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51.
Meat goat production in the eastern USA is increasing as a result of growing demand from various ethnic groups. Because goats naturally prefer a high proportion of browse in their diets, research was initiated to investigate various silvopastoral production systems. The genus Paulownia contains several species which exhibit rapid juvenile growth and other characteristics that justify research into their potential use in meat goat feeding systems. In May 1997, six Paulownia genotypes were planted in a randomized complete block experiment with six replications. Trees were between 6 and 12 cm in height at planting. Genotypes included: P. fortunei seedlings, P. tomentosa seedlings, P. elongata seedlings and three P. elongata clones. Each 4-m wide plot contained a single row of 12 trees with an intra-row spacing of 1 m. Plant measurements included height, root collar diameter (RCD) at 3 cm above soil surface, and the number of main branches. Leaf samples were collected from all six replications for estimates of herbage quality. During 1998, trees were browsed with goats on two occasions to assess palatability of the herbage and to determine any preference for specific genotypes by the animals. Compared with seedling trees of all three species, the three P. elongata clones were taller (clones: 79.7 cm, seedlings: 55.9 cm; P < 0.01), had larger RCDs (clones: 18.4 mm, seedlings: 13.9 mm; P < 0.01) and had a higher branching frequency (clones: 4.9, seedlings: 1.5; P < 0.01) by the end of the first growing season. Mortality averaged 4.8% across all treatments and ranged between 0 and 8%. Early in the 1998 growing season before trees were browsed, P. elongata clones grew more rapidly than seedlings (clones: 116.4 cm, seedlings: 84.1 cm; P < 0.01). Estimates of herbage quality indicated favorable concentrations of energy and protein for lamina. In vitro true dry matter disappearance ranged from 85.4 (blades) to 71.5% (petioles) and crude protein from 25.1 (blades) to 4.9% (petioles). Animals readily browsed the lamina during two separate sessions, but no clear preference trends were observed among the different Paulownia genotypes.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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Biogeochemical process models are increasingly employed to simulate current and future forest dynamics, but most simulate only a single canopy type. This limitation means that mixed stands, canopy succession and understory dynamics cannot be modeled, severe handicaps in many forests. The goals of this study were to develop a version of Biome-BGC that supported multiple, interacting vegetation types, and to assess its performance and limitations by comparing modeled results to published data from a 150-year boreal black spruce (Picea mariana (Mill.) BSP) chronosequence in northern Manitoba, Canada. Model data structures and logic were modified to support an arbitrary number of interacting vegetation types; an explicit height calculation was necessary to prioritize radiation and precipitation interception. Two vegetation types, evergreen needle-leaf and deciduous broadleaf, were modeled based on site-specific meteorological and physiological data. The new version of Biome-BGC reliably simulated observed changes in leaf area, net primary production and carbon stocks, and should be useful for modeling the dynamics of mixed-species stands and ecological succession. We discuss the strengths and limitations of Biome-BGC for this application, and note areas in which further work is necessary for reliable simulation of boreal biogeochemical cycling at a landscape scale. 相似文献
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The effects of j-rooting on water stress and growth of loblolly (Pious taeda L.) and eastern white pine (Pious strobus L.) were examined over three growing seasons in the field. Seedlings were planted in an area with severe herbaceous competition with either their roots planted straight or bent into a j shape. All seedlings were planted with their root collars placed at the soil surface. During the first year j-rooted seedlings consistently had lower water potentials but never statistically significant. Since both treatments were planted with the root collar at the soil surface, this trend was likely due to an initial shallower root system in j-rooted seedlings. In year three no differences in water potential were significant and no trends were evident. Growth did not differ significantly by treatment at any time but, by year three, j-rooted plants were consistently larger for both species. 相似文献
55.
