the Water mode of plants. Water deficiency and seasonal changes in water movement on a plant

you are: the Water mode of plants

On modern representations water movement in a plant is purely physical process defined by a gradient of pressure. The plant, apparently, has no active mechanism which would provide water delivery in its lack, and meanwhile plant water supply, as it is known, is supported both during a drought, and on a cold. strong coupling between molecules of water and their sticking to gidrofilnym to walls of cages ksilemy prevent kavitatsiju being in ksileme a solution almost in any conditions. However at strong deficiency of water in separate tubes ksilemy kavitatsija nevertheless begins; to be convinced of it it is possible, having pressed to a tree trunk a sensitive microphone - crackling will be audible. If in any tube ksilemy in the conditions of deficiency of water kavitatsija has occurred, this tube for a plant thereby is already lost, i.e. She more is not capable to spend water. In a plant, however, many such tubes, and as not all of them fail simultaneously, the water spending system of a plant as a whole continues to function. after normal water supply will be restored, functioning tubes provide runaway by water enough that it kamby could form new ksilemu. Certainly, runaway in which kavitatsija has occurred in all tubes ksilemy to recover cannot any more and is doomed to  destruction.

In the Winter trees also lack some water. At the trees dumping for winter leaves, transpiratsija decreases in the winter, and the tension in ksileme accordingly weakens. If the solution in ksileme freezes, it in some measure obstructs to water traffic, but after thawing the water current is usually restored. At some trees of a tube ksilemy function only one year; in the spring as soon as growth renews, kamby immediately forms new elements ksilemy.

Root pressure at normal transpirirujushchih plants does not play a leading role in water movement, however at some kinds it can serve original ' starting ' as the mechanism. At grapes, for example, large vessels ksilemy during winter time happen empty. Powerful root pressure under which action of a tube ksilemy are filled with water so by the time of expansion of leaves the continuous water column on all extent from soil before runaway appears restored spring develops. Further water inflow in the developed leaves is carried out at grapes the same as and at other plants, i.e. In its motive power is prisasyvajushchee action transpiratsii, caused negative water potential of atmosphere.