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Container-grown Viburnum plicatum Thunb. var. tomentosum (Thunb.) Miq. were transplanted on May 1 into tilled plots, tilled plots amended with aged pine bark, and untilled unamended plots (control) within a greenhouse. Plants were irrigated weekly for three months prior to drought initiation. Root growth, shoot growth, leaf water status, and leaf expansion rates were measured to determine whether tilling or site amending enhanced drought stress resistance. Prior to drought initiation amended treatments had the greatest new root length. New root dry weight of amended plots was 57% greater than controls and 32% greater than tilled plots. Mean root system diameter was 111 cm, 87 cm, and 61 cm for amended, tilled, and control plots, respectively. The mean ratio of new root length (cm) to leaf area (cm2) was 5.3:1 in amended plots, 2.2:1 in tilled plots, and 1.7:1 in controls. During the drought, midday relative leaf water content was lowest in controls, while the rate of leaf expansion was greatest in tilled plots. Changes in soil moisture were monitored using time domain reflectometry. Control plots had higher volumetric water content; however, moisture release curves suggest that tilled and amended plots contained more plant available water.
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).