Contribution of root respiration to soil surface CO2 flux in a boreal black spruce chronosequence 总被引:5,自引:0,他引:5
We quantified the contributions of root respiration (RC) and heterotrophic respiration to soil surface CO2 flux (RS) by comparing trenched and untrenched plots in well-drained and poorly drained stands of a black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Our objectives were to: (1) test different equations for modeling RS as a function of soil temperature; and (2) model annual RS and RC for the chronosequence from continuous soil temperature measurements. The choice of equation to model RS strongly affected annual RS and RC, with an Arrhenius-based model giving the best fit to the data, especially at low temperatures. Modeled values of annual RS were positively correlated with soil temperature at 2-cm depth and were affected by year of burn and trenching, but not by soil drainage. During the growing season, measured RC was low in May, peaked in late July and declined to low values by the end of the growing season. Annual RC was < 5% of RS in the recently burned stands, approximately 40% in the 21-year-old stands and 5-15% in the oldest (152-year-old) stands. Evidence suggests that RC may have been underestimated in the oldest stands, with residual root decay from trenching accounting for 5-10% of trenched plot RS at most sites. 相似文献
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We analyzed processes limiting photosynthesis in two-year-old, container-grown Pinus pinaster Ait. seedlings subjected to phosphorus (P) deficiency. After withholding P for 3 months, seedlings were supplied P at four relative addition rates (0, 0.005, 0.01 and 0.02 day(-1)) in a nutrient recycling system. At Weeks 12 and 22, responses of photosynthesis to CO(2) and irradiance were measured and the following parameters derived: maximal velocity of carboxylation by Rubisco, V(m); apparent quantum efficiency of electron transport, alpha maximal electron transport rate, J(m); stomatal conductance and relative stomatal limitation of photosynthesis. At Week 22, these measurements were combined with concurrent measurements of chlorophyll fluorescence to determine the quantum yield of PSII, and a theoretical partitioning of total light-driven linear electron flow between fractions used to regenerate carboxylated and oxygenated RuBP. After 12 weeks of treatment, needle P concentrations ranged from 0.04 to 0.15 x 10(-2) g g(DW) (-1), and then remained constant until Week 22. Values of J(m), alpha and V(m) increased with increasing needle P concentration (from 30 to 133 &mgr;mol m(-2) s(-1), 0.02 to 0.25 mol mol(-1) and 13 to 78 &mgr;mol CO(2) m(-2) s(-1) at the lowest and highest needle P concentrations, respectively). Under ambient conditions, net assimilation rates in P-deficient seedlings were limited by V(m) under saturating irradiance, and by J(m) under limiting irradiance, but not by triose-P regeneration. There was no detectable change in the partitioning of total light-driven linear electron flow between the fractions used for carboxylation and oxygenation. Predawn photochemical efficiency of PSII was significantly reduced in seedlings with low P concentrations. Although stomatal conductance tended to decrease with decreasing needle P concentration, relative stomatal limitation was not significantly affected. At Week 22, there was an attenuation of the effects of P nutrition on V(m) and an increase in alpha and J(m) that was probably related to cessation of growth and the seasonal decline in natural irradiance. 相似文献
58.
Phytopathogenic fungi associated with the bark beetles Tomicus piniperda and Orthotomicus erosus were isolated in various pine forests of Tunisia. Tomicus piniperda and its galleries yielded Leptographium wingfieldii, Ophiostoma minus, and Ophiostoma ips. Ophiostoma minus was the most frequent species associated with T. piniperda, in both the attacking and the emerging beetles. It was collected from most investigated forests, whereas O. ips and L. wingfieldii were obtained only from forests located in Central and Northern Tunisia. Frequencies of association with T. piniperda were always low, reaching 11.1% only once, for O. ips. Ophiostoma ips was the only blue stain fungus associated with O. erosus and its galleries. It was found in all the localities, but at a low and variable frequency, exceeding 15% very rarely. The virulence of 16 fungal isolates was tested by single inoculations into Pinus halepensis (Aleppo pine) at two localities. Differences were detected among species; L. wingfieldii was the most virulent and O. minus the least virulent species in terms of phloem reaction zone formation and fungal growth in the phloem. In a separate experiment, mass inoculations (400 and 800 inoculations per m2 of bole on 1‐m high belts) were performed with two isolates of L. wingfieldii on Aleppo pine and on Pinus brutia (Brutia pine). Three months later, measurements of sapwood status (% of conductive transversal section) and of its specific hydraulic conductivity, as well as of the phloem reaction zone lengths, did not show any isolate or density effect. At these experimental sites, Brutia pines appeared significantly more susceptible than Aleppo pines. 相似文献
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