Leaf dynamics and crop water status throughout the growing cycle of durum wheat crops grown in two contrasted water budget conditions

Abstract

Leaf and crop water measurements were analysed dynamically throughout the cycle of two crops of durum wheat subjected to contrasting conditions of water supply. The objectives were to compare short-and long-term crop reactions to water deficit, based on some hypotheses from the literature. Water status measurements were of the first type and phenological or morphological measurements of the second type. The droughted crop under a rainout shelter received no water between emergence and harvest, while the open-air crop was irrigated. Dynamic plant morphological measurements consisted of leaf area index and specific leaf area, and those characterising plant water status dynamics included predawn leaf water potential, bulk osmotic potential and the ratio of crop water uptake to evaporative demand. Continuous measurement of the surface temperature on the two plots served to calculate a degree-days temperature scale, allowing comparison of the two crops. We found that the droughted crop developed mechanisms of resistance to water deficit: the leaf area index and specific leaf area were reduced (from 6 to 1.5 m 2 m-2 and from 300 to 260 cm 2 g-1 for the maximum values of, respectively, the LAI and the SLA), the bulk osmotic potential was lower (from-2 to-3 MPa) and the soil layer affected by root uptake was deeper (from 50 to 100 cm) than that of the irrigated crop. The amount of water evapo-transpired by both crops was similar when related to climatic demand. Yet no clear relationship appeared between the specific leaf area index and osmotic potential. Furthermore, there appeared to be a clear difference between the vegetative and reproductive phases of both crops in terms of water functioning. The osmotic potential decreased markedly after anthesis and a peak of water uptake was observed in both crops during the grain-filling phase, which may have been linked to the specific functioning of the flag leaf or the ear. While this study demonstrated the efficiency of drought adaptive features in durum wheat, it also showed that the difference in the water behaviours of two contrasted durum wheat crops could be of the same order of magnitude as the differences between the vegetative and reproductive phases.

Drought stress effects on wheat are mitigated by atmospheric CO2 enrichment

“…It can be speculated that in the free air carbon dioxide enrichment study cited above , with an early start of the water deficit, plants adjusted to the drought stress primarily by reducing the transpiring leaf area, and consequently the radiation absorption and not the stomatal conductance of the remaining leaves. This is supported by field studies showing that radiation-use efficiency is hardly affected by early drought stress (Stone et al, 2001;O'Connell et al, 2004) and that the ratio of actual to potential evapotranspiration is independent of the water supply (Brisson and Casals, 2005).…”

“…It has been demonstrated that the decrease in available water under drought stress first affects leaf expansion and then stomatal conductance and gas exchange (Sadras and Milroy, 1996). The cessation of leaf area growth at low available water levels and the accelerated senescence of the existing leaves result in a decrease in radiation absorption by the green canopy (Brisson and Casals, 2005;Foulkes et al, 2001;Jamieson et al, 1998;O'Connell et al, 2004). This process * Corresponding author: remy.manderscheid@fal.de and the decrease in radiation-use efficiency due to the reduction in stomatal conductance (Foulkes et al, 2001;Jamieson et al, 1995) are responsible for the growth reduction under drought.…”

“…This process * Corresponding author: remy.manderscheid@fal.de and the decrease in radiation-use efficiency due to the reduction in stomatal conductance (Foulkes et al, 2001;Jamieson et al, 1995) are responsible for the growth reduction under drought. However, it seems that drought stress reduces plant growth more through a reduction of the amount of radiation intercepted than reduced radiation-use efficiency (Brisson and Casals, 2005;Jamieson et al, 1998;O'Connell et al, 2004).…”

Grain yield response of drought stressed wheat to foliar application of glycine betaine

“…Drought stress caused reductions in yield components such as DA, PT, NG/spike and TGW of selected genotypes though BW 9025, BW8362 and BWL0089 had better yield than others. Yield loss in wheat on exposure to drought stress is reported earlier due to impairments in nutrient uptake, lower photosynthetic rate, higher canopy temperature and chlorophyll degradation (Asch et al, 2005;Brisson and Casals 2005;Shahbaz et al, 2011). These physiological perturbations would limit the current assimilation and decrease the translocation of photoassimilates to reproductive organs alongwith accelerated senescence (Plaut et al, 2004).…”

Morphological and physiological responses of Galapagos endemic tree Croton scouleri to site conditions varying through its altitudinal range

“…Such a reduction in LAI has been recorded in many deciduous (drought-tolerating) species, such as C. macrostachyus (Gindaba et al 2004), as a response to drought, prompting a reduction in solar radiation interception (Brison and Casals 2005, Pettigrew 2004, Ares and Fownes 1999. However, other tropical trees retain all leaves during abnormal droughts (Borchert et al 2002).…”