Algal organic matter and plant growth.

Since investigations on the ecology of soil algae have shown that this microbial group constitutes an important component of the soil biota, the evaluation of the role played by micro-algae in soil economy and plant growth has caused a lively interest. Working in the well defined conditions of gnotobiotic cultures, it has been shown that micro-algae actively interact with higher plants at the level of the root apparatus. These interactions give rise to favourable effects on the growth of seedlings. The same results were obtained when the plants were grown in soil under axenic-conditions. Biosynthesis of growth-promoting substances by micro-algae must be considered a factor of primary importance in the explanation of these results. Nevertheless, the physiological and biochemical bases of plant-micro-algae interactions are more complex, and many other problems are to be taken into account before a satisfactory explanation can be put forward. The results summarized here on the favourable influences, exerted by some algal strains on the growth of higher plants, show that the study of the plant-micro-algae relationships, to which poor attention has been devoted up to this time, besides contributing to a better understanding of the role played by micro-algae in soil fertility, may be of interest in relation to agricultural applications and crop algalization.