Arbuscular mycorrhizal impacts on competitive interactions between Acacia etbaica and Boswellia papyrifera seedlings under drought stress

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses. In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies. We compared the extent of interspecific competition with that of intraspecific competition.Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza (AM) and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A. etbaica and the slowly growing species B. papyrifera. A factorial experimental design was used. The factors were AM, two water levels and five species combinationsImportant findings Seedlings of both species benefitted from AM when grown alone, and the positive growth response to pulsed water availability in B. papyrifera seedlings was in contrast with the negative growth response for A. etbaica seedlings. AM also affected the competitive performance of both species. B. papyrifera was not affected by intraspecific competition, whereas A. etbaica was negatively affected compared to the seedlings grown alone. This effect was stronger in the presence of AM. In interspecific competition, A. etbaica outcompeted B. papyrifera. Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition, and the aggressivity index of A. etbaica remained unchanged. The extent to which AM influences plant competition in a drought-stressed environment may depend on belowground functional traits of the species. AM and pulsed water availability could modify the balance between intraspecific and interspecific competition. By affecting the balance between intraspecific and interspecific competition, both factors could impact the establishment and survival of seedlings.     

Genetic enrichment of the arctic clonal plant Saxifraga cernua at its southern periphery via the alpine sexual Saxifraga sibirica

Isolation of populations at the margins of a species range may lead to decreasing genetic diversity via genetic drift and inbreeding. Hybridization between peripheral populations of two species can, however, counteract genetic impoverishment. The mainly clonal, polyploid plant Saxifraga cernua has a wide arctic distribution but also extends southwards into alpine sites. In the Ural Mountains, its peripheral distribution overlaps with that of its sexually reproducing, diploid relative Saxifraga sibirica, and fertile polyploids of more or less intermediate appearance are found in this overlap zone. We used amplified fragment length polymorphism (AFLP) analysis to address the potential impact of interspecific gene flow on genetic diversity in the peripheral populations. A total of 149 plants from 17 populations along a 1650 km south-north gradient were analysed for 253 markers. The results suggest that three Middle Ural populations containing fertile and morphologically more or less intermediate plants have been affected by hybridization. All of these plants formed a strongly supported (100%) group with S. cernua in a neighbour-joining tree, but their AFLP phenotypes assigned either to S. cernua or to artificial (simulated) F(1) hybrids between S. cernua and S. sibirica in multilocus assignment tests. The three populations were highly diverse with virtually every plant representing a distinct AFLP phenotype, providing additional evidence for formation of later-generation hybrids and/or backcrossing to S. cernua. In contrast, other peripheral populations of S. cernua were typically monoclonal, suggesting that hybridization with S. sibirica can increase genetic diversity in S. cernua at its southern periphery.     

Molecular evidence for polyploid origins in Saxifraga (Saxifragaceae): the narrow arctic endemic S. svalbardensis and its widespread allies

The recently described polyploid Saxifraga svalbardensis is endemic to the arctic archipelago of Svalbard. We investigated relationships among four closely related species of Saxifraga in Svalbard and tested three previously proposed hypotheses for the origin of S. svalbardensis: (1) differentiation from the morphologically and chromosomally variable polyploid S. cernua; (2) hybridization between the diploid S. hyperborea and S. cernua; and (3) hybridization between the tetraploid S. rivularis and S. cernua. Fifteen populations were analyzed using random amplified polymorphic DNAs (RAPDs) and nucleotide sequences of the chloroplast gene matK and the internal transcribed spacers (ITS) of nuclear ribosomal DNA (rDNA). RAPD and matK data suggest that S. svalbardensis has originated from a hybrid with S. rivularis as the maternal parent and S. cernua as the paternal parent, possibly a single time, whereas ITS data could not be used to discriminate among the hypotheses. The data also suggest that the diploid S. hyperborea is a progenitor of the tetraploid S. rivularis. The four populations examined of S. svalbardensis were virtually identical for RAPD and ITS markers, whereas S. cernua showed high levels of variation, suggesting that the latter polyploid either has formed recurrently or has undergone considerable differentiation since its origin.     

