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801.
Kana Yamashita Yasuhiko Hirakawa Shuetsu Saito Hiroshi Nakatani Motoyoshi Ikeda 《Journal of Wood Science》2011,57(5):363-370
To evaluate the bow variation in boxed-heart square timber of sugi (Cryptomeria japonica), bows from kiln-dried timber for five sugi cultivars with different longitudinal shrinkage trends were compared for two
stem heights. Two general trends were observed, depending on the cultivar: (1) either the bow was larger at the lower than
at the upper part of the stem, or (2) the bows at the lower and the upper parts of the stem were similar. In timber that had
larger bow values, the gradients of longitudinal shrinkage were large across the radius and along the length of the timber.
There was a positive relationship between the bow and longitudinal shrinkage. These results suggest that the bow variation
between the timbers was caused by a variation in longitudinal shrinkage, which was affected by the microfibril angle. Furthermore,
the bow was inversely proportional to the modulus of elasticity, which suggests that timber with a low modulus of elasticity
is susceptible to a large bow due to large longitudinal shrinkage. 相似文献
802.
To improve its overall performance, fast-growing poplar was modified using the vacuum-pressure-vacuum impregnation method
with a urea-formaldehyde resin-sodium montmorillonite intercalation as the modification solution. The results showed that
considerable amounts of urea-formaldehyde resin and montmorillonites entered the poplar tracheid, and some entered the microporous
wood. These substances formed bonds with the active groups in timber, causing reduced crystallinity in the amorphous region
of the poplar, a decreased level of free hydroxyl, and an enhanced association with hydroxyl and ether bonds. The density,
dimensional stability, and mechanical properties of poplar were markedly improved. The best results were obtained with 14%
sodium montmorillonite and 20% ureaformaldehyde resin: the bending resistance, compressive resistance, and elastic modulus
increased by 19.37%, 30.24%, and 50.06%, respectively. With elevated levels of sodium montmorillonite, the impact toughness
and wear rate decreased. 相似文献
803.
To improve the properties of particleboard, boards were produced using a sealed press. With the sealed press, boards were
processed under high-temperature and high-pressure steam. This increased the saturation temperature, causing a dramatic rise
in temperature inside the board, faster curing of the binder, and a shorter pressing time. The boards were bonded with urea
formaldehyde resin, melamine urea formaldehyde resin, or poly(methylene diphenyl diisocyanate) (PMDI). The sealed press improved
the internal bond strength and thickness swelling of boards regardless of the binder used during the reduced pressing time.
The increased bonding strength improved the board properties, allowing PMDI with a lower resin content to be used for bonding
the boards. 相似文献
804.
Growth,P uptake and rhizosphere properties of wheat and canola genotypes in an alkaline soil with low P availability 总被引:1,自引:0,他引:1
Zakaria Solaiman Petra Marschner Dongmei Wang Zed Rengel 《Biology and Fertility of Soils》2007,44(1):143-153
The aim of the present study was to assess the role of soil type on growth, P uptake and rhizosphere properties of wheat and
canola genotypes in an alkaline soil with low P availability. Two wheat (Goldmark and Janz) and two canola genotypes (Drum
and Outback) were grown in a calcareous soil (pH 8.5) at two P levels [no P addition (0P) or addition of 200 mg kg−1 P as Ca3(PO4)2 (200P)] and harvested at flowering or maturity. Shoot and root dry weight, root length and shoot P content were greater in
the two canola genotypes than in wheat. There were no consistent differences in available P, microbial P and phosphatase activity
in the rhizosphere of the different genotypes. Shoot P content was significantly positively correlated with root length, pH
and phosphatase activity in the rhizosphere. The microbial community composition, assessed by fatty acid methylester analysis,
of the canola genotypes differed strongly from that of the wheat genotypes. The weight percentage bacterial fatty acids, the
bacteria/fungi (b/f) ratio and the diversity of fatty acids were greater in the rhizosphere of the canolas than in the rhizosphere of the wheat
genotypes. In contrast to the earlier studies in an acidic soil, only small differences in growth and P uptake between the
genotypes of one crop were detected in the alkaline soil used here. The results confirmed the importance of root length for
P uptake in soils with low P availability and suggest that the rhizosphere microbial community composition may play a role
in the better growth of the canola compared to the wheat genotypes. 相似文献
805.
