The Study On Water Consumption And Photosynthetic Characteristics Of Four Fast-Growing Sapling Species

Fast-growing tree for forestation success or failure depends on its water characteristics and growth period under drought condition, For this harsh reality problem of frequent seasonal drought in the upper Yangtze river, has serious influenced new plant saplings and young forest growth. This test is intended for seasonal drought and water shortage areas to conduct a continuous observation of water consumption and photosynthetic characteristics of four major fast-growing species—Populus L., Eucalyptus grandis, Bamboo willow and Alnus cremastogyne. Compare the differences in water consumption and response to seasonal changes of four species, and provide theoretical basis for selection of species and water supply management for the afforestation in arid area.6 Repeats for each species, In mid-month of June 2013-May 2014 observations of daily water rates interannual variability, simultaneous determination of water consumption characteristics (consumption rates) and photosynthetic parameters (net photosynthetic rate, transpiration rate and water use efficiency) diurnal variation, Respectively in July 2013, October and January 2014, April measured per month growth and water demand, To further explore the various species transpiration respond to environmental factors, set different environmental factors (light intensity, temperature and soil moisture) Handling, compare transpiration rate of each species differences, Results of the study are as follows:1. Maintain observation month the soil quality water content about 20%, growth water consumption of four species is different in different seasons, In October grandis water consumption is maximum, the other three is least, Cremastogyne water consumption is balance all seasons(P>0.05); grandis is the highest consumption and cremastogyne is lowest all seasons, water consumption order of magnitude are basically the same, In April populus and bamboo willow water consumption is largest, and the difference was not significant(P>0.05); Thus inferred the strength of water requirements of each species in four seasons, summer and autumn is grandis>bamboo willow>populus> cremastogyne, winter and spring is grandis>populus> bamboo willow> cremaslogyne.2. Each species growth is different in different seasons, grandis height increment order is July>April>October>January, surface diameter increment order is October>July> January>April. Thus grandis water consumption used to height increment first and then surface diameter increment; In July height growth and water consumption changes is consistency. In January surface diameter increment and water consumption changes is consistency, indicates that water demand are transferred to the growth.3. Leaf area measurement results show that winter cremastogyne leaves little, populus and bamboo willow almost entirely leaves, and grandis is evergreen and not deciduous, leaf area affects the size of daily water rates. Analysis the daily water rate changes shows that the same species is difference in different seasons, populus and cremastogyne interannual variability is relatively stable, populus and bamboo willow changes magnitude is smaller in the summer and autumn, and the difference was not significant(P>0.05), when advance winter or early spring volatile is large, Preliminary determination is populus and bamboo willow leaves in winter caused.4. Analysis water consumption characteristics diurnal variation of each species concluded that the peak of consumption rate basic at 12:00-16:00 hours, In october peak of transpiration rate of each species were all in advance. Transpiration rate and water consumption rate trends are basically the same, transpiration rate and water consumption rate of grandis and bamboo willow has a significantly(P<0.01) positive correlation, and cremastogyne has a significant(P<0.05)correlation.5. Analysis photosynthetic characteristics diurnal variation of each species shows, net photosynthetic rate and water consumption, water consumption rate of bamboo willow and cremastogyne has a certain relevance; There was no correlation between water use efficiency and transpiration each species, but the peak of each species appeared before midday, it may indicates that fast-growing tree species drought resistance midday are weak than the morning. Photosynthetic and transpiration ratio of each species is different in four seasons, After the winter photosynthesis and transpiration of each species are weakened then the coming of spring as temperatures rise enhanced, so photosynthesis and transpiration lowest when in January.6. The impact of environmental factors on transpiration due to varying degrees of duress and different variations, on the whole, soil moisture decreases, the other three species except cremastogyne transpiration rate has declined, and grandis decline the largest while populus decline the smallest, appropriate drought may increase cremastogyne transpiration; Effect of light on grandis transpiration is weak, temperature is weakest to cremastogyne transpiration; Each factor changes impact populus transpiration is minimal, based on this test treatment, which can be obtained populus maximum transpiration rate environment factor to give 2500μ·m-2·s-1 light and 35℃ temperature.Conclusions from this study can be reached that the water consumption characteristics interannual variability and difference of four fast-growing species is the result of differences in their genetic characteristics and different responses to environmental factors because these factors affecting leaf internal and external vapor pressure and proliferation resistance Varying degrees.