Atomic force Microscopy of torus-bearing pit membranes

Atomic force microscopy was used to compare the structures of dried, torus-bearing pit membranes from four woody species, three angiosperms and one gymnosperm. Tori of Osmanthus armatus are bipartite consisting of a pustular zone overlying parallel sets of microfibrils that form a peripheral corona. Microfibrils of the corona form radial spokes as they traverse the margo. Margo microfibrils are loosely packed thus facilitating passage of water molecules. The pustular layer is removed by acidified sodium chlorite. Tori of Cercocarpus montanus also have a pustular surface, but lack a corona. Tori of Pinus taeda have a finely granular to amorphous torus matrix. Ulmus alata tori have microfibrils traversing the surface. The atomic force microscope proves itself a useful tool for high resolution study of pit membranes with only minimal specimen preparation.

TORUS LIGNIFICATION IN HARDWOODS

Tori in wood of Osmanthus americanus, Daphne odora, Celtis occidentalis and Ulmus alata were tested for lignins using KMnO4 staining in conjunction with TEM, and acriflavine staining in concert with CLSM. It was hypothesized that impregnation with lignin could explain torus survival during cytoplasmic apoptosis. KMnO4 staining indicated torus lignification in all four woods, whereas only Osmanthus and Daphne tested positive for lignin with acriflavine. Tori in Celtis and Ulmus showed some evidence of partial breakdown during cell maturation, which might expose non-lignin sites for KMnO4 binding and thus produce spurious results. The acriflavine data correlate with developmental studies in which torus ontogeny occurs by one method in Osmanthus and Daphne and by another method in Celtis and Ulmus.

White-Tailed Deer Browse Preferences in a Southern Bottomland Hardwood Forest

We examined spring and summer use of woody browse by white-tailed deer (Odocoileus virginianus) in forest gaps created by group selection timber harvest in a South Carolina bottomland hardwood forest during 1995 and 1996. Percent available twigs browsed, relative abundance, and relative use were calculated for each species with more than 50 twigs sampled. We used chi-square analysis to rate species as preferred, proportional, or low use. Total percent browsed was low in both years (2.5% in 1995; 3.0% in 1996). In 1995, 6 species were rated as high use, 4 species as proportional use, and 10 species as low use. In 1996, 6 species were rated as high use, 7 as proportional use, and 9 as low use. Species ratings generally were in agreement with other food habits studies in the Southeast. Preferred browse species included red maple (Acer rubrum), winged elm (Ulmus alata), greenbrier (Smilax spp.), and black willow (Salix nigra). The low rates of browsing probably were due to low use of the study area by deer during the growing season. Deer browsing likely had little impact on regeneration of most species in this bottomland hardwood forest. South. J. Appl. For. 23(2):78-82.

Cyclic Microirrigation in Container-grown Landscape Plants Improves Plant Growth and Water Conservation

Four tree (Acer rubrum L., Ulmus alata Michx., Quercus virginiana Mill, and Lagerstroemia indica L.) and two landscape shrub species (Rhododendron indicum L. ‘Formosa’ and Elaeagnus pungens Thunb.) were grown in 10-liter (#3) polyethylene containers. Plants were irrigated with overhead impact sprinklers (control) or with individual low volume spray stakes. Microirrigated treatments consisted of same or double volume per day per container as controls applied as one to three cyclic subvolumes. Shrub growth was seldom influenced by irrigation treatment. Xeric tree species (U. alata and Q. virginiana) grew as well with single volumes applied in 2 cycles as double volumes applied in 3 cycles; both produced significantly larger trees than the control. Mesic species (A. rubrum and L. indica) irrigated with double volumes in 3 cycles produced the largest trees that were significantly larger than single volume microirrigated or control trees. Growth of single cycle, single volume trees (overhead and microirrigation) was equivalent; thus, growth effects were due to cycling, not microirrigation. With commercially representative container spacings used, superior trees were produced with cycled microirrigation using 25% (xeric) or 50% (mesic) of the water volume per area applied through the overhead sprinkler. Further aspects of irrigation requirements and water efficiency are discussed.

Torus Structure and Development in the Woods of Ulmus Alata Michx., Celtis Laevigata Willd., and Celtis Occidentalis L.

