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| Title: | Study of some aspects of elm root sucker growth (Ulmus x hollandica Mill.) | | Year: | 1989 | | Author/s: | Dickon Peter Yau | | Degree: | Doctorate | | University/Institution: | University of Melbourne | | Abstract: | "Elm suckers developed from root buds and/or bud primordia formed on root surfaces, and originated from pericyclic tissues beneath the periderm, and are therefore of endogenous origin.
Elm root sucker formation was an auxin mediated process, and was related to the level of endogenous auxin at that particular time. Root segments suckered most in spring and least in autumn. Application of exogenous anti-auxin and cytokinin stimulated sucker formation from root segments in autumn, and application of auxin or growth inhibitors suppressed sucker formation in spring.
The elongation rate of root suckers of elms decreased as the soil dried out and the soil penetrometer resistance increased. The effect of the soil drying out on increasing the soil penetrometer resistance was not in itself sufficient to account for the reduction in elongation rate as the soil dried. It was suggested that the reduction in soil unsaturated hydraulic conductivity (and the consequent reduced water uptake by the sucker) as the soil dried out was an additional reason for the reduced elongation rate.
The osmotic potential of root suckers decreased as the soil dried out and as soil penetrometer resistance increased. In this instance, the effect of the soil drying out on increasing the soil penetrometer resistance was sufficient in itself to account for the reduction in osmotic potential (osmoregulation). As a consequence of this osmoregulation, turgor pressure either increased or was maintained at a constant value as the soil dried and as the soil penetrometer resistance was increased.
The soil penetrometer resistance was found to be three times the value of the soil mechanical resistance to sucker growth. The net growth pressure (turgor pressure less soil mechanical resistance) decreased with soil penetrometer resistance. Sucker elongation rate increased with net growth pressure, but sucker elongation rate also increased with soil water content at constant net growth pressure.
Elongation rate increased with time. Osmotic potential decreased, and turgor pressure and net growth pressure increased with time. The rate of decrease in osmotic potential and the rate of increase in turgor pressure and net growth pressure increased with soil penetrometer resistance, but this effect became less over time. The data suggest that elm root suckers can osmoregulate over time to reach a minimum value of osmotic potential (or maximum value of turgor pressure) which is independent of soil penetrometer resistance, but that the rate at which this minimum osmotic potential (maximum turgor pressure) is achieved increases with soil penetrometer resistance.
Elm sucker elongation rate increased as the axis of elongation approached the geotropically preferred axis, i.e. the vertical upright position.
Elm suckers exerted a maximum growth pressure of 0.63 MPa (SE = 0.057) in a critical time of 5 to 6 days. Elm suckers exerted a buckling pressure of 0.34 MPa (SE = 0.052) in a critical time of 24 hours to 30 hours.
Elm suckers could not detect cracks or holes in a compacted soil by remote sensing (i.e. no trematotropism in suckers). Root buds if pre-exposed to cracks had a better chance to develop into suckers than root buds not pre-exposed.
Suckers preferentially selected growth pathways in the vertical upright direction provided no pores wider than 2 mm existed in its way. If there were pores wider than 2 mm diameter in its way, the sucker abandoned its vertical growth path preference and selected the wider pores instead even though the wider pores were set at an angle from the vertical.
" | | Type: | Thesis |
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