Showing papers by "Ernst Detlef Schulze published in 1983"

Carbohydrate partitioning in relation to whole plant production and water use of Vigna unguiculata (L.) Walp.

Abstract: Increases in plant biomass are mainly a balance between growth of new leaves and growth of new roots, the new leaves having positive feedback upon the production process and the new roots having positive feedback upon the plant water status. Control of both opposing processes with respect to biomass production may be considered optimal whenever biomass of the plant reaches a maximum without adversely affecting plant water status. This occurs only if all carbohydrates are partitioned into growth of new leaves, unless water uptake is insufficient to meet the additional evaporative demand created by the newly grown leaf area without decreasing the water status of the plant. It is shown by theoretical considerations based upon optimization theory, especially by application of the Pontryagin Maximum Principle, that in this case carbohydrate partitioning is dependent upon the transpiration rate per leaf weight and upon the efficiency of the root at taking up water. Growth of Vigna unguiculata at two levels of air humidity and two levels of water uptake rate by the root was consistent with such a carbohydrate partitioning pattern. Growth of total biomass and its components (leaves, stems, and roots), whole plant transpiration, and the pattern of carbon partitioning were predicted and explained by applying the foregoing principles of optimization in a heuristic model for vegetative growth of an annual.

Responses of Vigna unguiculata (L.) Walp. to atmospheric and soil drought

Abstract: Growth responses, water relations, leaf conductance, and gas exchange of V.unguiculata were studied under conditions of drought in both the aerial and the soil environment. Dry air caused a significant reduction in whole plant biomass and all its components despite a plant water status which was not different from plants in humid air. Stomata closed in dry air and water loss per plant was lower in dry than in humid air because of both lower leaf conductances and a smaller total leaf area. Dry soil also caused decreases in biomass growth, but leaf growth continued at the soil water status at which stomata began to close (45% depletion of plant available water). Relative leaf expansion rate started to decline below the rate of control plants when 60% (humid air) or 65% (dry air) of plant available water was depleted. Therefore, in V. unguiculata, stomata appear to be more sensitive to soil drought than growth of leaves. Leaf relative water content and osmotic potential remained at the level of control plants when stomata started to close and decreased only slightly below the level of control plants even under severe water stress. A trend of decreasing osmotic potentials at 55-60% depletion of plant available water was observed, but leaf growth ceased only when 90% of plant available water was depleted. Leaf conductance decreased more rapidly than CO2 assimilation during development of soil drought.