天山南麓山前平原植物群落物种多样性及空间分异研究

荒漠灌丛是天山南麓山前平原主要植被类型.本研究定量分析了山前平原植物群落物种多样性及生境尺度异质性的影响.结果表明:(1)天山南麓山前平原的植物群落多样性指数Simpson、均匀度指数McIntosh及丰富度指数Margalef都较低,在地貌带的过渡上,植物分布呈现均匀化.(2)海拔和地下水埋深是影响天山南麓山前平原植物群落物种多样性的重要环境指标.海拔梯度与物种多样性指数Simpson、Margalef及McIntosh均呈显著的线性正相关关系,物种多样性均随海拔高度的增加而增加;地下水埋深与物种多样性指数呈极显著的线性负相关关系,物种多样性随地下水埋深的增加而减小.(3)土壤含盐量与物种多样性指标无显著关系,但土壤含盐量与地下水埋深相关性显著,这是天山南麓山前平原土壤盐分空间异质性的一个重要特点.土壤盐分含量变化影响着植物群落物种组成,随土壤盐分含量增加,群落中盐生植物种类逐渐占据优势.(4)海拔的变化是决定天山南麓山前平原灌丛群落生境差异的主导因子.海拔差异表征了山前平原地貌、水文地质条件及土壤的变化,而随海拔变化的水热、水盐等干扰体系的差异则进一步导致了异质性的生境,进而影响不同植被类型中群落组成结构和多样性的差异.     

天山南坡高寒草地海拔梯度上的植物多样性变化格局

山地气候随海拔梯度变化使山地成为研究生物多样性的热点区域。在天山南坡巴音布鲁克高寒草地,对不同海拔梯度下的物种多样性进行了研究。结果表明共调查样地9个,出现植物34种,分属17科29属;物种丰富度随海拔升高呈明显的偏峰格局,在海拔3060m的天山羽衣草(Alchemilla tianschanica)草甸,物种组成最为丰富,出现植物17种,分属12科17属;Shannon-Wiener指数的变化范围为2.02~2.40,最小值出现在海拔2760m以紫花针茅(Stipa purpurea)为优势种的高寒草原,峰值则出现在3060m的天山羽衣草草甸,Shannon-Wiener指数随海拔梯度的变化趋势与物种丰富度基本相同,呈明显的偏峰格局;随海拔升高,Cody指数表现出明显的单峰格局;Shannon-Wiener指数与生长季温度存在显著负相关,而与生长季湿度和土壤含水量存在显著正相关。     

金佛山自然保护区中国种子植物特有属

在野外调查和数量系统分析的基础上,对金佛山自然保护区的中国种子植物特有属进行了研究。结果表明,金佛山自然保护区分布有中国种子植物特有属51个,占该区种子植物属总数的4·59%,占全国同类属数的20·99%,其中裸子植物4属4种,被子植物4属65种。在被子植物中,双子叶植物占41属58种;单子叶植物占6属7种。在51个特有属中,单种属有39属,占总数的76·47%。唇形科、苦苣苔科、伞形科、兰科含特有属较多约占本区同类属的31·37%。特有属的生活型以多年生草本和落叶木本为主,两者共4属,占特有属总数的80·39%。特有属的分布区类型以东部和中部特有分布为主,并具有少量的南部特有分布成分,51个特有属的分布区类型表明了该区系由热带性质向温带性质的过渡性特征。本区的特有属植物多分布于低山和中山。金佛山与大巴山、武陵山、神农架关系较为密切,它们同属于川东-鄂西特有现象中心(或三峡中心)。在51个中国种子植物特有属中古特有属和珍稀濒危物种占有较大的比例,本区无疑是古植物区系的重要避难所。     

小相岭山系大熊猫大中型伴生兽类

本文总结了小相岭山系与大熊猫同域分布的大中型兽类的种类、主要遗留痕迹的鉴别特征以及对大熊猫的影响;统计了大熊猫伴生动物的样线遇见率,反映了不同伴生动物的相对数量。本文对进一步研究小相岭山系大熊猫的伴生动物,更好地保护大熊猫具有一定的参考价值。     

Dispersal differences predict population genetic structure in Mormon crickets

Research investigating the geographical context of speciation has primarily focused on abiotic factors such as the role of Pleistocene glacial cycles, or geotectonic events. Few study systems allow a direct comparison of how biological differences, such as dispersal behaviour, affect population genetic structure of organisms that were subdivided during the Pleistocene. Mormon crickets exist in solitary and gregarious 'phases', which broadly correspond with an east-west mtDNA division across the Rocky Mountains. Gregarious individuals form bands that can move up to 2 km daily. This study assessed whether population genetic structure results mainly from deep Pleistocene vicariance or if we can also detect more recent genetic patterns due to phase and dispersal differences superimposed on the older, deeper divisions. We found that separation in refugia was a more important influence on genetic divergence than phase, with the Rockies acting as a barrier that separated Mormon cricket populations into eastern and western refugia during Pleistocene glacial cycles. However, patterns of isolation by distance differ between eastern and western clades for both mitochondrial and nuclear DNA, with greater divergence within the eastern, solitary clade. An mtDNA haplotype mismatch distribution is compatible with historical population expansion in the western clade but not in the eastern clade. A persistent (and possibly sex-biased) difference in dispersal ability has most likely influenced the greater population genetic structure seen in the eastern clade, emphasizing the importance of the interaction of Quaternary climate fluctuations and geography with biotic factors in producing the patterns of genetic subdivision observed today.     