Two new species of Acacia (Leguminosae) from north-eastern Somalia

Acacia qandalensis , sp. nov., and A. tephrophylla , sp. nov., from north-eastern Somalia, are described and illustrated. A. qandalensis grows on limestone rocks, often in steep and exposed places, and is known from 600–1400 m altitude from the Cal Miskaat Mts in the west to near Bunder Murrayha in the east. A. tephropkylla obviously has a more restricted area of distribution and is known only from stony or rocky places on limestone at 1300–1800 m altitude in the Cal Miskaat Mts, where it is the dominant woody plant over large areas. Both species are related to A. etbaica.     

Same parental species, but different taxa: molecular evidence for hybrid origins of the rare endemics Saxifraga opdalensis and S. svalbardensis (Saxifragaceae)

Saxifraga opdolensis was described from Oppdal in southern Norway and hypothesized to have originated as the hybrid S. cernua × rivularis or to have been derived from a S . cernua-like progenitor. We tested these alternative hypotheses using uni- and biparentally inherited molecular markers observed in S. opdalensis and its putative parental species at the type locality: PCR-RFLPs (restriction fragment length polymorphisms in amplified fragments of chloroplast DNA; cpDNA), sequences of the cpDNA intron trnL and the spacer tmL-tmF , and RAPDs (random amplified polymorphic DNAs). The data provided unambiguous support for the hybrid hypothesis. The cpDNA analyses distinguished two well-differentiated chloroplast genomes, one in S. opdalensis and S. rivularis , and another in S. cernua . The majority of the RAPD markers showed distinct additivity in S. opdalensis relative to its postulated parental species. Thus, S. opdalensis has probably originated from a hybrid with S. rivularis as the maternal parent and S. cernua as the paternal parent. We also included S. svalbaardnsis in the present study because previous molecular analyses of Svalbard material have shown that this species had probably also originated as a hybrid between S. cernua and S. rivularis . The chloroplast genome of S. svalbaardnsis was identical to that of S. opdalensis , but the two species differed in many RAF'D markers. Although these two endemics probably have been derived from the same hybrid combination, they are morphologically and genetically distinct and should be referred to separate species. Differences between such independently originated hybrid taxa may result from intraspecific variation in their parental taxa. Saxufraga cernua comprises, for example, several highly divergent evolutionary lineages.     

Reproductive strategies in some arctic Saxifraga (Saxifragaceae), with emphasis on the narrow endemic S. svalbardensis and its parental species

Arctic saxifrages show conspicuous reproductive and chromosomal variation. We examined sexual and asexual traits in 43 phytotron-cultivated Svalbard populations of nine species, including the endemic, supposedly entirely asexual and aneupolyploid S. svalbardensis and its parental species, S. cernua and S. rivularis. All species were self-compatible hermaphrodites with low pollen/ovule ratios, including the strongly protandrous S. cernua , which previously has been reported as self-incompatible with an androdioecious mating system. Spontaneous selfing resulted in considerable seed set in several species and a few seeds in S. svalbardensis and S. cernua; hand-selfing and cross-pollination often increased seed set in the two latter species. Self-fertilized seeds of S. svalbardensis and S. cernua were viable and developed into normal, vigorous plants. Saxifraga rivularis and its close relative S. hyperborea were strongly autogamous. The bulbil-reproducing S. svalbardensis and S. cernua showed extreme variation in fertility, probably because of frequent aneuploidy. Many plants of S. cernua were fully fertile, suggesting that although natural seed set rarely has been observed, sexual reproduction is frequent enough to maintain its previously reported high levels of clonal diversity. Some plants of S. svalbardensis were also fairly fertile. This species may have considerable evolutionary potential; sexual events can lead to increasingly fertile genets with euploid chromosome numbers.     

