Simulated swards of Dactylis glomerata and Lolium perenne were grown in containers of sufficient depth to permit largely unrestricted root development. Flowering and non-flowering plants, subjected to cut and uncut treatments, were allowed to dry the profile and were compared with watered controls. The effects of a drying cycle on the growth, water balance and nutrient uptake were measured. The rate of dry weight increase was reduced by drought from an early stage. The cause appeared to be reduced leaf expansion rather than a decline in net assimilation rate. Root weight was particularly affected due to suppressed elongation of new adventitious roots. There was some compensatory growth at depth. Defoliation severely retarded root growth. Leaf water potential fell during the day in treatments and controls to levels which would be expected to affect growth processes. Defoliation reduced water stress and stomatal closure but not drought susceptibility. There was little relationship between leaf water potential and stomatal diffusion. Dactylis initiated water economy measures at a lower soil water deficit than Lolium, possibly because of a less vigorously extending root system. It was more sensitive to increasing deficit in terms of leaf water potential, relative turgidity and stomatal diffusion rate and so did not manifest the early abrupt exhaustion of water supplies typical of Lolium. Root density was adequate to allow current water requirements to be met from a small volume of wet soil, The effect of drying of a horizon was to shift the main uptake zone downwards, with no corresponding fall in leaf water potential. Calculated mean soil water potential was most closely related to coil water potential in the few zones of maximum uptake. Resistance to the movement of water from the soil to the roots was 10 superscript2 -10 superscript4 times smaller than resistance to Movement through the plant i.e. a major source of water stress lay within the plant itself. No evidence was found that droughted swards ceased growth due to N shortage. Reduced P uptake was detected.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:297050 |
| Date | January 1972 |
| Creators | Jackson, David Keith |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/20931 |
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