为探究珍贵树种闽楠冠层光环境对叶片结构与光合诱导特征的影响机制,选取22 a生闽楠冠层基部和顶部阳生叶(强光环境)、阴生叶(弱光环境)为研究对象,探讨不同光环境对闽楠不同冠层叶片形态结构、气孔特征、光响应特性及光合诱导特征的影响。结果表明:1)随着冠层光强减弱,闽楠冠层基部和顶部叶片厚度、栅栏组织厚度、海绵组织厚度、气孔密度和气孔相对面积有所减小,与强光环境相比,弱光环境下闽楠冠层基部和顶部叶片比叶质量、最大净光合速率、光补偿点和光饱和点均有所减小;2)弱光环境导致闽楠冠层基部和顶部叶片在1 000 μmol/(m²·s)光合有效辐射下叶片净光合速率(P_{n 1000})、电子传递速率(J_{1 000})和Rubisco最大羧化速率(V_cmax)显著下降(P<0.05);3)在光合诱导过程中,与弱光环境相比,强光环境下闽楠叶片达到P_{n 1000}的90%所需时间(t_90Pn)有所减少(P<0.05),且t_90Pn与气孔密度、叶片厚度、栅栏组织厚度、海绵组织厚度呈显著负相关,表明在强光环境下,闽楠可以通过增大表观量子效率、光补偿点、V_cmax和电子传递速率(J)等提高光合固碳能力,同时可通过增加气孔密度及在光合诱导后期快速开放气孔来提高光合诱导速率,增强光斑利用能力。

To investigate the mechanism by which the canopy light environment influences leaf structure and photosynthetic induction characteristics in Phoebe bournei,we examined the effects of contrasting light environments on the morphological traits,stomatal traits,photosynthesis-light response and photosynthetic induction of sun(high-light environments)and shade leaves(low-light environments)at different canopy positions in canopy of 22-year P.bournei.The results showed that:1)The leaf thickness,palisade tissue thickness,spongy tissue thickness,stomatal density,and stomatal relative area of leaves in the basal and upper part of P.bournei canopy were decreased with the reduction of canopy light intensity.Compared with the high-light environment,the low-light environment reduced the leaf mass per area,maximum net photosynthetic rate,light compensation point,and light saturation point of the basal and upper leaves of canopy.2)Under a photosynthetically available radiation of 1 000 μmol/(m²·s),low light significantly decreased(P<0.05)the net photosynthetic rate(P_{n 1000}),electron transfer rate(J_{1 000})and maximum carboxylation rate of Rubisco(V_cmax)in the basal and upper leaves of canopy.3)During photosynthetic induction,leaves in the high-light environment achieved 90% of P_{n 1000} (t_90Pn)significantly faster(P<0.05)than those in the low-light environment.Notably,t_90Pn was a significantly negatively correlated with stomatal density,leaf thickness,palisade tissue thickness,and spongy tissue thickness.In conclusion,P.bournei adapts to high-light conditions by enhancing photosynthetic carbon fixation capacity through increased apparent quantum yield,light compensation point,Rubisco carboxylation rate and electron transfer rate.Simultaneously,P.bournei enhances its photosynthetic induction rate by increasing stomatal density and promoting rapid stomatal opening during the late stage of photosynthetic induction,thereby enhancing its ability to utilize light patches.