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排序方式: 共有452条查询结果,搜索用时 15 毫秒
1.
ABSTRACT This study deals with the influence of electron beam irradiation (EBI) on the wettability of Norway spruce surface samples. To evaluate this possible effect in detail, the changes in chemistry and wood structure were analysed using the methods of IR spectroscopy and Scanning Electron Microscopy (SEM). The surface wettability was determined by the contact angle measurement method. The results of infrared spectra show decreased relative numbers of available hydrophilic groups (e.g. hydroxyl and carbonyl groups) in the wood surfaces due to the electron beam irradiation. This behaviour is consistent with the values from the surface wettability measurements. Structural differences of the wood surfaces after electron beam irradiation were not detectable. Based on these findings pre-treatment of wood surfaces for industrial usages can be a potential field of application of this technology. 相似文献
2.
N. Fenner D. J. Dowrick M. A. Lock C. R. Rafarel & C. Freeman 《Soil Use and Management》2006,22(3):267-273
The temperature dependence of chemical reaction rates and microbial metabolism mean that temperature is a key factor regulating soil trace gas emissions and hydrochemistry. Here we evaluated a novel approach for studying the thermal response of soils, by examining the effects of temperature on gas emissions and hydrochemistry in (a) peat and (b) soil from a Sitka spruce plantation. A thermal gradient was applied along an aluminium bar, allowing soil to be incubated contemporaneously from 2 to 18 °C. The approach demonstrated clear differences in the biogeochemical responses of the two soil types to warming. The peat showed no significant emission of CH4 at temperatures below 6 °C, while above 6 °C, a marked increase in the rate of release was apparent up to 15 °C (Q10 = 2.5) with emissions being similar between 15 and 18 °C. Conversely, CH4 emissions from the forest soil did not respond to warming. Nitrate availability in the peat decreased by 90% between 2 and 18 °C (P < 0.01), whereas concentrations in the forest soil did not respond. Sulphate availability in the peat decreased significantly with warming (60%, P < 0.01), while the forest soil showed the opposite response (a 30% increase, P < 0.01). Conventionally, thermal responses are studied by incubating individual soil samples at different temperatures, involving lengthy preparation and facilities to incubate samples at different temperatures simultaneously. Data collected on a given thermal response is usually limited and thus interpolated or extrapolated. The thermal gradient method overcomes these problems, is simple and flexible, and can be adapted for a wide range of sample types (not confined to soil). Such apparatus may prove useful in the optimization of management practices to mitigate the effects of climate change, as thermal responses will differ depending on land use and soil type. 相似文献
3.
The pathogenicity and growth of six cultures of the bark-beetle-associated blue-stain fungus Ceratocystis polonica were compared. Four were subcultures, established at different times, of the same isolate (80–53/7), and at least one of these was suspected to have lost its pathogenicity to Norway spruce ( Picea abies ) during subculturing. Two other cultures (93–208/115 and 94–169/13) were pathogenic. The pathogenicity of all cultures to Norway spruce was compared in three inoculation experiments, using (i) massive inoculation (≈144 inoculations per tree), (ii) low-density inoculation (14 inoculations per tree) of larger trees and (iii) single inoculation of 2-year-old seedlings. Fungal growth rates were tested in vitro on malt agar, and on malt agar under oxygen-deficient conditions. Isolates 93–208/115 and 94–169/13 and one of the subcultures of isolate 80–53/7 were pathogenic in all three inoculation experiments. Two other subcultures were nonpathogenic, while the last subculture was intermediate. The pathogenic cultures had higher growth rates on malt agar than the nonpathogenic and intermediate cultures, and they also grew better under oxygen-deficient conditions. These results demonstrate that blue-stain fungi may lose their pathogenicity after serial vegetative transfers on artificial substrates. The results are also consistent with the hypothesis that rapid growth and the ability to grow in oxygen-poor environments are important pathogenicity factors in blue-stain fungi. 相似文献
4.
Jonas Hafrén 《Journal of Wood Science》2007,53(2):143-146
Two methods of cytochemical staining using Coomassie dye and Cu+-bicinchoninic acid, respectively, showed that there are proteins in thermomechanical pulp (TMP) of Norway spruce. Protein
isolated from TMP was analyzed for amino acid composition. There was about twice the amount of acidic amino acid material
compared with basic amino acids, and the presence of glucosamine indicated that the isolated polypeptides also contained glycoproteins.
The presence of proteins in ray cells and fiber tracheids in TMP adds to the chemical heterogeneity of the structurally complex
high-yield pulp. 相似文献
5.
Mathieu Fortin Gaétan Daigle Chhun-Huor Ung Jean Bégin Louis Archambault 《European Journal of Forest Research》2007,126(4):573-585
This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity
in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance
structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level
approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum
likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized
residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover,
compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more
accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure
may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth
modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates
are valid when the number of observations is large. 相似文献
6.
The diversity of Ascocoryne cylichnium, Nectria fuckeliana and Neobulgaria premnophila isolates expressed as variation in their fatty acid and sterol composition was investigated. Despite high within-species variation, distinct differences in the fatty acid and sterol composition between species were evident. 相似文献
7.
