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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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本文以甜高粱秸秆汁为主要的发酵原料,对热带假丝酵母SG-1在15-L罐上产单细胞蛋白(SCP)的分批补料发酵过程进行研究。首先对分批发酵模式下的菌体代谢过程变化进行研究。研究发现,接种后菌体快速进入繁殖阶段,但是总糖在12 h处于耗竭状态,使得菌体量和SCP产量过早的在18 h就达到峰值。基于此,在15-L罐上建立了热带假丝酵母SG-1产SCP的分批补料发酵模式。结果表明:菌体代谢因基质的补加而得到进一步的延续,放罐时(42 h)其菌体干重和SCP产量分别达19.86 g/L和9.93 g/L,显著高于分批发酵模式的10.45 g/L和4.70 g/L。 相似文献
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为了研究葡萄糖对水热炭化反应过程和水热焦形成的影响,以麦秆为原料,利用高温高压反应釜,对麦秆在葡萄糖水溶液环境中的炭化反应过程和水热焦理化结构演变及液相产物主要组分浓度分布的变化进行了分析。研究发现,在反应温度220℃,停留时间120 min条件下,随着葡萄糖添加量的增加,水热焦产率和碳质量分数有所增加,而氢和氧质量分数未发生明显改变,当葡萄糖添加量为麦秆质量的0.4倍时,水热焦产率达68.56%;葡萄糖分子阻碍了麦秆中主要化学组分的分解与炭化反应,使得水热焦炭聚合物的红外吸收特征峰减弱,同时XRD衍射峰强度降低,热稳定性下降,如选择水热炭化过程水循环利用,可进行可溶性糖分离;在麦秆与葡萄糖共同水热炭化过程中,葡萄糖以分解反应为主,同未添加葡萄糖的麦秆水热炭化液相产物相比,糠醛、5-HMF和乙酸的质量浓度均有所增加,其中5-HMF增加最为显著,至葡萄糖添加量为4 g时,达20.21 g/L。 相似文献
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Chin-Chyuan Chang Zhi-Rong Wu Cheng-Shou Chen Ching-Ming Kuo Winton Cheng 《Aquaculture (Amsterdam, Netherlands)》2007,270(1-4):333-342
Levels of glucose, lactate, pO2, pCO2, HCO3−, TCO2, Na+, K+, Cl−, protein, and oxyhemocyanin in the hemolymph and its osmolality and pH were measured when tiger shrimp, Penaeus monodon (13.5 ± 1.5 g body weight), were individually injected with saline or dopamine at 10− 8, 10− 7, or 10− 6 mol shrimp− 1. Results showed that hemolymph glucose, lactate, pCO2, HCO3−, and TCO2 values increased from 2 to 4 h; hemolymph osmolality, Na+, and total protein had increased at 2 h; and hemolymph K+ decreased from 2 to 8 h after the dopamine injection. All physiological parameters returned to the control values 4–16 h after receiving dopamine. The dopamine injection also significantly decreased the oxyhemocyanin/protein ratio of P. monodon which occurred at 2 h, resulting from an elevation of hemolymph protein and a slight decrease of oxyhemocyanin. These results suggest that stress-inducing dopamine caused a transient period of modulation of energy metabolism, osmoregulation, respiration, and the acid–base balance in P. monodon in adapting to this environmental stress. 相似文献
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[目的]研究喷施蔗糖对蓝莓叶片和果实中可溶性糖含量变化的影响。[方法]以不同类型的2个蓝莓品种为试材,分析了喷施不同浓度(0.1%、0.5%和1.0%)的蔗糖溶液对蓝莓果实发育期叶片和果实中可溶性糖含量、组成的影响,并进行了相关性分析。[结果]在整个果实发育过程中(蓝丰:5月初~7月中旬;粉蓝:5月底~8月中旬),2品种叶片中可溶性糖总含量逐渐增加,但各个可溶性糖含量变化规律有所不同;2个品种果实成熟时期主要是积累葡萄糖和果糖为主,蔗糖含量很少,葡萄糖和果糖含量相当,并且随着果实的发育,各处理都可以不同程度地增加蓝莓果实的可溶性糖含量,其中喷施0.5%的蔗糖溶液增加最多;通过对各个处理叶片和果实可溶性糖含量的相关性分析可以看出,叶片和果实中可溶性糖含量显著相关。[结论]叶片喷施0.5%浓度的蔗糖对增加蓝莓果实中的糖度提高最多。 相似文献
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在红肉脐橙幼果期和着色前分2次喷施不同浓度的外源 ABA和 GA3,研究其对红肉脐橙果肉糖含量的影响。结果表明:10 mg/L ABA处理显著或极显著提高了果实成熟时的葡萄糖、果糖和总糖含量,50 mg/L ABA处理极显著提高了果实蔗糖含量,而100 mg/L ABA处理极显著降低了果实葡萄糖含量;中低浓度的 GA3(10、50和250 mg/L)极显著提高了果实蔗糖含量,10 mg/L GA3处理对果实葡萄糖和果糖含量无明显影响,但极显著提高了果实总糖含量,50、250和500 mg/L GA3处理极显著降低了果实葡萄糖、果糖和总糖含量。表明着色前较低浓度的外源 ABA处理(10和50 mg/L)可提高果实中一种或几种糖的含量,而较高浓度的 GA3处理(250和500 mg/L)则严重阻碍了果肉中糖的积累。 相似文献