The Effects of Root Pruning on the Water Relations ofHelianthus annuusL.

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Abstract
Four-week-old Helianthus annuus plants, grown in both soil and liquid culture, were root pruned at the point of root attachment to the stem. Transpiration, leaf water potential and leaf conductivity were monitored for several days after pruning. Pruning lowered transpiration and leaf conductivity in amounts proportional to the amount of pruning. In some experiments pruning caused a slight lowering of leaf water potential, while in others no pruning effect could be found. The effects of pruning varied depending upon culture conditions, with greater effects being found in soil and unaerated liquid culture than in aerated liquid culture. Soil water potential did not appear to have a strong influence on the magnitude of the pruning effect. The effects of root pruning are less than would be predicted by an Ohm's Law analysis of flow; possible reasons for this are discussed.