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71.
Catherine M. M. Felton 《Water, air, and soil pollution》1979,12(1):91-101
Energy and water budget analyses are employed as methods for assessing the effects of vegetation type, cultivation practices, and irrigation methods on the microclimate. A comparison is made of vegetation types that employ water received from (1) natural precipitation and (2) irrigation. Forest lands are compared to corn cultivated by conventional tillage and no tillage methods. The forest canopy generally has a lower surface albedo, greater surface roughness, higher transpiration rates, and increased water storage than the bare soil, mulched, and vegetated surfaces of a corn field. No tillage cultivation reduces wind and water erosion, lowers soil temperatures, and improves water retention compared to standard tillage used on corn fields. Irrigated agriculture has replaced much of the drought resistant vegetation of the Central Valley of California. The energy and water budgets of irrigated crops grown in the semi-arid climate of the Central Valley and irrigated by flood or sprinkler methods exhibit microclimates in which evapotranspiration dominates the energy and mass fluxes. Drip irrigation methods, by contrast, have reduced water losses compared to flood and sprinkler methods. The drip system supplies metered amounts of water to the base of each plant; low soil evaporation and improved water supply to the growing plant results from this method. The latent heat flux is reduced over that found in fields irrigated by flooding or spraying. Generally, agricultural transformation of large stands of natural vegetation is expected to change the micro- and macroclimate of the areas affected. 相似文献
72.
Catherine M. Riseng Robert W. Gensemer Susan S. Kilham 《Water, air, and soil pollution》1991,60(3-4):249-261
The growth rates of two diatoms, acidophilic Asterionella ralfsii and circumneutral A. formosa, were differentially affected by varying pH, Al, and EDTA in chemically defined media. Free Al ion concentration increased as pH and EDTA concentration decreased. Free trace metal ion concentration decreased as EDTA levels increased but increased by orders of magnitude upon addition of Al. pH had an overriding species specific effect on growth rate; at low pH A. ralfsii had higher growth rates than A. formosa and vice versa at high pH. For both species higher EDTA levels depressed growth rates. Moderate additions of Al generally resulted in growth stimulation. The growth rate stimulations, especially at 200 and 400 μg L?1 Al additions, correlate to increases in free trace metal ion concentrations. The EDTA-AI interaction effects on growth rate were both pH and concentration dependent: at pH 7 both species were stimulated by addition of Al at all EDTA levels (except A. ralfsii at 5.0 mM EDTA and A. formosa at 0.5 mNM EDTA); at pH 6 Al addition either stimulated or had no effect on the growth rates of both species (except at low EDTA and high Al levels); at pH 5 A. formosa did not grow and additions of 200 μg L?1 Al stimulated growth of A. ralfsii. It is likely that the effect of pH, Al, and EDTA on speciation of essential or toxic trace metals affects growth rates of these diatoms in a species specific manner. 相似文献
73.
Do multipurpose companion trees affect high value timber trees in a silvopastoral plantation system?
Establishment of native timber trees on deforested land may contribute to the livelihood of farmers, to improved ecosystem
services and to increased greenhouse gas uptake. Here, we present a new silvopastoral planting design to assess species performance
and interspecific competition or facilitation effects among native timber and multipurpose trees in Central America. Two timber
species, Tabebuia rosea and Cedrela odorata, were established in three low-density planting regimes allowing combined tree and future livestock production: (1) solitary
planting, (2) companion planting with Guazuma ulmifolia, and (3) companion planting with the nitrogen-fixing Gliricidia sepium. We quantified survival, growth and reforestation potential of the two timber species subjected to the different planting
regimes for the first 2 years after establishment. Nitrogen concentration as well as stable nitrogen and carbon isotope composition
(δ15N, δ13C) of leaves of the timber saplings were determined. T. rosea showed higher survival and better growth than C. odorata under varying environmental conditions (soil, concomitant vegetation). Performance of the timber saplings was unaffected
by either companion species. Planting regimes had no effect on foliar nitrogen concentration and δ15N of the two timber species, although δ15N values indicated nitrogen fixation activity in G. sepium trees. Planting regimes affected foliar δ13C values in T. rosea. δ13C values were significantly higher in solitarily growing individuals, suggesting lower exposition to water stress conditions
in saplings surrounded by companion species. As we found positively correlated growth traits among timber and multipurpose
trees, a combined planting may benefit farmers by providing additional goods and services. 相似文献
74.
