ALBERT

Notes: Summary Two alternative estimators of individual tree leaf area (A1) area are used to derive estimates of leaf-area index (L) for 40 plots in Pinus contorta Dougl. stands. One estimator of A1 is based on the common assumption of a constant ratio between A1 and sapwood cross-sectional area at breast height (As). The second estimator of A1 accounts for tree-to-tree variation in the relation between A1 and As. The apparent relationship between stand growth and leaf-area index is strongly dependent on the way leaf area is estimated. When L is derived from a constant A1∶As ratio, stand growth appears to be strongly correlated with L. However, when L is based on estmates of A1 that account for tree-to-tree variation in the A1 — As relation, stand growth is seen to be only weakly related to L. Stand structure, quantified as percent live-crown, accounts for a great deal of the observed variation in leaf-area efficiency. These contrasting relationships illustrate the importance of unbiased estimates of L in interpreting the link between stand-level processes and leaf area.

Notes: Abstract  Seedling growth and morphology are thought to reflect evolutionary responses to habitat or influences of seed size. To test these hypotheses, we selected fourteen species of North American oaks differing in soil moisture habitat preference and seed size. Seedlings were grown for 1 – 2 years with abundant soil water and moderate soil nutrition in pots placed outdoors and in a common garden. Oak species native to xeric environments produced the smallest seedlings. Oaks from hydric soils had more shoot weight per unit of root weight and more height per unit of total plant weight than did mesic or xeric oaks. Essentially no differences in leaf area per unit of total plant weight were detected. Species with thinner and larger individual leaves tended to produce larger seedlings. Within species, seed size was generally unrelated to seedling growth, although results may have been complicated by uncontrolled genotypic variability. However, when species were compared, those with larger mean seed size produced larger seedlings. Root/shoot allometry, height growth and leaf thickness in the tested species may reflect evolutionary responses to soil moisture and flooding. Although seed size influenced seedling growth, no clear relationship between seed size and soil moisture habitat was found.

Notes: Summary A few assumptions were used to generate a series of specific, quantitative predictions for the relationships between stand density and various dimensional measures of canopy structure. The predictions, each indicating an increase in mean crown size as density decreased, appeared to be reasonable and intuitive. Predictions were compared to data for two conifer species with different crown forms, Pinus contorta var. latifolia and Abies lasiocarpa. Results of these comparisons were mixed — the linear, directly measured dimensions were consistent with predicted relationships, but dimensions calculated from the linear measures were not. Re-examination of the original assumptions indicated that the model should account for crown shyness (engagement/disengagement) to adequately reflect the influence of stand density on canopy structure. The results also indicated a strong association between stand height and measures of mean crown size. Mean crown size of lodgepole pine was altered much more by density than was mean crown size of subalpine fir, due primarily to the different relative shade tolerances of the two species. Some of the observed differences between species may also reflect the range of densities examined and uneven spacing in the unmanaged natural stands.

Notes: Summary Incorporation of Virazole into potato explant and meristem culture media results in a higher percentage of virus-free progeny plants from virus-infected explant and meristem donor plants than are produced in tissue cultures in the absence of Virazole. Viruses eliminated, singly and as complexes, include potato viruses X, Y, S and M. The need for sensitive virus tests to distinguish between virus suppression and elimination is discussed and protein-A-linked immunoelectron microscopy is described and quantified for potato virus X.

Notes: Abstract Peroxidase (POD) activity was significantly stimulated in detached rice leaves by Fe2+. By electric focusing with thin-layer scanning, three new bands were identified in Fe2+-treated leaves, and the activities of other isozymes were also drastically increased, of which a band with a pI of ca. 9.8 was enhanced from trace amount (invisible) in the control to a large band in the Fe2+-treated leaves. How Fe2+ induced POD activity was investigated. Cycloheximide completely blocked the stimulation of POD activity by Fe2+, but actinomycin D could not inhibit it effectively, indicating that the stimulated activity resulted from inducing de novo biosynthesis of the enzyme at translational level rather than at transcriptional level. When same molar concentration of H2O2 as Fe2+ and sublethal and lethal concentrations of paraquat were introduced to the rice leaves, no significant stimulation of POD activity was observed compared with Fe2+-induced activity, and scavengers of free radicals still could not inhibit the induction of POD by Fe2+. Several chemicals such as EGTA, LaCl3, CPZ, verapamil, which were known to interfere with the action of calcium/calmodulin, were not able to retard POD induction by Fe2+. From these results it appears that the process of Fe2+-induced POD may not be mediated by free radicals or calcium/calmodulin action.

