Response Process And Mechanism Of Water Use In Maize Leaves To Progressive Drought

Drought stress is one of the most important environmental factors affecting plant growth and development,and it is also a major limiting factor for global food production.Global climate warming has caused increased variations in the temporalspatial patterns of precipitation and enhanced evapotranspiration.The intensity and frequency of drought events are expected to increase in the near future.Current studies were mainly focused on assessment and prediction to the impacts of drought on crops,little attention was paid to the characteristics of crop water-use and its strategies.Therefore,a thorough understanding of the response process and mechanism of crops to drought stress is of great significance in ensuring safe crop production.This study was based on the field simulation experiment of drought,which was conducted with various growth stages and irrigation regimes during the growing season of maize from 2013 to 2014.A number of physiological and ecological traits,such as leaf water content,gas exchange parameters,photosynthetically active radiation,leaf area and biomass of maize were monitored during the experiment period.Firstly,the water-use characteristics of maize leaves and their critical thresholds under prolonged drought stress in the different growth stages were determined.Then,the response features and mechanism of physiological and ecological functional traits of maize to drought stress were also clarified.Finally,the strategies of water use efficiency of maize in response to drought stress were revealed.The main conclusions of this study were as follows:(1)The water status of the first fully expanded leaf on the top of a maize plant was closely related to other leaves and plant-scale leaves,stem,and aboveground biomass,which suggested that it can be used as an indicator leaf to represent the plant water condition.Based on the response process of photosynthetic rate to leaf water content,the range of available leaf water content was determined to be about 68.3% ? 84.1%.The response characteristics of leaf water content to available soil water content were displayed as an “S” type distribution,that was,it firstly remained stable with soil water,then decreased rapidly as soil water decreased,and then decreased slowly again.The maximum leaf water content and the minimum leaf water content supported by soil water were about 84.6 ± 1.1% and 70.9 ± 0.8%,respectively.(2)Specific leaf area was an important functional trait of maize.Regardless of drought stress,specific leaf area showed a continuous decline during the growth period.Moreover,the decline rate in the vegetative growth stage was significantly greater than that in the reproductive growth stage.Plant leaf area and dry mass were induced to decrease severely by drought stress,but the adverse effects imposed on specific leaf area were not significant.The inhibition effects of drought stress timing on specific leaf area were greater than drought stress intensity.When drought treatment began in the three-leaf stage,the main factor influencing the dynamic change of specific leaf area was soil moisture,while it was thermal condition when drought treatment began in the three-leaf stage.Therefore,there was a trade-off mechanism between the heat and water conditions in shaping specific leaf area.(3)Leaf water use efficiency was not a constant parameter during the growing season,with obviously fluctuation along with the continuous growth and development of maize.Leaf water use efficiency of maize was increased under mild and moderate drought stress,while decreased under severe drought stress.Leaf water use efficiency at different leaf positions was spatially stable in the specific time and was conservative with age.The main reason was that the photosynthetic rate and transpiration rate were coordinated between different leaf positions.(4)Trade-off and synergistic strategies were two important ways for plants in response to environmental change.Leaf water use efficiency were increased under mild and moderate drought stress,but it turned out to be a decrease in the leaf radiation use efficiency.The relationship between leaf water-use efficiency and radiation use efficiency in response to drought stress was complementary to some degree.There was a trade-off or synergistic relationship between canopy water use efficiency and radiation use efficiency responding to soil drying.Specifically,canopy water use efficiency and radiation use efficiency had shared a trade-off relationship under mild and moderate drought stress,while they had a synergistic relationship under severe drought stress.