A comparison of regression methods for estimating soil-atmosphere diffusion gas fluxes by a closed-chamber technique

Continuous changes in methane (CH₄) and carbon dioxide (CO₂) concentrations inside a closed chamber were measured on the forest floor at three sites: a deciduous forest and a coniferous forest in Hokkaido, Japan, and a birch forest in West Siberia, Russian Federation. Flux estimations by three types of regression methods, exponential, nonlinear, and linear, were examined using field-collected concentration data. The pattern of change with time of the gas concentration in the headspace differed, mainly according to site but also, to a lesser extent, according to the gas. This was a function of both the chamber height and surface soil property relating to soil gas diffusion and the gas concentration profile. Flux estimations did not differ statistically between the exponential and nonlinear methods for either gas at any site, because both of those regression methods were based on diffusion theory. However, the flux values estimated by linear regression were significantly different from those estimated by the other two methods for both CH₄ and CO₂ at the deciduous forest site and for CO₂ at the coniferous forest site. Shortening the chamber deployment period improved the linearity of the curve, but did not completely eliminate the error. Our results suggest that linear regression is not a good model of the change in headspace concentration with time.     

Mineralization of hydroxylated isoproturon metabolites produced by fungi

When exposed to the herbicide isoproturon, some soil fungi in pure culture metabolize the substance to hydroxylated metabolites. Hydroxylated metabolites of isoproturon have also been detected in soil studies. In an agricultural soil not previously exposed to isoproturon we found that the hydroxylated isoproturon metabolite N-(4-(2-hydroxy-1-methylethyl)phenyl)-N′,N′-dimethylurea mineralized faster than both isoproturon and its N-demethylated metabolite N-(4-isopropylphenyl)-N′-methylurea (MDIPU), thus indicating that mineralization of isoproturon is stimulated by fungal hydroxylation in this soil. In soils previously treated with isoproturon, in contrast, isoproturon and both its hydroxylated and demethylated metabolites mineralized at almost the same rate with up to 52% of the ¹⁴C-ring-carbon being degraded to ¹⁴CO₂ within 63 days. Thus hydroxylated metabolites of isoproturon do not seem to be more persistent than isoproturon, and hence may degrade before they can leach from topsoil and contaminate the aquatic environment. While an isoproturon-mineralizing bacterium Sphingomonas sp. SRS2 and a MDIPU-mineralizing mixed bacterial culture were able to deplete the medium of hydroxylated metabolites, little or no mineralization took place. This indicates that other bacteria must be present in the soil that are able to benefit from isoproturon being made available to mineralization by fungal hydroxylation.     

N2O emissions from different cropping systems and from aerated,nitrifying and denitrifying tanks of a municipal waste water treatment plant

Nitrous oxide emissions, nitrate, water-soluble carbon and biological O₂ demand (BOD₅) were quantified in different cropping systems fertilized with varying amounts of nitrogen (clayey loam, October 1991 to May 1992), in an aerated tank (March 1993 to March 1994), and in the nitrification-denitrification unit (March to July 1994) of a municipal waste water treatment plant. In addition, the N₂O present in the soil body at different depths was determined (February to July 1994). N₂O was emitted by all cropping systems (mean releases 0.13–0.35 mg N₂O m^-2 h^-1), and all the units of the domestic waste water treatment plant (aerated tank 0–6.2 mg N₂O m^-2 h^-1, nitrification tank 0–204,3 mg N₂O m^-2, h^-1, denitrifying unit 0–2.2 mg N₂O m^-2 h^-1). During the N₂O-sampling periods estimated amounts of 0.9, 1.5, 2.4 and 1.4 kg N₂O–N ha^-1, respectively, were released by the cropping systems. The aerated, nitrifying and denitrifying tanks of the municipal waste water treatment plant released mean amounts of 9.1, 71.6 and 1.8 g N₂O–N m^-2, respectively, during the sampling periods.The N₂O emission were significantly positively correlated with nitrate concentrations in the field plots which received no N fertilizer and with the nitrogen content of the aerated sludge tank that received almost exclusively N in the form of NH ₄ ⁺ . Available carbon, in contrast, was significantly negatively correlated with the N₂O emitted in the soil fertilized with 80 kg N ha^-1 year. The significant negative correlation between the emitted N₂O and the carbon to nitrate ratio indicates that the lower the carbon to nitrate ratio the higher the amount of N₂O released. Increasing N₂O emissions seem to occur at electron donorto-acceptor ratios (C_H2_O or BOD₅-to-nitrate ratios) below 50 in the cropping systems and below 1200–1400 in the waste water treatment plant. The trapped N₂O in the soil body down to a depth of 90 cm demonstrates that agricultural production systems seem to contain a considerable pool of N₂O which may be reduced to N₂ on its way to the atmosphere, which may be transported to other environments or which may be released at sometime in the future.Dedicated to Professor J.C.G. Ottow on the occasion of his 60th birthday     

地膜覆盖对土壤中N2O释放的影响

研究地膜覆盖下土壤中N₂O释放可为进一步探明膜下土壤中N₂O的传输、消耗和排放到大气的动力学过程提供理论依据。在2001年3月至6月和2001年10月至2002年6月连续两个冬小麦生长季，采用静态漏斗法和揭膜—封闭箱法测定了地膜覆盖下耕层5、10、20 cm土层处和地表处N₂O的释放特征及相应土壤性质。结果表明：地膜覆盖下，地表和耕层10、20 cm土层处N₂O释放通量显著增加；0～5 cm土层土壤水分和10～20 cm土层土壤硝态氮的浓度的变化分别解释了休闲地和冬小麦地土壤中N₂O释放通量85.23%和92.11%的变异，它们是膜下休闲地和冬小麦地土壤中N₂O释放通量增加的主要原因。该结论对地膜覆盖下科学地控制农田水分、养分以及地膜覆盖在中国西北地区的科学使用和推行具有实际意义。     

