Influence of soil drying on root development, water relations and leaf growth of Ceratonia siliqua L.

Abstract

Seedlings of Ceratonia siliqua L., an evergreen sclerophyll species native to the Mediterranean region, were grown in 30-cm deep tubes of John Innes II potting compost in a growth cabinet maintained at 15° C during a 12-h day where PAR was 400 μmol m s. After a period of acclimatisation to the conditions in the cabinet during which plants were watered every day, water was withheld from the soil in some tubes for 24 days. These conditions may be regarded as a simulation of the natural situation. Estimates of leaf and root water potential and solute potential, leaf growth and root development were made at intervals during the soil drying cycle on both watered and unwatered plants. Water potential and solute potential measurements were made both on young expanding and on fully expanded leaves. During the experimental period, root growth of C. siliqua was not much affected by soil drying, and roots in both the watered and the unwatered columns penetrated to the bottom of the soil tubes by the end of the drying treatment. Expanded leaves showed significant limitation in stomatal conductance as soil drying progressed. Leaf water potential of fully expanded leaves of unwatered plants declined substantially. In contrast, water potential of young expanding leaves on unwatered plants declined to only a limited extent and turgor was sustained. As the soil dried, stomatal conductance of young leaves was always higher than that of mature leaves; also, placticity and elasticity of young leaves slowly decreased whereas mature leaves became stiff. Changing leaf cell wall properties may determine different patterns of water use as the leaves age. A mechanism of continuous diffusion of water through the soil towards the tip and pumping towards the young leaves is proposed.

Seasonal variations of leaf water potential and growth in fertigated carob-trees (Ceratonia siliqua L.)

“…Considering fruit production per unit of available water it is expected that non-irrigated trees would present higher rates of water use efficiency (Correia and MartinsLouqao, 1993b). Although soil drying will eventually reduce root growth (Rhizopoulou and Davies, 1991), it is also established that N accumulation is able to function not only as a N source but also as an osmoticum (Leidi and Lips, 1990). This is in agreement with recent work which shows that osmotic potential can control carob drought stress tolerance (Nunes et al, 1989) and could explain the low values of midday LWP in non-irrigated trees during the summer drought period (Fig.…”

“…Similar conclusions were suggested by Nunes et al (1992) also for mature carob-trees. Rhizopoulou and Davies (1991) also found that, in young carob tree plants submitted to soil water deficit for 3 weeks, deep penetration of some roots was enough to supply substantial amounts of water to shoot growth. On the other hand, the direct response of predawn LWP values to irrigation in 1991 (Fig.…”

Stomatal responses of Eucalyptus species to elevated CO2 concentration and drought stress

“…For these species, stomatal conductance of the drought-stressed plants started to decline when the volumetric soil moisture reached approximately 50% of avail- smaller than in the other species, which would lead to a higher sensitivity of stomata to soil drought. A prolonged, comparative study of the biology of root development and water status in relation to drought stress between species of these two subgenera might contribute to a better understanding of these observed differences (Rhizopoulou & Davies, 1991). able capacity.…”

Modelling leaf expansion in a fluctuating environment: are changes in specific leaf area a consequence of changes in expansion rate?

“…Eqn 2 Turgor is well maintained in plants subjected to water deficit (Rhizopoulou & Davies, 1991), to changes in temperature (Pritchard et al, 1990) or to nitrogen deprivation (Palmer et al, 1996). Changes in expansion rate are therefore essentially linked to cell-wall rheological properties, via the activities of enzymes such as xyloglucan endotransglycosylase (XET) (Pritchard et al, 1993), expansins (MacQueen-Mason & Cosgrove, 1995 ;Reinhardt et al, 1998) or peroxidases (Thompson et al, 1998), under the control of chemical signals such as ABA (Ben Haj Salah & Tardieu, 1997) and\or of hydraulic signals (Chazen & Neuman, 1994 ;Ben Haj Salah & Tardieu, 1997).…”