Use this URL to cite or link to this record in EThOS:
Title: Field and experimental studies on the water relations of Calluna vulgaris (L.) Hull, with special reference to the effects of the wind
Author: Hinshiri, Hussein Mehdi
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1973
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
The effects of water stress and wind on the physiological activities of Oalluna vulgaris (L.) Hull of three different growth-forms growing at different altitudes have been investigated in an attempt to interpret the different growth-forms and to discover whether physiological differences reflect their tolerance to exist and grow in exposed situations. Experiments to show the effects of wind trimming on'plant growth "imitation of destructive action of wind" showed that plants typically grew erect with an erect main stem and lateral stems curving sharply upwards with normal vigour. Those plants which received various intensities of clipping to simulate the effects of wind damage encountered in high altitude habitats became prostrate with a low compact growth-form and with stem curling and intertwining. The annual course of relative water content was followed in material collected from the field. Relative water contents were lowest in Calluna from 870 m altitude and highest in Oalluna from 91 m. Calluna at 457 m was intermediate. The relative water contents were generally lower in winter in association with the desiccating environmental conditions. In the laboratory, it was found that the transpiration rate of turgid shoots was higher in Calluna from the high altitude, because of higher stomatal conductance and lower stomatal resistance, in agreement with the field measurements of low relative water content at high altitude. The plants at low altitude showed a more effective control of water loss. A high stomatal conductance of turgid shoots, as in the high altitude plants, was associated with a low relative water content at stomatal closure. A higher hydraulic resistance to flow of liquid water in Calluna from the low altitude was found and appeared to be due to the greater length of the stem, which was almost four times as long as in the high altitude plant. Despite this the low altitude plants maintained a better water balance than the. high altitude plants. The relation between leaf relative water content and water potential varied in different growth-forms: water potential at 5Ofo relative water content was -65, -52 and -34 bar for Calluna from 91, 457 and 870 m respectively. As a result, relative water content alone could not be taken as an adequate description of water status. The net photosynthetic rate was higher in Calluna from low altitude under full turgor, and water stressed conditions. The differences between the high and low altitude plants were caused by differences in both stomatal and mesophyll resistances to COg supply to the chloroplast. Under water stress, the mesophyll resistance increased more than the stomatal resistance in shoots from both altitudes. With lowering the water potential, the respiration rate of Qalluna from 91 and 870 m decreased between water potentials of -2.3 bar to -22.8 bar and then increased. or Oalluna from 457 m there was an initialincrease in respiration rate at -2.3 bar which continued down to -46.3 bar. In all growth-forms the peak rate of respiration was found at a water potential of -46.3 bar. The evaporation rate from Calluna turf under different windspeeds depended on the leaf and air temperatures, net radiation, saturation deficit of the air, the boundary layer and stomatal resistances. The evaporation rate was higher in Calluna from high altitude primarily because of a thinner boundary layer resistance that influenced the fluxes of sensible heat towards the turf and latent heat away from the turf. The leaf and turf resistances were also smaller in the high altitude plants. The results are interpreted to show that Calluna plants from low altitude are better adapted to water stress over a range of windspeeds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available