花期高温对玉米穗粒数形成的影响机理及模拟

Increasing heat stress around maize flowering is expected under climate warming, characterized by increased extreme high temperature events which are likely to cause great negative impacts on maize production. Heat stress negatively affects kernel number per plant (KNP), leading to severe decline in maize yield. However, the mechanisms and modeling of the effect of heat stress on kernel set are poorly known. In this study, we combined the data reported in literature and our temperature-controlled field experiment to elucidate the effects of heat stress on ear growth, plant growth and kernel set during maize flowering stage. The different responses for maize cultivars to heat stress will be expressed as KNP loss rate. The variations in kernels per plant when exposed to different heat stress treatments will be explained by the relationships between KNP and plant growth rate/ear growth rate at pre-silking and post-silking stages, which will mainly determine the critical period and variables of heat stress effects on KNP. Then, the stress functions will be developed through analyzing the relationship between KNP loss rate and daily maximum temperature, which quantify the effect of heat stresses on KNP. Based on our new findings, finally, we will update the default heat stress function in APSIM-maize and evaluate the performance of the updated APSIM-maize in simulating KNP under heat stress. The results will improve the understanding of the effect of heat stress on maize production and provide scientific basis for better management of maize production under global warming.

花期高温对玉米产量影响巨大，随着气候变暖背景下高温事件的频发，玉米花期高温发生频率也在不断增加，因此花期高温对玉米产量的影响受到广泛重视。花期高温对玉米产量的影响主要在于穗粒数的减少，然而花期高温对穗粒数形成的影响机理尚不明确。本项目拟结合大田高温试验和文献发表的大田高温试验数据，通过全面分析花前、花后和花期不同高温处理下的穗粒数损失率及高温处理下穗粒数变化与单株生长速率、雌穗生长速率的关系，明确花期高温对不同品种穗粒数的影响程度及高温对穗粒数形成的影响机理；基于穗粒数损失率与日最高温度的关系建立花前和花后高温穗粒数胁迫函数，量化花期高温对穗粒数的影响。将建立的高温胁迫函数嵌入APSIM-maize模型中改进花期高温穗粒数响应模块，并评估改进后模型对高温条件下穗粒数的模拟能力。研究结果将在理论上丰富花期高温对玉米生产影响的认识，实践上为制定防灾减灾应对措施提供科学依据。

花期高温对玉米产量影响巨大，随着气候变暖背景下高温事件的频发，玉米花期高温发生频率也在不断增加，因此花期高温对玉米产量的影响受到广泛重视。花期高温对玉米产量的影响主要在于穗粒数的减少，然而花期高温对穗粒数形成的影响机理尚不明确。围绕该科学问题，本项目通过实施3年玉米季大田增温试验，将试验数据和文献数据相结合，深入探究了不同阶段花期高温对不同耐热型品种穗粒数的影响机理及品种间差异，取得的主要成果如下：（1）花后高温对穗粒数的降低程度大于花前高温，DH605穗粒数的降低程度大于ZD958。穗粒数降低程度与雌穗伸长关键期内（V15-吐丝后7d）平均日最高温度呈显著正相关，花期高温对穗粒数产生严重胁迫的日最高温度阈值为40℃。（2）花期高温导致穗粒数下降的主要原因是散粉量减少，散粉持续时间缩短，ASI延长，小花受精率下降；花期高温对雄穗形态指标、雄穗干物重及花粉活力无显著影响。高温条件下，开花吐丝期延迟与叶片数目及叶片展开速率无关，可能与高温抑制花药外露及花丝伸长速率有关。（3）籽粒败育率增加也是花期高温导致穗粒数下降的重要原因。花期高温对吐丝期冠层截光率、LAI、穗位叶净光合速率及成熟期单株干物重无显著影响，但对雌穗干物重及雌穗干物质分配比例影响较大。高温条件下，库受限是导致产量下降的主要原因。（4）自然条件下，穗粒数决定因子为花期单株和雌穗干物质累积速率；高温条件下，开花期动态是影响穗粒数的重要因素。本项目已发表SCI文章1篇，申请发明专利3项，研究结果在理论上丰富了花期高温对玉米生产影响的认识，实践上为制定防灾减灾应对措施及培育耐高温新品种提供了科学依据。