修剪频率对混播草坪土壤呼吸特征的影响

以草地早熟禾(Poa pretensis)和高羊茅(Festuca arundinacea)混播草坪为研究对象,采用开路式土壤碳通量测量系统Li-8100对不同修剪频率下草坪的土壤呼吸昼夜变化特征进行研究,旨在探讨修剪对城市草坪土壤呼吸特征的影响。结果表明:草坪在1周修剪1次、2周修剪1次和常规修剪(对照)这3种情况下,其土壤呼吸速率昼夜变化均呈单峰曲线模式,且3种情况下草坪土壤呼吸速率日最高值均出现在12:00-14:00,而日最低值出现的时间不一;从草坪土壤日呼吸总量来看,6月与7月草坪在1周修剪1次处理、2周修剪1次处理和对照之间差异均不显著,8月草坪在1周修剪1次处理下与对照之间差异不显著,而两者与草坪2周修剪1次的处理之间差异显著(P<0.05);从整体来看,3种情况下草坪的土壤呼吸速率均与5 cm土层地温成显著正相关(P<0.05),与其他温度指标的相关性因不同月份和不同处理而不同,而草坪土壤呼吸的Q₁₀值的大小基本上都随着土层深度增加而增加。     

翻耕短期内对草原土壤呼吸的影响

以呼伦贝尔草甸草原为研究对象,研究不同翻耕深度(10cm和20cm)对土壤呼吸的影响。结果表明:翻耕短期内明显加速土壤呼吸速率,且随着翻耕深度的增加而增加。在翻耕后15d内,翻耕10cm和翻耕20cm处理的土壤呼吸速率平均值分别为3.79μmol CO2/m2/s和4.78μmol CO2/m2/s,分别是天然草地的1.33和1.68倍,这种影响持续一段时间后趋于稳定。在翻耕30d后,不同处理的土壤呼吸速率间差距明显减小,天然草地、翻耕10cm和翻耕20cm处理的土壤呼吸速率,在翻耕后第30~47d内测定的平均值分别为2.23μmol CO2/m2/s、1.90μmol CO2/m2/s、2.14μmol CO2/m2/s。     

Soil salinity and sodicity effects of wastewater irrigation in South East Australia

Although ‘sewage farming’ or wastewater irrigation started in Australia in the latter parts of the 19th century, it was in the late 1960s that a considerable interest was revived in arid and semi-arid parts of the world due to scarcity of alternative water sources and the urgency to increase local food production. The practice has manifold benefits in the form of water conservation, nutrient recycling, surface and ground water pollution prevention. But for arid and semi-arid regions like many parts of Australia, while wastewater irrigation can be an attractive solution to irrigation water problems, it might not be the ideal solution for the common soil types encountered in these regions. Due to characteristic low rainfall, high evaporation and low leaching, these soils tend to have higher salt accumulations. This paper examines the soil salinity and sodicity effects of wastewater irrigation in soil types typical to South Eastern Australia and takes the soils of Western Treatment Plant (WTP) as a case study to highlight these issues.     

A nonlinear, dynamic, simulation model for transport, and whole plant allocation of systemic xenobiotics following foliar application. IV: Physicochemical properties requirements for optimum absorption and translocation

The relationship between the physicochemical properties (molar volume, partition coefficient, and dissociation constant) of slow-acting systemic postemergence xenobiotics and their uptake and translocation to the sites of action was investigated using the nonlinear, dynamic simulation model ERMESSE. When the pK_a was held constant at 4.0, the model enables the prediction of the uptake of a systemic xenobiotic as a function of its partition coefficient and molar volume. The model also considered the effects of the physicochemical properties of a systemic xenobiotic on its long-distance translocation within the vascular tissues. For instance, when the log K_ow and pK_a were held constant at 1.5 and 6.0, respectively, the model predicted a higher translocation rate (55%) for molecules with a small (e.g., MV = 100 cm³ mol⁻¹) as opposed to a large (e.g., MV = 300 cm³ mol⁻¹, 33%) molar volume. In addition, the theoretical predictions from the ERMESSE model showed that any xenobiotic with a molar volume not exceeding 300 cm³ mol⁻¹ could provide an uptake ?50% and a translocation rate ?25% when its log K_ow is between −0.5 and 2.5 and its pK_a is between 0.0 and 8.0.     

