The Morphogenetic Effect of Oxygen on Roots

Aeration as a factor influencing root growth has been investigated repeatedly (8, 12, 16). Root elongation has been found to be especially sensitive to aeration, 02 being the essential and morphogenetically effeotive part of the air (9, 15). The results of investigations on the effect of aeration on root branching are not in accordance. There are observations indicating increased number of laterals in nonaerated water cultures (7), whereas other reports describe decreasing root branching with decreasing 02 level (6, 10,16, 18). Under natural conditions in soils, the 02 supply to the -roots is controlled by the 02 diffusion through the soil (6, 23), the rate of diffusion depending largely on the soil water content (24). Frequent changes in the degree of aeration, caused mainly by increasing or decreasing water content of the soil, result in the roots being subjected to very low levels of 02 in water-saturated soils and a relatively favorable supply under drier conditions. But there have been no investigations on the effect of changing aeration on root growth, although this effect is one of the main characteristics controlling the 02 supply to roots under natural conditions. An attempt was therefore made to study root growth responses to changing aeration. The adaptation of the root morphology to prevailing soil conditions has been emphasized as an important feature in the uptake of water and nutrients from the soil (14,19). The results of the present investigations will therefore be expressed in values which describe the root habit in terms of root elongation, root length, number of laterals and density of the root system, rather than in terms of fresh weight or dry matter production.