膜下滴灌对棉花生育后期叶片与苞叶光合特性的影响

在新疆气候生态条件下,选用新陆早33号和新陆早46号棉花品种,设置2个膜下滴灌量处理,测定棉花叶片和苞叶的光响应曲线、CO2响应曲线、荧光参数等相关光合生理指标,探讨生育后期棉花叶片与苞叶光合能力的差异及对滴灌量的响应。结果表明,棉花生育期间,高温强光下苞叶最大羧化速率与最大电子传递速率的比值(Jmax/Vc,max)较高,气孔导度(Gs)较低。棉花生长发育后期,苞叶面积、含水量、叶绿素含量、净光合速率(Pn)、光系统II实际光化学效率(?PSII)、Rubisco含量显著低于叶片,但随着生育进程降幅显著低于叶片。与常规滴灌处理相比,节水滴灌处理棉花叶片含水量降幅显著高于苞叶;叶片叶绿素含量、Pn和Rubisco含量显著降低,而苞叶的变化不显著。棉花生育后期苞叶面积、含水量、叶绿素含量、Pn、ΦPSII、Rubisco含量的稳定性高于叶片,表明生育后期叶片衰老较快,但苞叶仍能保持较稳定的光合能力,对光合物质的贡献逐渐增大,常规滴灌下达7.22%~8.83%,节水滴灌下达10.24%~12.53%。

Effects of Drip Irrigation on Photosynthetic Characteristics of Leaves and Bracts in Cotton at Late Growth Stage

Themajority of cotton (Gossypium hirsutum L.) photosynthetic products comes from leaves, but non-foliar green organs of cotton such as bracts also contain chlorophyll and may contribute to the yield. We selected Xinluzao 33 and Xinluzao 46 with two irrigation treatments (normal drip irrigation and water-saving drip irrigation) to determine physiological indices including response curves of net photosynthetic rate (P_n), photosynthetically active radiation (PAR), intercellular CO₂ concentration (C_i), fluorescence parameters, and water content of cotton bracts and leaves and to explore the difference of photosynthetic capacity between bracts and leaves under drip irrigation conditions. The results showed that bracts showed greater RuBP regeneration/RuBP carboxylation capacity ratio (J_max/V_c,max) and lower stomatal conductance under high irradiance and temperature conditions. Photosynthetic area per plant, chlorophyll content, water content, P_n, the actual photochemical efficiency of PSII (Φ_PSII), and Rubisco content were less in bracts than in leaves, but the decline of the indices showed a significantly faster in leaves than in bracts at the late growth stage. Compared with normal drip irrigation, the decreased degree of water content under water-saving drip irrigation was significantly higher in leaves than in bracts of cotton plants, and chlorophyll content, P_n, and Rubisco content decreased in leaves under water-saving drip irrigation, but there was no significant changed in bracts. The stabilities of bracts area, water content, chlorophyll content, P_n, Φ_PSII, rubisco content in bracts were higher than those in leaves. It indicated the photosynthetic activity of leaves decreased rapidly. The bracts contributed approximate 7.22%–8.83% of the total photosynthate at the late growth stage under normal drip irrigation, and 10.24%–12.53% under water-saving drip irrigation. We concluded that bracts can increase the photosynthate of plant at the late growth stage under water-saving drip irrigation.