Carly Green Brian Tobin Michael O’Shea Edward P. Farrell Kenneth A. Byrne 《European Journal of Forest Research》2007,126(2):179-188
Reporting carbon (C) stocks in tree biomass (above- and belowground) to the United Nations Framework Convention on Climate
Change (UNFCCC) should be transparent and verifiable. The development of nationally specific data is considered ‘good practice’
to assist in meeting these reporting requirements. From this study, biomass functions were developed for estimating above-
and belowground C stock in a 19-year-old stand of Sitka spruce (Picea sitchensis (Bong) Carr.). Our estimates were then tested against current default values used for reporting in Ireland and literature
equations. Ten trees were destructively sampled to develop aboveground and tree component biomass equations. The roots were
excavated and a root:shoot (R) ratio developed to estimate belowground biomass. Application of the total aboveground biomass function yielded a C stock
estimate for the stand of 74 tonnes C ha−1, with an uncertainty of 7%. The R ratio was determined to be 0.23, with an uncertainty of 10%. The C stock estimate of the belowground biomass component was
then calculated to be 17 tonnes C ha−1, with an uncertainty of 12%. The equivalent C stock estimate from the biomass expansion factor (BEF) method, applying Ireland’s
currently reported default values for BEF (inclusive of belowground biomass), wood density and C concentration and methods
for estimating volume, was found to be 60 tonnes C ha−1, with an uncertainty of 26%. We found that volume tables, currently used for determining merchantable timber volume in Irish
forestry conditions, underestimated volume since they did not extend to the yield of the forest under investigation. Mean
stock values for belowground biomass compared well with that generated using published models. 相似文献
8.
Surveys were made at the end of the 1990 and 1991 growing seasons for root-inhabiting fungi in the genera Fusarium, Cylindrocarpon and Pythium from the roots of one year-old container-grown Douglas-fir and spruce seedlings grown under greenhouse conditions. In the 1990 survey of four nurseries, it was found that 61–97% of both Douglas-fir and spruce roots were colonized with Fusarium, Cylindrocarpon or Pythium. There were significantly (p0.05) more Douglas-fir roots than spruce roots colonized by Fusarium at all nurseries, however, there were significantly (p0.05) more spruce roots than Douglas-fir roots colonized by Cylindrocarpon and Pythium. Root colonization of Douglas-fir and spruce by the three fungal genera during 1991 varied from 0–82% at three nurseries, however, only at a south coastal nursery was there significantly (p0.05) more spruce than Douglas-fir roots colonized by Cylindrocarpon. Significantly more seedlings were infected in 1990 than in 1991. In 1991, there were few significant differences between Douglas-fir and spruce, in the percentage of seedlings with colonized roots and in the percentage of growth medium colonized by the fungi. However, there were significant differences between nurseries. 相似文献
9.
We studied the influence of temperature and near- and sub- optimal mineral nutrition of black spruce seedlings (Picea mariana [Mill.] B.S.P.) during their second growing period on bud set, bud development, growth, mineral content and cold tolerance. Bud break and growth after bud break were also studied. Seedlings were grown for 106 d in growth chambers under three temperature regimes in combination with three concentrations of a fertilizer. They were then cold hardened for 56 d and dehardened for 66 d.Under these near- and sub-optimal N levels, bud formation occurred during the growing season. Bud formation was accelerated with decreasing fertilization, but was not affected by temperature treatments. Needles from seedlings with 0.64% N (dry mass basis) before hardening did not harden. Those with 0.87% N showed a lesser degree of hardiness than those with 1.28% N. Stem diameter increased at the beginning of the hardening period. During this acclimation period, shoot dry mass decreased with time at a constant rate and at the same rate over time for all treatments whereas root dry mass was more variable. Total number of needle primordia was low and no difference was observed among growing conditions. Bud break was similar in all treatments. Following bud break, shoot height and stem diameter increases were small but their magnitude varied with the nutritional regimes applied during the previous growing period. During hardening, nitrogen concentration of shoot tissues first increased and then decreased; phosphorus concentration first increased and then remained stable; potassium concentration remained stable. Concentration of these three elements generally decreased in the roots during this hardening. 相似文献
10.
Walter Seidling 《European Journal of Forest Research》2007,126(4):529-544
Crown transparency estimates of Scots pine, Norway spruce, common beech, pedunculate and sessile oak, annually surveyed between
1990 and 2004 within a grid over Germany, provide a suitable response variable to study drought effects on forest trees. Major
climatic factors, available on a monthly basis as plot-specifically interpolated values and parameters of site and stand conditions,
biotic and other relevant factors were used as predictors in different cross- and length-sectional, and longitudinal models.
Stand age is a considerable and most constant driver of crown transparency in all species. Pine, spruce and beech responded—mainly
with a delay of 1 year—with some foliar loss in areas where there was a surplus of temperature after the generally hot and
dry summer of 2003. Parallel time-series analyses delivered species-specific geographic large-scale patterns with delayed
or recent precipitation deficits or temperature surpluses. Even if beech is partly responding in current years with leaf loss
towards precipitation surpluses, defoliation is especially high 1 year after hot summers, partly a result of high seed sets
after such summers. Crown condition of oak responds in dry and warm areas according to the drought stress hypothesis, however,
in cool and wet mountainous ranges oak responds after wet summers with higher defoliation. Longitudinal approaches revealed
for all 4-tree species significant relationships between crown condition and deviations from the long-term means of temperature,
precipitation but also global radiation and wind speed. Results do not always match the drought stress hypothesis, however,
this is not to expect considering the heterogeneous site, stand and climatic conditions across Germany. Complex interactions
of climatic and biotic factors also impede simple relationships. Soil-related clusters reveal higher sensitivity of spruce
and beech towards climatic drought factors on more acid soils with thin humus layers. Also clusters constructed from plot-specific
courses of defoliation reveal groups with rather closer relationships like a group of pine plots in the Oberpfalz, which seems
to be especially sensitive to summer drought. 相似文献