Leaf water status, carbohydrate levels, net photosynthesis, stomatal conductance, ABA, dihydrozeatin riboside (DHZR), and trans-zeatin riboside (ZR) levels were determined in a greenhouse during rooting of stem cuttings of Acer rubrum L. `Red Sunset' taken on 3 Sept. 1987 and 28 May 1988. Leaf water status deteriorated before rooting and improved after root emergence. Leaf carbohydrate concentrations (glucose, sucrose, total soluble sugars, and total carbohydrates) increased until rooting and decreased after rooting, while changes in starch concentrations were trendless. ABA levels increased after insertion of cuttings into the rooting medium, but decreased before rooting. No correlation between timing of rooting and concentrations of the cytokinins ZR or DHZR was observed. Photosynthetic rates during rooting were higher for the Sept. 1987 cuttings and did not decrease to the compensation point as did those for May 1988 cuttings. Low photosynthetic rates and stomatal conductance of the cuttings during rooting were associated with water stress. The relationship between photosynthetic rates of such cuttings and cytokinin (CK) or ABA content was unclear. Chemical names used: [S-(Z,E]-5-(1-hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3-methyl-2, 4-pentadienoic acid (abscisic acid, ABA); 2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin, Z).
Container-grown Viburnum plicatum Thunb. var. tomentosum (Thunb.) Miq. `Mariesii' were planted in unamended planting holes, tilled plots, and tilled plots amended with aged pine bark. A 36-day drought was initiated 108 days after planting. Amending induced N deficiencies, reduced shoot growth, and increased root growth. Plants harvested from tilled and planting-hole plots at drought initiation had 63% and 68% more dry weight, respectively, than plants from amended plots. Between 8 and 19 days after drought (DAD) initiation, plants from tilled plots maintained higher relative leaf water content (RLWC) than plants from planting holes. Plants in amended plots maintained higher RLWC than both other treatments between 7 and 33 DAD. Amended and tilled treatments had higher relative leaf expansion rates (RLERs) than the planting-hole treatment 8, 11, 13, and 15 DAD. As the drought lengthened, plants in amended plots maintained higher RLERs than plants in tilled plots. While plants in pine bark-amended plots were more drought tolerant than those in tilled plots, it is unclear if increased drought tolerance was caused by the improved rooting environment or N deficiency.
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