CO_2浓度、氮素和水分对春小麦碳素固定的影响

试验设350μmolmol-1和700μmolmol-12种CO2浓度水平,湿润、干旱2种水分处理和施N0、50、100、150和200mgkg-15个水平。结果表明,CO2浓度增加,春小麦地上部碳固定量和碳固定总量均增加,但与氮肥施用水平有关。在中氮和高氮时,CO2浓度增高,地上部碳固定量和碳固定总量明显增加,而不施氮肥和低氮时,增加则不明显。不同水分处理地上部碳固定量和碳固定总量也没有明显差别,这表明,CO2浓度升高对氮素和水分胁迫及对春小麦碳固定并没有补偿作用。     

粘土土壤孔隙大小分布及其与土壤有机质的相关性

Soil pore size distribution(PSD) directly influences soil physical,chemical,and biological properties,and further knowledge of soil PSD is very helpful for understanding soil functions and processes.In this study,PSD of three clayey soils collected from the topsoil(0-20 cm) of Vertisols in Northern China was analyzed using the N_2 adsorption(NA) and mercury intrusion porosimetry(MIP) methods.The effect of soil organic matter(SOM) on the PSD of clayey soils was also evaluated.The differential curves of pore volume of clayey soils by the NA method exhibited that the pores with diameter 0.01 μm accounted for more than 50%in the pore size range of 0.001 to 0.1 μm.The differential pore curves of clayey soils by the MIP method exhibited three distinct peaks in pore size range of 60 to 100,0.3 to 0.4 and 0.009 to 0.012 μm,respectively.In the three clayey soils,the ultramicropores(5-0.1μm) were determined to be the main pore class(on average 35.5%),followed by macropores( 75 μm,31.4%),cryptopores(0.1-0.007μm,16.0%),micropores(30-5 μm,9.7%) and mesopores(75-30 μm,7.3%).The SOM greatly affected the pore structure and PSD of aggregates in clayey soils.In particular,SOM removal reduced the volume and porosity of 5-100 μm pores while increased those of 5 μm pores in the 5-2 and 2-0.25 mm aggregates of clayey soils.The increase in the volume and porosity of 5 μm pores may be attributed to the disaggregation and partial emptying of small pores caused by the destruction of SOM.     

干旱胁迫对橙红丹桂叶片光合性能的影响

采用盆栽控水法人工模拟干旱胁迫,设置土壤含水量为土壤田间持水量的15%(W1)、30%(W2)、45%(W3)、60%(W4)和充足供水(ck)5个水平,研究干旱对3年生橙红丹桂(Osmanthus fragransChenghongdangui)叶片光合性能的影响。结果表明:①干旱胁迫下,净光合速率Pn、气孔导度Gs、胞间CO2浓度Ci和蒸腾速率Tr降低,水分利用效率WUE升高;②在土壤含水量比较充足的环境条件下(W4和ck),橙红丹桂对强光(1 000~2 000μmol.m-2.s-1)有较强的耐受能力,同时对弱光(0~400μmol.m-2.s-1)也有较高的转化和利用效率;③干旱胁迫下,表观量子效率AQY、光饱和点LSP、表观羧化效率ACE降低,光补偿点LCP、CO2补偿点CCP升高。     

二冲程醇类混合燃料发动机点火提前角调节系统的研究

通过分析点火提前角对发动机性能的影响,得出使用醇类混合燃料的二冲程发动机需要改进点火系统的结论。将现阶段汽车工业在点火系统上采用的微机控制点火技术加以改进后移植到二冲程发动机上,在原点火系统中加装点火控制单元ECU并将其改造成电控点火系统。改进后的点火系统可对点火提前角进行标定,对发动机在不同转速和工况下的点火提前角进行实时调节,找到发动机在该转速和工况下的理想点火提前角。改进后的二冲程汽油机可进一步改善发动机的动力性、经济性以及排放性能。     

牡丹PsAP2基因的克隆及表达

以牡丹品种‘赵粉’为试材,采用RT-PCR和RACE方法从花瓣中获得1个牡丹APETALA2基因cDNA全长,命名为PsAP2,GenBank登录号为HM167511。序列分析结果表明:PsAP2全长2138bp,包含47bp的5'非编码区、557bp的3'非编码区和1个长度为1533bp编码510个氨基酸的开放阅读框。氨基酸序列分析显示该基因属于AP2家族。序列比对和系统进化分析表明,PsAP2与葡萄的亲缘关系最近,相似性达70%以上。相对荧光定量PCR分析表明,PsAP2在根、茎、叶和四轮花器官中均有表达。花瓣中的表达量最高,叶片中表达量最低。     

茴香脑衍生物的合成工艺研究

以茴香脑为原料经H2O:氧化合成茴香脑环氧化物2-(4-甲氧基苯基)-3-甲基环氧乙烷,产率91%,并研究了溶剂配比、物料配比、催化剂用量、反应温度、反应时间等因素对产物产率的影响.实验结果表明:乙腈与甲醇体积比为1:5、茴香脑与H2O2的物质的量之比为1:2.5、原料与无水碳酸钠的物质的量之比为1:0.8、反应时间为...