Vegetational stability and rare species from Early Holocene Lewis

Summary

Strata of complex geomorphological origin at Skigersta in the northeast of the Isle of Lewis include organic sediments which have provided a detailed pollen profile and two Early Holocene radiocarbon dates. These two sources of evidence suggest that a stable, pre-woodland, species-rich grass and sedge landscape may have existed for at least one thousand radiocarbon years (10,250 to 9250 BP). Included in the pollen taxa are Koenigia islandica and Polemonium caeruleum, neither of which is now native to Lewis. The former was present in the Middle Devensian (c. 30 kyr BP), perhaps hinting at survival in a local refugium during the Late Devensian glaciation.     

Divergence in germination traits among arctic and alpine populations of <Emphasis Type="Italic">Koenigia islandica</Emphasis>: light requirements

Light is known to regulate conservative germination strategies and the formation of seed banks. Although these strategies are crucial to survival in tundra environments—especially for annuals—light requirements for germination in arctic–alpine species are seldom investigated. Furthermore, environmental differences between arctic and alpine regions are expected to lead to evolutionary divergence among conspecific populations in seed germination strategies. In this study, we report important differences in germination light requirements among six arctic and alpine populations of the annual Koenigia islandica. Light had little effect on germination of the seeds from Iqaluit (Nunavut, Canada), Yukon (Canada), and Jasper (Alberta, Canada), whereas the seeds from the most severe climates, Svalbard (Norway) and Colorado (USA), had strong light requirements. Stratification of the seeds had little influence on their germination light requirements, with the exception of the population from Dovre (Norway), in which it induced a strong light requirement. Possible adaptive explanations and some implications of these observed germination patterns are discussed.     

中国蓼属分叉蓼组和冰岛蓼属植物叶下表皮微形态研究

采用光学显微镜对中国蓼属分叉蓼组(Polygonum section Aconogonon)和冰岛蓼属(Koenigia)的21种植物的叶下表皮微形态进行了观察研究。结果表明,其叶下表皮微形态特征可分为三种类型：（1）气孔器类型为无规则型,表皮细胞多边形,垂周壁为波状;（2）气孔器类型为无规则型兼有非典型不等型,表皮细胞为多边形或不规则形,垂周壁为平直弓形或波状;（3）气孔器类型为不等细胞型,表皮细胞多边形,垂周壁为平直弓形。分叉蓼组（西伯利亚蓼除外）植物的叶表皮气孔器类型具有高度一致性,说明该组是一个自然类群。本文研究结果不支持将大铜钱叶蓼(Polygonum forrestii Diels)、铜钱叶蓼(P. nummularifolium Meissner)划归于冰岛蓼属的处理意见;支持将西伯利亚蓼(P. sibiricum Laxm.)独立成属,即西伯利亚蓼属(Knorringia Tzvel.)的观点;同时也支持仍将多穗蓼(P. polystachyum Wall.ex Meissner)和松林蓼(P. pinetorum Hemsl.)归在分叉蓼组的处理意见。     

分子证据支持蓝药蓼和大铜钱叶蓼归入冰岛蓼属

蓝药蓼Polygonum cyanandrum Diels和大铜钱叶蓼P.forrestiiDiels是否应归于冰岛蓼属Koenigia至今未得到很好的解决。本文利用叶绿体DNA的atp B-rbc L序列来评价这两个物种的亲缘关系和属的归属。对这两个物种以及相关代表种的atp B-rbcL序列分析发现,该片段的长度有较大的变异。从753bp到902bp;存在丰富的系统发育变异位点。系统发育分析表明：蓝药蓼和大铜钱叶蓼与冰岛蓼丘islandica聚为支持率较高的分支。而蓼属Polygonum代表种和其他属的代表种组成另外的分支,表明这两个种应置于冰岛蓼属。这一结果与花粉和染色体证据相吻合。根据这些证据以及形态学特征,还对冰岛蓼属与蓼属的范围与界定进行了讨论。     

