the Water mode of plants. transpiratsija

you are: the Water mode of plants

Number ustits and their placing at different kinds of plants strongly vary. At kserofitov, i.e. At the forms adapted for dwelling in droughty areas, on surface unit usually it is necessary menype ustits, than at mezofitov; besides, ustitsa sometimes settle down at them in deepenings strongly kutinizirovannoj surfaces of leaves or a stalk that also reduces water loss as limits turbulence in adjoining to ustitsu air layer. at bolshej parts of plants ustitsa are available on both parties of sheet - top and bottom; is, however, and such kinds at which ustitsa settle down only on the bottom party of leaves. The number ustits on 1 sm2 of a surface of sheet exceeds 60 000 at a cucumber, and at some cereals does not reach and 8000. Even on the same plant leaves can differ very strongly both on number, and on an arrangement ustits; in ' shadow ' leaves, for example, the number ustits on surface unit usually is less, than in ' light '. By the estimations made for the most different plants, ustitsa in completely open kind occupy 1-3% of all area of sheet, diffusion of water steams from sheet goes at opened ustitsah actually with the same speed as from a free surface this circumstance and that fact speaks that in the conditions of good humidifying, on bright to light and at a plant heat lose a water large quantity.

Intensity transpiratsii, i.e. Water evaporation by elevated parts of plants (fig. 6.13), depends on width ustichnyh cracks, on a difference of water potentials of air inside both outside of sheet and from turbulence of air. The atmospheric air, the more low (is more negative) its water potential is less damp. (Pressure of water steams and relative humidity which also serve as a moisture content measure in atmospheric air, too thus more low) When air is sated by a moisture, its water potential is equal to zero. At decrease in relative humidity of air of all on 1-2% the water potential falls very sharply. When relative humidity decreases approximately to 50%, the water potential of atmospheric air is expressed by already negative size of an order of several hundreds bar. In sheet cages the water potential seldom happens more low-20 a bar, and consequently water from mezhkletnikov (in which air is sated by it half, and water potential

In a sunny day the temperature in sheet can be on 10 °s above, than in air. Because of this difference of temperatures amplifies transpiratsija as air in sheet is sated by a moisture, and pressure of sated steam with rise in temperature increases. Turbulence of air also promotes transpiratsii as fast removal of steams of water from a layer of air adjoining sheet raises a diffusion gradient (and consequently, and speed of diffusion) from sheet in atmosphere. therefore in dry windy sunny days, in particular during the droughty periods, water often evaporates from a plant faster, than roots have time to submit it. When loss of water by leaves exceeds for a long time its receipt through roots, a plant zavjadaet. In hot summer day transpiratsija quite often outweighs water absorption even if in soil of water it is enough; In such conditions leaves of all kinds of plants and stalks of grassy plants at afternoon o'clock often slightly privjadajut. Along toward evening transpiratsija weakens also plants start to recover from zavjadanija. Throughout night water deficiency in sheet cages decreases as plant roots nasasyvajut water from soil; it proceeds until sheet cages completely will not restore the of tourist's mountains - usually by the morning all signs zavjadanija disappear. similar everyday time zavjadanie, so-called day zavjadanie, - the phenomenon quite usual; it does not harm to a plant, short of some easing of photosynthesis owing to closing ustits. Other business then a plant long time does not receive a moisture from soil; in these conditions time zavjadanie passes in long and if it proceeds long the plant perishes.

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