Unit 12: Plant Growth
The growth of plants is a dynamic, integrated process that is expressed in the pattern of development of individual organs.
Early studies of plant tolerance to environmental stresses by Wood and Petrie were of the effects upon this pattern of the plant responses.
Wood initiated physiological studies of the ontogeny of the very tolerant Australian native flora and these were continued by other workers.
Much of the earlier work was reviewed by Wood.
He found that the morphological characters of the Australian xerophytic flora that he studied differed from mesophytic flora in much the same manner as did plant associations in other climatic regions.
But, the schlerophyll leaves of Australian xerophytes had a high degree of lignification as a result of a partial diversion of the normal carbohydrate flux, that resulted in an accumulation of tannins.
In the tomentose succulent leaves of the and saltbush steppes the diversion was to pentosan formation.
This led to detailed biochemical studies of responses to water shortage and focussed attention on sulphur containing amino acids and protein metabolism by Wood.
Levitt went further and studied sulphydryls as an important factor in frost hardiness.
In these early studies Wood concluded that "Water does not exert an effect as such, that is, as a molecular species through its activity".
However, that view has required modification, as will be pointed out here from the ontogenetic studies undertaken on a range of plant tolerances.
Previous volumes have described the many climatic changes to which agricultural plants have adapted to varying degrees in widely diverse regions,
and have pointed to the anticipated trends in climate to which mankind is contributing and which will fundamentally affect the productivity of his agriculture.
Climatic change not only affects aerial environment but leaves its imprint upon the edaphic environment in which plants grow.
There are numerous examples: The aerial deposits of soil from the Gobi Desert now constitute the highly fertile loessial soils of China;
The impoverished soils of Australia result from aeons of leaching during previous periods of higher rainfall;
The nutrient leached soils of the lush Amazon region lead to shallow rooted tropical vegetation;
The fertile river deltas of East China;
Thailand and the Nile River are the product of heavy rains in higher regions upstream;
and The cyclic salt of Australian soils results from thousands of years of wind borne sea spray deposited far inland from coastal regions.
These are but a few of the examples.