The effects of solar radiation and nutrient solution temperature on the uptake of oxygen by submerged roots of mature tomato plants

Summary A statistical analysis of data on oxygen uptake by submerged roots of mature tomato plants, from a nutrient solution containing sufficient oxygen, has demonstrated that variations in oxygen uptake are positively related to variations in solar radiaton, particularly at radiation levels below 2.0 MegaJoules.h⁻¹.m⁻². Above this level, however, anegative relationship is indicated, suggesting that intense solar radiation reduces the ability of plant roots to obtain sufficient oxygen for optimum growth processes. It also appears that there is atime lag of about one to two hours between the effects of solar radiation on oxygen uptake. Greenhouse air temperature is positively correlated with radiation, with little or no time lag, and variations in greenhouse air temperature effect variations in solution temperature with a time lag of 2 to 3 hours. Greenhouse air temperature affects respiration in the submerged roots indirectly, with a 1 to 2 hour lag, by effecting the nutrient solution temperature, and possibly by affecting the growth processes in thesubaerial roots, which in turn may result, in some way, in increased oxygen uptake by the submerged roots, partly bypassing the restraining effects of lagging nutrient solution temperature. Variations in nutrient solution temperature do not appear to be causally related in effecting variations in oxygen uptake in a major way, probably because a considerable time lag of around 3 hours seems to exist between variations in radiation and solution temperature, in this experiment. As such, radiation and greenhouse air temperature appear to be rather important and dominant variables, effecting changes in oxygen uptake. In addition, the results suggest thatdaytime, variable heating of the nutrient solution, in step with the variations of solar radiation, as well as shading of the tomato crop under conditions of intense solar radiation would likely be beneficial for plant growth and crop production.