To assess the contribution of belowground biomass allocation towards total carbon (C) allocation of two provenances of loblolly pine (Pinus taeda L.), we examined the total biomass allocation of a fast- and slow-growing family from each provenance. Since planting on a xeric, infertile site in Scotland County, N.C., U.S.A., trees in this study have been subjected to one of two nutrient treatments: optimal nutrition or control (no fertilization). Total biomass of 24 (1 tree/family plot × 2 families × 2 provenances × 2 treatments × 3 blocks) 5-year-old (juvenile) trees was harvested in January 1998. Fertilization increased total root, total shoot, and total tree biomass in all families as compared with harvested trees in control plots. Fertilization also increased biomass of coarse-root, woody-root, taproot, stem, branch, and foliar components of families as compared with trees in control plots. Although there were treatment and family differences in standing-crop biomass of the total root, total shoot, total tree, and various individual root and shoot components, the percent biomass (whole-tree) allocation to these tissues remained similar across treatments. Total nonstructural carbohydrate (TNC) analysis indicated some treatment, family, and provenance differences in TNC concentrations and partitioning to starch and soluble sugars. At the time of harvest, TNC concentrations of belowground tissues were much higher than those of aboveground tissues, and enhanced partitioning towards starch in root tissues indicates an important C storage role for belowground tissues at this time. Indeed, more than 90% of the trees starch content was present in root tissue in January. Although constrained by a sample size of three harvested trees per family, this study suggests that biomass allocation on a whole-tree level was similar between fast- and slow-growing families of different provenances of juvenile loblolly pine and was not affected by fertilizer treatment.
Comparison of basal area increments of paired healthy and declined oak trees shows a marked disjuncture beginning in the early 195O's at 3 of 4 sample locations across the southeastern United States. An argument is presented^ that the change in growth was caused (or accelerated) by a series of severe regional droughts in the early 1950*s that impacted the trees which then responded by formmg two distinct populations consistmg of: I. relatively healthy trees, and 2. declined trees. Both populations produced less annual basal area increment after several subsequent short-term droughts, but marked crown deterioration and death appeared in the declined population after a moderately severe drought in the early 198O's.
Plant physiological models are generally parameterized from many different sources of data, including chamber experiments and plantations, from seedlings to mature trees. We obtained a comprehensive data set for a natural stand of ponderosa pine (Pinus ponderosa Laws.) and used these data to parameterize the physiologically based model, TREGRO. Representative trees of each of five tree age classes were selected based on population means of morphological, physiological, and nearest neighbor attributes. Differences in key physiological attributes (gas exchange, needle chemistry, elongation growth, needle retention) among the tree age classes were tested. Whole-tree biomass and allocation were determined for seedlings, saplings, and pole-sized trees. Seasonal maxima and minima of gas exchange were similar across all tree age classes. Seasonal minima and a shift to more efficient water use were reached one month earlier in seedlings than in older trees because of decreased soil water availability in the rooting zone of the seedlings. However, carbon isotopic discrimination of needle cellulose indicated increased water-use efficiency with increasing tree age. Seedlings had the lowest needle and branch elongation biomass growth. The amount of needle elongation growth was highest for mature trees and amount of branch elongation growth was highest for saplings. Seedlings had the highest biomass allocation to roots, saplings had the highest allocation to foliage, and pole-sized trees had the highest allocation to woody tissues. Seedlings differed significantly from pole-sized and older trees in most of the physiological traits tested. Predicted changes in biomass with tree age, simulated with the model TREGRO, closely matched those of trees in a natural stand to 30 years of age.
Batch extraction and leaching studies were conducted with potential green roof substrates (e.g., Axis, Arklayte, coal bottom ash, Haydite, Lassenite, lava rock, and composted pine bark). The results indicated that these materials would not likely be sources of Cr, Cu, Fe, Ni, or Zn and that Lassenite would be considered a source of Mn if the leachate concentrations were compared to USEPA drinking water standards for these elements. Lassenite would not be a source of Mn if the data was compared to a USEPA standard for Mn toxicity to aquatic life. All of the substrates tested leached Cd and/or Pb concentrations that exceeded the USEPA water quality standards at least once during the 6-month leaching study, so these materials may be potential sources of Cd and Pb in green roof storm water runoff. The leaching of Cu, Cd, Fe, Mn, Pb, and Zn was differentially influenced by time and/or the presence of a single Sedum hybridum 'immergrauch' plant. The leaching of Cd, Cu, and Pb displayed complex, three-way interactions between main effects (substrate type and the presence or absence of a plant) and between leaching events. For all substrates except Lassenite, the presence of a S. hybridum plant decreased the leaching of Pb over time. The leaching of Cd was generally enhanced by plants for most substrates with time. Collectively the results suggest that changes in the biogeochemical conditions within green roof systems may alter metal solubility, decreasing the leaching of some elements and increasing the leaching of others.
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