影响土壤真菌多样性的土壤因素

土壤真菌是土壤微生物的重要组成部分,常作为衡量土壤肥力好坏的指标。采用标准土壤养分测定方法研究了土壤速效养分、有机肥、含水量、土壤质地对土壤真菌多样性的影响,以期为保护地蔬菜合理种植、防治土传病害提供理论依据。结果表明:在土壤因子中,以有机肥含量对土壤真菌的数量和种类的影响最大,相关系数分别为0.976和0.960。而其他土壤因子与真菌数量和种类关系不大。同时采用形态标准鉴定出24属74种真菌,分别为疫霉(Phytophthora)、毛霉(Mucor)、共头霉(Syncephalastrum)、毛壳(Chaetomium)、青霉(Penicillium)、曲霉(Aspergillus)、镰孢菌(Fusarium)、枝顶孢(Acremonium)、炭疽菌(Colletorichum)、头孢霉(Cephalosporium)、被毛枝葡萄孢(Botryotrichum)、漆斑菌(Myrothecium)、被孢霉(Mortierella)、细基束梗霉(Cephalotrichum)、圆酵母(Torula)、粘帚霉(Gliocladium)、毁丝霉(Myceliophthora)、金孢(Chrysoporium)、轮枝菌(Vertillium)、弯颈霉(Tolypocladium)、腐质霉(Humicola)、葡萄穗霉(Stachybotrys)、木霉(Ttrichoderma)和丝核菌(Rhizoctonia)。

土壤呼吸主要影响因素的研究进展

影响土壤呼吸的因子有很多,在不同时间空间的不同生态系统其影响因子各不相同。综述了土壤呼吸主要影响因子的研究进展,主要从土壤温度、土壤湿度、降水、土壤C/N等非生物因子,植被类型、生物量、叶面积指数、植被凋落物等生物因子以及人类活动等方面阐述对土壤呼吸产生的影响。在此基础上对土壤呼吸的Q10值、关键影响因子及各种生态环境因子的综合影响进行了讨论。从众多研究中发现土壤温度、湿度是影响土壤呼吸的主要因子,建立土壤温度及湿度影响下的土壤呼吸模型更有助于对土壤呼吸进行定量的描述。但是在土壤温度及湿度过高或过低的情况下会出现较大的误差,为了尽量减少土壤呼吸的误差,给出了如下建议:①加强土壤呼吸和生态系统自动碳通量的结合研究;②加强对不同生物和非生物生态环境因子的同步测定,特别重视生物因子对非生物因子的调节和影响;③加强典型物候期和不同季节典型天气土壤呼吸的测定;④加强模拟试验研究和模式研究。总之,土壤呼吸是一个比较复杂的过程,虽然有规律可循,但是,很多时候由于因子间交互作用而表现偏离,对其准确估算需要找出关键因子,并综合分析其它因子的影响。

大庆市碱草草场主要土壤环境因子对土壤呼吸的影响

影响土壤呼吸的因子有很多,在不同时间空间的不同生态系统其影响因子各不相同。本文研究了土壤呼吸的主要影响因子,包括地温、土壤湿度等非生物因子。发现地温、湿度是影响大庆市碱草草场土壤呼吸的主要因子,并从而建立了以地温及湿度为影响因子的土壤呼吸定量描述模型。

Research Advance on Influencing Factors of Crop Water Use Efficiency

The research advance on the influencing factors of crop water use effi-ciency （WUE） was reviewed in this paper. Based on the discussion on the conno-tation of crop WUE, the influencing factors of crop WUE, such as crop, environ-ment, chemicals, cultivation measures, cropping systems, etc, were elaborated. A-mong them, the species and varieties of crop, soil and chemicals were discussed in detail.

Available Contents of Trace Nutrient Element and Factors Affecting Their Availability in Western Jilin

Based on the assay of the total content and available content of the trace nutrient elements and the soil pH and organic matter of the soil samples,the characteristic of the available content of the trace nutrient elements and their affecting factors are studied. The results show that the available B in western Jilin is in a middle level,the content in Nong'an is higher than that in the others; the available Mn is extremely abundant; the available Cu in Nong'an is obviously higher than other areas,and the content in Da'an differs greatly; the available Zn is in a middle level; the severe shortage of available Mo differs between different areas; and the available Fe is extremely abundant. The available Mn,Cu and Fe have significantly positive correlation with their total content; the available B has significantly positive correlation with pH,and Zn has obviously negative correlation with pH; the available Mn and Fe had significantly positive correlation with soil organic matter.

