砒砂岩区小流域土壤有机质空间分布特征及其影响因素

为了探究砒砂岩区小流域土壤有机质空间分布特征,该文以砒砂岩区典型流域鲍家沟小流域为研究对象。采用网格法布设取样点,2018年7月取样,按照0～20、20～40、40～60 cm划分取样层次。采用重铬酸钾外加热法测定土壤有机质,采用激光粒度测定仪测定土壤粒度,采用样方拍照法计算植被覆盖度。运用地统计学和约束性排序相结合的方法,研究环境因子影响下砒砂岩区土壤有机质的空间变异特征。结果表明:砒砂岩区小流域土壤有机质质量分数在0.98～15.45 g/kg之间,不同地形土壤有机质含量呈沟底坡面山脊的规律;研究区土壤有机质的空间分布规律可以用半方差函数的指数模型进行良好的模拟,块金效应在55.1%～57.5%范围内,属中等程度变异。小流域土壤有机质呈中间高边缘低的规律;冗余分析的结果显示,第1轴的特征值为0.58,解释量为58%,第1轴对响应变量的累积解释量为96.1%,前两轴对响应变量的累计解释量达到了99.3%。各环境因子与第1排序轴的相关系数大小顺序为植被覆盖度土壤侵蚀程度土壤颗粒平均粒径坡位高程坡度,第1排序轴可以定义为植被-土壤侵蚀因子,坡度因子与第2排序轴的相关系数高于其他环境因子,第2排序轴可以定义为坡度因子。植被覆盖度是影响砒砂岩区小流域土壤有机质空间变异的主导因素,土壤侵蚀程度是决定土壤有机质垂向变异的关键因素。砒砂岩区的土层浅薄且贫瘠的地带,不宜开展大面积的整地和造林工作,而土层深厚且水肥条件良好的区域可以营造合理密度的灌木林、乔木林以及经济林。     

排序方法在土壤粒径分布研究中的应用——以策勒河流域为例

基于土壤结构的自相似性,分形理论目前被广泛用于土壤粒径分布(particle size distribution,简称PSD)研究中[1],即以相对较多的土壤粒级数据,利用单重或多重分形技术获取参数(分形维)形式揭示PSD特征。量化得出的分维值,能较全面反映土壤PSD特征及其之间的差异性,但会受限于PSD差     

Riparian plant composition in an urbanizing landscape in southern California,U.S.A.

In coastal southern California, natural riparian corridors occur in a landscape mosaic comprised of human land uses (mainly urban and suburban development) interspersed among undeveloped areas, primarily native shrublands. We asked, does the composition of the landscape surrounding a riparian survey point influence plant species distribution, community composition, or habitat structure? We expected, for example, that invasive non-native species might be more abundant as the amount of surrounding urbanization increased. We surveyed 137 points in riparian vegetation in Orange County, California, along an urbanization gradient. Using logistic regression we analyzed 79 individual plant species’ distributions, finding 20 negatively associated and 12 positively associated with the amount of development within a 1-km radius around the survey points, even after accounting for the effects of elevation. However, after summarizing plant community composition with Detrended Correspondence Analysis we observed that, overall, community composition was not statistically correlated with the amount of development surrounding a survey point once the association between development and elevation was taken into account. Non-native species were not particularly associated with increasing development, but instead were distributed throughout vegetation and urbanization gradients. However, the extent of the tree and herb layers (structural attributes) was associated with development, with the tree layer increasing and the herb layer decreasing as urbanization increased. Thus, although the degree of surrounding urbanization appears to influence the distribution of a number of individual plant species, overall composition of the community in our study system seemed relatively unaffected. Instead, we suggest that community composition reflected larger-scale environmental conditions, such as stream order and other variables associated with elevation, and/or regional-scale disturbances, such as historic grazing or enhanced atmospheric deposition of nitrogen.     

