the Water mode of plants. Adaptation to deficiency of water

you are: the Water mode of plants

As issushenie always poses for plants the main threat, the kinds growing in droughty districts, have usually any special mechanisms providing their survival in these conditions. In deserts rains seldom happen so strong, that soil: remained damp at least throughout several weeks, i.e. During time necessary for development of just appeared sprouts; therefore in deserts seeds of many annual plants do not leave a rest condition at slight rains and sprout, only when the rain is long enough. Such regulation of germination by various ways is reached. at one kinds seeds have very thick, badly nontight covers which become impregnated with water only at a long rain. At others in seeds contain water-soluble ingibitory germinations - they are washed away from seeds during a rain; Such seeds sprout only after removal bolshej parts ingibitora, and it is possible only at the rains impregnating soil slowly and thoroughly. There are kinds at which duration of an obligatory dormant period of seeds very strongly varies, therefore at them only very small share of seeds simultaneously sprouts; it increases probability of that though any seeds will sprout when conditions for fructification of the given kind will appear optimum. deserts Odnoletniki after germination usually grow quickly; the reproductive cycle comes to the end at them sometimes for some weeks so by the time of when around again sets in sush, a plant already has time to provide to itself an existence continuity - to form drought-resistant based seeds.

For vegetation of deserts dwarfish growth and the small area of a sheet surface that reduces intensity transpiratsii is characteristic. Reduce transpiratsiju and some structural adaptations: plants of deserts have usually small, thick, is strong kutinizirovannye leaves and small shipped ustitsa (fig. 6.11). The most remarkable that ustitsa at some kserofitov open at night, i.e. At weak transpiratsii, also are closed in the afternoon about what it was already told in gl. 4. As water evaporation is interfaced to cooling, it would be possible to think that at kserofitov with their low intensity transpiratsii leaves should overheat, especially in hot sunny days. It is known, however, that at many kserofitov the top party of leaves is covered by the numerous small hairs reflecting beams of the sun, - thanks to it thermal loading decreases (fig. 6.20). Strong opushchennost, thus, represents the adaptive mechanism; It very often meets at plants of droughty places and, probably, serves a plant for thermoregulation.

Among the various reasons causing water deficiency, the important role plays salinity of soil because presence of the dissolved substances reduces); a soil solution. Presently salinity of soil becomes one of serious world problems. The reasons of it in expansion of the irrigated areas, in the strengthened application of fertilizers and, at last, that with population growth also the number of a soluble waste steadily grows. As roots of plants absorb water from soil mainly osmotic way, water arrives in roots only in the event that f root cages more low, than soils. Successfully grow on the salted soils of a plant with low size internal f which is caused by accumulation of unusually considerable quantities of the dissolved substances in vakuoljah root cages. If to allow to ripen to such plants, and then to clean them from that soil on which they grew its arable properties will improve because a little, taking from salt soil, these plants thereby reduce its salinity. Many plants of this type have special secretory pieces of iron (fig. 6.21) through which of a plant considerable quantities of salts are actively allocated. Ions of sodium and chlorine which could suppress a cellular metabolism are in certain cases deduced preferably, and other ions are kept that supports the corresponding osmotic potential. Botany try to reveal as much as possible such plants, capable to take from salt soil so that they could be used for land improvement of soils. At introduktsii new kinds it is necessary to consider their water balance as one of the primary factors defining their survival rate and efficiency, so, finally and value of these new kinds for the person.