Notes: Abstract Five exopolysaccharide-deficient mutants were isolated after rhizobial strain 107 was subjected to transposon Tn5 mutagenesis. The amount of EPS produced by the mutants was dramatically decreased to between 3% and 6% of wild-type level. All mutants carried a singel copy of Tn5. Two mutants (NA3 and NA10) were complemented by the R. meliloti exoA gene and the functionally equivalent exoD gene of Rhizobium sp. strain NGR234. Two other mutants (NA7 and NA8) were complemented by the R. meliloti exoB gene and the functionally equivalent NGR234 exoC gene. The remaining mutant (NA11) was not complemented by any exo genes of R. meliloti or Rhizobium NGR234. All mutants induced normal nitrogen-fixing nodules on Astragalus sinicus, an indeterminate nodulating host.

Notes: Abstract The relationships between field performance of Douglas-fir (Pseudotsuga menziesii) 2+0 seedlings and their initial diameter and root mass were evaluated on five sites in Oregon in the early 1980s to identify opportunities for improving seedling grading prior to planting. Survival and height 3–5 years after planting were positively related to seedling size at the time of planting. On all sites, survival nearly doubled from the smallest to largest diameter classes. Root mass had a similar relationship to survival on sites with environmental stress. Increasing root size class increased survival more for the small diameter classes than for the larger diameter clases. On the other hand, increasing root size class increased total height more for the large diameter class than the smaller ones. Although height was not as strongly affected as survival on several sites, height differences among initial seedling diameter classes were still significant and increasing after five years. Root class effects on height were less important than diameter class effects.

Notes: Abstract Planted forests are often considered to consist of tree plantings at a scale large enough to satisfy such objectives as commercial production of timber and fiber, protection of watersheds, and preservation of natural habitats. However, trees are planted also at greatly reduced scales in agroforestry systems or as community woodlots to provide a mixture of products and services to resident households, local communities, and regional cultures. Agroforestry systems represent a major form of small-scale tree planting, where trees are grown in purposeful combinations with agricultural crops and/or livestock in order to take advantage of tree-crop interactions, and thereby enhance crop production, diversify farm output, stabilize or improve soils, or ameliorate harsh environmental conditions. Some important examples of these systems in tropical countries include homegardens, alley cropping, improved fallows, intercropped trees for shade and fodder production, and trees planted in hedgerows and along fence lines. Throughout the tropics, there is a large variety of indigenous practices and species mixtures that represent adaptations of these systems to meet localized needs and opportunities. Research and development programs have supported the expansion and refinement of many of these systems during the last 20 years, but substantial constraints on tree planting still exist in the form of land-tenure practices, population pressures that relegate agroforestry practices to degraded lands, subsistence needs that prevent extended periods of tree growth, and insufficient technical information or technology dissemination. Agroforestry systems in temperate, industrialized countries include combinations of trees, pasture, and livestock; fruit or nut trees interplanted with vegetable or grain crops; windbreaks and shelterbelts; multispecies riparian buffer strips; and forest farming systems for specialty crops. Compared to the tropics, however, temperate-zone systems tend to focus on one or two high-value crops, often involve some level of mechanization, and frequently represent an opportunistic approach to improving the economic profitability of farms rather than meeting subsistence needs. In both tropical and temperate regions, agroforestry systems and community woodlots will be an important component of new sustainable agriculture and environmental protection programs. Although species diversity is an essential feature of all agroforestry systems, community forests generally involve planting only a few species in small woodlots near farms, around villages, along roads, and as riparian buffers. Provincial or state governments and the local populace are often involved in landownership and plantation establishment. Major objectives of these forests are production of fuelwood for local consumption and of other tree products for market; soil stabilization, reclamation, or improvement; and protection of water quality. As with many other planted forests, the number of species widely used in community forests has been relatively small, with the genera Eucalyptus, Pinus, and Acacia providing the bulk of the species. Major issues with these “planted forests” focus on rights for use of the products, tending responsibilities once trees are established, protection until trees are large enough for their designated use, increasing interest in using “native” species, and greater community involvement in planning and management. Trees planted along streets and waterways, or as woodlots in parks and other public places, represent a major group of planted forests in many urban and periurban landscapes. In addition to providing many of the same environmental services that agroforests and community forests do, these urban plantings have unique aesthetic and recreational value. For much of the world's ever-increasing urban population, these may be the only tangible reference points for understanding planted forests. These relatively little-recognized forms of planted forests -- planted trees, to be more appropriate -- are now receiving much greater attention. There are, however, some serious technical and sociopolitico-institutional constraints to their development as more widely adopted systems in both tropical and temperate regions.