Temperature signals contribute to the timing of photoperiodic growth cessation and bud set in poplar
Bud set, the cornerstone delimiting the seasonal growth period in trees, is the dynamic net result of the often photoperiod-controlled growth cessation and the subsequent bud formation. Here, we show that in hybrid poplar, the critical day length for growth cessation and the duration of bud formation each vary with local climatic conditions in identical genotypes. The detailed dissection of bud set suggests temperature as one additional environmental factor that modifies the sensitivity to day-length signals at growth cessation and influences the duration of bud formation in poplar. The ability of perennial plants to integrate additional environmental signals with photoperiod signaling may add to short-term acclimatization to the predicted longer growing seasons in future climates. 相似文献
75.
Mirco PlathKarsten Mody Catherine PotvinSilvia Dorn 《Forest Ecology and Management》2011,261(3):741-750
Plantations of native timber species established on former pasture are a potential strategy to reduce the logging pressure on remnant natural forests in the tropics. Such plantations may help to mitigate or reverse the negative impacts of land degradation, and they may contribute to the long-term livelihood of livestock farmers. Planting native trees is, however, perceived as a risky activity due to limited knowledge of their performance and due to marked losses of newly established seedlings attributed to insect pests. Our study focuses on the small-scale effects of environmental heterogeneity, tree diversity and insecticide treatment on the performance of three native Central American timber species two years after establishment, and on damage inflicted by insect herbivores. Growth, survival and herbivore leaf damage were quantified for Anacardium excelsum (Anacardiaceae), Cedrela odorata (Meliaceae) and Tabebuia rosea (Bignoniaceae) planted in an experiment in Panama as (1) monocultures, (2) mixed stands, and (3) mixed stands protected by insecticides. Our study revealed that small-scale effects can have a substantial impact on the success of timber trees planted on former pasture. Growth performance and survival of the three species was strongly affected by small-scale environmental heterogeneity, which was expressed as significant differences in growth and survival among different plantation plots at the same study site. Establishment of trees in mixed stands did not have significant effects on tree survival and growth compared to pure stands, although it reduced herbivore pressure in one of the studied tree species. All tree species grew best and suffered lowest leaf damage when protected by insecticides, indicating a general influence of insect herbivory on growth of newly established trees. In contrast to growth performance, survival was not significantly affected by different management practices or herbivory. The large variability among plots in tree survival and growth, and also in the effects of management practices such as planting design and insecticide treatment, emphasizes the importance of small-scale environmental heterogeneity on tree survival and growth. 相似文献
76.
Mendes-Pinto MM Silva Ferreira AC Caris-Veyrat C Guedes de Pinho P 《Journal of agricultural and food chemistry》2005,53(26):10034-10041
Carotenoids and chlorophyll-derived compounds in grapes and Port wines were investigated by HPLC-DAD and HPLC-DAD-MS (ESP+) analysis. A total of 13 carotenoid and chlorophyll-derived compounds are formally reported in grapes, 3 are identified for the first time, pheophytins a and b and (13Z)-beta-carotene, and 3 others remain unknown. In Port wines 19 compounds with carotenoid or chlorophyll-like structures are present, 8 still unidentified. The young wines showed higher total carotenoid content and chlorophyll-like compounds compared to aged Ports, with lutein and beta-carotene as major carotenoids. Among samples analyzed of monovarietal Vitis vinifera L. cultivar wines produced with the five most important Douro varieties, Tinta Roriz contained the highest levels of carotenoids and Touriga Franca the lowest. The forced-aging study indicated that lutein was more sensitive to temperature than beta-carotene. Additionally, aged wines showed higher ratios of beta-carotene/lutein concentrations compared to new Ports. Rates of degradation of chlorophyll derivative compounds were higher than those for carotene and lutein. 相似文献
77.
In search of a maize ideotype for cell wall enzymatic degradability using histological and biochemical lignin characterization 总被引:1,自引:0,他引:1
Méchin V Argillier O Rocher F Hébert Y Mila I Pollet B Barriére Y Lapierre C 《Journal of agricultural and food chemistry》2005,53(15):5872-5881
Grass cell wall degradability is conventionally related to the lignin content and to the ferulic-mediated cross-linking of lignins to polysaccharides. To better understand the variations in degradability, 22 maize inbred lines were subjected to image analyses of Fasga- and M?ule-stained stem sections and to chemical analyses of lignins and p-hydroxycinnamic acids. For the first time, the nearness of biochemical and histological estimates of lignin levels was established. Combination of histological and biochemical traits could explain 89% of the variations for cell wall degradability and define a maize ideotype for cell wall degradability. In addition to a reduced lignin level, such an ideotype would contain lignins richer in syringyl than in guaiacyl units and preferentially localized in the cortical region rather than in the pith. Such enrichment in syringyl units would favor wall degradability in grasses, contrary to dicots, and could be related to the fact that grass syringyl units are noticeably p-coumaroylated. This might affect the interaction capabilities of lignins and polysaccharides. 相似文献
78.
