The substituent effects in the Birch reduction reaction of substituted benzenes are discussed. Anonplanar, boat-form conformation is suggested for the benzene radical anion formed by the transfer of an electron to a s...The substituent effects in the Birch reduction reaction of substituted benzenes are discussed. Anonplanar, boat-form conformation is suggested for the benzene radical anion formed by the transfer of an electron to a substituted benzene molecule. In this conformation ,the 1,4-dienyl radical anion has two double bonds isolated, the negative charge is localized on posion 6 and the single electron is on position 3, the farthest position from the negative chareg, when the substituent is electron-withdrawing. Both alkyl and alkoxy groups are considered to be electron-withdrawing. These substituents should be activating groups for their inductive effect. The reaction rate decreasing of alkyl benzenes may be cansed by reasons other than electronic effect. The reduction of benzoic acid and benzamide, in which 1,4-dihydro benzenes are obtained, is considered to be an exceptional example, in which an extra stabilized Y-aromatic radical anion may be invilved.展开更多
The mutual-belt selective cutting was conducted in the secondary poplar-birch forests. The changes of environmental factors after cutting were observed. The environmental factors of effect belts(cutting belts) of 15m ...The mutual-belt selective cutting was conducted in the secondary poplar-birch forests. The changes of environmental factors after cutting were observed. The environmental factors of effect belts(cutting belts) of 15m in width had great changes. 10-m effect belts had unnoticed changes in environmental factors. The reserved belts with 10-m effect belts had a greater increase in DBH growth rate and volume growth rate. The reserved belts for 6-m and 8-m effect belts had lower increase in DBH and volume. The environmental factors of 6-m and 8-m effect belts did not change much. comparing with their reserved belts. Cluster analysis and principal component analysis for environmental factors between each two belts were also made. and the results proved that 10-m cutting belt is the best way for management of the secondary poplar-birch forests.展开更多
This paper aims at analyzing changes in soil respiration depending on the levels of soil moisture and aeration. Organic forest soil was used in the experiments. Watering of the soil was applied starting from two initi...This paper aims at analyzing changes in soil respiration depending on the levels of soil moisture and aeration. Organic forest soil was used in the experiments. Watering of the soil was applied starting from two initial moisture contents: 1) GWC > 0.1, desiccated soil, respiration equals to zero;2) GWC between 0.46 - 0.78, moisture of the soil approximately the same as at the time of sample collection. Watering of the soil was applied once or continuously during the experiment. The experiments were conducted under both: unrestricted air-supply and anoxic conditions. Measurements of: oxygen consumption, carbon dioxide emission, and RQ were determined with a volumetric respirometer. Soil desiccation, which occurs under good access of the air, and leads to the increase of respiration rate (the “Birch effect”), is predominantly related to aerobic respiration following the change in soil aeration. If respiration of non-desiccated soil is assumed as 100%, the oxygen consumption of desiccated soil equaled to 209.90% of such value in the non-desiccated soil at the lowest moisture level, and only to 51% at the highest. Carbon dioxide emission equaled to 191.92% and 111% at the lowest and the highest moisture levels, respectively. Desiccation did not increase the respiration rate under anoxic conditions. It either decreased or remained statistically unchanged. However, obtained values of RQ index suggest that under anoxic conditions desiccation affects fermentation processes in the soil. The value of RQ index at the moisture level lower than GWC 1 was very low attaining merely 0.3 - 0.4, which suggests active fermentation processes. At higher moisture content yet, RQ value exceeded 2.展开更多
Altered drying-rewetting(DRW)procedures due to climate change may influence soil microbial properties and microbially-mediated carbon cycling in arid and semi-arid regions.However,the effects of DRW of different inten...Altered drying-rewetting(DRW)procedures due to climate change may influence soil microbial properties and microbially-mediated carbon cycling in arid and semi-arid regions.However,the effects of DRW of different intensities on the microbial properties and respiration are not well understood.Thus,the responsive patterns of microbial communities and carbon mineralization in agriculture soil on the Chinese Loess Plateau to DRW treatments with different wetting intensities(5%-25% and 5%-36%)and frequency(1-cycle to 4-cycle)were investigated.Continuous moisture levels of 5%,25% and 36% were used as control.Results revealed that the reduction of bacterial diversity and richness were greater for 5%-36% than 5%-25% treatment,while diversity of fungi was similar for different wetting intensities.Bacterial communities became clustered by wetting intensity rather than cycle number,however fungal community was unaffected by DRW.The complexity of bacterial co-occurrence network increased because of higher nodes,edges,average degree,diameter and average cluster coefficient after 4-cycles,and the interaction was more complex after 1-cycle for fungi.Rewetting caused a pulse-like increase of respiration rate,and the pulse amplitude was greater for DRW with high rewetting intensity and decreased with the increase of cycle number.The cumulative CO_(2) emission for DRW treatments was lower than that for the continuous moisture conditions.The net reduction of carbon release for 5%-36% treatment was 1.18 times higher than that for 5%-25% treatment.Our study provides experimental evidence of the positive potential of DRW processes for maintaining soil carbon stock in an agriculture system on the Loess Plateau.展开更多
文摘The substituent effects in the Birch reduction reaction of substituted benzenes are discussed. Anonplanar, boat-form conformation is suggested for the benzene radical anion formed by the transfer of an electron to a substituted benzene molecule. In this conformation ,the 1,4-dienyl radical anion has two double bonds isolated, the negative charge is localized on posion 6 and the single electron is on position 3, the farthest position from the negative chareg, when the substituent is electron-withdrawing. Both alkyl and alkoxy groups are considered to be electron-withdrawing. These substituents should be activating groups for their inductive effect. The reaction rate decreasing of alkyl benzenes may be cansed by reasons other than electronic effect. The reduction of benzoic acid and benzamide, in which 1,4-dihydro benzenes are obtained, is considered to be an exceptional example, in which an extra stabilized Y-aromatic radical anion may be invilved.