中国广义冰岛蓼属果实形态特征

应用扫描电镜对冰岛蓼属（Koenigia L.）8个物种的果实形态与果皮微形态进行了观察。结果表明,这些果实可分为3类：类型Ⅰ：瘦果长卵形至宽卵形,中部或中上部最宽,双凸镜状或3棱状,棱脊有或无;表面粗糙或光滑,具纵向断棱状纹饰,或具波状纹饰,这种类型有冰岛蓼、铜钱叶蓼、青藏蓼、大铜钱叶蓼4种;类型Ⅱ：瘦果卵形,中部膨大,具有3棱脊,但棱脊不显著。这种类型仅小叶蓼1种;类型Ⅲ：瘦果卵形,中间最宽但不膨大,具有3棱脊,且棱脊显著;表面光滑,具多皱纹饰,或凹凸不平纹饰,或具疣状纹饰,这种类型包括细茎蓼,蓝药蓼和柔毛蓼3种。研究结果支持将柔毛蓼与蓝药蓼作独立分种处理、而冰岛蓼与青藏蓼关系很近。     

基于trnL-F序列推测冰岛蓼属的系统发育

冰岛蓼属的界定一直存在争议,本实验以塔黄为外类群,采用最大简约法对冰岛蓼属及其近缘类群的trnL-F序列进行了系统发育分析,结果表明:(1) 冰岛蓼(Koenigia islandica)和大铜钱叶蓼(Polygonum forrestii)为姊妹群,自展分析的支持率为100%,因此,大铜钱叶蓼应归于冰岛蓼属;(2) 冰岛蓼和分叉蓼组植物聚在一起,自展支持率为99%,说明它们之间有很近的亲缘关系.     

中国冰岛蓼属植物花粉形态的研究

采用光学显微镜和扫描电镜对国产冰岛蓼属Koenigia L. 9种植物的花粉形态进行了观察。结果表明：花粉均为球形;直径为17.0-32.5 μm（包括刺长）;萌发孔有7(-8)赤道环沟、散沟、散孔;外壁纹饰均为刺状。根据萌发孔类型和外壁纹饰,将该属花粉划分为3种类型,即细冰岛蓼型（Delicatulum-type）、大连线冰岛蓼型（Forrestii-type）及冰岛蓼型（Koenigia-type）。细冰岛蓼型花粉的主要特征是具7(-8)赤道环沟,覆盖层无穿孔,外壁纹饰为显著的长刺状,此种类型的植物有细冰岛蓼K. delicatula （Meisn.） Hara。大连线冰岛蓼型花粉的主要特征是具12散沟,覆盖层无穿孔,外壁纹饰为显著的长刺状,此种类型的植物有大连线冰岛蓼K. forrestii (Diels) Měsíek & Soják 及连线冰岛蓼K. nummularifolia (Meisn.) Měsíek & Soják。冰岛蓼型花粉的主要特征是具15,20(-30)散孔,覆盖层无穿孔,外壁纹饰为显著的长刺状,此种类型的植物有冰岛蓼K. islandica L.、蓝蕊冰岛蓼K. cyanandra (Diels) Měsíek & Soják、线茎冰岛蓼K. nepalensis D. Don、柔毛蓼K. pilosa Maxim.、陕甘蓼K. hubertii (Lingelsh.) Měsíek & Soják及青藏蓼K. fertilis Maxim.。结果表明冰岛蓼属的花粉形态具有重要的分类学意义,研究结果支持Koenigia的属的地位,大铜钱叶蓼Polygonum forrestii Diels和铜钱叶蓼P. nummularifolium Meisn.应从蓼属分叉蓼组Polygonum L. sect. Aconogonon Meisn.中移入冰岛蓼属中,细冰岛蓼、蓝蕊冰岛蓼、青藏蓼、陕甘蓼、线茎冰岛蓼和柔毛蓼应从蓼属头状蓼组Polygonum L. sect. Cephalophilon Meisn.中移入冰岛蓼属中。