Impacts of the local land-use system in a semi-arid region of northeastern China on soil properties, crop growth, and weed communities

We examined changes in soil properties, crop biomass, and weed communities in the Horqin Sandy Land of China to elucidate cropland degradation. We studied three local cropland types having periods of cultivation of up to 20 years: maize cropland on lowlands without irrigation (nonirrigated lowland), maize cropland on flat sandy lands with irrigation (irrigated flatland), and bean-centered cropland on sand dunes without irrigation (nonirrigated dunes). Soil properties and crop biomass were more degraded in nonirrigated lowland and nonirrigated dunes than in irrigated flatland. Weed communities in the nonirrigated croplands were the type that become established in drier conditions, whereas wetland weeds were more abundant on irrigated flatland. Trends of change in each indicator did not always occur in parallel and differed statistically among the cropland types. Monitoring these indicators within the context of local land-use systems can provide scientific evidence on which to base local management practices or recommendations for change.     

宁波市2013年夏季干旱分析

2013年夏季干旱给宁波市带来了极大的损失。本文利用全市63个国家基本雨量站资料,采用连续无雨日法和降水量距平法评估此次干旱的干旱等级,并提出了回归分析的改进方法。通过与历史同期旱情进行对比分析,认为宁波市2013年夏季干旱为近60年比较严重的年份之一,频率分析达到30年一遇。     

吉林省城市增长与收缩的分异特征、成因与对策

利用人口与经济变化组合关系和二分类Logistic回归模型,探索新时期吉林省城市发展的空间分异现象及成因。结果表明:(1)吉林省形成了绝对增长型、绝对收缩型、精明增长型和人口集聚中心4种城市发展类型。(2)绝对增长型城市产业结构不断多样化,科技发展对经济增长的贡献率日益提高;精明增长型城市先进制造业、生产性服务业迅速发展,但生活性服务业发展相对不足;绝对收缩型城市以传统制造业为主导产业,城市竞争力不断丧失,存在持续收缩的发展趋势;人口集聚中心凭借发达的公共服务业抑制了主导产业衰退背景下的人口流失现象。(3)产业结构、企业组织、政府调控以及集聚-扩散效应是新时期吉林省城市增长与收缩分化的成因。顺应区域城市发展趋势,编制存量和减量规划,分类引导城市的精明增长与收缩,是未来吉林省空间重构的主要发展路径。     

能源转型背景下不可忽视的新能源:天然氢

世界能源结构正面临着从化石能源向非化石能源过渡的第3次转变,氢气作为易燃且燃烧时不产生污染的清洁能源,将在其中起到重要作用.目前,氢的工业生产主要通过煤、天然气等化石燃料以及电解水制取,对天然氢的勘探开发刚刚起步,仅在非洲马里开采出天然氢.但是,天然氢已在世界各地被陆续发现,据相关文献报道:天然氢可能来源于深源、水岩反...     

关于气候变化与荒漠化关系的新认知

IPCC于2019年8月7日通过了《气候变化与土地特别报告》决策者摘要,报告第3章评估了气候变化与荒漠化的关系,取得了一些新认识,包括全球旱地(dryland)和荒漠化的范围、荒漠化过程与影响因素、荒漠化的检测与归因、荒漠化对自然和社会经济系统的影响、荒漠化对气候变化的反馈、未来气候变化对荒漠化的影响与风险,应对荒漠化与适应和减缓气候变化的联系。在估计荒漠化变化、荒漠化变化检测与归因、荒漠化对自然和社会经济系统的影响、荒漠化对气候变化的反馈、应对荒漠化与适应和减缓气候变化联系方面还存在不足。这些评估结果对我国认识旱地和荒漠化范围的变化、影响荒漠化因素、荒漠化过程、荒漠化变化检测与归因,荒漠化对自然和社会经济系统的影响、荒漠化对气候变化的反馈、未来气候变化对荒漠化的影响与风险,以及防治荒漠化与适应和减缓气候变化方面等都有重要的启示。     

试论粤方言新词语的特点及其成因

新词语是社会变革发展的一面“镜子”,它既丰富了现代汉语的词汇,又对社会发展带来深远的影响。近二十年来,处于改革开放前沿的粤方言区产生了许多方言色彩浓厚的新词语。以粤方言为研究对象,描述了粤方言新词语的特点,并分析其形成具有:经济、地缘、文化、心理等方面因素。     

产业集群成因的演变对集群成长、发展的影响分析——以江苏省宿迁市杨树产业集群为例

对宿迁市杨树产业集群的成因分析发现,资源禀赋、比较优势、集聚效应、政府支持和企业家精神是集群形成的主要原因。这些成因具有演替的特点,且其自身处于不断变化之中,这些变化对认识集群的发展趋势、对集群进行调控具有重要的启发作用。为解决当前宿迁市杨树集群发展中的低端恶性竞争、集群外部环境恶化等困境,调整产业结构、营造创新的氛围、大力培养和引进创新型人才,逐步建立自主品牌,开拓新的市场、化解农民种树的风险作等措施成为必然选择。     

黔南岩溶石山区电测深法异常类型及其成因探讨

大量的抗旱打井找水开发深层岩溶地下水资源实例证明,黔南岩溶石山区不同岩溶形态富水电测深法异常类型及成因有一定规律可循,单支电测深曲线异常类型可划分为缓升型、缓降型、低阻平台型、低阻V型、低阻平升型.低阻降尾型,富水地段电测深视电阻率断面等值线异常类型可划分为低阻U型、低阻O型、低阻梯度带型、低阻台阶型.     

鲁卜哈利沙漠的特点及成因

地处阿拉伯半岛南部的鲁卜哈利沙漠是世界上最大的流动沙漠,其沙丘的移动主要由季风引起,并且由于风向和主流风的差异,沙漠的沙丘被分成3个类型区,即东北部新月形沙丘区、东缘和南缘星状沙丘区、整个西半部线形沙丘区。对于鲁卜哈利沙漠的成因,国内外一直缺少系统的研究。通过对现有资料的分析,可以发现气候、地形、古地理等自然因素是影响鲁卜哈利沙漠形成的主要因素,人类的影响不明显。     

Vegetation pattern variation,soil degradation and their relationship along a grassland desertification gradient in Horqin Sandy Land,northern China

The Horqin Sandy Land is one of the most severely desertified regions in northern China. Plant communities and soil conditions at five stages of grassland desertification (potential, light, moderate, severe and very severe) were selected for the study of vegetation pattern variation relating to soil degradation. The results showed that vegetation cover, species richness and diversity, aboveground biomass (AGB), underground biomass, litter, soil organic carbon (C), total nitrogen (N), total phosphorus (P), electrical conductivity, very fine sand (0.1–0.05 mm) content and silt (0.05–0.002 mm) content decreased with the desertification development. Plant community succession presented that the palatable herbaceous plants gave place to the shrub species with asexual reproduction and sand pioneer plants. The decline of vegetation cover and AGB was positively related to the loss of soil organic C and total N with progressive desertification (P < 0.01). The multivariate statistical analysis showed that plant community distribution, species diversity and ecological dominance had the close relationship with the gradient of soil nutrients in the processes of grassland desertification. These results suggest that grassland desertification results in the variation of vegetation pattern which presents the different composition and structure of plant community highly influenced by the soil properties.