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991.
992.
Hossein Izadi-Vasafi Gity Mir Mohamad Sadeghi Amir Babaei Faezeh Ghayoumi 《Fibers and Polymers》2016,17(3):311-323
A novel biodegradable polylactic acid-based polyurethane (PU) was synthesized via a chain extension reaction between hydroxylated polylactic acid (PLA-OH) and hydroxylated tung oil (HTO) using 1,6-hexamethylene diisocyanate (HDI) to link the two polyols and dibutyltin dilaurate (DBTDL) as a catalyst. Both PLA-OH and HTO, as polyols, were separately synthesized in our laboratory. Three different molecular weights of PLA-OH prepolymers were used, and the molar ratio of PLA-OH to HTO was also changed to investigate the effect of these two parameters on the structure and properties of the final PUs. Chemical structures of PLA-OH, HTO, and final PUs were investigated by Fourier transform infrared (FTIR) and Hydrogen-1 nuclear magnetic resonance (1HNMR) spectroscopies. Thermal transitions and thermal stability of the final PUs were, respectively, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR and 1HNMR results showed that the chain-extension reaction of the two polyols with HDI was sufficiently achieved. The TGA results showed that the polyurethanes based on the lower molecular weight PLA segments were more thermally stable; it was not degraded up to 270 °C. DSC results showed that incorporating HTO in the PU chains led to formation of more flexible PU chains, while the glass transition temperatures of the PUs of higher PLA-OH molecular weights were higher than those of lower ones. 相似文献
993.
Amanda D. Bambrick Joann K. Whalen Robert L. Bradley Alain Cogliastro Andrew M. Gordon Alain Olivier Naresh V. Thevathasan 《Agroforestry Systems》2010,79(3):343-353
Land use affects the carbon sequestration potential of soils across landscapes. Tree-based intercropping (TBI) systems where
annual crops are grown between established tree rows are expected to exhibit spatial heterogeneity in the soil organic carbon
(SOC) content due to differences in carbon input and decomposition rates of litter from trees and herbaceous plants. This
study aimed to quantify variability in the SOC of TBI systems, compare the SOC content of TBI and nearby conventional agroecosystems,
and determine if SOC was related to soil fertility. The TBI research sites were established 4 years (St. Paulin and St. Edouard,
Quebec, Canada), 8 years (St. Remi, Quebec, Canada) and 21 years (Guelph, Ontario, Canada) before soil samples were collected
for this study. The SOC content was greater within 0.75 m of the tree row than in the intercropped space at the St. Edouard
and St. Remi sites. At the Guelph site, the SOC was spatially heterogeneous in plots with Norway spruce (Picea abies L.) but not hybrid poplar (Populus deltoides × P. nigra clone DN-177), probably due to litterfall distribution. Formerly a tree plantation, the TBI system at St. Remi contained
77% more SOC than a nearby conventional agroecosystem, while there was 12% more SOC in the TBI system than the conventional
agroecosystem at Guelph. There was no difference in the SOC content of 4-year old TBI sites and nearby conventional agroecosystems.
However, an increase in SOC at all TBI sites was positively related to the plant-available N concentrations, indicating the
benefit of temperate TBI systems for soil fertility. 相似文献
994.
Mary Nyawira Muchane Bashir Jama Caleb Othieno Robert Okalebo David Odee Joseph Machua Jan Jansa 《Agroforestry Systems》2010,78(2):139-150
A field study was carried out on a six-year-old on-farm field trial during long-rains season (April–August) 2003 to investigate
the effect of improved fallow systems and phosphorus application on arbuscular mycorrhiza fungi (AMF) symbiosis in maize.
The trial comprised of maize rotated with a fast growing leguminous Crotalaria
grahamiana fallow and a non-leguminous Tithonia diversifolia fallow for 3 years followed by continuous maize. The experiment was randomized complete block design with three cropping
(continuous maize, Crotalaria fallow and Tithonia fallow) systems and two phosphorus levels (0 and 50 kg P/ha). AMF colonization in maize roots, maize yield and macro-nutrients
uptake were recorded. Phosphorus applications improved (P < 0.05) early (<8 weeks old maize) AMF colonization, nutrient uptake and maize yield in improved fallow systems. Greater
differences due to phosphorus application were noted in maize in Tithonia fallow than in Crotalaria fallow. Following phosphorus application, a positive relationship existed between early AMF colonization and maize yield
(r = 0.38), and phosphorus and nitrogen uptake (r = 0.40 and r = 0.43, respectively), demonstrating the importance of phosphorus fertilization in enhancing low-input technologies (improved
fallows systems) in phosphorus deficient and acidic soils of western Kenya. 相似文献
995.