文摘The mutual-belt selective cutting was conducted in the secondary poplar-birch forests. The changes of environmental factors after cutting were observed. The environmental factors of effect belts(cutting belts) of 15m in width had great changes. 10-m effect belts had unnoticed changes in environmental factors. The reserved belts with 10-m effect belts had a greater increase in DBH growth rate and volume growth rate. The reserved belts for 6-m and 8-m effect belts had lower increase in DBH and volume. The environmental factors of 6-m and 8-m effect belts did not change much. comparing with their reserved belts. Cluster analysis and principal component analysis for environmental factors between each two belts were also made. and the results proved that 10-m cutting belt is the best way for management of the secondary poplar-birch forests.
文摘This paper aims at analyzing changes in soil respiration depending on the levels of soil moisture and aeration. Organic forest soil was used in the experiments. Watering of the soil was applied starting from two initial moisture contents: 1) GWC > 0.1, desiccated soil, respiration equals to zero;2) GWC between 0.46 - 0.78, moisture of the soil approximately the same as at the time of sample collection. Watering of the soil was applied once or continuously during the experiment. The experiments were conducted under both: unrestricted air-supply and anoxic conditions. Measurements of: oxygen consumption, carbon dioxide emission, and RQ were determined with a volumetric respirometer. Soil desiccation, which occurs under good access of the air, and leads to the increase of respiration rate (the “Birch effect”), is predominantly related to aerobic respiration following the change in soil aeration. If respiration of non-desiccated soil is assumed as 100%, the oxygen consumption of desiccated soil equaled to 209.90% of such value in the non-desiccated soil at the lowest moisture level, and only to 51% at the highest. Carbon dioxide emission equaled to 191.92% and 111% at the lowest and the highest moisture levels, respectively. Desiccation did not increase the respiration rate under anoxic conditions. It either decreased or remained statistically unchanged. However, obtained values of RQ index suggest that under anoxic conditions desiccation affects fermentation processes in the soil. The value of RQ index at the moisture level lower than GWC 1 was very low attaining merely 0.3 - 0.4, which suggests active fermentation processes. At higher moisture content yet, RQ value exceeded 2.
基金financially supported by the Hundred-talent Project of the Chinese Academy of Sciences(A315021407).
文摘Altered drying-rewetting(DRW)procedures due to climate change may influence soil microbial properties and microbially-mediated carbon cycling in arid and semi-arid regions.However,the effects of DRW of different intensities on the microbial properties and respiration are not well understood.Thus,the responsive patterns of microbial communities and carbon mineralization in agriculture soil on the Chinese Loess Plateau to DRW treatments with different wetting intensities(5%-25% and 5%-36%)and frequency(1-cycle to 4-cycle)were investigated.Continuous moisture levels of 5%,25% and 36% were used as control.Results revealed that the reduction of bacterial diversity and richness were greater for 5%-36% than 5%-25% treatment,while diversity of fungi was similar for different wetting intensities.Bacterial communities became clustered by wetting intensity rather than cycle number,however fungal community was unaffected by DRW.The complexity of bacterial co-occurrence network increased because of higher nodes,edges,average degree,diameter and average cluster coefficient after 4-cycles,and the interaction was more complex after 1-cycle for fungi.Rewetting caused a pulse-like increase of respiration rate,and the pulse amplitude was greater for DRW with high rewetting intensity and decreased with the increase of cycle number.The cumulative CO_(2) emission for DRW treatments was lower than that for the continuous moisture conditions.The net reduction of carbon release for 5%-36% treatment was 1.18 times higher than that for 5%-25% treatment.Our study provides experimental evidence of the positive potential of DRW processes for maintaining soil carbon stock in an agriculture system on the Loess Plateau.