Sunflower (Helianthus annuus L.) response to broomrape (Orobanche cernua Loefl.) parasitism: induced synthesis and excretion of 7-hydroxylated simple coumarins

The interaction of the parasitic plant Orobanche cernua with resistant and susceptible cultivars of Helianthus annuus L. was investigated. Using different bioassays to evaluate the early stages of the parasite life cycle (germination, attachment, penetration, and establishment), differences were observed between O. cernua-resistant and O. cernua-susceptible sunflower varieties. Germination of O. cernua seeds in the presence of resistant sunflower roots was approximately half that of germination in the presence of susceptible roots, and germinated seeds displayed enhanced browning symptoms. Parasite radicles or host-tissue around the contact point turned brown after O. cernua attachment to sunflower roots, especially in the resistant varieties. These observations suggested the possible accumulation of toxic compounds as a defence strategy in the resistant sunflower varieties. Sunflower 7-hydroxylated simple coumarins may play a defensive role against O. cernua parasitism by preventing successful germination, penetration and/or connection to the host vascular system. This hypothesis is supported by the following data: (i) coumarins inhibited the in vitro germination of O. cernua seeds induced by the strigol analogue GR(24) and caused a browning reaction in germinated seeds and (ii) resistant sunflowers accumulated higher levels of coumarins in roots and excreted greater amounts than susceptible varieties in response to O. cernua infection.     

Comparative studies on Orobanche cernua L. and O. cumana Wallr. (Orobanchaceae) in the Iberian Peninsula

The systematic treatment of Orobanche cumana Wallr. and O. cernua L. is controversial. Whereas some authors consider O. cumana as an infraspecific taxon of O. cernua , others treat it as a separate species. Furthermore, the nomenclature of the sunflower broomrape is unclear, and both names arc found without qualification in the literature. The objective of the present study has been to evaluate the distribution, morphology, and ecology of O. cernua and O. cumana in the Iberian Peninsula, as well as their seed oil fatty acid profile, which is a trait of great chemotaxonomic value. O. cernua was found parasitizing wild Compositac, mainly Artemisia spp., whereas O. cumana was exclusively found on cultivated sunflower. Both species clearly differ in morphological traits, especially plant height and build, length and structure of the inflorescence, corolla length and colour. Both species are characterized by contrasting seed oil fatty acid profiles, with high oleic acid concentration in O. cernua and high linoleic acid concentration in O. cumana. The evaluation of both taxa in the Iberian Peninsula gives additional support to those authors that treat them as separate species.     

Strigolactone analogues and mimics derived from phthalimide, saccharine, p-tolylmalondialdehyde, benzoic and salicylic acid as scaffolds

A series of new strigolactone (SL) analogues is derived from simple and cheap starting materials. These SL analogues are designed using a working model. The first analogue is a modified Nijmegen-1, the second contains saccharin as substituent (bio-isosteric replacement of a carbonyl in Nijmegen-1 by a sulfonyl group) and the third one is derived from p-tolylmalondialdehyde. These new SL analogues are appreciably to highly active as germination stimulants of seeds of Striga hermonthica and Orobanche cernua. The SL analogue derived from saccharin is the most active one. A serendipitous and most rewarding finding is that the compound obtained by a direct coupling of saccharin with the chlorobutenolide exhibits a high germination activity especially towards O. cernua seeds. Two other SL mimics are obtained from benzoic and salicylic aid by a direct coupling reaction with chlorobutenolide, both of them are very active germinating agents. These SL mimics represent a new type of germination stimulants. A tentative molecular mechanism for the mode of action of these SL mimics has been proposed.     

Cytogenetics and taxonomy of the genus Globba L. (Zingiberaceae) in Malaya

Hexaploid chromosomal races of Globba cernua Bak. and G. patens Miq. show overlap in geographical distribution. Hybrid swarms in three separate localities on the Main Range in Malaya are analysed both morphologically and cytologically. Evidence indicates that introgressive hybridization of G. cernua Bak. by G. patens Miq. has taken place.     