Pit membranes between tracheary elements of Ulmus alata, Celtis laevigata, and Celtis occidentalis often contained tori. The degree of development of tori varied and was greatest in those membranes connecting elements of small diameter. Complete tori consisted of two wall thickenings adjoined by a central layer. In three dimensions the shape of the torus often approximated a grooved wheel. Initiation of thickening in the pit membrane occurred first on the side of the older cell and was well underway prior to the beginning of secondary wall synthesis. Torus formation resulted from the thickening of the primary walls of the pit membrane. Development of the torus was associated with membranous vesicles and cisternae but not with microtubule complexes as was reported in Osmanthus. The pit membranes in this study are capable of aspiration, and the tori may prevent rupture of the pit membrane during this process.

Seasonal Response of Woody Plants to Tebuthiuron Pellets

Pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was hand broadcast at 2.2 and 4.5 kg ai/ha every month for 2 yr on an area infested with live oak (Quercus virginianaMill. ♯4QUEVI), post oak (Q. stellataWangenh. ♯ QUESL), parsley hawthorn (Crataegus marshalliiEgglest. ♯ CSCMS), and yaupon (Ilex vomitoriaAit. ♯ ILEVO) on the Gulf Coast Prairie near Cordele, TX. Live oak, post oak, and parsley hawthorn trees were killed at most rates and dates of tebuthiuron application. Applications of 2.2 kg/ha of tebuthiuron killed 90% or more of the yaupon plants when it was applied in October and December 1975 and February, March, and June 1976 and less than 90% when applied at other dates. On another site, pelleted tebuthiuron was aerially applied at 2.2 and 4.5 kg/ha every 3 months during 1978 and 1979 in the Post Oak Savannah near Bryan, TX. At 2.2 kg/ha, tebuthiuron killed all post oak and 80% or more of the blackjack oak (Q. marilandicaMuechh.), yaupon, winged elm (Ulmus alataMichx. ♯ ULMAL), and mockernut hickory (Carya tomentosaNutt.) regardless of date treated. Tree huckleberry (Vaccinium arboreumMarsh.) killed by tebuthiuron when applied at 2.2 kg/ha ranged from 34% in July 1979 to 69% from application in February 1978. Application of 4.5 kg/ha of tebuthiuron killed 83% or more of the tree huckleberry when it was applied in January and April 1978 and January, April, July, and October 1979. Herbaceous plant cover usually increased by the second season.

Brush Response to Spacing and Individual-Plant Herbicide Treatments

Soil-applied herbicides were evaluated for control of blackjack oak (Quercus marilandicaMuenchh.), huisache [Acacia farnesiana(L.) Willd.], honey mesquite [Prosopis juliflora(Swartz) DC. var.glandulosa(Torr.) Cockerell], live oak (Quercus virginianaMill.), Macartney rose (Rosa bracteataWendl.), winged elm (Ulmus alataMichx.), and yaupon (Ilex vomitoriaAit.) in Texas. Various spacing of spot treatments of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} on huisache and live oak and picloram (4-amino-3,5,6-trichloropicolinic acid) on Macartney rose up to a 2.7-m square grid did not change herbicide effectiveness. Pelleted tebuthiuron at 2.2 kg/ha reduced the canopy of live oak and killed a significant percentage of plants; however, differences among herbicide formulations and distance of placement in a grid were small. On unburned plots, 2.2 kg/ha of tebuthiuron applied as pellets at 2.7-m centers and as a broadcast wettable-powder treatment killed fewer yaupon than pellets applied in most broadcast treatments. In individual-plant treatments, bromacil (5-bromo-3-sec-butyl-6-methyluracil) and picloram solutions at 2 g/plant killed 45% of the yaupon 1.5 to 2 m tall on a fine sandy loam, whereas 0.5 g/plant of either herbicide killed 70% or more of the yaupon plants 1 m tall on a loamy fine sand. Both bromacil and picloram at 1 g/plant killed all blackjack oak and winged elm sprouts 1 to 2 m tall. On a clay soil, 1 g of bromacil/plant killed 79% of the live oak and 88% of the winged elm plants, whereas picloram killed only 38 and 45%, respectively. Neither bromacil nor picloram was effective as soil treatments for killing honey mesquite.