JXB Advance Access originally published online on May 7, 2004
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Journal of Experimental Botany, Vol. 55, No. 401, pp. 1371-1382, June 1, 2004
© 2004 Oxford University Press
RESEARCH PAPER |
Hydraulic conductance and rootstock effects in grafted vines of kiwifruit
Received 19 December 2003; Accepted 26 February 2004
Horticulture and Food Research Institute of New Zealand, Te Puke Research Center, RD 2 Te Puke, New Zealand
* To whom correspondence should be addressed. Fax: +64 7 573 3871. E-mail: mclearwater{at}hortresearch.co.nz
Whole-plant hydraulic conductance, shoot growth, and leaf photosynthetic properties were measured on kiwifruit vines with four clonal rootstocks to examine the relationship between plant hydraulic conductance and leaf stomatal conductance (gs) and to test the hypothesis that reduced hydraulic conductance can provide an explanation for reductions in plant vigour caused by rootstocks. The rootstocks were selected from four species of Actinidia and grafted with Actinidia chinensis var. chinensis Hort16A (yellow kiwifruit) as the scion. Total leaf area of the scion on the least vigorous Actinidia rootstock, A. kolomikta, was 25% of the most vigorous, A. hemsleyana. Based on shoot growth and leaf area, the selections of A. kolomikta and A. polygama are low-vigour rootstocks, and A. macrosperma and A. hemsleyana are high-vigour rootstocks for A. chinensis. Whole-plant hydraulic conductance, the ratio of xylem sap flux to xylem water potential, was lower in the low-vigour rootstocks, reflecting their smaller size. However, leaf-area-specific conductance (Kl) and gs were both higher in the low-vigour rootstocks, the opposite of the expected pattern. Differences in Kl were found in the compartment from the roots to the scion stem, with no difference between rootstocks in the conductance of stems or leaves of the scion. There was no evidence that the graft union caused a significant reduction in hydraulic conductance of vines with low-vigour rootstocks. Leaf photosynthetic capacity did not vary between rootstocks, but photosynthesis and carbon isotope discrimination (
13C) under ambient conditions were higher in the low-vigour rootstocks because gs was higher. gs and
13C were positively correlated with Kl, although the mechanism for this relationship was not based on stomatal regulation of a similar xylem water potential because water potential varied between rootstocks. For Actinidia rootstocks, changes in Kl do not provide a direct explanation for changes in vigour of the scion. However, depending on the rootstock in question, changes in hydraulic conductance, biomass partitioning, and crown structure are involved in the response.
Key words: Actinidia, hydraulic conductance, kiwifruit, photosynthesis, rootstock effects, stomatal conductance, water relations.
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