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1.
Fungal N2O production results from a respiratory denitrification that reduces NO3−/NO2− in response to the oxidation of an electron donor, often organic C. Despite similar heterotrophic nature, fungal denitrifiers may differ from bacterial ones in exploiting diverse resources. We hypothesized that complex C compounds and substances could favor the growth of fungi over bacteria, and thereby leading to fungal dominance for soil N2O emissions. Effects of substrate quality on fungal and bacterial N2O production were, therefore, examined in a 44-d incubation after soils were amended with four different substrates, i.e., glucose, cellulose, winter pea, and switchgrass at 2 mg C g−1 soil. During periodic measurements of soil N2O fluxes at 80% soil water-filled pore space and with the supply of KNO3, substrate treatments were further subjected to four antibiotic treatments, i.e., no antibiotics or soil addition of streptomycin, cycloheximide or both so that fungal and bacterial N2O production could be separated. Up to d 8 when antibiotic inhibition on substrate-induced microbial activity and/or growth was still detectable, bacterial N2O production was generally greater in glucose- than in cellulose-amended soils and also in winter pea- than in switchgrass-amended soils. In contrast, fungal N2O production was more enhanced in soils amended with cellulose than with glucose. Therefore, fungal-to-bacterial contribution ratios were greater in complex than in simple C substrates. These ratios were positively correlated with fungal-to-bacterial activity ratios, i.e., CO2 production ratios, suggesting that substrate-associated fungal or bacterial preferential activity and/or growth might be the cause. Considering substrate depletion over time and thereby becoming limited for microbial N2O production, measurements of soil N2O fluxes were also carried out with additional supply of glucose, irrespective of different substrate treatments. This measurement condition might lead to potentially high rates of fungal and bacterial N2O production. As expected, bacterial N2O production was greater with added glucose than with added cellulose on d 4 and d 8. However, this pattern was broken on d 28, with bacterial N2O production lower with added glucose than with added cellulose. In contrast, plant residue impacts on soil N2O fluxes were consistent over 44-d, with greater bacterial contribution, lower fungal contribution, and thus lower fungal-to-bacterial contribution ratios in winter pea- than in switchgrass-amended soils. Real-time PCR analysis also demonstrated that the ratios of 16S rDNA to ITS and the copy numbers of bacterial denitrifying genes were greater in winter pea- than in switchgrass-amended soils. Despite some inconsistency found on the impacts of cellulose versus glucose on fungal and bacterial leading roles for N2O production, the results generally supported the working hypothesis that complex substrates promoted fungal dominance for soil N2O emissions. 相似文献
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[目的]研究添加麸皮与纤维素酶对笋壳青贮后氰甙含量的影响。[方法]采用异烟酸—吡唑啉酮比色法研究添加麸皮与纤维素酶对笋壳青贮后氰甙含量的影响。[结果]添加麸皮与纤维素酶均可降低笋壳青贮后的氰甙含量。麸皮添加水平越高,青贮笋壳毒性越低,当麸皮添加水平为15%时笋壳青贮后氰甙含量最低。[结论]该研究可为笋壳饲料的资源化利用提供理论依据。 相似文献
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杨木爆破处理及制板的研究 总被引:4,自引:0,他引:4
用I-72杨为原料,经高温高压爆破处理,处理后的杨木各化学组分发生变化,用不同的分析方法对各组分进行分析。在不加任何化学助剂的条件下,依靠自身化学组分的转化,对爆破处理过的试材,经热压制出刨花板。分析研究压板前后化学组成变化和板材物理力学性质,其结果为:①比较不同爆破条件下,同一种试样化学组成的变化,爆破条件越激烈,纤维素降解越显著,收获率超低;游离糖则相应增加;木质素含量先增加,然后降低;热水抽出物含量也是先增加,然后再降低。②扫描电镜观察爆破处理后的试样,纤维排列有变化,整齐的排列变为弯曲和分开。③经爆破处理的试样相对结晶度增加,结晶区增加。总之,爆破后的试材可压制出耐水性能好的刨花板。 相似文献
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This study examined how boiling and drying treatments influenced various physical properties of the tension wood with gelatinous
fibers (G-fibers) of a 29-yearold Zelkova branch. By boiling treatment, tension wood with numerous G-fibers contracted considerably in the longitudinal direction and
the longitudinal Young’s modulus decreased in spite of the water-saturated condition. The drying treatment caused green tension
wood and boiled tension wood with numerous G-fibers to shrink longitudinally and increased their longitudinal Young’s moduli.
These specific behaviors in tension wood were highly correlated with the proportion of G-fibers in a specimen and were probably
caused by the microscopic behavior of cellulose microfibril (CMF) in the gelatinous layers (G-layers). The longitudinal shrinkage
of tension wood due to drying suggests the existence of a hygro-sensible, noncrystalline region in the CMF, which is abundant
in the G-layer. Furthermore, the noncrystalline region in the CMF softens during boiling treatment, resulting in the reduction
of the longitudinal Young’s modulus in tension wood. The longitudinal contraction of tension wood with G-fibers by boiling
might be caused by the tensile growth stress remaining in green G-layers. However, no changes were detected in the 004 d-spacing of cellulose crystal in tension wood from the boiling and drying treatments, regardless of the proportion of G-fibers. 相似文献
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天然木质微/纳纤丝增强纳米复合材料的研究现状 总被引:4,自引:0,他引:4
纤维素是世界上最丰富、可再生且能生物分解的天然高分子聚合物,其强度主要来源于镶嵌于木素和半纤维素形成的基质结构中的微/纳纤丝或针状晶体——一种完美的高强度的纳米晶体结构。近二十多年来,如何从纤维素中分离微/纳纤丝和用其来增强高分子聚合物受到许多学者的关注。本文简要叙述了木质微/纳纤丝的分离和性能评价方法以及其增强的纳米复合材料的制备和特性检测手段。 相似文献
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The chemical conversion of Japanese beech (Fagus crenata Blume) in water-added supercritical methanol was studied for a wide range of water content using a batch-type reaction vessel to obtain chemicals from lignocellulosics. It was consequently found that addition of water enhanced the decomposition of wood cell wall components; cellulose, hemicelluloses, and lignin. In cases of high water content, however, it resulted in low solubility of lignin-derived products causing an increase in the mass of the residue. The water content was thus optimized to be around 10% (v/v) for the decomposition of wood. Concomitantly, the yields and selectivity of the chemicals from wood could be regulated by the addition of water, especially for the lignin-derived products. As a result, the monomeric compounds of lignin, coniferyl alcohol and sinapyl alcohol, were recovered as their γ-methyl ethers in the presence of water in higher yields than those obtained without addition of water. 相似文献