Search Results
You are looking at 1 - 4 of 4 items for
- Author or Editor: R. A. Mecklenburg x
Abstract
The annual cycle of root-regeneration potential (RRP) of 3 year old Taxus hunnewelliana Rehd., plants was evaluated by recording the number of new root initials produced 6 weeks after bare root transplanting. During the summer (June, July and August) few root initials were produced. The RRP increased throughout the fall (September to December) reaching a peak in January. This was followed by a drop in RRP through the spring and early summer (February to June).
Root dormancy of 1 year old Taxus cuspidata Sieb. and Zucc., can be broken in February by an exposure to 7 weeks of chilling at 35°F. Shoot bud dormancy can be broken by an exposure to 3 weeks of chilling at 28°F. The chilling treatment breaking root dormancy appears to be sensed primarily by the root system. Chilling shoots only increased growth of dormant roots but does not substitute for the chilling requirement of the dormant root.
The annual cycle of root-regeneration potential can be partially explained by root dormancy or root-shoot competition for photosynthate. The root-regeneration potential for transplanted Taxus hunnewelliana appears to be controlled by the same factors as the annual cycle of rooting for stem cuttings.
Abstract
An electrophoretic mobility technique utilizing molecular probes was employed to study the freezing patterns in apical stems of 2 azalea cultivars, Rhododendron yedoense var. poukhanense (Levi.) Nakai (unnamed clone termed ‘Poukhanense’ herein for convenience) and R. × ‘Maryann’ [R. indicum × (R. yedoense var. poukhanense × kaempferi)]. Excised twigs were frozen at 2°C per hr during which current and voltage were measured, and tissue resistance was calculated. As freezing occurred there was a dramatic increase in tissue resistance, indicating that ice quickly filled the extracellular space. This rapid ice formation is a nonequilibrium process independent of temperature change once nucleation has begun. Injury due to the rapid formation of extracellular ice, at temperatures well below the freezing point, may be a factor influencing winter survival.
Abstract
Two evergreen azalea clones, Rhododendron × ‘Maryann’ and R. poukhanense Levl., were studied in outdoor and controlled freezing experiments during 2 winters. Outdoor experiments revealed that 1) flower bud injury occurred in mid-winter, 2) flower buds of R. poukhanense were less hardy than those of R. ‘Maryann’, 3) splitting of apical stems often accompanied injury in R. poukhanense, and 4) a significant difference existed between the 2 clones in apical stem water percentage during December and January. In the laboratory freezing tests, initial injury occurred in the apical stem pith and at a higher temp than that which injured the flower bud. When twig water content of R. poukhanense was reduced prior to freezing, stem splitting was prevented and the twigs survived exposure to lower temp. Large ice masses were observed in the vascular tissue of R. poukhanense when the frozen twigs were sectioned. Water content and ice crystal development were the primary factors affecting survival of both clones.
Abstract
Plants have a great impact upon the urban microclimate in contrast to dry structural materials. Infrared surface temp can be substantially modified by evaporative cooling and the interception of radiant energy by plants to reduce the heat island characteristic of the summer urban microclimate.
High temp characteristic of surfaces such as artificial turf can be reduced by irrigation. Outdoor athletic areas covered with artificial turf should be either irrigated to permit evaporative cooling or shaded to intercept solar radiant energy.
Coniferous trees appear capable of providing a small amount of attenuation for environmental noises that are either predominantly low or high frequency in composition. However, dense wide plantings are necessary to achieve effective environmental noise attenuation from vegetation alone in urban areas and the practical value of plants as an urban “sound barrier” appears questionable.