Evidence of synergy with ‘stacked’ intrarow cultivation tools

Intrarow cultivation efficacy is often low and highly variable. As the mechanisms affecting weed mortality likely vary by tool, several companies have developed cultivators with the ability to use several different intrarow tools at once. We evaluated the potential for such ‘stacking’ of cultivation tools to increase efficacy. We used different sequences of torsion weeders, finger weeders and row harrows in a test crop of maize with surrogate weeds, Sinapis alba and Panicum miliaceum. Most tool combinations resulted in an additive increase in efficacy compared with the individual tools, but the combination of torsion–finger–row harrow demonstrated a synergistic increase in efficacy. In separate experiments, forward speed, soil moisture and weed size were negatively correlated with efficacy, but the torsion–finger–row harrow combination continued to demonstrate a synergistic increase in efficacy compared with the individual tools in 7 of 11 cases. The drawback was high crop mortality (16.0 ± 1.16%); further mechanistic research is needed to reduce crop mortality while maintaining high mean efficacy, through tool design, adjustment and cultural factors.     

黄河大柳树灌区土壤类型特征与合理开发途径

该文分析了黄河大柳树灌区土壤类型形成条件与分布格局和主要土壤类型的基本特征,在此基础上结合发展灌溉农业对土壤条件的要求,提出土壤资源合理利用与发展灌溉农业的有关问题。     

Impact of great gerbils(Rhombomys opimus) on desert plant communities

Great gerbil(Rhombomys opimus) colonies, with bare soil and herbaceous plants, are conspicuous to the background environment throughout their range area. In order to quantify the engineer role of great gerbils, we investigated the plant communities of 20 active colonies in the Junggar Basin, Xinjiang, China. In areas without disturbance, desert plant communities were dominated by the shrubs with low level species richness. In burrow areas and surrounding intermediate areas, which were disturbed by great gerbils, the shrubs were suppressed with the decrease of vegetation cover and aboveground biomass. As a result, "niche gaps" were created in disturbed areas and worked as a refuge for herbaceous annuals and perennials. So the existence of great gerbils increased the overall species richness of the desert. Furthermore, herbaceous annuals and perennials are the major food source for great gerbils in spring, indicating that great gerbils have a mutually beneficial relationship with herbaceous plants.     

Diuron mineralisation in a Mediterranean vineyard soil: impact of moisture content and temperature

BACKGROUND: The diuron‐mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS: The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 °C/19.3% for maximum mineralisation rate and 21.9 °C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 °C versus 28 °C) or incubate (28 °C versus 20 °C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION: Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues. Copyright © 2010 Society of Chemical Industry     

Influence of salinity and moisture on the threshold shear velocity of saline sand in the Qarhan Desert,Qaidam Basin of China: A wind tunnel experiment

Determination of the threshold shear velocity is essential for predicting sand transport, dust release and desertification. In this study, a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand. Saline sand samples (mean particle size of 164.50-186.08 μm and the total silt, clay and salt content of 0.80%-8.25%) were collected from three saline sand dunes (one barchan dune and two linear dunes) in the Qarhan Desert, Qaidam Basin of China. Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation, respectively. Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment. The motion of sand particles was determined by the observers with a solid laser. The laser sheet (0.80 cm thick), which was emitted by the solid laser, horizontally covered the sand surface and was bound to the sand. Results show that the cohesion of saline sand results from a combination of salt and water. The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes. There is a positive linear correlation between the original moisture content and relative threshold shear velocity. The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content. Our results will provide valuable information about the sand transport of highly saline soil in the desert.     

局地尺度高寒草原土壤真菌多样性对地上植物多样性与生产力关系的调控作用

为研究局地尺度高寒草原土壤真菌多样性对地上植物多样性与生产力关系的调控作用,本研究以青海省湟源县局地尺度高寒草原为研究对象,对不同植物多样性梯度的地上生产力、土壤理化性状和土壤真菌多样性等指标进行调查、采样和分析。通过偏回归分析（partial least squares regression,PLSR）、方差分解分析（variance partitioning analysis,VPA）、构建结构方程模型（structural equation model,SEM）等分析手段,分析了土壤真菌多样性对地上植物多样性与生产力关系的调控作用。结果表明,高寒草原植物多样性与地上生产力存在显著线性正相关关系;土壤真菌多样性分别与植物多样性和地上生产力呈显著正相关关系;通过PLSR,VPA,SEM等方法控制土壤非生物因子效应后,真菌多样性与二者的显著正相关关系仍存在。综上所述,局地尺度下青海省湟源县高寒草原土壤真菌多样性是调控地上植物多样性与生产力正向关系的关键生物因子。