Changes in soil hydraulic conductivity, runoff, and soil loss due to irrigation with different types of saline–sodic water

Irrigation with saline–sodic water causes sodic conditions in the soil which reduces soil productivity. We evaluated the changes in a number of important indices related to soil structural stability when treated wastewater (TWW), albeit with higher loads of organic matter and suspended solids, was used instead of more saline–sodic irrigation water, under different degrees of aggregate slaking. We studied soil saturated hydraulic conductivity (HC) using disturbed samples packed in columns, and soil infiltration rate, runoff and erosion under simulated rainfall. Aggregate slaking was manipulated by wetting the samples prior to all tests at either a slow (1–2 mm h^− 1) or a fast (50 mm h^− 1) rate. Samples of a calcareous silty clay (Typic Calciorthids) from the Bet She'an Valley, Israel, were taken from plots irrigated for three years with either TWW, saline–sodic Jordan River water (JRW), or moderately saline–sodic spring water (SPW), and also from a non-cultivated area (control). With little or no aggregate slaking (use of slow wetting), higher HC values and lower amounts of total runoff and soil loss were measured compared to when more severe aggregate slaking was induced (use of fast wetting). The HC values for the TWW treatment were similar to, or lower than, those for the control and significantly higher than those for the JRW treatment. For the runoff and soil loss data, differences among the water quality treatments were, generally, more pronounced when aggregate slaking was substantially reduced, and were related to soil sodicity. Under the latter condition, runoff and soil loss from the TWW treatment were comparable with those from the control and significantly lower than those from the JRW treatment. Our results suggested that replacing saline–sodic irrigation water with TWW could have favorable effects on soil structural stability, especially under conditions where aggregate slaking can be reduced (e.g., in regions with low to moderate rain intensities; and/or use of low intensity irrigation systems).     

基于合成孔径雷达的农作物后向散射特性及纹理信息分析——以吉林省农安县为例

及时掌握农作物类型、时空分布和结构信息,是合理调整农业结构的重要科学依据。针对光学遥感依赖于太阳辐射,在农作物生长周期内常受制于云雾的影响而无法获取到光学遥感数据的问题,本文采用全天时全天候、不受云雾等天气影响的合成孔径雷达（synthetic aperture radar,SAR）影像,探讨典型农作物的后向散射特性和纹理特征,为采用合成孔径雷达影像实现高精度农作物大面积监测提供科学依据。以吉林省农安县为例,利用12景Sentinel-1B双极化SAR影像数据,经影像预处理和统计分析,研究不同极化的农作物后向散射特性和纹理信息。结果表明：3种作物（大豆、玉米、水稻1和水稻2）同极化（VV）的SAR后向散射系数在生长周期内均高于交叉极化（VH）,农作物植株形态改变极化方式的能力为-25~-15 dB。3种作物在整个生长期内,后向散射系数呈现较大波动,各阶段后向散射特征差异明显。在生长初期,土壤对后向散射特征起主要作用,在SAR图像上表现为暗色调;随着作物生长,冠层散射叠加土壤散射作用占据主要位置,散射值随作物生长呈现逐渐增加的趋势,在SAR图像上表现为亮色调;拔节（分枝）后（7月10日后）作物的后向散射信号除冠层散射作用外,还主要受到土壤含水量及其与作物相互作用的影响,因此拔节后两种水稻后向散射系数下降幅度较大。水稻对雷达波的吸收强于玉米和大豆,整体上后向散射系数第2种水稻<第1种水稻<玉米<大豆,尤其在VH极化方式下表现更明显。对作物SAR纹理信息的研究表明纹理信息的均值、方差和协同性对于农作物的SAR识别更有效,最佳纹理信息为VH极化均值,有利于识别3种作物;VV极化方差和VV协同性有助于区分两种水稻;SAR影像识别作物的最佳时相为5月23日至7月10日。     

