Arbuscular mycorrhizal colonization and spore density across different land‐use types in a hot and arid ecosystem,Southwest China

We investigated the arbuscular mycorrhizal (AM) colonization and spore density in cropped land, fallow land, and an undisturbed savanna ecosystem under hot and arid climatic conditions in a valley of southwest China. Plants surveyed in the three land‐use types showed heavy arbuscular mycorrhizal colonization, indicating a high mycorrhizal dependency of plants in this environment. One‐way analysis of variance (ANOVA) showed that the colonization of different AM structures and the spore density varied greatly among plant species both within and between different land‐use types. The AM colonization and spore density were higher in undisturbed than in fallow or cropped land. No significant correlation between AM colonization and spore density was observed when land‐use types were either considered separately or together. Cluster analysis based on the similarity in AM status with respect to both colonization and spore density showed similarities between fallow land and the undisturbed savanna. The results indicate that continuous cropping reduces AM colonization and spore density. These parameters appear to nearly fully recover when the land has been left to fallow for 4 years.     

Infection of valuable broadleaf hardwood trees by Glomus mosseae: growth and mineral nutrition

In the past century, the excessive exploitation of the environment by human beings has resulted in the depletion of valuable broadleaf hardwood trees in Italian forests, creating a need for re-forestation. The aim of this research was to verify whether a vescicular-arbuscular mycorrhizal (VAM) fungus is able to colonise the root of valuable hardwood trees and to evaluate the impact of the VAM fungus on growth and macroelement nutrition of its plant hosts.Four species of valuable broadleaf hardwood trees, Prunus avium L., Fraxinus excelsior L., Acer pseudoplatanus L., and Juglans nigra L., were inoculated with Glomus mosseae, a VAM fungus, and cultivated in a greenhouse. Infection after inoculation and root colonization by the fungus, tree growth, and macro-element nutrition were evaluated two-years after inoculation. G. mosseae formed mycorrhizae on all plants. However, different morphological aspects - predominantly the formation of Arum type arbuscles in P. avium and F. excelsior - were observed. A general improvement of macro-element nutrition from species to species characterised an enhanced growth of mycorrhizal plants. Therefore, it is plausible that the association of VAMs with these broadleaf trees, could overcome the difficulties encountered in the transplanting and the slow growth typical of these tree species.Although numerous articles have reported the beneficial effects of ectomycorrhizal fungi on trees, there is a sparse literature on the association of VAM with tree species. Therefore, this study contributes to the understanding of the role of the symbiosis between valuable broadleaf trees and VAM fungi in macroelement nutrition.     

Geomorphological significance of lichen colonization in a present snow hollow: Hoya del Cuchillar de las Navajas, Sierra de Gredos (Spain)

This paper discusses the results of a lichenometrical and geomorphological study of one of the few remaining active snow hollows in the central region of the Iberian Peninsula. The study area, located on a glacial shoulder, is called Hoya del Cuchillar de las Navajas. A protalus rampart occurs at the base of the hollow. Our studies, conducted between 1992 and 1998, were designed to determine the geomorphological characteristics of Hoya, the mobility of the deposits, and the characteristics of the snow cover. These data formed the basis for a study of the lichen colonization on the blocks and on the wall surrounding the snow hollow. All of the lichen species found were analyzed according to their abundance, distribution and the extent of their surface cover. Measurements of the diameter of the thalli of the species Rhizocarpon geographicum were also obtained. Thalli of this species were found to require a mean snow-free growing season of at least 95 days (13.5 weeks) per year. Maximum mean thallus diameters indicate that the protalus rampart was formed during the Little Ice Age and became inactive 130 years ago.     

附生细菌在微囊藻（Microcystis）藻华颗粒上的定殖和生长

通过测定微囊藻模拟藻华颗粒和微囊藻水华藻华颗粒表面附生菌数量的变化,分析微囊藻（Microcystis）与附生假单胞菌（Pseudomonas）之间相互作用关系。结果表明,在死亡藻体的模拟藻华颗粒表面附生菌数量迅速增加,而活藻藻华颗粒表面附生菌数量增长缓慢,在培养后期藻体大量死亡,附生细菌的数量不断增加,最后超过死亡藻体的模拟藻华颗粒的附生细菌数量。附生细菌在天然微囊藻藻华上定殖和生长也呈现类似的趋势,由于附生菌同藻华中微囊藻之间存在竞争,附生菌的存在促进藻体团聚,抑制附生细菌的定殖,但是在微囊藻的衰亡期产生的大量营养物质有利于附生细菌的生长,水体中附生细菌的数量不断增加,同时天然藻华上附生细菌的数量也大量增加,有利于其生长和定殖。     

湿地松半同胞家系净光合速率日变异规律研究

 使用LI-6400便携式光合测定系统,对湿地松优良半同胞家系净光合速率的日变异规律进行了研究,结果表明1年中湿地松各半同胞家系3~8月典型天气的Pn值日变化模式为‘双峰’型,其余各月即1、2、9、10、11、12月的Pn值日变化模式为‘单峰’型,各家系1龄针叶的Pn值显著高于2龄针叶的Pn值,全天以傍晚时的Pn值为最低。湿地松优良半同胞家系的Pn值显著高于普通种的Pn值,表明通过遗传改良,提高了湿地松的光合能力,从而提高了湿地松良种的生长量和产量。     

基于粗糙集理论的立地类型分类规则探讨

利用粗糙集理论（（Roughset））中的知识表达系统和约简算法。在研究区内选取与立地因子关系最密切的树高因子为决策属性，以海拔、母岩、坡度、坡位、土类和土层厚度作为条件属性；决策属性动态聚类和各条件属性值域离散化后，建立立地类型分类决策表，计算决策属性的依赖度及其相对约简，得到马尾松林分立地类型的分类因子为土层厚度、坡位和母岩，并且其重要性分别为0．6923、0．5385和0．3077．     

显像管玻壳铅尘环境化学行为的研究

以显像管玻壳铅尘为对象,通过测定铅在不同深度的土壤中各种形态的含量,系统地研究了玻壳铅尘在土壤中的形态及其在土壤剖面中的迁移转化规律,为农业铅污染的防治提供了理论依据。     

水稻潜根线虫的生物学特性及田间发生消长动态研究

对水稻潜根线虫的形态特征.侵染循环及对温、湿度的适应性等有关生物学特征,进行了描述调查结果证实.该虫在湖南省稻区广泛发生.田间发生消长动态曲线表明.湖南省稻根带虫量全年在田间出现3次高峰.     

黄河上游贵德--民和段两岸植被分布特征

根据黄河上游贵德—民和段河岸植被类型的垂直带谱变化规律,采用样地调查方法,分荒漠草原、温性灌丛草原、山地森林草原、高山灌丛和高山草甸等植被带对植被分布特征进行了研究分析。     

人才培养模式探析

人才培养模式是对人才培养过程的总体表述，属于过程范畴，它和办学模式、教学模式、培养途径、培养方法等其它教育范畴存在着差异，人才培养模式由培养目标、培养制度、培养过程和培养评价四个子系统的构成，是系统性与独立性的统一，是中介性与操作性的统一，是稳定性与灵活性的统一，是个性与共性的统一。