The importance of water relates to its essential functions in perpetuating both plant and animal life. It is an absolute requirement for all living organisms. Anaerobic organisms can live without oxygen, but they cannot without water.
In crop agriculture, water is an important climatic factor. It affects or determines plant growth and development. Its availability, or scarcity, can mean a successful harvest, or diminution in yield, or total failure. According to FAO (2011), irrigation typically doubles farm yields and the number of crops grown in one year is increased from 1 to 2.
But plant responses differ and the importance of water likewise differ depending on plant species. Most plants are mesophytes, that is, they are adapted to conditions with moderate supply of water. But some, called hydrophytes,
require watery or water-logged habitats while others, called xerophytes, are more tolerant to dry conditions. The resurrection plants
are in fact capable of surviving near complete dessication. They are capable of
losing 90% or more of cellular water in their vegetative tissues and still
remain alive. They can remain dried and appear
somewhat dead for several years but, when rehydrated, suddenly spring back to
life (Le and McQueen-Mason 2006).
But before proceeding further, what is water?
Water is a chemical compound consisting of
two atoms of hydrogen joined to one atom of oxygen (H2O). But there are more
about it. There is simply no single generic answer to the question that will
apply in all situations and to everybody.
is a substance with the unique property of being able to exist in three states:
liquid, solid, and gas. As a liquid it is clear, colorless and odorless. In
such state of matter it has been described as a fluid, a substance which flows freely without fixed shape. It melts
and freezes at 0°C (32°F) and boils
at 100°C (212°F) under normal
Through precipitation mainly rainfall, liquid water is
made available to plants as surface water, soil moisture, or groundwater. It
comprises about 70-90% of the body or even more on fresh weight basis, although
only a small fraction of the water absorbed is utilized. Most of the absorbed water
in plants is lost through transpiration and
only about 1 percent or less is used in
the various biochemical processes (Devlin, 1975; Mader, 1993).
participates directly or indirectly in all metabolic processes in living
organisms. It is considered the universal solvent because it dissolves many
substances. As a solvent, it also serves as a transport medium for mineral
nutrients from the soil, as well as in the translocation of organic substances
within the plant. It is a chemical reactant in photosynthesis hence vital to life. It is a product of respiration. It is also
believed responsible, or at least contributing, to the cooling of plants through the process of transpiration. In addition, it serves
as a growth medium in hydroponics, the culture of plants in soilless nutrient
However, the importance of water in plants can be
negated in some cases. As with other climatic factors, water can possibly cause
unfavorable effects on plant growth and development. Excess water in the soil can
injure flood prone plants, like corn (maize), due to lack of oxygen. In this
case water stress due to flooding means oxygen stress by deficiency
(hypoxia) or total absence (anoxia).
Excess water within the plant can also cause injury. Edmond, et al. (1978) explained that under conditions that favor high absorption and low transpiration rates, there is build-up of high turgor pressure in the region of cell elongation which causes maximum swelling of the cells. This results to the development of leggy seedlings. Likewise, under similar conditions, growth cracks occur as exemplified by bursting heads of cabbage and cracked fruits of tomato and roots of carrot and sweet potato.
On the other hand, the injury caused by acid rain indicates that purity and quality relate to the importance of water. With dissolved sulfuric acid and nitric acid that are formed in the air from sulfur dioxide and nitric oxide generated by power plants, smelters, other industrial plants, factories and cars, acid rain can seriously injure plants (Miller, 2001). To be clear, however, it is not water per se that causes damage in this case. Rather, it is the acid(s) which is dissolved in water.
REFERENCES[FAO] Food and Agriculture Organization of the United Nations. 2011. Fast facts: The state of world’s land and water resources. Retrieved Mar. 24, 2013 from http://www.fao.org/fileadmin/user_upload/newsroom/docs/en-solaw-facts_1.pdf.
DEVLIN R. 1975. Plant Physiology. New York, NY: D. Van Nostrand Company. 600 p.
EDMOND JB, SENN TL, ANDREWS FS, HALFACRE RG. 1978. Fundamentals of Horticulture. 4th ed. McGraw-Hill, Inc. p. 87-130.
LE TN, MCQUEEN-MASON SJ. 2006. Dessication-tolerant plants in dry environments. In: Amils R, Ellis-Evans C, Hinghofer-Szalkay H, editors. 2007. Life in Extreme Environments. Dordrecht, Netherlands: Springer. p. 269-279.
MADER SS. 1993. Biology Part 1: The Cell. 4th ed. Duburque, IA, USA: Wm. C. Brown Communications, Inc. 152 p.
MILLER GTJr. 2001. Environmental Science: Working With the Earth. 8th ed. Pacific Grove, CA: Brooks/Cole. 549 p.
(Ben G. Bareja March 2013)