Levels of study

All life forms on earth are totally dependent on water. In plants it generally constitutes 80–90% of herbaceous tissues and over 50% of woody tissues. In seeds and spores the content may drop to 20% or below although ultimately desiccation tends to kill even seeds as some residual metabolism is required to maintain viability. Indeed, in the case of the so called ‘recalcitrant’ seeds (e.g. acorns) this minimum can be quite high. On the other hand the dormant stages of some plants (the cryptograms) can withstand total desiccation. The biophysics of these that allows such behaviour is far from understood.

Water plays diverse physical and chemical roles in plants. Meidner & Sheriff classify these into processes that involve structural, physical (such as translocation) and metabolic processes. The varied physical processes that involve water have been grouped into a class of phenomena that have been termed water relations.

The water relations of plants may be studied over a range of levels. These extend from the biophysical role of water at the molecular level to the global role of water in weather systems in agriculture and plant communities. At one extreme the focus is at atomic resolution, at the other the focus of resolution may be intercontinental. The often conflicting importance of water to agriculture and industry in areas of the world deficient in the commodity (not all of them poor by any means) has recently increased interest and effort towards an understanding of the role of water in plant life.