Yuyou Zhi Peng Li Jiachun Shi Lingzao Zeng Laosheng Wu 《Journal of Soils and Sediments》2016,16(2):467-475
Purpose
Cadmium (Cd) is regarded as one of the most toxic heavy metals in the environment and can undermine the ecosystem function and human health at trace level due to its high toxicity. In order to reduce the anthropogenic Cd input into agricultural soil, it is of utmost importance to pinpoint the sources of Cd in soils and apportion their respective contributions.Materials and methods
One hundred twenty-seven topsoil samples and 21 subsoil samples were collected from croplands of Meishan Basin, Changxing County, Zhejiang Province, Eastern China, and analyzed for concentrations of Cd and other heavy metals. Finite mixture distribution model (FMDM) was employed to fit the data to obtain the local soil Cd threshold value, a critical indicator to assess soil heavy metal contamination. Then, principal component analysis (PCA) and geographic information system (GIS) were used to identify the potential sources of Cd. Finally, positive matrix factorization (PMF) was applied to apportion the source contributions.Results and discussion
Among the 127 topsoil samples, 71 were subject to Cd contamination with a mean concentration of 0.66 mg kg?1 while the others were considered as background with a lower mean concentration of 0.145 mg kg?1, close to the local background concentration of 0.142 mg kg?1. Further, three components were extracted by PCA and interpreted as natural background, lead-acid battery manufacturing plants, and construction material associated activities, respectively. Additionally, most of the topsoil samples around the lead-acid battery manufacturing plants, construction material plants, and limestone/marble quarries were classified as Cd contaminated. However, PMF failed to get a successful portioning.Conclusions
Lead-acid battery manufacturing plants and construction material associated activities were the main anthropogenic sources of soil Cd contamination. With the help of FMDM, it is possible to distinguish the contaminated soil and estimate the contribution of anthropogenic sources to soil Cd. The apportionment by PMF was not successful in this paper due to the high skewness or outliers of Cd concentration in sampling sites and violation of the assumption that all samples have the same sources.806.
Yalong Liu Ping Wang Genxing Pan David Crowley Lianqing Li Jinwei Zheng Xuhui Zhang Jufeng Zheng 《Journal of Soils and Sediments》2016,16(5):1460-1471
Purpose
Rice paddy soils undergo pedogenesis driven by periodic flooding and drainage cycles that lead to accumulation of organic matter and the stratification of nutrients and oxygen in the soil profile. Here, we examined the effects of continuous rice cultivation on microbial community structures, enzyme activities, and chemical properties for paddy soils along a chronosequence representing 0–700 years of rice cropping in China.Materials and methods
Changes in the abundance and composition of bacterial and fungal communities were characterized at three depths (0–5, 5–10, and 10–20 cm) in relation to organic carbon, total nitrogen, dissolved organic carbon, microbial biomass carbon/nitrogen, and activities of acid phosphatase, invertase, and urease.Results and discussion
Both soil organic carbon and total nitrogen increased over time at all three depths, while pH generally decreased. Microbial abundance (bacteria and fungi) and invertase and urease activity significantly increased with the duration of rice cultivation, especially in the surface layer. Fungal abundance and acid phosphatase activity declined with depth, whereas bacterial abundance was highest at the 5–10-cm soil depth. Profiles of the microbial community based on PCR-DGGE of 16S rRNA indicated that the composition of fungal communities was strongly influenced by soil depth, whereas soil bacterial community structures were similar throughout the profile.Conclusions
Soil bioactivity (microbial abundance and soil enzymes) gradually increased with organic carbon and total nitrogen accumulation under prolonged rice cultivation. Microbial activity decreased with depth, and soil microbial communities were stratified with soil depth. The fungal community was more sensitive than the bacterial community to cultivation age and soil depth. However, the mechanism of fungal community succession with rice cultivation needs further research.807.
Lydie-Stella Koutika Sonia Vanderhoeven Lydie Chapuis-Lardy Nicolas Dassonville Pierre Meerts 《Biology and Fertility of Soils》2007,44(2):331-341
Invasive exotic plants can modify soil organic matter (SOM) dynamics and other soil properties. We evaluated changes in particulate
organic matter (POM) and carbon (C) mineralisation in adjacent plots invaded by Solidago gigantea, Prunus serotina, Heracleum mantegazzianum and Fallopia japonica, and non-invaded control plots on different soils in Belgium. Litter decomposition of S. gigantea and P. serotina was compared to that of the native species Epilobium hirsutum, Betula pendula and Fagus sylvatica. Disregarding the differences in site characteristics (soil texture, parental material and plant species), we argued that
the invasion by S. gigantea and P. serotina enhance SOM dynamics by increasing C mineralisation in 2 out of 3 sites invaded by S. gigantea and in 1 out of 3 sites invaded by P. serotina; C in coarse POM (cPOM, 4,000–250 μm) and fine POM (fPOM, 250–50 μm) in 1 site invaded by S. gigantea and C content in total POM (tPOM, 4,000–50 μm) and the organo-mineral fraction (OMF, 0–50 μm) in 1 site invaded by P. serotina. H. mantegazzianum and F. japonica slowed down SOM dynamics by reducing C mineralisation in three out of four sites; C and nitrogen (N) of fPOM in the invaded
compared with the non-invaded plots at one site invaded by H. mantegazzianum. However, N content of cPOM (4,000–250 μm) was higher in the invaded sites by F. japonica compared with the non-invaded plots. Our results indicated that the effects of invasion by exotic plant species were not
species-specific but site-specific. 相似文献
808.
