TranspirationTranspiration is the loss of water from plant leaves. Water exits the
leaf through stomata, which are tiny pore spaces in the leaf. The rate of transpiration
depends on air temperature and solar radiation. As pointed out earlier, transpiration is a
cooing process for plants when temperatures or incident light rise too high and cause
heating of the plant. Low humidity, often aided by windy conditions, creates a vapor
gradient between the plant and the air. This too induces transpiration. Soil factors are
important control over transpiration. If the pore space between soil particles are too
large the soil will have poor or low soil capillary. That is, the rate of
water rise is too low for plants to extract water from the soil and
maintain
proper moisture supply. Low soil capillary results from soil drying too. Figures below
indicate seasonal changes in plant transpiration. During the moist season, ample soil
water is available to line soil particles to aid the movement of soil water upwards to the
root zone.
Figure BE.4 Plant transpiration during wet periods. However, during the dry season, a dry layer of soil develops
beneath the root zone inhibiting the upward movement of capillary water
causing a
capillary lag. The plant ultimately wilts as it cannot extract enough water to meet the
increasing demand for water during warm seasons. A small soil moisture reserve will inhibit transpiration too. Figure BE.5 Plant transpiration during dry periods.
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