干旱-复水条件下氮素对高粱光合特性及抗氧化代谢的影响

采用盆栽试验，以持绿性品系高粱B35和非持绿性高粱品系三尺三为试验材料，设置两个施氮处理（每盆0和6 g尿素），在灌浆期干旱-复水条件下测定光合特性及抗氧化代谢指标。结果表明，氮素显著提升B35和三尺三在干旱胁迫下净光合速率（Pn）、胞间CO₂浓度（Ci）和蒸腾速率（Tr），提高了光系统II（PSII）反应中心活性；干旱胁迫下，施氮显著提高磷酸烯醇式丙酮酸羧化酶（PEPCase）活性，施氮使B35和三尺三PEP羧化酶分别提高了29.17%和25.66%, 而二磷酸核酮糖羧化酶（RuBPCase）活性对氮素不敏感。与三尺三相比，氮素对B35的光合能力的促进作用更加明显。干旱胁迫下氮素显著提升了超氧化物歧化酶（SOD）和过氧化物酶（POD）活性，B35和三尺三的SOD活性分别提高了25.56%和17.07%，POD活性分别提高了48.97%和76.62%。B35抗氧化酶的活性均高于三尺三。同时，氮素降低了B35和三尺三丙二醛（MDA）含量。复水后，氮素显著提升B35和三尺三Pn、Tr和PEP羧化酶活性，Pn升高幅度分别为33.66%和60.01%，Tr升高幅度分别为36.59%和41.57%，PEP羧化酶活性升高幅度分别为23.47%和18.64%，同时显著降低了初始荧光值（Fo），Fo降低幅度分别为18.50%、10.98%。施氮有利于提高复水后的B35和三尺三抗氧化酶活性，降低细胞膜脂过氧化程度。复水后，与三尺三相比，B35的光合特性和抗氧化酶活性较高。两个施氮处理的B35产量均高于三尺三，氮素使B35和三尺三生物产量分别增加9.73%和10.08%，籽粒产量分别增加24.47%和21.79%。氮素调节气孔导度及光系统Ⅱ活性，降低干旱对光合机构的损伤；复水后，氮素通过提高光系统Ⅱ活性，提高光合酶活性，光合性能提升。干旱及复水条件下，施氮提升抗氧化酶活性，减轻膜脂过氧化的损伤。氮素有利于干旱及复水条件下B35和三尺三光合特性及抗氧化酶系统能力的提升。

Effects of nitrogen on photosynthesis and antioxidant enzyme activities of sorghum under drought stress and re-watering

In this study, stay-green sorghum (B35) and non-stay green sorghum (Sanchisan) were used as experimental materials. Sorghum plants were planted in pots with two N application levels (0 and 6 g N per pot, respectively) to determine photosynthetic properties and antioxidant enzyme activities under drought stress and re-watering during filling stage. The results showed that nitrogen significantly increased the photosyntheticrate (Pn), intercellular CO₂ concentration (Ci), transpiration rate (Tr),and activity of reaction center in photosystem II activity (PSII) under drought stress. Under drought condition, the activities of phosphoenolpyruvate carboxylase (PEPCase) in B35 and Sanchisan were increased by 29.17%and 25.66% with nitrogen application,respectively. Nevertheless, the activity of ribulose diphosphate carboxylase (RuBPCase) was not sensitive to nitrogen.Compared with Sanchisan, the photosynthetic ability of B35 was obviously promoted by nitrogen. Under drought stress, nitrogen significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD).The activities of SOD and POD in B35 and Sanchisan were increased by 25.56% and 17.07%, and 48.97% and 76.62% with nitrogen application,respectively. The activities of antioxidant enzymes in B35 were higher than that of Sanchisan. At the same time, nitrogen decreased the malondialdehyde (MDA) contents of B35 and Sanchisan. After Re-watering, nitrogen significantly increased Pn, Tr and PEPCase activity and reduced the initial fluorescence value (Fo). Pn, Tr and PEPCase activity of B35 and Sanchisanwere promoted by 33.66% and 60.01%, 36.59% and 41.57%, and 23.47% and 18.64%, respectively. However, Fo was decreased by 18.50% and 10.98%. Nitrogen application was beneficial to improve the activities of antioxidant enzymes of B35 and Sanchisan; and reduced the degree of lipid peroxidation in cell membrane after re-watering. After re-watering, the photosynthetic characteristics and antioxidant enzyme activities of B35 were higher than that of Sanchisan. The yield of B35 in two different nitrogen levels was higher than Sanchisan.The biological and grain yield of B35 and Sanchisan with nitrogen application were increased by 9.73% and 10.08%, and 24.47% and 21.79%, respectively. The damage of photosynthetic apparatus by drought was alleviated with nitrogen application by regulating stomatal conductance and photosystem II activity. After re-watering, the photosynthetic ability was promoted by higher photosystem II activity and the activities of photosynthetic enzyme which were increased with nitrogen application. Under drought and re-watering conditions, nitrogen increased antioxidant enzyme activities and reduced the degree of lipid peroxidation in cell membrane. Nitrogen is beneficial to the enhancement of photosynthetic and antioxidant enzyme systems ability of B35 and Sanchisan under drought and re-watering conditions.