ASPECTS OF THE ECOLOGY OF KNERIA AURICULATA (PELLEGRIN, 1905) (PISCES: KNERIIDAE) FROM THE EASTERN TRANSVAAL SOUTH AFRICA

SUMMARY

Seven natural populations of Kneria auriculata occur in tributaries of the Crocodile River (Incomati System) on the eastern Transvaal escarpment. The routes it probably used to colonize these streams are discussed and used to explain its current restricted distribution with reference to its ecological requirements. Fish up to a fork length of 2,0 cm feed on invertebrates while larger fish utilize ‘Aufwuchs’, especially diatoms. This dietary difference results in an increase in the food spectrum and possibly also serves to limit competition between smaller and larger lengths groups. Relative gut lengths increase with an increase in fork length and this is correlated with a change in diet from invertebrates to diatoms. Observations on captive fishes indicated that adult fish are able to survive on a diet of Daphnia spp. The habitat of K. auriculata is considered to be unstable due to the occurrence of unpredictable summer floods in escarpment streams. As a result the species has a prolonged breeding season (October to April) while the presence of two size classes of ova indicate that it is a multiple spawner. This breeding strategy minimizes mortality in escarpment streams. The colonization by this fish of previously unsuitable and unavailable habitat indicates that it is a generalist. Its feeding habits and reproductive strategy indicate, however, that it has developed a certain degree of specialization in order to survive in a relatively unpredictable habitat. The conservation prospects of the seven natural and one translocated population varies from uncertain to good. Medium and long term conservation measures are needed to ensure the survival of this fish in the Transvaal.     

伸筋草类药用植物资源的初步研究

本文报道6种商品伸筋草类药用植物的本草考证、理化分析及药理试验。豚鼠离体肠平滑肌实验结果表明:玉柏石松(Lycopodium obscurum L.)和华中石松(L.centro-chinese Ching)的总提取物有较强兴奋作用,其次是扁枝石松(Diphasiastrum complanatum (L.) Holub),再次是垂穗石松(Palhimhaea cernua (L.) Franco et Vase)、石松(Lycopodium japonicum Thunb.)及藤石松(Lycopodiastrum casuarinodes (Spring) Holub)。这与各自的总生物碱含量相吻合。从抗血小板凝聚试验来看。玉柏石松总提取物作用最强,其次是扁枝石松。     

Angola’s central scarp forests: patterns of bird diversity and conservation threats

Despite Angola’s central scarp forests being recognised as a critical global priority for bird conservation, fine-scale information on threatened bird distributions and patterns of bird diversity are lacking. These data are essential to identify sites within the Western Angola Endemic Bird Area that should be targeted for conservation. First endemic and near-endemic species and subspecies, and species with isolated populations along the Angolan scarp were identified to highlight taxa of greatest priority for conservation and for use in studying the evolutionary origins of the region. Thereafter survey data collected during 2005 from 13 forest sites along the central scarp was analysed. These data show that there are three distinct bird communities across the width of the escarpment, each associated with a distinctive forest type. Of note is the finding that threatened and Near Threatened endemic species occur almost exclusively in the dry forests adjacent to the main escarpment, rather than in the moistest forests found on the main escarpment, which instead are richer in Congo Basin forest birds. Based on these data, summaries of ranges, populations and conservation threats are given for the seven most threatened bird species. Attention is drawn to threats to the habitats of greatest importance to these species. A conservation area network should be established that encompasses the full spectrum of bird diversity described, to ensure survival of current unique taxa and the future evolutionary potential of the area.     

新疆准噶尔盆地三个泉地区几种始新世哺乳类

本文记述了准噶尔盆地北缘三个泉地区依希白拉组中采到的踝节类、蹠行类、全齿类和恐角类化石。根据这些化石,依希白拉组的时代可能和北美中始新世勃力吉期相当。文内,通过文献分析,认为周明镇和胡长康(1956)记述的真恐角兽的前臼齿可能产自三个泉附近的依希白拉组。     

A new species of Farsetia (Brassicaceae) from Somalia

Farsetia frutkans , sp. nov., from a limestone escarpment of NE Somalia is described and illustrated.     

Andrachne fragilis (Euphorbiaceae), a new species from Somalia

Andrachne fragilis is described from north-facing limestone rocks of the escarpment in NE Somalia.     

