Question

Plant root exudates and seed germination

Answer 1

link.springer.com
Plant root exudates

Albert D Rovira
The botanical review 35 (1), 35-57, 1969
Conclusions

Although the quantities of organic compounds exuding from roots is not large, seldom exceeding 0.4% of the carbon photosynthesized, they do exert a very strong influence on the soil microorganisms and may be significant in affecting plant nutrient availability. There is evidence that exudates from the roots of some plants are toxic to roots of neighboring plants and to the germination of some seeds.
Most of our information on root exudates has been obtained from solution-grown plants so that there are still some important questions to be answered about root exudates from soil-grown plants: (a) How much organic material is exuded from roots into soil? (b) How far from roots do the compounds diffuse? (c) What concentration gradients exist? (d) What effects do soil properties have upon exudation? (e) What are the main sites of exudation? The application of C14-labeling techniques offers a powerful tool with which to answer these questions. Use of radioisotopes to investigate the sites of exudation along roots and the role of lateral roots in the exudation process should enable us to determine what part of the soil will be most affected by root exudates.
It has now been demonstrated conclusively that application of certain compounds to leaves affects the quantity and types of exudates. The use of foliar sprays to modify root exudation has important implications in the fields of plant nutrition, root hygiene, and control of plant-plant interactions. Thus, we have before us an exciting field of study involving the combined efforts of plant physiologists, microbiologists, and soil scientists.