Honey locust (Gleditsia triacanthos var. inermis Wind.) and tree-of-heaven Ailanthus altissima (Mill.) Swingle] sometimes are exposed to high root-zone temperatures in urban microclimates. The objective of this study was to test the hypothesis that seedlings of these species differ in how elevated root-zone temperature affects growth, leaf water relations, and root hydraulic properties. Shoot extension, leaf area, root: shoot ratio, and root and shoot dry weights were less for tree-of-heaven grown with the root zone at 34C than for those with root zones at 24C. Tree-of-heaven with roots at 34C had a lower mean transpiration rate (E) than those grown at 24C, but leaf water potential (ψ1) was similar at both temperatures. In contrast, shoot extension of seedlings of honey locust grown with roots at 34C was greater than honey locust at 24C, E was similar at both temperatures, and ψ1 was reduced at 34C. Hydraulic properties of root systems grown at both temperatures were determined during exposure to pressure in solution held at 24 or 34C. For each species at both solution temperatures, water flux through root systems (Jv) grown at 34C was less than for roots grown at 24C. Roots of tree-of-heaven grown at 34C had lower hydraulic conductivity coefficients (Lp) than those grown at 24C, but Lp of roots of honey locust grown at the two temperatures was similar.
Two native shrubs, Spiraea alba (meadowsweet) and Spiraea tomentosa (hardhack or steeplebush), have potential as landscape plants, but little is known about light requirements for these species. The performance of plants from four geographical seed sources of each species was evaluated in the field under six different light treatments: full sun; morning full sun; afternoon full sun; and 40%, 60%, and 80% shade. Provenance differences did exist for height, flowering, and leaf greenness. Growth, flowering, and canopy density were greater in full sun and 40% shade and least in 80% shade. Both species responded to shade with increased individual leaf area and higher specific leaf area. Relative leaf greenness decreased with shade in S. tomentosa but did not change in S. alba. Plants grown in morning or afternoon shade were shorter and smaller and had fewer inflorescences than did the full-sun plants. These species can survive in deep shade, but based on growth and appearance, they are best suited to full sun or light shade in the landscape.
Juniperus chinensis (L.) ‘Sea Green’ from 3.8 1 (#.1) containers (CG) and comparably sized field grown plants balled and burlapped (B&B) were planted in clay and loam soil in mid-June. Prior to transplanting, root balls of the CG plants were either mechanlcally disrupted by vertical cuts (D/CG) or left undisturbed (CG). Root growth beyond the original root ball and shoot extension growth in loam soil were determined at 8 and 12 weeks, while similar data were collected from loam and clay soils at 16 wks. B&B plants and D/CG plants produced greater dry weight of new roots, but less shoot growth at 8 wks than CG plants with an undisturbed root ball. By 16 wks, B&B plants had produced greater new root dry weight than either CG treatment and shoot growth was not different among treatments. In clay soil B&B plants produced greater dry weight of new roots than CG plants. Root ball disruption reduced new root growth in the heavy soil compared to CG plants. Shoot growth was not different among treatments in the heavy soil, but was significantly diminished compared to shoot growth on the lighter, loam soil.
Imported sphagnum peat holds a significant share of the US market for horticultural growing media, but the price of the product is relatively high due to transportation costs. Low-quality alfalfa may provide an effective substitute. The purpose of this research is to identify the characteristics consumers want in a horticultural organic material, to determine the cost competitiveness of an alfalfa-based substitute, and to determine the product's market potential. Results suggest that most consumers would accept alfalfa as a substitute. Production cost estimates range from $111.10 to $162.71 per short ton, depending on the quality of the raw material used. Due to lower transportation costs, the wholesale and retail prices of this new product are estimated to be about 30% lower than sphagnum peat.This research was supported in part by the Indiana Department of Commerce through the Center for Value Added Research. Greendell Farms Inc. provided economic engineering data and facilities for experiments. Linda and Brian Whipker provided helpful comments on an earlier version of this paper. The suggestions of an anonymous reviewer are gratefully acknowledged.
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