The release of CO2 by soil microorganisms after the addition of nitrogen and glucose in excess and calibration additions of phosphorus has successfully
been used to assess microbial available P, assuming the native soil P pool is then limiting respiration. However, in P-fixing
soils and soils with high P content, carbon can be exhausted before the available soil P pool. It is not possible to simply
increase the amount of glucose as then the glucose concentration would be lethal for microorganisms. A modified method was
tested where soil is mixed with perlite. It was hypothesised that perlite, having a high water holding capacity, would dilute
the concentration of glucose, while maintaining the bioavailability of added nutrients, thus avoiding carbon limitation. Factorial
combinations of amount of soil and perlite (both adjusted to −25 kPa water potential) were tested to examine if perlite as
such had any effect on the respiration. Five tropical soil samples with a sharp gradient in P availability and one N-limited
compost material were used. The method successfully reduced the risk of carbon limitation. Microbial indices, such as basal
respiration, substrate-induced respiration and maximum P-limited respiration, were directly proportional to the amount of
soil in the experiments but unrelated to the amount of perlite, showing that perlite did not affect microbial measurements. 相似文献
809.
Andargachew Gedebo Maigull Appelgren Asmund Bjornstad Admasu Tsegaye 《Genetic Resources and Crop Evolution》2007,54(7):1429-1436
For the first time we report that diverse types of Arisaema schimperianum Schott locally called amochi, are grown and managed as an off-season food crop in Southern Ethiopia. Participatory Rural
Appraisal (PRA) and formal survey studies on 204 households were conducted over two consecutive years (2003–2004) in Chencha
and Dita sub zones of Southern Ethiopia, to identify indigenous production methods and farm based biodiversity of amochi.
Amochi is propagated from seed tubers and tuber parts left in the soil from the preceding harvest and grow during the dry
season, February to June. Average share of proportion in the annual household consumption from amochi tubers was 9% and 4%
for Chencha and Dita respectively. Uncooked amochi is irritating in contact to skin and mouth. Fifteen amochi types were identified
in Dita and 12 in Chencha. They differ in the level of irritation, maturity and yield. Rich farmers with large family size
as a working force, large farm size to support larger number of livestock that is source of farmyard manure, have farms with
larger diversity of amochi than their poor counterparts, suggesting that its diversity is influenced by house hold characteristics
and favoured under relatively fertile soil conditions. In both sub zones women had better experience in identifying amochi
types than men. Further study is needed to identify chemical contents; and genetic variation using morphologic and molecular
traits, in order to develop a strategy to assess and utilise the existing genetic diversity. 相似文献
810.
One hundred and forty-seven Chinese barley varieties maintained at the Gene Bank of the National Barley Improvement Centre,
Zhejiang, and 84 progenies from these varieties were tested at the seedling stage for their reaction to 32 selected pathotypes
of Blumeria graminis f. sp. hordei. Eighteen resistance spectra were identified comprising single or combined resistances from eight known (Ml(Bw), Ml(Ch), Mla7, Mla8, Mla9, Mla13, MlaRu4 and Mlg) and six unknown resistance genes. The most frequent gene was Ml(Bw), which was found in 69 varieties and previously detected in only a few European winter barley varieties. The genes Mla8 and Ml(Ch) were also often present, but other resistance genes were rare. After inoculation, considerably fewer pathogen colonies were
observed in ‘Aiganqi’ and one line of ‘Tong5’. Twenty varieties were composed of lines with different resistance genes. China
is likely to be a region of origin of the genes Ml(Bw), Mla7, as well as three unknown genes found in original landraces and perhaps another three unknown genes detected in cultivars
bred in China. The resistances of varieties from the Zhejiang province and those originating from 11 other Chinese provinces
were quite different. Unfortunately, none of the varieties are promising sources of resistance to powdery mildew and China
does not seem to be a region suitable for identifying such sources. 相似文献