Wien Effect in Suspensions of Electrodialyzed Soil Particles and Its Influencing Factors

The electrical conductivity of suspensions and their supernatants from theelectrodialyzed clay fractions of latosol, yellow-brown soil and black soil equilibrated withnitrate solutions were determined at different field strengths using a short high-voltage pulseapparatus to demonstrate the Wien effect in soil suspensions and to investigate factors affectingit. It was found that Wien effect was much stronger in suspensions with a clay content of 30 gkg^(-1) from the soils equilibrated with a 1 X 10^(-4) KNO_3 solution than in their supernatants.The threshold field strength (TFS), at which the relative conductivity is equal to 1.05, i.e., theWien effect begins to be obvious, of the yellow-brown soil suspensions (clay content of 30 gkg^(-1)) equilibrated with different nitrate solutions of a concentration of 1 X 10^(-4)/z molL^(-1), where z is the valence, varied with the type of nitrates, being lowest for NaNO_3 (47 kVcm^(-1)) and highest for Ca(NO_3)_2 (98 kV cm^(-1)). At high field strengths (larger than 130 kVcm^(-1)), the relative conductivities of yellow-brown soil suspensions containing different nitratesdiminished in the order: NaNO_3 > KNO_3 > Mg(NO_3)_2 > Zn(NO_3)_2 > Ca(NO_3)_2. The rates andintensities of the Wien effect in the suspensions of the three soils equilibrated with 5 X 10^(-5)mol L^(-1) Ca(NO_3)_2 solution were in the order of the yellow-brown soil > the latosol > the blacksoil. The results for the yellow-brown soil suspensions (clay concentration of 30 g kg )equilibrated with KNO_3 solutions of various concentrations clearly demonstrated that the moredilute the solution, the lower the TFS, and the larger the relative conductivity of the suspensionsat high field strengths. The results for yellow-brown soil suspensions with different clayconcentrations indicated that as the clay concentration increased, the low field electricalconductivity, EC_0, also increased, but the TFS decreased, and the Wien effect increased.

Factors Affecting Phytoextraction： A Review

Hyperaccumulators concentrate trace metals and heavy metals in their shoots when grown in metal-contaminated soils and these trace metal-loaded plants may be removed by harvesting the fields. Studies exploring the beneficial role of these hyperaccumulators to clean up the environment have led to the development of phytoextraction. The success of phytoextraction depends upon the high biomass of plant species and bioavailability of metals for plant uptake. The phytoavailability of metals is influenced by soil- associated factors, such as pH, redox potential, cation exchange capacity, soil type, and soil texture, and by plant-associated factors, such as root exudates and root rhizosphere processes （microorganisms）. Efficiency of phytoextraction can be improved by advanced agronomic practices including soil and crop management by application of genetic engineering to enhance the metal tolerance, shoot translocation, accumulation, and sequestration and by application of chelate treatments to enhance metal bioavailability. Application of microorganisms including bacteria and mycorrhiza may facilitate the phytoextraction application at commercially large scale.

Factors Affecting the Occurrence of Palygorskite in Central Iranian Soils Developed on Tertiary Sediments

Limited information is available on the distribution and origin of palygorkite in soils developed on Tertiary sediments as the major soil parent materials in central Iran and other Middle Eastern countries. The objectives of this study were to determine the distribution and origin of palygorskite in soils developed on Tertiary sediments, and to identify the major soil properties that influence palygorskite distribution in the soils studied. Sixteen soil profiles developed on Paleocene, Eocene, Oligocene, Oligocene-Miocene, Miocene and Pliocene sediments were studied by X-ray diffraction analysis, transmission electron microscope, and scanning electron microscopy. Physicochemical characteristics of the soils and sediments including particle size distribution, pH, electrical conductivity, organic carbon, gypsum, carbonates, and soluble Si, Ca and Mg were determined. The principal component analysis was used to establish the relationships between palygorskite and the physicochemical characteristics of the soils studied. Results showed that clay fraction of all the soils in the study area was dominated by palygorskite. The highest amount of palygorskite was found in horizons where simultaneous accumulation of both carbonates and gypsum occurred. Limited amount of palygorskite was found in salic and calcic horizons. Palygorskite seemed to be of eolian origin in the surface horizon of all the soils. Using principal component analysis, the soluble Mg/Ca ratio, pH, soluble Si and gypsum contents were identified as the most important factors affecting the distribution and genesis of palygorskite in the soils studied. Results might suggest the neoformation of palygorskite by precipitation from solutions in which evaporation fluxes were very high. However, palygorskite in soils developed on Tertiary sediments in central Iran seems to be of both inherited and pedogenic origins.