Paul A. Arp Catherine Akerley Kajetan Mellerowicz 《Water, air, and soil pollution》1989,48(1-2):277-297
Two adjacent soils with contrasting sulfate sorption were examined in terms of (i) water-soluble and ion-exchangeable Al, Fe, Ca, Mg, K, Mn and Zn, (ii), water- and bicarbonate-extractable sulfate, (iii) Truog-extractable P, (iv) dithionite-extractable Al, Mn and Fe and (v) treatment response to irrigation with simulated acid precipitation. The biomass of 8 year old black spruce saplings growing on the soils, and the distributions of Al, Fe, Ca, Mg, K, Mn, P and Zn within these plants, were also examined. The soils were well to moderately-well drained, with the mineral soil exposed by site preparation prior to planting. The exposed soil underneath individual saplings was treated with acid sulfate solutions (75 mm containing 2 to 50 mg L?1 H2SO4) applied during each of three consecutive growing seasons. The results indicate that Al, much like Fe, Ca, Mn and Zn, accumulated with time in the foliage, but K, Mg and P were highest in young plant tissues. Much of Al and Fe taken up remained in the fine roots. Aluminum uptake increased with the amount of dithionite-extractable Al (free Al oxide) in the soil. Growth of the black spruce saplings was not visibly affected by readily accessed Al in each soil, or by acid irrigation.Instead, growth was restricted by factors other than soil Al and acid irrigation in spite of (i) low soil pH, (ii) high levels of exchangeable Al, and (iii) high levels of Al in fine roots. Sulfate retention across and within the two soils was positively correlated with free Al oxide. The two soils responded to acid irrigation by accelerated silicate weathering and enhanced ion leaching. Sulfate sorption reduced these effects. 相似文献
79.
Mi-Young Kang Catherine W. Rico Sang-Chul Lee 《Journal of Crop Science and Biotechnology》2011,14(2):111-118
The physicochemical properties of pigmented (Midorimochi, Jeokjinjubyeo, and Heukmichalbyeo) and non-pigmented (Hwayoungbyeo)
rice varieties were investigated. Starch from non-pigmented rice consisted mainly of large polyhedral granules that were more
loosely packed than those of the non-pigmented sample. Pigmented rice showed higher linoleic acid content (36–40%) and hydrolysis
rate (63–79%) but lower oleic acid content (35–39%), blue value (0.05–0.17), and viscosity values than the non-pigmented one.
Significantly higher mineral content, blue value, and pasting and viscosity values were observed in the Jeokjinjubyeo sample
compared to those of the other pigmented rice samples. The Midorimochi variety, on the other hand, exhibited the highest total
amino acid (816.82 ng mg−1) and sugar (0.15–3.35 μg g−1) contents and the lowest pasting and viscosity values. No substantial difference in the X-ray diffraction pattern was observed
among the samples. Results of this study could serve as baseline information for the quality evaluation of three pigmented
rice cultivars and provide a better understanding of their potential uses and food industry applications. 相似文献
80.
T cell activation by lipopeptide antigens 总被引:2,自引:0,他引:2
Moody DB Young DC Cheng TY Rosat JP Roura-Mir C O'Connor PB Zajonc DM Walz A Miller MJ Levery SB Wilson IA Costello CE Brenner MB 《Science (New York, N.Y.)》2004,303(5657):527-531
Unlike major histocompatibility proteins, which bind peptides, CD1 proteins display lipid antigens to T cells. Here, we report that CD1a presents a family of previously unknown lipopeptides from Mycobacterium tuberculosis, named didehydroxymycobactins because of their structural relation to mycobactin siderophores. T cell activation was mediated by the alphabeta T cell receptors and was specific for structure of the acyl and peptidic components of these antigens. These studies identify a means of intracellular pathogen detection and identify lipopeptides as a biochemical class of antigens for T cells, which, like conventional peptides, have a potential for marked structural diversity. 相似文献