Substrate Effects on Plant Transpiration Rate under Several Vapour Pressure Deficit (VPD) Levels

Panicum maximum (guinea grass) preferably grows in tropical and subtropical areas of the world on a wide variety of soil. Motta also reported that Guinea grassesare well adapted to a wide range of soils. It is tolerant to light frost and low soil pH.Cook et al.also mentioned that guinea grasses are drought tolerant and they can survive a shortage of water.

VPD is a good indicator of plant stress, brought about by either excessive transpiration of water (high VPD values) or the inability to transpire adequately (low VPD values). Vapor pressure deficit is the difference between the vapor pressure atambient conditions and the vapor pressure at saturation point for the sametemperature. Because saturation vapor pressure increases exponentially with temperature, VPD increases with temperature exponentially if absolute humidity is held constant. Therefore, temperature and vapor pressure deficit (VPD) effects on plant growth are usually confounded. Increasing VPD rates raise up the atmospheric demand and consequently higher plant transpiration. Stomatal closure limits the transpiration rate and sometimes a decrease at high VPD. Therefore, stomatal closure restricts the corresponding decrease in plant water potential and prevents excessive water loss.