花铃期干旱胁迫下氮素水平对棉花光合作用与叶绿素荧光特性的影响

于2004—2005在江苏南京农业大学卫岗试验站进行盆栽试验, 设置干旱与对照2个土壤水分处理, 每个处理再设置3个氮素水平, 研究了花铃期干旱胁迫下氮素水平对棉花叶片光合作用与叶绿素荧光参数的影响, 以期为棉花花铃期干旱时的合理氮肥运筹提供理论依据。结果表明, 与对照相比, 干旱处理显著降低了棉株凌晨叶水势、土壤相对含水量、净光合速率(P_n)、气孔导度(G_s)与胞间CO₂浓度(C_i), 但提高了叶绿素a(Chl a)、叶绿素b(Chl b)、总叶绿素(Chl a+b)及类胡萝卜素(Car)的含量。干旱处理下, P_n、G_s、C_i、Chl a、Chl b、Chl a+b及Car均以240 kg hm^-2氮素水平最高。干旱胁迫下叶绿素初始荧光(Fo)明显升高, 且随氮素水平的提高而增大; 而最大光化学效率(F_v/F_m)、光系统II(PS II)量子产量(ΦPS II)、电子传递速率(ETR)与光化学猝灭系数(qP)均显著降低, 干旱胁迫亦增大了非光化学猝灭系数(NPQ)。干旱胁迫下F_v/F_m、ΦPS II、ETR与qP均以240 kg hm^-2氮素水平最高。干旱胁迫显著降低叶片蒸腾速率(Tr), 导致叶温升高, 增施氮肥进一步增大了叶温。干旱胁迫降低了棉株各器官干物质重, 而施氮则增大水分胁迫指数。综合分析认为, 过量施氮或施氮不足均不利于提高棉花叶片光合性能。两年试验结果表明, 在本试验设置的3个氮素水平中, 花铃期干旱胁迫下以240 kg hm^-2纯氮, 且基施50%, 初花期追施50%较适宜。

Effects of Nitrogen Levels on Photosynthesis and Chlorophyll Fluorescence Characteristics under Drought Stress in Cotton Flowering and Boll-Forming Stage

The flowering and boll-forming stage is the key yield determinant period of upland cotton. Short-duration water stress occurring during this stage significantly reduced cotton development and final productivity. Nitrogen application plays an important role in alleviating the adverse effects of dry soil on plant development. In order to explore effects of nitrogen on cotton photosynthesis under drought stress. The photosynthesis and chlorophyll fluorescence characteristics of cotton with different nitrogen application were examined under developing gradually drought stress during flowering and boll-forming stage. Leaf water potential, soil relative water content, net photosynthetic rate (P_n), stomatal conductance (G_s), and intercellular CO₂ concentration (C_i) were reduced, but the pigment contents of cotton leaf were increased under soil drought stress. The reduced degree of P_n was increased with increasing nitrogen levels. Under drought stress, P_n, G_s, C_i, Chl a content, Chl b content, Chl a+b content. and Car content in 240 kg N ha^-1 treatment was the highest among the three nitrogen levels. Drought stress caused a significant decline in the maximum photochemical efficiency of photosystem II (F_v/F_m), the quantum yield of electron transport (ΦPS II), the electron transport rate (ETR) and the photochemical quenching co-efficient (qP). These changes were accompanied by an increase in both the minimal fluorescence (Fo) and the non-photochemical quenching co-efficient (NPQ). F_v/F_m, ΦPS II, ETR, and qP were higher at 240 kg N ha^-1 level than at 0 and 480 kg N ha^-1 levels. The transpiration (Tr) of cotton was reduced and the temperature of leaf was enhanced under drought. The dry matter of cotton decreased under drought. Nitrogen application increased dry matter weight and augmented the water stress indexes. All results suggest that 240 kg N ha^-1 is the optimal nitrogen application rate under drought, deficient (0 kg N ^ha-1) and excessive (480 kg N ^ha-1) nitrogen application are of disadvantage to photosynthesis and chlorophyll fluorescence characteristics.