Higher Plant Water Research Articles

Stomatal responses to changes in temperature at increasing water stress

The response of stomata to a gradual increase in temperature at increasing plant water stress was studied in a hot desert habitat (Negev, Israel) in the field, but under controlled temperature and humidity conditions. Four native species (Zygophyllum dumosum, Artemisia herba-alba, Hammada scoparia, Reaumuria negevensis) and one cultivated plant (Prunus armeniaca) were used in these studies. The stomatal response to temperature was compared with the response in well-irrigated plants of the same species.At low water stress, the diffusion resistance for water vapour decreased in response to a gradual increase in temperature. Transpiration increased accordingly. This response was reversible. All species responded in the same way. The opening of stomata with increasing temperature was apparently independent of the stomatal response regulated by atmospheric humidity. At high plant water stress, the stomatal response was reversed, i.e., the stomata closed when temperature was gradually increased. This stomatal closure was also independent of the closure regulated by atmospheric humidity. The plant water potential at which the stomatal response to temperature was reversed, differed among the species investigated.

EFFECTS OF SIMULATED DROUGHT ON SHOOT DEVELOPMENT IN LIRIODENDRON SEEDLINGS

SummaryShoot extension, leaf growth, xylem radial growth, and xylem structure in i‐year old Liriodendron tulipifera L. seedlings maintained in a growth chamber were affected more by reduction of atmospheric relative humidity from about 95 to about 45% than by simultaneous reduction of the root medium water potential (Ψsoi) from – 0.4 to about –11 bars. For plants subjected to the same minimum Ψsol, the rate of change of Ψsol during the imposition and relief of simulated drought had no apparent effect on growth. Xylem formed near the stem base during a period of simulated drought resembled that characteristic of the terminal stage of seasonal growth under normal conditions; vessel elements, fibres and ray parenchyma cells were narrower in the radial direction, vascular rays increased in width, and more vertical parenchyma was evident than under conditions of rapid growth. The differences between the structure of xylem formed at high and low plant water potentials diminished towards the apex of the stem, and it is suggested that these differences may be due chiefly to an impairment of synthesis and translocation of growth factors.