授粉期高温胁迫对夏玉米植株形态、叶片光合及产量的影响

Effects of high temperature stress during pollination on plant morphology,leaf photosynthetic characteristics,and yield of summer maize

针对黄淮海地区花期高温影响夏玉米安全生产的问题,本研究以热敏感型品种‘先玉335’为试验材料,以大田常温为对照(CK),设置授粉期高温处理(HT),研究授粉期高温胁迫对夏玉米植株形态、叶片光合特性、干物质积累与分配及产量形成的影响。结果表明:2021年和2022年,HT处理的冠层最高温度超过40℃的天数分别为7 d和8 d,高温处理期间冠层最高温度分别较CK高1.7~6.8℃和1.5~4.6℃。HT处理显著提高了夏玉米株高和穗位高,对茎粗和叶面积无显著影响,但延缓了生育后期叶片衰老,2021年和2022年成熟期的叶面积较CK分别显著提高34.69%和163.72%。高温处理期间,HT处理的玉米叶片气孔导度、蒸腾速率和胞间CO_(2)浓度显著升高(P<0.05,P<0.01),叶片羧化效率、气孔限制值和水分利用效率显著降低(P<0.05,P<0.01);叶片净光合速率随处理温度而变化,处理温度过高(一般>40℃时)则显著降低(P<0.05),反之则显著升高(P<0.05)或无显著变化,叶片整体光合性能下降。高温胁迫解除后,HT处理的叶片光合性能相关参数逐渐与CK趋于一致。经授粉期高温胁迫处理后,玉米茎秆、叶片、苞叶、穗轴和单株干重降低,其中穗轴干重降幅最大,而雄穗和花丝干重增加,使得干物质向茎秆、叶片、雄穗、花丝等部位的分配比例增加,而向穗轴的分配比例显著减少(P<0.05)。至成熟期,HT处理造成玉米籽粒和单株干重显著减少48.32%和16.71%(P<0.05),而玉米茎秆和叶片干重显著增加35.01%和9.48%(P<0.05)。HT处理的结实率和穗粒数分别显著下降54.43%和53.19%(P<0.05),百粒重显著提高10.13%(P<0.05),但籽粒产量显著降低46.82%(P<0.05)。综上,授粉期高温胁迫增强了玉米叶片气孔蒸腾,增加了胞间CO_(2)浓度,降低了叶片羧化效率和水分利用效率,导致植株整体光合性能下降,制约了光合同化物积累及向穗部的转移分配,导致结实率显著下降,穗粒数显著减少,制约了花后光合同化物从“源”(茎秆和叶片)向“库”(籽粒)的转运,最终导致籽粒产量大幅下降。

High temperatures during the flowering period seriously affect the safe production of summer maize in the Huang-Huai-Hai region.In this experiment,the heat-sensitive variety‘Xianyu 335’was used as the test material;the effects of high temperature stress during pollination on plant morphology,leaf photosynthetic characteristics,dry matter accumulation and distribution,and yield of summer maize were studied by setting up normal field temperature treatment(CK)and high temperature treatment during pollination(HT).The results showed that in 2021 and 2022,the number of days with maximum canopy temperatures exceeding 40℃in the HT treatment group was 7 and 8 d,respectively,and the maximum canopy temperatures in the HT treatment group were higher than those in the CK group by 1.7−6.8℃and 1.5−4.6℃,respectively.HT treatment significantly increased the plant height and ear height of summer maize but had no significant effect on stem diameter and green leaf area during the high-temperature treatment period.However,HT treatment delayed leaf senescence in the late reproductive stage of maize,and the green leaf area at maturity was 34.69%and 163.72%higher than that in the CK group in 2021 and 2022,respectively.During the high-temperature treatment period,leaf stomatal conductance,transpiration rate,and intercellular CO_(2)concentration were significantly higher and leaf carboxylation efficiency,stomatal limitation value,and water use efficiency were significantly lower in the HT treatment group than in the CK treatment group.The net photosynthetic rate of maize leaf in the HT treatment group varied with the treatment temperature:it significantly reduced when compared with that in the CK treatment group only when HT treatment temperature was too high(generally>40℃).High-temperature stress during pollination led to a decrease in the overall photosynthetic performance of the maize leaves.After exposure to 10 d of high temperature stress during pollination,the dry weights of maize stems,leaves,bracts,cobs,and individual plants decreased significantly.The dry weight of the cobs decreased the most,while those of the male ears and filaments increased significantly.HT treatment resulted in an increase in the partitioning of dry matter to stems,leaves,male ears,and filaments,and a significant decrease in partitioning to the cobs.At maturity,HT treatment significantly reduced the dry weights of maize grains and plant by 48.32%and 16.71%,respectively,while those of maize stems and leaves increased by 35.01%and 9.48%.HT treatment resulted in a significant decrease of 54.43%and 53.19%in the seed setting rate and grain number per ear,respectively;a significant increase of 10.13%in 100-grain weight;and a significant decrease of 46.82%in the grain yield.In conclusion,high temperature stress during pollination enhanced the stomatal transpiration of maize leaves,increased intercellular CO_(2)concentration,and decreased leaf carboxylation efficiency and water use efficiency.It also led to a decline in the overall photosynthetic performance of the plant and restricted the accumulation of photosynthetic products and their transfer and partitioning to the ear,resulting in a significant decrease in seed setting rate and grain number per ear.This decline also restricted the post-flowering transport of photosynthesized assimilated compounds from the“source”(stems and leaves)to the“sink”(grains),which ultimately led to a significant decrease in grain yield.