Influence of Soil Water Supply on the Plant Water Balance of Four Tropical Grain Legumes

Abstract

The water balance of soybean (Glycine max), cowpea (Vigna unguiculata), black gram (Vigna mungo), and pigeonpea (Cajanus cajan) grown in pots was studied during a soil drying cycle. The response of the plants was analysed for three distinct stages of dehydration. In stage I, the rate of transpiration remained constant and equal to that of well watered plants even though soil water status fell by more than 50%. Stage II began when the rate of soil water supply to the plant was less than potential transpiration and stomates closed resultingjn the maintenance of plant water balance. When soil water content was expressed as a fraction of transpirable soil water, all species showed a transition from stage I to stage II at a fraction of transpirable soil water of about 0.3 to 0.2. As the soil water declined further, all species had a similar decrease in relative transpiration rate. Consequently, the responses of the four species in stages I and II were essentially identical, except that pigeonpea extracted a slightly greater amount of soil water. Stage III occurred once stomates had reached minimum conductance and water loss was then a function of the epidermal conductance and the environment around the leaf. Substantial differences were found among the four grain legumes in epidermal conductance. Soybean had the highest conductance, followed by black gram, cowpea and pigeonpea. Substantial variation in dehydration tolerance among the four grain legumes was also found: the ranking of dehydration tolerance based on the relative water content was pigeonpea > cowpea > mungbean > soybean. Differences among the four grain legume species in the duration of stage III which finished when plants died, were consistent with differences in epidermal conductance and in dehydration tolerance of leaves.

Daily balance of leaf sugars and amino acids as indicators of common bean (Phaseolus vulgaris L.) metabolic response and drought intensity

“…When a severe water deficit was imposed over ten days at the pollination stage of both genotypes, the Ψ l response can be analyzed as proposed by Sinclair and Ludlow (1986), in three distinct stages of dehydration: stage I, mild water deficit, where the rate of transpiration caused no reduction in Ψ l , until the day six of stress in this assay (Fig. 2); stage II, moderate water deficit, where Ψ l dropped quickly from stress day six to day eight; and stage III, severe water deficit on days nine and ten (Fig.…”

“…In this study, the hypothesis that leaf carbohydrate and free amino acid daily balances are another useful tool to evaluate the severity of drought, i.e. the stage of water deficit as stated by Sinclair and Ludlow (1986), and photosynthetic response of common bean genotypes was investigated.…”

Deficiência hídrica no solo e seu efeito sobre transpiração, crescimento e desenvolvimento de mudas de duas espécies de eucalipto

“…A redução da água disponível no solo para a planta influencia negativamente o seu crescimento e desenvolvimento (Sinclair & Ludlow, 1986). Dessa forma, a produtividade agrícola e florestal é influenciada pela disponibilidade de água no solo.…”

“…No conceito da FATS, assume-se que o conteúdo de água no solo utilizado pela planta para a transpiração varia entre o conteúdo de água no solo na capacidade de campo, quando é máxima, e o conteúdo de água no solo, quando a transpiração da planta é igual a 10 % da máxima (Sinclair & Ludlow, 1986). Este parece ser o conceito que mais se aproxima como indicador da quantidade real de água no solo que pode ser extraída pelas plantas para a transpiração (Santos & Carlesso, 1998).…”

“…Para a determinação da FATS, são considerados dois estádios (Sinclair & Ludlow, 1986;Muchow & Sinclair, 1991;Bindi et al, 2005): o estádio I, quando a água está disponível livremente no solo e a planta não tem deficiência hídrica e sua condutância estomática e transpiração são máximas, ou seja, o conteúdo de água transpirável no solo não limita a condutância estomática e a transpiração; o estádio II, quando a água disponível no solo diminui e a planta diminui sua condutância estomática e transpiração para manter seu balanço hídrico e turgescência celular.…”