土种与土系参比的初步探讨——以海南岛土壤为例

为取得我国土种与土系研究成果的信息交流与知识共享,本文简述了土种与土系的概念及其区别、土种与土系的参比原则和依据,以海南岛土壤为例进行了参比。     

若尔盖高原湿地土壤硒的数量、形态与分布

用连续浸提的方法研究了若尔盖高原4种湿地土壤(风沙土、草甸土、沼泽土和泥炭土)中硒的含量、形态、剖面分布及其影响因素,以期为该区人、畜缺硒症的防治积累科学资料。结果表明,该区土壤属于低硒环境,表层土壤全硒含量范围为65～260μg/kg。在各种形态硒中,水溶性硒仅占土壤全硒含量的1.12%～3.08%,交换态硒占2.91%～6.03%,有机态硒占10.28%～45.63%,酸溶态硒、硫化态硒和残余态硒3种无效态硒共占60%以上。在土壤有机态硒组成中,胡敏酸结合态硒(HA-Se)占有机态硒的57.84%,富里酸结合态硒(FA-Se)占42.16%。土壤总硒和有机态硒的含量与分布主要受土壤有机碳的影响,且其影响程度随着深度的不同而改变,湿地土壤丰富的有机碳有利于土壤有机态硒和总硒的积累。土壤总硒含量低、有机态硒的比例较高以及胡敏酸结合态硒占优势导致硒的生物利用率低,可能是该区域人、畜硒缺乏症发生的重要原因。     

Polypore diversity in managed and old-growth boreal Picea abies forests in southern Finland

Polypore communities were compared between mature managed, overmature managed, and old-growth spruce-dominated forests in southern Finland. A total of 85 polypore species, with 6000 records, were found in 16 sample plots, each 4 ha in size. Old-growth stands had on average 80% more species than mature stands, and 38% more species than overmature managed stands. Variation in polypore species richness was best explained by diversity of dead wood and the number and volume of dead trees. The best predictor for the number of threatened polypore species was the number of cut stumps. Threatened species were practically confined to old-growth forests and to stands in which the amount of dead wood exceeded 20 m³/ha. This figure appears to represent a stand-level threshold value for the amount of dead wood, below which the persistence of threatened species becomes unlikely. Our results suggest that a significant increase in the amount of dead wood (e.g. by leaving large retention trees and even by killing trees) is needed in managed forests before they become suitable habitats for threatened polypores.     

陇东黄土高原沟壑区各立地类型水保适生树种的确认

在黄委会西峰水保站关于陇东黄土高原沟壑区立地条件类型划分和拟定的适生树种基础上,针对这里干旱少雨的突出特点,本着乡土树种为主、引进树种为辅的原则,采取自采、自育、自造和以抗旱为中心的造林技术,在西峰水保站南小河沟试验场应用大断面法布设“地树对位”试验区,以相对成活率、相对保存率和相对生长率计算得到的适生值为主要依据,对陇东黄土高原沟壑区8种立地条件类型的适生树种分别进行了确认,共确认乔灌木树种16种。     

小叶锦鸡儿放牧场沙漠化过程中植物多样性的变化

对科尔沁沙地小叶锦鸡儿放牧场在沙漠化过程中物种多样性的变化特征进行了研究。分析了植物种类消长规律、生活型结构变化、优势度以及生态位宽度的变化情况。物种多样性指数分析表明，沙漠化过程是一个物种多样性衰减的过程，沙漠化导致大多数原生性物种消失。固定沙丘到半固定沙丘这一过程是整个沙漠化过程中物种多样性丧失最快的阶段。从生活型来看，地面芽植物受沙漠化影响最大。采用Levins公式测度了科尔沁沙地不同沙漠化阶段中17个主要种群生态位宽度变化情况。结果表明，大多数原生植物种群的生态位宽度沙漠化进程中逐渐降低，而侵入的沙生植物则呈现了相反的变化趋势。     

黄土丘陵区不同土壤地类造林树种选择与配置技术研究

通过 5年实验研究 ,观测了杨树、沙棘、柏树、刺槐、元宝枫纯林和沙棘与杨树、沙棘与柏树、刺槐与柠条的混交林在风化岩沫土土壤、红胶泥土壤、黄绵土土壤上的成活率、年枝条生长量、5 a林冠面积、5 a郁闭度 ,分析得出了黄土丘陵区不同土壤类型造林树种选择和配置的模式。结果表明 :黄土丘陵区造林常见树种及其混交形式在不同土壤类型上呈现不同结果 ,风化岩沫土适合柏树纯林和沙棘与杨树混交、沙棘与柏树混交 ,红胶泥土壤最佳树种为沙棘、刺槐纯林及沙棘与杨树混交 (阴坡 )、沙棘与柏树混交、刺槐与柠条混交 ,而刺槐、柠条纯林和沙棘与杨树混交、沙棘与柏树混交、刺槐与柠条混交适合于黄绵土土壤。此外 ,在各种土壤类型上混交林都优于纯林 ,建议黄土丘陵区造林应乔灌混交为主。该项研究技术在延安市山川秀美工程中推广 ,效果明显 ,建议在黄土丘陵区推广该技术。     