Fujio Hyodo Takashi F. Haraguchi Muneto Hirobe Ryunosuke Tateno 《Journal of Forest Research》2016,21(4):170-177
Forest development in temperate regions is considered to be a global carbon sink. Many studies have examined forest development after harvesting or fire from aboveground (e.g., biomass) or belowground (e.g., soil nutrient) perspectives. However, few studies have explored forest development from both perspectives simultaneously in cool-temperate forests in Japan. In this study, we examined changes over 105 years in both aboveground and belowground components during secondary natural succession. The aboveground biomass increased for 50 years and reached a plateau in a 105-year-old stand. The N mineralization rate increased during succession for 50 years, but showed a decline in the 105-year-old stand due to the decrease in the nitrification rate in late succession. The percent nitrification (i.e., relative contribution of nitrification to N mineralization) decreased significantly with increasing forest stand age. The N mineralization rates had significant relationships with N concentrations of the dominant tree foliage and litter fall and with the amount of litter fall N. Meanwhile, other belowground properties (i.e., soil pH, phenol concentration, soil microbial respiration, and litter mass loss) did not show any significant relationship with forest stand age. This may be because the soil at the study sites was heterogeneous and consisted of Cambisols and Andosols, the latter of which originally has high organic matter content, and thus may have buffered the effect of the aboveground development. These results indicate that belowground N dynamics are more closely associated with aboveground development than other belowground properties in these forests. 相似文献
996.
• Introduction
The annual development cycle of boreal and temperate trees results from an evolutionary trade-off between two opposing forces. These are namely, the adjustment of leaf phenology to the timing of frost occurrence at the beginning and/or the end of the growth season countered by an effective adjustment to the duration of the growth season to maximise photosynthesis and biomass production during the growing season. 相似文献997.
Dawn B. Woodard Robert L. Wolpert Michael A. O’Connell 《Journal of Agricultural, Biological & Environmental Statistics》2010,15(2):209-227
We develop a method for multiscale estimation of pollutant concentrations, based on a nonparametric spatial statistical model.
We apply this method to estimate nitrate concentrations in groundwater over the mid-Atlantic states, using measurements gathered
during a period of 10 years. A map of the fine-scale estimated nitrate concentration is obtained, as well as maps of the estimated
county-level average nitrate concentration and similar maps at the level of watersheds and other geographic regions. The fine-scale
and coarse-scale estimates arise naturally from a single model, without refitting or ad hoc aggregation. As a result, the
uncertainty associated with each estimate is available, without approximations relying on high spatial density of measurements
or parametric distributional assumptions. 相似文献
998.
E. Sunderasan Rusni A. Kadir Valérie Pujade-Renaud Frédéric de Lamotte H. Y. Yeang Sheila Nathan 《Journal of General Plant Pathology》2009,75(1):19-26
Corynespora leaf disease poses a serious threat to rubber cultivation because infected leaves develop necrotic lesions and
abscise, leaving the tree unproductive. The destructiveness of Corynespora cassiicola has been largely attributed to cassiicolin, a protein toxin secreted by the fungus. Recombinant antibody technology offers
hope to curtail the disease whereby single-chain variable fragments (scFv) specific to cassiicolin could bind and deactivate
the toxin in genetically modified rubber trees that harbour the antibody gene. A scFv phage library was constructed from heavy
and light variable chains of IgG from cassiicolin immunized Balb/C mice spleen. Biopanning of the phage library yielded a
scFv clone with high specificity to cassiicolin. The nucleotide sequence and deduced amino acid sequence information of the
scFv were obtained. Hemagglutinin (HA)-tagged scFv expressed in Escherichia coli is discerned as a band at ca. 30 kDa on SDS-PAGE, and the corresponding band was detected by anti-HA IgG on a Western immunoblot.
Deactivation of cassiicolin by the affinity-purified scFv was demonstrated in a detached-leaf bio-assay on selected susceptible
Hevea clones (PB 260, RRIM 2020, RRIM 901 and RRIM 929). The assay was also performed on clones that are relatively more resistant
to the fungus (RRIM 600 and GT-1), and the results were as expected. Thus, we have successfully demonstrated that the cassicolin-specific
scFv can effectively reduce cassicolin toxicity. 相似文献
999.
We investigated C management index (CMI; an indicator of sustainability of a management system and is based on total and labile
C) and soil aggregation in medium-textured soils (silt loam and silty clay loam) under different cropping systems as follows:
maize-wheat (M-W), rice-wheat (R-W), soybean-wheat (S-W), Guinea grass, and Setaria grass. Field experiments were 6–32 years
long and were located in the wet-temperate zone of northwest Himalayas. The plant nutrients were applied through chemical
fertilizers (urea, superphosphate, and muriate of potash) with or without organic materials (FYM, wheat straw, and Lantana spp.). The content of total C (CT), labile C (CL), CMI, mean weight diameter (MWD), and aggregate porosity varied significantly under different cropping systems. The range
was 1.59 (R-W)–4.29% (Setaria) for CT, 1.23 (R-W)–3.89 mg/kg (Guinea grass) for CL, 52.09 (R-W)–129.77 (Guinea grass) for CMI, 0.90 (R-W)–5.09 (Guinea grass) for MWD, and 41.5 (R-W)–56.8% (S-W) for aggregate
porosity. Aggregate porosity was highest (56.8%) under S-W, followed by grasses (50.1–51.2%), and M/R-W (41.5–50.0%). As per
these data, (a) continuous use of N alone as urea lowered soil sustainability over control (no fertilizers); (b) use of NPK
at recommended rates improved soil productivity over control; (c) the NPK + organic amendments further improved soil sustainability;
and (d) the sustainability under different cropping systems followed the order: perennial grasses > soybean-wheat > maize-wheat
> rice-wheat. 相似文献
1000.
Ulrich Förstner 《Journal of Soils and Sediments》2007,7(4):270-270