Tree-line changes along the Andes: implications of spatial patterns and dynamics

The Andes provide an extensive latitudinal and topographical framework for studying the factors that control the spatial patterns of forests (timberlines) and their species components expressed through the presence of tree growth forms (tree lines). Despite consistent overall similarities in landscape patterns, many processes must be unique, given the dramatic differences in species richness and biophysical constraints along the Andes. In all cases evaluated to date, morphological plasticity is a common trait of plant species that dominate at tree lines. In fact, many changes observed can be related to species-specific traits. Physiological limitations on tree growth form only explain species limits, while disturbances and cyclical climate fluctuations interact to affect many landscape patterns. Over long periods of time, tree lines provide unique habitats and perhaps opportunities for speciation. Understanding the spatial organization of tree-line dynamics is one viable research approach for evaluating the likely past fluxes and possible future changes.     

Mechanisms underlying the impacts of exotic annual grasses in a coastal California meadow

Biological invasions can impact the abundance and diversity of native species, but the specific mechanisms remain poorly discerned. In California grasslands, invasion by European annual grasses has severely reduced the quality of habitat for native forb species. To understand how introduced grasses suppress native and exotic forbs, we examined the response of a Southern California grassland community to factorial removals of live grass and the litter produced in previous seasons. To examine the role that belowground competition for water plays in mediating the impact of grasses, we crossed grass and litter removal treatments with water addition. Our results show that forbs were almost equally suppressed by both competition from live grass and direct interference by litter. Water addition did not ameliorate the effect of grass competition, suggesting that water was not the resource for which plants compete. This evidence is consistent with the susceptibility of forbs to light limitation, especially considering that litter does not consume water or nutrients. Interestingly, despite different histories of co-occurrence with annual grass dominants, native and exotic forbs were comparably suppressed by exotic grasses. Our results indicate that suppression by both live and dead stems underlie the influence of exotic grasses on forb competitors.     

Les palynomorphes du Bajocien supérieur : un premier PALYNO-DATA pour les Monts de Rhar Roubane (Algérie nord occidentale)

Apart from the few works carried out in the North Tethyan basins, the palynological study of Mesozoic outcrops is still rare. Thus, the present study devoted to the Zahra Marls Formation (upper Bajocian) of the Rhar Roubane Mountains (northwestern Algeria), allowed us for the first time to inventory 44 different taxa. The palynological assemblages studied are strongly dominated by trilete spores (17 genera and 26 species), the most abundant of which are Concavissimisporites variverrucatus, Cyathidites australis and Cyathidites minor. Pollen grains are relatively frequent (10 genera and 16 species), while acritarchs and algae are represented by only two taxa (Micrhystridium sp. and Botryococcus sp.). In addition, the sporopollinic spectra dominated by the terrestrial elements are represented mainly by the spores of Pteridophyta and Bryophyta and gymnosperm pollen.     

近60年秦岭山地旱涝变化规律

随着极端气候变化,山地灾害频发。基于秦岭山地32个气象站点的实测数据,以标准化降水蒸散指数(SPEI)为旱涝量化指标,研究了过去60年秦岭山地旱涝时空变化特征、频率、周期等变化规律,结果表明：(1)1960—2019年,秦岭山地年SPEI指数以0.124/10a的速度下降,其中,90.23%的面积呈显著下降趋势,1.96%的面积呈显著上升趋势,并在1990年发生干旱突变;秦岭北坡的干旱化趋势大于南坡,且高海拔地区干旱化更为明显。(2)突变前秦岭山地湿润比例平均值为36.94%,突变后下降为18.19%;干旱比例由突变前的17.64%急剧上升到突变后的38.19%;突变前30年秦岭山地极端干旱事件、严重干旱事件极少发生,发生频率几乎为0;突变后30年严重干旱和极端干旱事件发生频率增加,秦岭南北坡极端湿润和严重湿润事件近乎销声匿迹。(3)整体上,太阳黑子与秦岭山地旱涝变化以显著负相关关系为主;ENSO事件对秦岭山地的旱涝变化影响较大,在La Nina年易发生洪涝事件,在El Ni1o年易发生干旱事件;在不同时域范围内,海表温度距平(SSTA)对秦岭山地旱涝变化的影响不同：1990年以前,S...     

秦岭南坡松栎林群落演替过程中种间联结性和相关性研究

为了揭示秦岭南坡松栎林群落动态变化过程中物种间关系与群落演替的相互作用,基于2×2列联表,采用方差比率法、χ2检验、Jaccard指数和Spearman秩相关性系数探讨了油松林→松栎混交林→锐齿栎林演替序列过程中3个演替阶段群落优势种群的种间联结性和相关性。结果表明:(1)油松林、松栎混交林和锐齿栎林群落总体联结性均为显著正联结,各自具有相对的稳定性。(2)油松和松栎混交林群落正负联结性和相关性比例较小,群落稳定性均低于锐齿栎林群落。(3)先锋种间及其与前期过渡种间、顶级种间及其与后期过渡种间竞争较为激烈,过渡种间(包括前期过渡种间、前期过渡种与后期过渡种间、后期过渡种间)正联结占优势,较为稳定。(4)不同演替阶段群落可分别划分为4个、5个、4个生态种组。研究认为,秦岭南坡松栎混交林演替过程中种间关系逐渐趋于稳定共存,实践中及时调整种间关系可促使秦岭南坡松栎林群落趋于健康稳定,有效缩短演替的进程。