Edwin C. Townsend

Decomposition of leaf litter in an Appalachian forest: effects of leaf species, aspect, slope position and time

Abstract Leaf decomposition was studied using leaves of three species (yellow-poplar, red maple, and chestnut oak). Litterbags containing 10 g of leaves were placed on a northeast-facing slope and a southwest-facing slope and at three slope positions (upper, middle, and lower) on each aspect. Bags were initially placed in January and samples were removed to determine mass loss beginning in April, then at 2 month intervals until December. The main effects (aspect, species, slope position and time of removal) were all statistically significant. Yellow-poplar and red maple litter decomposed much faster than did chestnut oak, and leaves placed on north-facing slopes decomposed faster than those on south-facing slopes. Generally, leaves placed at the middle slope position decomposed slower than at those at either the upper or lower positions. We examined the microarthropods in leaf litter during the growing season and found that Oribatei and Collembola dominated the populations present. They were generally more abundant in leaves on north-facing slopes, and numbers of microarthropods generally increased throughout the year. Chemical analysis of decomposing leaf litter revealed that nitrogen and phosphorus contents of leaves were relatively stable over time. Sodium dropped quickly at first, then stabilized. Potassium and magnesium decreased with the time whereas calcium increased in the leaves of some species and decreased in others.

Changes in nutrient composition and pH of the culture medium during in vitro shoot proliferation of crabapple and pear

Shoot tips of Seckel pear and Almey crabapple were cultured on liquid MS medium containing 8.8 μM BA. Changes in shoot proliferation and growth and in nutrient and carbohydrate composition of the medium were determined during a 9 week culture period. Whereas shoot proliferation in crabapple increased linearly during the culture period, it levelled off after week 4 in pear. Explant dry weight in both genera showed a linear increase over time. Culture medium pH decreased in the initial weeks and increased thereafter. There was a rapid decline in medium P and Fe concentration with both genera and of Zn in the medium of crabapple. In no instance did the rate of depletion of any nutrient from the medium of pear cultures exceed that measured in the crabapple medium. The decline in sucrose concentration in the medium was similar for both genera and was accompanied by an increase in the level of glucose and fructose. At the end of the culture period slightly over half of the initial carbohydrate level remained in the medium.

Relationship between calcium and agar on vitrification and shoot-tip necrosis of quince (Cydonia oblonga Mill.) shoots in vitro

Shoot-tip cultures of Quince C (Cydonia oblonga Mill.) initiated on Murashige & Skoog (MS) medium containing 5 μM BA and 0.6% Phytagar showed both shoot-tip necrosis and severe vitrification. Culturing explants on medium containing 1.2% Phytagar and Ca levels of 3 mM (MS medium), 18 mM and 30 mM showed a decrease in growth with increasing medium Ca levels, being especially severe at 30 mM. The Ca content of the explants increased linearly with increasing medium Ca. Culturing explants on medium containing 3 mM, 9 mM, and 18 mM Ca at 0.6, 0.9, and 1.2% agar resulted in reduction in growth, shoot-tip necrosis, and vitrification when either factor was increased. The reduction in shoot-tip necrosis could be accounted for primarily by an increase in medium Ca levels but may also be affected by a change in explant growth. Increasing Ca concentration in the medium resulted in a linear increase in explant K, Ca, Mg, and B levels and a decrease in Mn and Na. Although increasing medium Ca or agar levels reduced vitrification, it is unclear whether they were the direct cause of the reduction in vitrification or whether this response was an effect of the reduction in culture fresh weight.

Radial growth response of understory sugar maple (Acer saccharum Marsh.) surrounding openings

Abstract Understory sugar maple around openings 15 to 75 m in diameter in mature hardwood stands gave a radial response over a 5-year period. Size of opening and distance into the uncut stand from opening edge, especially, affected the increase in diameter growth. The trend of response with distance ranged from a nearly 300% increase near the opening to 12% at 30 m into the stand, with opening sizes grouped, indicating that the openings affected growth more than 30 m into the stand. The interaction, opening size × distance, gave a strong relationship, significant at the 0.005% level because effect of opening size diminished as distance from opening increased. Sunlight intensity and available soil moisture were collected from three new openings, 15, 30, and 45 m in diameter and one new clearcut. Sunlight intensity dropped from about 33% along the opening edge to about 5% at 15 m into the stand. Percentage sunlight was directly related to percentage radial response (significant at 0.01% level) similar to the response relationship. However, no relationship were found for the interaction of available soil moisture with radial response as the moisture data ranged from 10 to 14% throughout the 30 m distance.

Agar Induced Variations on the Nutritional Composition of Pear and Crabapple Shoots in vitro

The objective of this investigation was to determine whether nutritional differences in explants on media solidified with 3 agar brands would explain agar-induced variations in proliferation and growth responses. Shoot-tips of ‘Almey’ crabapple and’ seckel’ pear were cultured on Murashige and Skoog (MS) salt mixture supplemented with 10 mg/1 myo-inositol, 0.4 mg/1 thiamine, 30 g/1 sucrose, and 2 mg/1 N -benzyladenine (BA). Media were solidified with either Bacto-agar, Phytagar, or T.C. agar at concentrations ranging from 0.3 to 1.2%. A liquid medium treatment was used to obtain a comparative benchmark for expiant nutrient levels. Expiant nutrient levels determined after 8 weeks were influenced both by agar brand and concentration. Although large differences in a number of elements occur both in agar brands and in expiants cultured on media containing similar concentrations of these brands, variations in proliferation and growth cannot be explained based on differences in individual elements. From a nutritional standpoint, modification of the elemental composition of the basal medium may be one cause of the growth variations induced by different agar brands.