综合世界植被和中国植被的分类进展,以群落外貌、结构、动态、种类组成、成因和生境相结合为依据,提出一个新改进的中国植被分类系统.该分类系统仍坚持将植被型(Vegetation type)、群系(Alliance)和群丛(Associaton)作为植被分类的基本等级,但群系的英文建议用"Alliance",而不用"Formation".植被型以上设置植被纲(Class of vegetation types)、植被亚纲(Subclass of vegetation types)和植被型组(Group of vegetation types)作为辅助分类单位,植被型以下建议不设过多的分类辅助等级.我们将自然植被分类系统的高级分类单位分为3个植被纲,7个植被亚纲,12个植被型组,76个植被型.植被型等级编排了分类代码.新改进的分类系统与中国植被1980分类系统的主要区别是:将冻原、荒漠、沼泽分别作为一种植被类型的生长环境,而非作为一种植被类型来看待,以示与地貌学和自然地理学相关概念区分;新增簇生叶类植被亚纲和相关植被型,将竹类分别归并到森林植被和灌丛植被相关等级;依据草本植物的生态类型、植被成因及其动态,将草本植被分成草原、草甸和草丛3个植被型组.植被命名的方法作为植被分类的重要内容之一,也在文中进行了重点探讨.

Using Landsat remote sensing images in 1990, 2000, 2010 and 2019, land use types in the dry⁃hot valley area of Jinsha River Basin are classified by combining visual interpretation with maximum likelihood, and the spatiotemporal change and transfer process of land use types in the dry⁃hot valley area of Jinsha River Basin are also studied. The InVEST model combining meteorological, soil and topographic data are used to evaluate the water⁃producing and water⁃conserving function of different land use types in the dry⁃hot valley area of Jinsha River Basin from 1990 to 2019. The main conclusions

以1995年、2005年、2015年3期Landsat卫星遥感影像为基础,分别对滇池流域土地利用数量变化、空间变化和景观生态安全3个方面开展研究,分析滇池流域土地利用演变特征及景观生态安全格局.结果 表明:1995-2015年,研究区土地类型以建设用地、耕地、林地和水域为主,其中林地、耕地和湿地面积减少,建设用地及未利用地面积增加,水域和灌草地面积波动变化;1995-2015年,研究区耕地转移面积最多,20 a缩减46％,主要转变为建设用地.建设用地新增面积最多,2015年面积是1995年的1.6倍,转入源主要来自耕地、湿地及林地;1995-2015年,研究区面积以较高安全区及中度安全区为主,3个时期景观生态安全指数均值分别为38.16、41.50、42.19,安全等级呈缓慢增长趋势.

The objective of this study is to understand the role of bark water uptake in refilling of xylem vessels after embolism in Salix matsudana. Further, we determined expression of genes closely related to xylem embolism repair. The isolated branch segments of S. matsudana were soaked in deionized water and after 2 h, the micro-computed tomography (CT) images, volume of xylem sap, osmotic potential of xylem sap, and the content of starch and soluble sugar were measured. At the same time, Illumina high-throughput sequencing (Hi Seq TM) was applied to obtain the xylem transcriptome profiling. The results showed that the soaked branches had 58.86 % fewer embolized vessels than branches before soaking. The volume of xylem sap was increased by 21.51 % in comparison with initial sample and the osmotic potential (Ψs) of xylem sap was decreased by 87.18 %. The content of ions and soluble sugars in the xylem sap significantly increased after soaking. Fourteen genes were clarified and found to have a significant correlation with osmotic potential of xylem sap. Our findings showed that water can enter the xylem vessels through the bark and can repair the xylem embolism in branches. The saccharides played an important role in osmotic potential difference formation and the genes UXL1 (uridine diphosphate-xylose synthase 1), UGDH (uridine diphosphate-glucose 6-dehydrogenase), BGLU40 (β-glucosidase 40), PPE8B (pectinesterase/pectinesterase inhibitor), UG1 (uridine diphosphate-glucuronate 1), and XYL4 (β-D-xylosidase 4)) were the key genes to promote embolized vessels refilling.

Few study examined the possible influence of artificially altering soil moisture content on stem respiration (Rs) and stem chemical composition together, we artificially simulated four soil moisture gradients in Dalbergia odorifera (D. odorifera) plantations and investigated Rs, predawn shoot water potential (ψpd), nitrogen content, and non-structural carbohydrates (NSCs) over time. Stem temperature (Ts) and Rs declined continuously during the dry period and reached their minimum values in January. Irrigation increased the Rs rate, while drought decreased it. The nitrogen content of the sapwood remained constant until December, after which it decreased when winter began. During the winter, the sapwood nitrogen increased under irrigation but Seite 348 ZY Cui, ZJ Yang, DP Xu, RC Xi, NN Zhang, XJ Liu & Z Hong decreased under drought conditions. The soluble sugars tended to increase during the dry period at the cost of starch, which caused a small but non-significant increase in NSCs. The effect of water treatments on total NSCs was limited; however the drought treatments increased the soluble sugars content but decreased the starch content. Rs explained 49, 72 and 40% of the seasonal variation in the stem nitrogen, starch and soluble sugars, respectively. The ψpd significantly explained 49, 79 and 85% of the variation in the Rs, stem starch and soluble sugars, respectively. Thus, soil moisture content likely affects Rs by affecting the amount of sapwood nitrogen, starch and soluble sugars. Low soil moisture content induced by drought enhanced the transformation of starch to soluble sugars during the winter, when heartwood formed. These strong relationships may provide interesting implication for future study on heartwood formation.