UV-B辐射促进红壤水稻土中碳氮转化

以母质相同而有机质含量不同的两种水稻土(高有机质土,HO;低有机质土,LO)为对象,研究了三种强度的紫外(UV-B)辐射对两种土壤碳、氮转化的影响。结果表明:随着UV-B辐射强度的增加,土壤有机碳(TOC)含量降低,而可溶性有机碳(DOC)含量增加;UV-B辐射促进了土壤有机碳的降解和硝态氮的增加。在高强度的UV-B(2.83 W·m^(-2))辐射处理96 h后,LO和HO土壤的TOC含量分别减少了9.89%和10.16%,而DOC含量分别提高了39.24%和50.50%;同样辐射条件下,LO和HO土壤NO_3^--N含量分别比接受辐射前增加了74.48%和81.87%。因此,在农业生产中为了保护土壤碳库,减少氮素损失,应尽量避免地表裸露以降低UV-B辐射对土壤碳、氮转化的影响。

Transformation of Carbon and Nitrogen by Earthworms in the Decomposition Processes of Broad-leaved Litters

Earthworms are the important constituents in the decayed food web and the main ecological conditioners in the process of decomposition and nutrient mineralization. The transformation of organic carbon (C) and total nitrogen (N) in the broad-leaved litters ingested by earthworms was researched by means of a laboratory experiment. Experimental samples were collected from broad-leaved Korea Pine mixed forest in Liangshui National Natural Reserve (47°10′50″N, 128°53′20″E) in the northeastern Xiao Hinggan Mountains of Northeast China. The contents of organic C and total N in earthworms, leaf litters and earthworm faeces were analyzed. Results show that the organic C content was in the fol- lowing order: leaf litters>faeces>earthworms, while total N content was contrary to that of the organic C. The organic C contents in the different leaf litters were in the following order: Tilia amurensis>Betula costata>Acer mono, whereas the total N contents in the different leaf litters were: Betula costata>Tilia amurensis>Acer mono. The contents of organic C and total N in the faeces from the different leaf litters were almost consistent with the contents of the leaf litters. After the leaf litters were ingested by earthworms, the organic C, which was transformed to increase earthworms' weights, ac- counted for 3.90%-13.31% of the total ingestion by earthworms, while that in the earthworm faeces accounted for 6.14%-13.70%. The transformed organic C through the other metabolism (e.g., respiration) of earthworms accounted for 75.04%-89.92%. The ingested organic C by earthworms was mostly used for metabolic activities. The N ingested by earthworms was less than organic C. It is estimated that 37.08% of total N was transformed to increase the earthworm's weight, 19.97% into earthworm faeces and 47.86% for the consumption of the earthworm's activities. The earthworms not only increased the content of organic C and total N in the soil, but also decreased the values of C/N in the soil and leaf litters. Earthworms play a major role in the leaf litters' decomposition and transformation.

Carbon and Nitrogen Transformations in Surface Soils Under Ermans Birch and Dark Coniferous Forests

Soil samples were taken from an Ermans birch （Betula ermanii）-dark coniferous forest （Picea jezoensis and Abies nephrolepis） ecotone growing on volcanic ejecta in the northern slope of Changbai Mountains of Northeast China, to compare soil carbon （C） and nitrogen （N） transformations in the two forests. The soil type is Umbri-Gelic Cambosols in Chinese Soil Taxonomy. Soil samples were incubated aerobically at 20℃ and field capacity of 700 g kg^-1 over a period of 27 weeks. The amount of soil microbial biomass and net N mineralization were higher in the Ermans birch than the dark coniferous forest （P 〈 0.05）, whereas the cumulative C mineralization （as CO2 emission） in the dark coniferous forest exceeded that in the Ermans birch （P 〈 0.05）. Release of the cumulative dissolved organic C and dissolved organic N were greater in the Ermans birch than the dark coniferous forest （P 〈 0.05）. The results suggested that differences of forest types could result in considerable change in soil C and N transformations.

无泡充氧膜生物反应器对生活污水处理效果的研究

针对低碳氮比的实际生活污水,设计了一种以疏水性微孔膜作为无泡充氧和生物膜载体的膜生物反应器,研究了水力停留时间(HRT)、充氧方式、水温对反应器处理效果的影响,并探究碳、氮元素的转化途径。结果表明,在HRT为24 h、水流速度为0.068 m/s、水温为28~36℃、DO为(1.6±0.2)mg/L、充氧强度为0.035 MPa条件下,系统对COD、NH4^+-N和总氮的平均去除率可分别达到85.43%、72.22%、57.95%。在碳、氮元素的转化途径上,污水在通过由无泡充氧形成的生物膜的不同氧浓度梯度分层结构后,可进行同步硝化反硝化,对氨氮的去除主要依靠硝化菌完成,去除率为72.18%,对TN的去除率约为56%,而在反硝化过程中COD主要作为碳源被大量消耗,平均去除率达到85%以上。反应器主要耗能为空压机、循环泵和进水隔膜泵的电耗,无泡充氧的氧体积传质系数约为传统鼓泡式充氧的8.7倍,节约充氧电耗的潜能可达88.5%。

Role of Carbon Substrates Added in the Transformation of Surplus Nitrate to Organic Nitrogen in a Calcareous Soil

Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizers or manures used in combination with low carbon inputs. We investigated the potential of different carbon substrates added to transform soil nitrate into soil organic N （SON）. A 56-d laboratory incubation experiment using the 15N tracer （K15NO3） technique was carried out to elucidate the proportion of SON derived from accumulated soil nitrate following amendment with glucose or maize straw at controlled soil temperature and moisture. The dynamics and isotopic abundance of mineral N （NO3 and NH4＋） and SON and greenhouse gas （N20 and CO2） emissions during the incubation were investigated. Although carbon amendments markedly stimulated transformation of nitrate to newly formed SON, this was only a substitution effect of the newly formed SON with native SON because SON at the end of the incubation period was not significantly different （P 〉 0.05） from that in control soil without added C. At the end of the incubation period, amendment with glucose, a readily available C source, increased nitrate immobilization by 2.65 times and total N20-N emission by 33.7 times, as compared with maize straw amendment. Moreover, the differences in SON and total N20-N emission between the treatments with glucose and maize straw were significant （P 〈 0.05）. However, the total N20-N emission in the straw treatment was not significantly （P ~ 0.05） greater than that in the control. Straw amendment may be a potential option in agricultural practice for transformation of nitrate N to SON and minimization of N20 emitted as well as restriction of NO3-N leaching.

Lewis base-CO2 adducts as organocatalysts for CO2 transformation

In the recent decade, the development and application of organocatalysis for CO_2 transformation into useful chemicals have attracted much attention. Among these organocatalysts, Lewis base-CO_2 adducts(LB-CO_2) were found to be more efficient.The used Lewis base has great effect on the catalytic activity of its CO_2 adduct. This review reports the recent progress in LB-CO_2 adducts catalyzed the cyclization of CO_2 with epoxides or aziridines to afford cyclic carbonates or oxazolidinones,the carboxylation of CO_2 with propargylic alcohols to α-alkylidene cyclic carbonates, and the reduction of CO_2 to methanol,formamides and methylamines, with the focus on the catalytic mechanism.