Rhizosphere physiology of crested wheatgrass and legume seedlings: Root‐shoot carbohydrate interactions

Abstract

Energy‐dependent physiological functions in roots depend upon the translocation of respiratory substrates within the plants for metabolic energy. Root H⁺ efflux and chemical reduction mechanisms can be limited by the allocation of photoassimilates and stored reserves to the roots. The limitation was shown to be particularly significant in germinating seedlings with depleted cotyledonary supplies before new leaves developed into exporter organs. This is a sensitive period in seedling establishment.

Environmental stresses that influence carbohydrate availability in soybean (Glycine max L. (Merr.), snap bean (Phaseolus vulgaris L.), and crested wheatgrass (Agropyron spp. L.) plants altered the rhizosphere physiology. Elevated temperatures which increased respiration rates led to Fe‐chlorosis symptoms in temperature‐intolerant genotypes. Treatments with respirable substrates stimulated Fe‐deficiency stress‐response functions in the plants.

Grasses (Strategy II plants) are believed to rely on the production of Fe(III)‐complexing phytosiderophores to mobilize iron in their root microenvironments. Nevertheless, new roots growing from the bases of vigorous crested wheatgrass plants where soluble sugars are highest were also capable of acidifying their root microenvironments. Older roots were inactive unless treated with external sugar applications.

Key words:

• Acidification
• Iron‐Reduction
• Chlorosis