Date of Award:

5-1-1981

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

Herman H. Wiebe

Committee

Herman H. Wiebe

Committee

Martyn Caldwell

Committee

Frank Salisbury

Committee

Neal Van Alfen

Committee

Mike Walsh

Abstract

This study investigated the effects of root pruning in plant water potential, leaf conductivity and transpiration. Roots of four-week-old Helianthus annuus L., grown either in soil or solution, were pruned 25, 50 or 75% and the plants observed for several days following pruning. The taproots of the plants had been removed at the age of one week. This resulted in a root system of more or less equal members. Pruning was performed on selected laterals where they attached to the taproot stub. Observations on root distribution within the soil indicated that the roots had a relatively uniform distribution both before and after pruning. Root pruning reduced transpiration, plant water potential and leaf conductivity, with more severe pruning causing greater reductions in these parameters. Pruning was more effective in soil than in solution and in some experiments was more effective in dry soils than in moist soils. In liquid culture pruning was only effective if the solutions were unaerated or if the plants were under relatively intense light regimes. In both the liquid culture experiments and the soil experiments where the plants were watered daily, the difference between pruned and unpruned plants diminished with time, indicating a recovery in the pruned plants. In those soil experiments where the plants were not watered daily, the more rapid transpiration rates of the pruned plants resulted in more rapid soil water loss. And in these experiments the transpiration, leaf water potential and leaf conductivity were the lowest in the unpruned plants after four days. When roots of solution culture plants were pruned under water the reductions in plant water potential, transpiration and leaf conductivity were not as great as when roots were pruned in air. Pruning under water should decrease root resistance by giving water direct passage to the xylem and, therefore, these results supported the idea that root pruning influenced plant water potential, transpiration and leaf conductivity by changing root resistance. Root conductance measurements with a pressure bomb indicated that the root conductance per unit length of root (root conductivity) remained roughly constant after pruning. But calculations of apparent plant resistance for pruned and unpruned plants based on the Ohm's Law analogy indicated lesser changes in plant resistance than would be predicted based on the extent of pruning. Possible explanations of this discrepancy are discussed.

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