Notes: Abstract Studies of net primary production in four contrasting tropical grasslands show that when full account is taken of losses of plant organs above- and below-ground these ecosystems are far more productive than earlier suggested. Previous values have mainly been provided by the International Biological Programme (IBP), where estimates of production were based on a change in vegetation mass alone and would not necessarily have taken full account of organ losses and turnover. Calculation at three of our sites based on estblished methodology using changes in plant mass alone (i.e. that used by the International Biological Programme, IBP) proved to be serious underestimates of when acount was taken of losses simultaneously with measurement of change in plant mass. Accounting for the turnover of material at these three sites resulted in productivities up to five times higher than were obtained using the standard IBP procedure. An emergent C4 grass stand at a fourth site in the Amazon achieved a productivity which approached the maximum recorded for agricultural crops. In this case, productivity values, when organ losses were taken into account, only slightly exceeded that obtained with IBP methods. The findings reported here have wider implications, in prediction of global carbon cycling, remote sensing of plant productivity and impact assessment of conversion to arable cropping systems.

Notes: Abstract A field experiment was conducted with flue-cured tobacco,Nicotiana tabacum L., to examine the hypothesis that after removal of the reproductive tissues (topping), which is coincident with rapid depletion of soil nitrate, the growing apical leaves receive their N primarily from older, senescing leaves. On the 83rd day after transplanting (crop day 83) the nitrate remaining in the plow layer was leached downward and replaced with an equivalent quantity of15N-labeled nitrate. Theoretically, any N taken up by the plants thereafter could be distinguished from the endogenous N present in the plant on crop day 83, thus allowing remobilization of the latter to be estimated. However, some soil N remained accessible to the plants throughout the remainder of the growing season, and as a consequence may have limited the remobilization of endogenous N. Plants were harvested and sectioned into 11 different plant parts at six intervals up to crop day 127. The nitrogen in each plant tissue was fractionated into nitrate-N, soluble reduced-N (SRN), and insoluble N (IN). Tissue nitrate, which accounted for less than 0.7% of total N in the tissue, remained relatively constant throughout the 44 day period. In contrast, SRN and IN fluctuated appreciably. During a 6-day period of water stress, 25% of the IN in the root and leaf lamina was hydrolized to SRN. It was postulated that the drought initiated a type of reversible senescence in which protein was hydrolyzed to amino acids, thereby increasing the osmotic potential of the tissues and improving cell survival. During recovery from water stress, SRN was reincorporated into IN in all tissues except the lower leaves, which were senescing. Root growth was predominant during this period and was supported by N remobilization from the lower leaves and root stump. After subsequent harvest of the lower and middle leaves, growth of the remaining upper leaves was supported in part by remobilization of N from the adjacent stalk tissue.