海岛棉和陆地棉叶片光合能力的差异及限制因素

研究海岛棉和陆地棉两个栽培种间叶片的光合特性及组织解剖结构特性，揭示不同棉花栽培种叶片的光合能力的差异，探讨如何进一步提高海岛棉的光合物质生产能力，以期为高光效棉花品种选育和高产高效栽培实践提供理论基础。在新疆气候生态条件下，选用北疆棉区有代表性的海岛棉品种新海22号和陆地棉品种新陆早13号为试验材料，分别测定了两棉花栽培种叶片的净光合速率（PN）、气孔导度（Gs）及叶片温度的日变化，PN-PPFD（光量子通量密度）响应曲线，PN-Ci（胞间CO2浓度）响应曲线以及叶绿素含量、叶片面积、比叶重和地上部生物量等指标，并观察了叶片的形态解剖结构特性。研究结果表明，当新陆早13号叶片被固定于水平方向上以后，日进程中新海22号的叶片温度显著高于新陆早13号。在上午和下午光强较低时，新海22号和新陆早13号的PN和Gs无明显差异；12:00h至16:00h（北京时间，下同），新海22号叶片的PN和Gs均显著低于新陆早13号。新海22号和新陆早13号叶片的PN-Ci响应曲线无明显差异。新海22号叶片的Pmax（最大光合速率）低于新陆早13号，而两者的AQY（表观量子效率）无显著差异。新海22号叶片的栅栏组织厚度、比叶重和生物量均显著低于新陆早13号，而叶绿素含量和叶片面积均显著高于新陆早13号。因此，田间条件下，海岛棉叶片的实际光合能力低于陆地棉，但两者具有相似的光合潜力。气孔导度是导致海岛棉和陆地棉叶片实际光合能力存在差异的重要原因，而栅栏组织较薄限制了海岛棉叶片光合潜力的进一步发挥。

Difference in leaf photosynthetic capacity between pima cotton (Gossypium barbadense) and upland cotton (G.hirsutum) and analysis of potential constraints

Cottons (Gossypium spp.) are of tropical origin, and are the most important textile fibre crops in the world. The most widely distributed commercial cotton species worldwide is upland cotton (G. hirsutum) which has superior yield, followed by pima cotton (G. barbadense) which has superior fibre properties. However, both lower pima cotton yields and the need for a longer growing season restrict the production of this higher quality cotton which has particularly promising for cotton production. From now on, breeding programmes for produce commercially viable genotypes have failed through incorporating the desirable fibre traits of pima cotton into upland cotton. In china, pima cotton production uniquely concentrates in Xinjiang Province. Here, compared with upland cotton, lower of photosynthate production of pima cotton was one of mainly reasons for its lower yield. The principal aim of this study was to reveal underlying mechanism attributed to the difference of photosynthetic capacity between pima cotton and upland cotton and to explore the possibilities of improving the photosynthate production of pima cotton. The experiment was conducted in Xinjiang Province, northwest China. Two typical cotton cultivars, pima cotton Xinhai 22 and upland cotton Xinluzao 13 were selected as the experimental materials. We measured diurnal time course of net photosynthetic rate (PN), stomatal conductance (Gs) and leaf temperature. On the day of measurement, leaves of Xinluzao 13 were brought to the horizontal position and retained in that position by nylon strips tied to a metal frame in order to remove the difference of incident leaf sunlight because Xinluzao 13 has diaheliotropic leaf movement but Xinhai 22 has not. We also measured the PN-Ci (intercellular CO2 concentration) response curve, PN-PPFD (photosynthetic photon flux density) response curve, chlorophyll content, leaf area, leaf mass per area and above-ground biomass, as well as leaf anatomy. The results showed that if leaves of Xinluzao 13 were restrained to the horizontal position throughout the day, the leaf temperature in Xinhai 22 was higher than that in Xinluzao 13. In the early morning and late afternoon where sunlight intensity was low, there was no difference in PN and Gs between Xinhai 22 and Xinluzao 13. From 12:00 h to 16:00 h, both PN and Gs in Xinhai 22 were lower than that in Xinluzao 13. A significantly positive line regression was found between PN and Gs. Both cotton cultivars had similar PN-Ci response curves. Pmax (light-saturated photosynthetic rate) and AQY (apparent quantum yield) were derived from PN-PPFD response curve. Compared with Xinluzao 13, Xinhai 22 had lower Pmax, whereas both cotton cultivars had similar AQY. Both leaf thickness and palisade tissue length in Xinhai 22 were thinner than that in Xinluzao 13. Xinhai 22 had higher chlorophyll content and leaf area than Xinluzao 13. Nevertheless, compared with Xinhai 22, both leaf mass per area and above-ground biomass were higher in Xinluzao 13. All results suggested that pima cotton had lower actual photosynthetic capacity than upland cotton in the field even if diaheliotropic leaf movement of upland cotton resulting in high incident leaf sunlight was not considered. However, both cotton cultivars inherit similar photosynthetic potential. Stomatal conductance was an important reason for difference of actual photosynthetic capacity between pima cotton and upland cotton. Furthermore, thinner palisade tissue in pima cotton leaves limited the expression of photosynthetic potential in the field.