼吸速率(Rd)大小顺序则相反,高冠层叶片的饱和光强(Isat)较大,而光补偿点(Ic)却较低,且3个冠层各参数差异均达到显著或极显著水平;3个冠层叶片的初始羟化效率(α),光合能力(Amax)的顺序相同,均为冠层C>冠层B>冠层A,而二氧化碳补偿点(Γ)顺序相反,光呼吸(Rp)变化与光合作用保持着平行关系;3个冠层的光合有效辐射(PAR),蒸腾速率(Tr)与叶片温度(T)的日变化为单峰型,净光合速率(Pn)与气孔导度(Gs)日变化曲线呈双峰型,但峰值出现的时间均不同,3个冠层胞间二氧化碳摩尔分数(Ci)的日变化一致,为"U"型曲线,均在13:00出现最低值;通径分析结果表明:光合有效辐射与气孔导度对3个冠层净光合速率的直接通径系数绝对值均较大,表明光合有效辐射及气孔导度是影响格木人工林3个冠层叶片的净光合速率的主要因子。格木高冠层叶片具有更高的光合速率和更强的潜在光合能力,对光合物质的积累能力较强,消耗光合产物较少。

To evaluate the photosynthetic characteristics of different canopy positions and to provide a photosynthetic physiological basis for pruning in an Erythrophleum fordii plantation,light intensity,light response curve,CO_2 response curve,and the dynamic changes of photosynthetic factors were measured in different canopy positions of an E.fordii × Pinus massoniana plantation.Also,photosynthetic capacity of branches in different canopy positions was analyzed and a path analysis was conducted.Results showed that the different canopy positions significantly affected on initial slope photo inhibition（P〈0.05） and maximum net photosynthetic rate（P〈0.01）,and ranked as canopy Ccanopy Bcanopy A;however,dark respiration rate was opposite.There was significant difference in the saturation light and light compensation point in different canopy positions（P〈0.01）,the saturation light of higher canopy was greater,but the light compensation point was lower.Initial carboxylation efficiency and photosynthetic capacity higher in the canopy were greater than lower in the canopy with highly significant difference（P〈0.01）,and the carbon dioxide compensation point of different positions in the canopy was in the reverse order.The relationship between photorespiration and photosynthesis was parallel.Daytime change of photosynthetic active radiation,transpiration rate,and leaf temperature in the three canopy positions appeared as a single peak and the diurnal variation net photosynthetic rate and stomatal conductance showed a typical curve with a double peak,but the time of the peaks was different.The diurnal change of intercellular CO_2 concentration in the three canopies was consistent,as a ＂U＂ type curve.The path analysis indicated that photosynthetic available radiation and stomatal conductance were the key factors for the net photosynthetic rate in leaves of the three canopy positions of the E.fordii plantation.The high canopy position＇s photosynthetic rate,potential photosynthetic capacity,and photosynthetic material accumulating ability were stronger,and less of the photosynthetic product was consumed higher in the canopy than lower in the canopy,which could provide scientific guidance to determine the pruning intensity in E.fordii plantation.