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Influence of water deficit on physiological characteristics of selected species of green leafy vegetables
Kraus, Kamil ; Hnilička, František (advisor) ; Dana, Dana (referee)
The harmful influences on plants are called stress factors. The stress itself does not slow down only vital functions of plants but influences directly the size and quality of final product as well.
Worldwide, we count the so called abiotic stresses as the most significant crop production stressors. These include in recent years extremely high temperatures and unequal rainfall distribution both areal and during vegetation period.
The water deficit (drought) belongs to the most important stress factors in agriculture. It influences crop production all over the world. Also vegetables are responsive to water deficit, especially the species with huge amount of water in their tissue. Therefore, the goal of this thesis is to assess the impact of water stress on gas exchange and photosynthetic activity of mangold "Beta vulgaris", salad rocket "Eruca sativa" and lettuce "Lactuca sativa", which were placed at water deficit.
The plants - mangold, salad rocket and lettuce - were grown in a partly controlled greenhouse conditions under the Department of Botany and Plant Physiology FAPPZ ČZU in Prague. The plants were grown at a temperature of 25°C in daytime and 18°C at night under natural light conditions. They were grown in containers of size of 11x11 cm in a mixture of garden substrate A and silica sand in the ration 2:1. The experimental scheme included two variants - control and stressed. The control group of plants was watered, and the second half of plants was left under stress for 22 days, when the water deficit was induced by gradual drying for one month, the experiment took place from 1.6 2015 to 22.6 2015. The speed of gas exchange by plants was measured by apparatus LCpro+. From the values of photosynthesis and transpiration water use efficiency (WUE) and chlorophyll fluorescence were calculated.
The gained results proved difference at reaction to water stress between observed kinds of leaf vegetables.
The speed of photosynthesis and transpiration of observed plant species was measured, which decreased due to impact of water deficit. The average speed of photosynthesis of stressed plants was the lowest by lettuce (11,16 "mikro"mol CO2.m-2.s-1), contrarily the highest by mangold (13,2"mikro"mol CO2.m-2.s-1). In case of control plants was the lowest speed of photosynthesis noticed by lettuce (12,03"mikro"mol CO2.m-2.s-1) and the highest by mangold (14,00"mikro"mol CO2.m-2.s-1). In comparison with control group, the speed of photosynthesis of lettuce decreased significantly by impact of water deficit (difference make 7,23 %). On the other hand the lowest decrease of photosynthesis from stressed plants 5,93% was noticed for mangold.
In case of speed of transpiration, it is possible to note, that the lowest transpiration of control group shows mangold with the average speed of transpiration 1,82 mmol H2O.m-2.s-1, by contrast the highest transpiration was measured by lettuce 3,20 mmol H2O. m-2.s-1. In the case of stressed plants moved the average speed of transpiration between 1,54 mmol H2O.m-2.s-1 for lettuce and 1,79 (mmol H2O.m-2.s-1) for mangold. Also, between control and stressed plants of the same species were found differences, and salad rocket reacted to stress of drought more sensitively and mangold less sensitively. For these two plant species was noted decrease of transpiration in the amount of 23,80% and 1,76%.
From the measured value of photosynthesis and transpiration was calculated water use efficiency (WUE). The calculated values show that stressed plants have higher value of WUE in comparison to control plants. The lowest water efficiency from control plants produced salad rocket
(6.51 x 10-3), while the highest mangold (10.31 x 10-3). In the case of stressed plants was the lowest value of WUE noted for salad rocket (8.96 x 10-3), while for mangold was the highest (10.71 x 10-3).
Chlorophyll fluorescence of the experimental plants was also measured. This characteristic was not influenced by plant species, because in case of control plants, there were no differences found between observed plant species. The lowest difference in value of fluorescence had plants of lettuce (0,69) while the highest mangold and salad rocket (0,7). In conclusion it is possible to note, that more sensitive to water deficit are plants of lettuce. As more tolerant to water deficit seems mangold and salad rocket.
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