PLANT-WATER RELATIONSHIPS

Germination depends to a large extent on temperature and moisture conditions prevailing in the soil. The effect of soil temperature on germination demonstrates a hyperbolic relation between minimum and optimum temperature from which heat units can be calculated. The heat unit can be used for the prediction of germination and gives an indication as regards its sensitivity towards adverse soil moisture conditions. The optimal soil moisture tension range for germination appears to be rather narrow and is affected by soil type.

The shoot/root ratio depends on the species and the prevailing climatic and soil conditions. A high ratio may be permitted with an intensive cultivation with automatic water and fertilizer supply. A low ratio and a great root depth is required with an extensive cultivation. The transition from vegetative to generative phase in plant development is important because root growth ceases during which the plant becomes rather sensitive towards drought conditions.

The pathway of water within the plant can be described on the basis of potential gradients and resistances in which the endodermis cells play an important role not only acting as a barrier for solutes but also because of their sensitivity as regards their resistance towards soil temperature and oxygen supply. Some consequences of physiological disorders related to Ca deficiency have been discussed.

The relation between transpiration and photosynthesis in the gaseous pathway has been described by means of gradients and resistances. Some consequences of the various photosynthetic pathways have been reviewed and also the effect of environmental factors on water use efficiency.

Download Adobe Acrobat Reader (free software to read PDF files)