A new species of Microcharis (Leguminosae) from Somalia

The new species Microcharis omissa , from the sandstone escarpment near Yasoomman in central Somalia, is described. This apparently narrow endemic is closely related to M. sessilis in north-eastem Somalia.     

The use of drinking sites, wallows and salt licks by herbivores in the flooded Middle Zambezi Valley

In the unflooded Middle Zambezi Valley, water was available for drinking in zoogenous pools in the deciduous woodlands of the escarpment hills only during, and for a short period after, the rains. For 5 or 6 months each year these pools were dry. During the dry season the majority of large mammals drank either from remnant pools in stream beds, or migrated to the Zambezi flood plain where water was available in the Zambezi River and in pools on the flood plain. In the part of the valley filled by Lake Kariba the Zambezi and its flood plain have been inundated, and the lake shore now lies permanently in the deciduous woodlands of the escarpment hills. Although the former riverine dry-season water sources have been removed, new sources are available along the lake shore. The suitability of the shore as a drinking site is affected by its exposure to wave action, its pitch, its soil type, and the vegetation type abutting on it, as well as by the preferences of the species using it. Elephant modify drinking sites on the shore by digging water-filled holes at the water's edge in clay soil, and elephant, buffalo and rhinoceros create wallows in similar situations. The holes dug by elephant are much used by antelope, especially impala, for drinking. By analogy with elephant-created pools in the woodlands, these zoogenous pools on the lake shore may have been a source of sodium for species drinking there. Such sources were not widely available in the dry season in the unflooded Zambezi Valley.     

On the occurrence of sexual reproduction in Saxifraga cernua and S. foliolosa (Saxifragaceae)

In all contemporary floras, the two circumpolar arctic species Saxifraga cernua and S. foliolosa are claimed to reproduce only by vegetative means (bulbils) and to have abandoned sexual reproduction. Scattered records in the literature indicate that this is erroneous, and that seed is set irregularly and at a low rate in both species. An inventory of herbarium material supports this view. Field studies at Latnjajaure, N Swedish Lapland, demonstrate that both species have an androdioecious mating system, a phenomenon which is extremely rare in natural plant populations. The two gender classes within each species are maintained by self-incompatibility in hermaphorodites and a higher rate of vegetative propagation in female-sterile plants. Hermaphrodites are rare, especially in S. cernua , and most populations consist exclusively of female-sterile plants. The sparsity of fruiting material in herbaria is regarded to be, in part, a result of low frequency of collecting, due to the in-conspicuousness of the plants in this stage. Scanning electron micrographs of seeds of the two species are provided.
Flora Nordica Notes no. 5.     

The effects of abrupt topography on plankton dynamics

Plankton population dynamics in the upper layer of the ocean depends on upwelling processes that bring nutrients from deeper waters. In turn, these depend on the structure of the vertical velocity field. In coastal areas and in oceanic regions characterized by the presence of strong submarine topographic features, the variable bottom topography induces significant effects on vertical velocities and upwelling/downwelling patterns. As a consequence, large plankton and fish abundances are frequently observed above seamounts, canyons and steep continental shelves. In this work, the dynamics of an NPZ (nutrient-phytoplankton-zooplankton) system is numerically studied by coupling the ecosystem model with a quasi two-dimensional (2D) fluid model with topography. At variance with classical 2D approaches, this formulation allows for an explicit expression of the vertical motions produced when fluid columns are squeezed and stretched as they experience changes of depth. Thus, input or output of nutrients at the surface are associated with fluid motion over the bottom topography. We examine the dynamics of a cyclonic vortex over two basic topographies: a steep escarpment and a submarine mountain. We show that plankton abundance over the escarpment is modulated by the passing of topographic Rossby waves, generated by the vortex-topography interaction. In such configuration, advection effects driven by the flow over the escarpment are of limited relevance for the dynamics of biological fields. By contrast, we find that the flow resulting from the interaction of a vortex with a seamount is sufficiently strong and persistent to allow for a remarkable increase of nutrients, and a corresponding enhancement of phytoplankton and zooplankton concentrations. Over the seamount, advection effects associated with trapped flow perturbations around the summit play an essential role.