自组织神经影射网络排序及其在植物群落分析中的应用

自组织神经影射网络(SOFM)对复杂问题和非线性问题具有较强的分析和解决功能,其特征完全适合植物群落的排序研究。该文介绍了SOFM的基本原理和排序分析过程及方法,并应用SOFM网络排序对太行山中段植物群落进行了排序分析。其计算过程在Matlab 65神经网络工具箱中实现。结果将68个样方排列在SOFM拓扑空间,排序轴反映了明确的生态梯度,能够反映植物群落间的生态关系,生态意义明确,符合植被实际,表明SOFM网络是有效的植物群落排序方法。在SOFM排序过程中也很容易进行聚类,有利于群落分类和排序的结合。      

山西果园秋季杂草群落数量分类和排序分析

通过野外调查,应用双向指示种分析法(TWINSPAN)分类和无趋势对应分析法(DCA)排序,对山西省农业科学院果树研究所果园秋季杂草群落进行了数量分类和排序分析。根据TWINSPAN分类结果,并结合生态特性,将所调查的果园69个样方划分为12个群丛,论述了各群丛的群落学特征。TWINSPAN分类结果较好地反映了杂草群落类型与环境梯度之间的关系,并在DCA二维排序图上得到较好的验证。DCA排序进一步说明了群系的分布格局与土壤养分、土壤水分和海拔的密切关系。结果表明,组成果园杂草的种群对群落生境具有指示作用,能客观反映群落的生境特征。     

山西太行山南段峡谷区荆条灌丛数量分析

以太行山南段峡谷区荆条Vitex negundo群落为对象,沿不同海拔布置样方,应用TWINSPAN和DCA相结合的方法,对样方进行数量分类和排序,并进行了环境解释。TWINSPAN等级分类把47个样方分为11个群丛,DCA排序结果同TWINSPAN分析结果相吻合。DCA结果揭示出,其中第一轴显著地反映出各个群系的坡向变化趋势,而第二轴则反映出坡度的梯度变化,表明样方所在地的坡向和坡度是决定群丛分布的主要环境因素。     

地震干扰后恢复群落的数量分类与排序

根据对四川王朗自然保护区地震干扰后恢复群落的野外调查数据,运用二元指示种分析(TWINSPAN)和除趋势对应分析(DCA)对该地区恢复群落进行了数量分类与排序。结果显示,可将所调查的植物群落划分为3种群落类型:重度干扰群落(群落E)、中度干扰群落(群落T)和轻度干扰群落(群落F)。排序结果也得到了相同的结论,并显示3种群落分布与一定的环境因子密切相关,群落E与岩石裸露度呈正相关,而与土壤厚度、土壤水分、苔藓盖度及盖度等环境因子呈负相关,群落F则与岩石裸露度呈负相关,而与土壤厚度、土壤水分、苔藓盖度及盖度等环境因子呈正相关。     

Phenotypic relationships among Australian and Mexican wheat cultivars

Summary Plants of 43 Australian wheat cultivars of historical and contemporary importance and 7 Mexican introductions were grown in a glasshouse and measured for 27 morphological and physiological attributes.Phenotypic relationships among the cultivars across all attributes were examined by hierarchical classification and ordination procedures. Seven major groups of cultivars delimited in the classification were broadly related to extremes of plant type (3 tall, late-flowering Australian wheats and 2 early-flowering Mexican wheats of high harvest index were contrasting extremes), region of breeding origins (southern/western versus northern Australian cereal regions) and pedigree (strong influences of the Norin 10 x Brevor cross in some Mexican cultivars and Mexican derivatives; of Federation and Early Gluyas in the pedigrees of southern/western wheats; and of Gabo in the northern wheats). Some attributes of the Australian cultivars were correlated with the year of release suggesting the progressive development of cultivars that are shorter. earlier to ear emergence and with a high harvest index.     

太行山低山石灰岩区水土保持林地类型研究

通过对太行山低山石灰岩区水保林定性和定量兼有的１３个变量，１７０块标地调查，采用主成分分析方法，对该区的水保林进行排序，结果≤５００ｍ丘陵区可划分为四个类型：灌木盖度〉２０％侧柏，山皂荚乔灌草型，灌木盖度≤２０％侧柏，白草乔草灌云南省 枯落物荆条，酸枣灌草型；无枯