我国省际区域生态效率的空间收敛性研究

基于新古典经济增长理论,构建了区域生态效率空间收敛分析的理论框架。利用2004—2015年的我国省际面板数据,运用超效率DEA模型测算了各省的生态效率,分析了区域生态效率的区间差异,然后利用空间滞后模型讨论了β收敛情况。结果显示:1)区域生态效率逐年改善,区域差异明显,但大部分区域的差距在缩小;2)全国和东中西部地区均不存在σ收敛,考虑空间互相关下,全国和东中西部地区均存在β收敛,收敛速度呈现东部最快、中部次之、西部最慢的格局;3)在引入城镇化等控制变量后,β条件收敛速度上升,东部和西部尤为明显;4)城镇化和市场化促进了生态效率提升,产业结构优化给生态环境带来了压力。因此,提升区域生态效率收敛依赖于新型城镇化建设的进程、市场化改革的程度和产业结构优化的落实。     

SAR图像边缘检测方法综述

边缘检测是SAR图像解译的基本问题之一。固有的乘性噪声特性使得经典的梯度边缘检测方法并不适用于SAR图像,因此研究针对SAR图像的边缘检测方法具有重要的意义。本文对SAR图像边缘检测问题进行了系统的研究,简单描述了SAR图像边缘检测问题,讨论了现有的SAR图像边缘检测方法,总结了SAR图像边缘检测中存在的两个问题——边缘细化和边缘定位,对检测结果的性能评估方法也进行了概括。最后在总结现有研究成果的基础上展望了SAR图像边缘检测的发展方向。     

Costs and trade-offs associated with induced resistance

Plants resist attack by pathogens and herbivorous insects through constitutive and inducible defences. Based on differences in signalling pathways and spectra of effectiveness, different types of induced resistance have been defined. Systemic acquired resistance (SAR) occurs in distal plant parts following localized infection by a necrotizing pathogen. It is controlled by a signalling pathway that depends upon the accumulation of salicylic acid (SA) and the regulatory protein NPR1. In contrast, induced systemic resistance (ISR) is induced by selected strains of non-pathogenic plant growth promoting bacteria (PGPR). ISR functions independently of SA, but requires NPR1 and is regulated by jasmonic acid (JA) and ethylene (ET). It is generally believed that induced resistance evolved to save energy under pathogen or insect-free conditions, although costs still arise when defences are activated following attack. Costs can arise from the allocation of resources to defence and away from plant growth and development, and there are also ecological costs which result from trade-offs between induced resistance and the plant's interaction with beneficial organisms e.g. mycorrhizal fungi. To date, few studies have examined the costs and trade-offs associated with induced resistance to pathogens. There is a clear need for long-term studies of costs and trade-offs associated with induced resistance in crops under commercial conditions. Without such information, the potential offered by induced resistance is unlikely to be realized.     

Forest Mapping with ERS SAR Tandem Data

The feasibility of ERS SAR Tandem data for mapping forest and non-forest cover in China was evaluated over Zengcheng County in the South China. An accuracy of 75% has been achieved. Then, the MACFERST (Mapping China Forest with ERS SAR Tandem data) project started by the Ministry of Science and Technology (MOST) of China and the European Space Agency (ESA) in 1999. The generation of a large-scale forest map requires solving problems such as the georeferencing and mosaicking of very long image strips covering huge regions and the adaptation of the classification algorithm to account for radiometric differences. Approaches to solve these problems and the classification results in the Northeastern of China will be presented in this paper.     

HRAP基因诱导型植物表达载体的构建及烟草转化

系统获得性抗性是植物抵御病菌侵染的一种独特的防御机制.HRAP基因是一种从甜胡椒中克隆的蛋白质激发子,可以有效引发植物系统性抗性.SAR8.2b基因是烟草系统获得性抗性信号传导途径中下游响应基因,受病原物和水杨酸诱导.本试验根据Genebank发布SAR8.2b基因的启动子序列,利用PCR技术,克隆了SAR8.2b基因的完整启动子,命名为SAR8.2bP,然后将SAR8.2bP构建到pUC18-HRAP载体中命名为pUC18-SAR8.2bP-HRAP,然后用SAR8.2bP-HRAP替换p2300-121载体中的35S启动子和GUS基因,重组子命名p2300-SAR8.2bP-HRAP.将构建的植物表达载体转化农杆菌GV3101,利用叶盘法转化烟草,通过PCR筛选,获得了转基因植株.为进一步验证转基因烟草的抗病效果奠定了基础.