香樟冠层光环境对叶片功能性状和光合特性的影响

Effects of light environments within Cinnamomum camphora canopy on leaf functional traits and photosynthetic characteristics

为了解香樟冠层不同光环境叶片光合能力的适应机制,提升冠层碳汇功能,本文选取香樟单株冠层南向外侧(100%全光)、南向内侧(34%全光)和北向(21%全光)3个方位的叶片,研究光环境对叶片形态结构、营养和生理性状以及光合特性的影响,分析弱光环境下导致光合能力下调的主要限制因子。结果表明:随着冠层光强减弱,叶片的比叶重、表皮角质层厚度、下表皮厚度、栅栏组织厚度、栅栏组织细胞数和细胞宽度、栅栏组织与海绵组织的厚度比、细胞结构紧密度均显著降低,而海绵组织厚度、栅栏组织细胞长宽比、细胞结构疏松度均显著升高。与全光环境相比,2个弱光环境下叶片的碳含量、可溶性糖、淀粉和可溶性蛋白含量均显著降低,而氮含量在北向显著升高。弱光导致净光合速率(P_(n))、暗呼吸速率、CO_(2)气孔导度(g_(sc))、叶肉导度(g_(m))、CO_(2)总导度(g_(tot))、胞间CO_(2)浓度(C_(i))、叶绿体CO_(2)浓度(C_(c))等气体交换参数显著下降,且P_(n)与g_(sc)、g_(m)、g_(tot)、C_(c)呈显著正相关。尽管最大光化学量子效率、实际光化学量子效率、光化学猝灭系数、最大羧化效率(V_(c max))和最大电子传递速率(J_(max))在不同光环境间均无显著差异,但V_(c max)和J_(max)与P_(n)呈显著正相关。g_(m)是弱光下光合速率降低的主要限制因子,且随着光照的进一步减弱,g_(sc)限制逐渐增强,而生化限制对净光合速率的影响相对较小。综上,全光照可以提升香樟冠层叶片的光合潜力,降低g_(m)和g_(sc)对光合性能的限制,增强碳同化能力。

To explore the adaptive mechanism of leaf photosynthetic capacity in different light environments within Cinnamomum camphora canopy and enhance carbon sequestration,we investigated morphological structures,nutritional and physiological traits and photosynthetic characteristics of leaves in different orientations of C.camphora canopy,southern side in the outer layer(100%full light),southern side in the inner layer(34%full light)and northern side(21%full light).We analyzed the main limitation resulting in down-regulation of photosynthetic capacity in low light environments.Results showed that specific leaf weight,the thickness of lower and upper epidermal cuticle,lower epidermis,palisade tissue as well as cell number and width of palisade tissue,the thickness ratio of palisade to spongy tissue,cell structure closely degree significantly decreased with decreasing light intensity within canopy,opposite to the responses of spongy tissue thickness,cell length-width ratio of palisade tissue,and cell structure loose degree.The contents of leaf carbon,soluble protein,soluble sugar and starch were significantly lower in two low light environments compared with full light,whereas nitrogen content was markedly higher in north side.Low light prominently reduced gas exchange parameters,i.e.,net photosynthetic rate(P_(n)),dark respiration rate,stomatal conductance to CO_(2)(g_(sc)),mesophyll conductance to CO_(2)(g_(m)),total conductance to CO_(2)(g_(tot)),intercellular CO_(2)concentration(C_(i)),CO_(2)concentration at the chloroplast(C_(c)).P_(n)was positively correlated with g_(sc),g_(m),g_(tot)and C_(c).There were no differences in maximum quantum photochemical efficiency,actual quantum photochemical efficiency,photochemical quenching coefficient,maximum rate of Rubisco carboxylation(V_(c max))and maximum rate of electron transport(J_(max))among light environments.V_(c max)and J_(max)were positively correlated to Pn.Of the shading-induced limitations to photosynthesis,gm limitation was the most important,and gsc limitation was enhanced with further weakened light intensity while biochemical limitation was rather limited.In summary,the results suggested that full light could improve leaf photosynthetic potential in C.camphora canopy leaves,reduce the effects of gm and gsc limitation on photosynthesis,and consequently enhance carbon assimilation capacity.