Urbanization as a major cause of biotic homogenization

When measured by extent and intensity, urbanization is one of the most homogenizing of all major human activities. Cities homogenize the physical environment because they are built to meet the relatively narrow needs of just one species, our own. Also, cities are maintained for centuries in a disequilibrium state from the local natural environment by the importation of vast resources of energy and materials. Consequently, as cities expand across the planet, biological homogenization increases because the same “urban-adaptable” species become increasingly widespread and locally abundant in cities across the planet. As urbanization often produces a local gradient of disturbance, one can also observe a gradient of homogenization. Synanthropic species adapted to intensely modified built habitats at the urban core are “global homogenizers”, found in cities worldwide. However, many suburban and urban fringe habitats are occupied by native species that become regionally widespread. These suburban adapters typically consist of early successional plants and “edge” animal species such as mesopredator mammals, and ground-foraging, omnivorous and frugivorous birds that can utilize gardens, forest fragments and many other habitats available in the suburbs. A basic conservation challenge is that urban biota is often quite diverse and very abundant. The intentional and unintentional importation of species adapted to urban habitats, combined with many food resources imported for human use, often produces local species diversity and abundance that is often equal to or greater than the surrounding landscape. With the important exception of low-income areas, urban human populations often inhabit richly cultivated suburban habitats with a relatively high local floral and faunal diversity and/or abundance without awareness of the global impoverishment caused by urbanization. Equally challenging is that, because so many urban species are immigrants adapting to city habitats, urbanites of all income levels become increasingly disconnected from local indigenous species and their natural ecosystems. Urban conservation should therefore focus on promoting preservation and restoration of local indigenous species.     

Does nectar reward affect rarity and extinction probabilities of orchid species? An assessment using historical records from Belgium and the Netherlands

The long-term persistence of plant populations may partly depend on pollination processes and seed production. The exact role of pollination in determining plant population viability still remains largely unclear. Orchid species have often been shown to be pollinator limited. Especially, non-rewarding species are characterized by infrequent pollinator visits and low seed set. Therefore, it can be hypothesized that, if overall population fitness of orchid species is influenced by seed production, non-rewarding species should be more prone to local extinction than rewarding species. To study the importance of nectar reward on orchid persistence, we collected historical records about the distribution of 32 orchid species in Flanders (Belgium) and 37 orchid species in the Netherlands. For both regions, present distribution patterns were compared with historical data. Between 1930 (Flanders) or 1950 (the Netherlands) and 2000, 26 (81%) species showed decreases in distribution range in Flanders, eight of which had gone extinct, whereas 29 (78%) species showed declines in distribution area in the Netherlands, five of which went extinct. Contrary to previously reported results, orchid distribution patterns were not related to nectar reward. There was also no significant relationship between nectar reward and extinction for both regions. Orchids typically occurring in wet grasslands and heathlands suffered greater losses than orchids typically confined to forest habitats or calcareous grasslands. We conclude that the production of nectar does not represent a safeguard for local extinction of orchid species. Habitat loss and other deterministic threats associated with habitat fragmentation and deterioration are more important determinants of orchid persistence.     

Diversity for abiotic and biotic stress resistance in the wild annual Cicer species

Data on 228 accessions of eight annual wild Cicer species and 20 cultivated chickpea check lines were evaluated for diversity in response to six of the most serious biotic and abiotic stresses which reduce crop yield and production stability of chickpea, i.e., ascochyta blight, fusarium wilt, leaf miner, bruchid, cyst nematode, and cold. Relative frequencies of score reactions to the above six stresses were recorded from all the annual wild Cicer species and the cultivated taxon. Patterns of distribution and amount of variation of the resistance reactions differed between stresses and species. C. bijugum, C. pinnatifidum and C. echinospermum showed accessions with at least one source of resistance (1 to 4 score reactions) to each stress. Overall, C. bijugum showed the highest frequencies of the highest categories of resistance. Next in performance was C. pinnatifidum followed by C. judaicum, C. reticulatum and C. echinospermum. Furthermore, C. bijugum had the highest number of accessions with multiple resistance to the six stresses; two accessions were resistant to five stresses and 16 to four. According to the Shannon-Weaver diversity indices (H), five species showed discrete mean diversity indices which varied from 0.649 in C. pinnatifidum to 0.526 in C. judaicum, whereas C. chorassanicum, C. cuneatum and C. yamashitae showed the lowest Hs, which were respectively 0.119, 0.174 and 0.216. Pair-wise correlations among the six biotic and abiotic stresses showed the possibility of combining these resistances. Interestingly, multiple resistant accessions were predominantly of Turkish origin.