夏玉米对土壤水分持续减少的响应及其转折点阈值分析

玉米是世界三大粮食作物之一,玉米生产在中国粮食安全与畜牧业发展中具有举足轻重的作用。干旱是夏玉米生产最主要气象灾害,及时准确地获取干旱信息对夏玉米安全生产至关重要。以夏玉米郑单958品种为材料,设置充分供水和拔节期开始土壤水分持续减少两种水分处理,研究夏玉米对土壤水分持续减少的响应及其转折点阈值,为夏玉米干旱识别与监测提供依据。结果表明,土壤水分持续减少10d后生理指标开始陆续受到胁迫,20d后生物量积累受到抑制,30d左右形态特征开始受到胁迫。夏玉米生理指标中最先受到胁迫的是顶端第1片完全展开叶的含水量和水势,生物量积累指标中为茎生物量,形态指标中为叶数。夏玉米顶端第1片完全展开叶的含水量或水势、茎生物量和叶数开始受到土壤干旱过程胁迫的时间阈值分别为11、21、27d,水分亏缺阈值分别为34、66、86mm,土壤相对湿度阈值分别为64%、56%和52%。表明夏玉米对土壤干旱过程的响应首先表现为生理特征变化、其次为生物量积累变化、最后为形态特征变化。研究结果可为客观辨识夏玉米干旱的发生发展及监测预警提供参考。

Responses and tipping point of summer maize to consecutive soil water decrease

Maize plays an important role in food security and the development of livestock husbandry in China. Drought is the most important meteorological hazard for summer maize production. Drought accounts for 64% of the total area affected by the four meteorological disasters (drought, flood, storm, and cold) in major summer maize producing areas in China. Accurate and timely access to drought information is critical to the safety of summer maize production. Drought indicators can indicate the occurrence and degree of drought. The plant eco-physiology indicators can reflect the degree of water shortage and drought tolerance of plants directly. There are tipping points for the response of summer maize to drought. That is, when water is below a certain critical point, it will have a significant impact on plant physiology and other indicators. The different sensitivity of indicators to drought results in different tipping points. In this study, two water treatments (adequate water supply and stop water supply from jointing stage) were designed to simulate the responses and tipping point of summer maize "Zhengdan 958" to consecutive decrease in soil water. The study was conducted at the station of ecological environment and agro-meteorology of the China Meteorological Administration (39°08''N, 115°40''E) in 2015. Six plots (2m×4m) were used for the two water treatments (three replicates for each). The results indicated that:the physiological indicators were adversely affected after 10 days when water deficit accumulated to 34mm and relative soil water content decreased to 64%. Biomass was restricted after 20 days when water deficit accumulated to 66 mm and relative soil water content decreased to 56%. Morphological characteristics began to be depressed when water deficit accumulated to 86mm and relative soil water content decreased to 52%. Among the physiological indicators, the water content and water potential of the first fully expanded leaf at the top were affected first. The sensitivity of physiological indicators'' response to consecutive soil water decrease was ranked as:the water content and water potential of first fully expanded leaf at the top > the water content of third fully expanded leaf at the top > the water content of total leaves > the water content of stem=the chlorophyll content of third fully expanded leaf at the top > the chlorophyll content of first fully expanded leaf at the top, and their tipping points in terms of the relative soil water content were 64%, 62%, 61%, 60%, 60%, and 59%, respectively. In terms of the accumulative biomasses, the stem biomass was the first to be impacted, followed by root biomass; and the tipping points in terms of the relative soil water content for both were 56%. For morphological characteristics, the number of leaves decreased first. The sensitivity of morphological indicators to consecutive soil water decrease was ranked as:leaf number > plant height > total leaf area; and the tipping points in terms of the relative soil water content were 52%, 47%, and 46%. The response of summer maize to soil drought process was as follows:physiological characteristics changed firstly, followed by biomass accumulation, and finally morphological characteristics. These results can provide a reference for the development and monitoring of drought in summer maize objectively.