田间条件下海岛棉和陆地棉花铃期叶片光保护的机制

研究海岛棉(Gossypium barbadense)和陆地棉(G. hirsutum)两个棉花栽培种的光合作用特性, 探讨两个栽培种光合机构的光抑制以及防御保护机制, 以期为新疆棉花高光效品种选育和高产高效栽培实践提供理论基础。在新疆生态气候条件下, 系统测定了海岛棉和陆地棉的叶片运动、叶片接受光量子通量密度(PFD)、叶片温度、叶绿素荧光参数、气体交换参数和光呼吸速率的日变化。研究结果表明: 陆地棉叶片的“横向日性”较强而海岛棉较弱, 导致海岛棉叶片接受PFD较低, 但其叶片温度较高。海岛棉叶片的光合速率和气孔导度均显著低于陆地棉。在8:00-10:00 (北京时间, 下同)海岛棉叶片的光呼吸速率略低于陆地棉, 其余时间段海岛棉和陆地棉叶片的光呼吸速率相似。不同栽培种间, 叶片的最大光化学效率和实际光化学效率的日变化均无明显差异。除14:00-16:00以外, 海岛棉叶片的表观电子传递速率和光化学猝灭系数均显著低于陆地棉。8:00以后, 海岛棉叶片的非光化学猝灭显著高于陆地棉。因此, 在新疆生态气候条件下, 海岛棉和陆地棉叶片“横向日性”运动能力和气孔导度的差异导致叶片所处的光温环境不同, 同时造成海岛棉叶片的碳同化能力较低。为阻止光合电子传递链的过度还原, 减轻光合机构的光抑制, 陆地棉叶片主要通过光合机构的电子流途径耗散激发能, 而海岛棉叶片通过热耗散途径和相对较高的光呼吸能力来耗散激发能。

Mechanism for photoprotection of leaves at the bolling stage under field conditions in Gossypium barbadense and G.hirsutum

Aims Our principal aim was to test the hypothesis that pima cotton (Gossypium barbadense) and upland cotton (G. hirsutum) have different photoinhibition and photoprotection strategies due to differences in light capturing and photosynthetic characteristics. Methods We measured diurnal leaf movement, incident photon flux density (PFD) on leaves, leaf temperature, maximal photochemical efficiency of PSII (F_v/F_m), PSII photochemical efficiency (Φ_PSII), electron transport rate (ETR), photochemical quenching coefficient (q_P), non-photochemical quenching (NPQ), net photosynthetic rate (P_n), stomatal conductance (G_s) and photorespiration (P_r) in pima and upland cotton. Important findings Upland cotton had higher P_n and G_s than pima cotton. Nevertheless, the ratio of photorespiration rate to gross photosynthetic rate was generally higher in pima cotton. Pima cotton and upland cotton had similar degrees of photoinhibition. Furthermore, pima cotton had generally higher thermal energy dissipation capacity than upland cotton. All results indicated that differences in leaf diaheliotropic movement and G_s in pima cotton and upland cotton resulted in differences of both incident PFD on leaves and leaf temperature. Upland cotton and pima cotton preferentially used electron transport flux and thermal energy dissipation, respectively, for light energy dissipation toward photoprotection to against photoinhibition. Nevertheless, more electron transport flux was distributed into the photorespiration pathway to prevent over-reduction of the photosynthetic electron transport chain and photoinhibition in pima cotton.