Influence of Light on Bacterial Flora of Roots

Abstract

ALTHOUGH considerable work has been done on the influence of various factors such as type, moisture content, reaction and treatment of the soil and kind and age of plant on the microflora of the rhizosphere¹, very little has appeared concerning the response of the normal rhizosphere micropopulation to the changes in plants growing under different light intensities. The studies that have been made deal primarily with specific phenomena such as symbiotic nitrogen fixation², mycorrhizal development³ and susceptibility of roots to infection⁴. However, Rovira⁵ has recently reported that “the numbers of bacteria in the rhizosphere of tomato were reduced by 60 per cent when plants were shaded to 40 per cent of full sunlight”; the conditions under which the plants were grown were not given. We have recently completed experiments on the influence of light on the microbial population of wheat roots. These were selected for analysis rather than the soil adhering to them because it was considered that the organisms in intimate contact with the roots would reflect more accurately the changes produced in the plant by differences in illumination than would the organisms in the rhizosphere soil, where a dilution of the effect would probably occur. Certain of our findings relating to the bacterial flora are presented here. Full details of these experiments will be published elsewhere.