The influence of transpiration rates on leaf water potential (1 - leaf water stress) in potted sunflower plants (Helianthus annuus L.) rooted in water saturated garden soil, fine sand, silica sand, ballotini and water culture solution was investigated to evaluate the nature of resistance to water flow through the root system. It was invariably observed that the resistance to flow through the root systems varied with the change of rooting materials, watering regimes, size of pots and age of plants especially in silica sand grown plants. Both curvilinear and linear relationship between leaf water potential and transpiration rates was observed in plants grown in the same amount of silica sand under the same watering regime but at different ages. A curvilinear relationship is observed as being fundamental to, and occuring invariably in most water saturated rooting media. Whilst linearity is an artifact, evidence put forward suggesting that it results from an increased percentage of moribund and dead roots, and it is considered to be due to an interaction of coarse rooting particles, size of pots, watering regimes and age of plants. It is suggested that the cause of interaction depends on the prehistory of the plant growth conditions. A study of the hydraulic resistance of the soil: plant water relations of a physical model clearly demonstrates that the drop of pressure under steady state conditions is greatest at the soil: root interface. The magnitude of the interfacial resistance for a given rate of flow is found to vary depending on the composition of the rooting material. Interfacial resistance also changes with alteration of flux and hydraulic tension in the same rooting material. It is evident from this model study that as the interfacial resistance increases, increased stress within the plant results. Hydraulic conductivity of soil and other parameters were determined to evaluate the applicability of the hypothesis of the soil: root interface being a high resistance barrier to water flow through the soil: plant system. Other parameters measured were soil water content: soil water potential; root density; total root length and surface area of roots; transpiration rate; leaf area; leaf water potential; leaf water status and stomatal resistance of potted sunflower plants, and growing in a growth room under controlled growth conditions. The result of the present study favours the existence of an interfacial resistance and also suggest that the interfacial resistance depends on a positive feed-back since the resulting stress in the plant tissues cause tissue contraction and there is a contraction of the roots and an opening of gaps between the root surface and the soil.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:451441 |
| Date | January 1979 |
| Creators | Chowdhury, Mohammed A. M. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU446992 |
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