Gunnar Horn

At the peak time of the sailing ship trade in the latter half of the nineteenth century, ballast was brought to Vestfold partly from vessels loading timber, lumber or ice, and partly from vessels brought to the numerous shipyards for careening and repair. Most of the alien plants which were introduced with ballast into Vestfold were casuals, which disappeared when the ballast traffic ceased at the time of World War I. Others, like Euphorbia peplus (Petty Spurge, Byvortemelk), may still be found close to some of the old ballast heaps. A few have managed to extend their area: Melilolus officinalis (Common Melilot, Lege-sleinkløver) and M. alba (White Melilot, Kvit sleinkhver) are established at several ruderal places. Malricaria matricarioides (Rayless Mayweed, Tunbalderbrå) occurs today at most built-up areas in the province.     

Ballastplassene fra seilskutetiden – innfallsporter for fremmede planter til Norge

Shipping statistics, state and local by-laws concerning harbours, and reports from harbour authorities have been investigated to obtain a picture of the size and pattern of ballast traffic in Norway in the era of sailing ships. Alien plants invaded the country through ballast thrown ashore, e.g. public ballast heaps, ballast brought by the captains to their properties, and ballast unloaded from vessels brought to shipyards for careening and repair.     

Vegetational development from about 12,000 to 6,000 years B.P. in the counties of Agder and Telemark,South Norway

Sediment cores from several localities in Agder and Telemark are pollen analytically investigated. The immigration of some plant species during the time interval from about 12,000 to 6,000 years B.P. is discussed. The oldest samples contained pollen typical of a pioneer vegetation. The plant immigration is partly ¹⁴C-dated, partly dated only by interpolation or estimation based on the ¹⁴C-dates. From these data, immigration and migration routes are suggested. Betula nana, Salix, Juniperus, Betula, Populus and some herbs immigrated to Vest-Agder from the south or west, Ulmus, Quercus and possibly Tilia platyphylla from the south, Hippophaë and possibly Alnus from the east. It is suggested that Corylus may have come to the area with the first human inhabitants. Perhaps Tilia cordata has more immigration routes. Pinus and Calluna were among the early but not the first immigrants. Their immigration routes arc uncertain.     

Distribution and density of maguey plants in the arid Zacatecas Plateau, Mexico

The distribution and density of Agave salmiana ssp. crassispina within the state of Zacatecas, Mexico in the period from May 2001 to October 2002 is reported here for the first time. A field sampling was conducted based on a stratified random design. The resulting sample size was 154 plots, which were distributed randomly in three strata: high, medium, and low density. In each plot the following parameters were determined; latitude, longitude and number of agave plants that were classified into the following stages: juvenile; pre-reproductive; reproductive; and mature. The spatial data analysed using GIS showed that Agave salmiana ssp. crassispina is distributed over approximately 59,905 ha. Out of this total area, about 1142 ha were classified as high density, 51,529 ha as medium density, and 7234 ha as low density. The estimated density of agave plants in high-density strata was an average of 3125 individuals per hectare in comparison with 788 and 652 individuals per hectare for medium, and low density, respectively. It is recommended to protect the areas with higher density and to establish plantations in those with low density, but with the necessary conditions for the development and sustainability of this specie.     

湖南山区发展苎麻的气候生态环境优势

分析了湖南山区芒麻生长的气候生态环境条件，探讨了在山区加大竺麻生产力度的可能什，井就湖亩山区合理安排芒麻十产棵出了律议．     

Effects of sand burial on survival and growth of Artemisia halodendron and its physiological response

There is a great deal of literature on the effects of sand burial upon the survival and growth of desert plants, but the physiological adaption mechanisms of desert plants to sand burial have as yet ra...     

A paleolimnological record of Holocene climate and environmental change in the Temagami region,northeastern Ontario

The Arcellacean (Thecamoebian) fauna was assessed in five Holocene sediment cores obtained from James and Granite lakes in the Temagami region of northeastern Ontario. In addition, palynological analysis was carried out on two of these cores, one each from James and Granite lakes. The first indication of postglacial colonization by plants was the appearance of rare Cupressaceae pollen, dated to 10,800 yr BP. Plant diversity began to increase by 10,770 yr BP when Pinus spp. and Larix migrated into the area. The first appearance of arcellaceans occurred after 9650 yr BP in assemblages dominated by Centropyxis constricta and opportunistic Centropyxis aculeata. High abundances of charophytes in the cores until 8800 yr BP indicated that macroalgae were proliferating at this time. This deposition is interpreted to have occurred during the draining of an ice-marginal lake following the retreat of the Laurentide Ice Sheet. Based on pollen analysis, warmer conditions associated with the Holocene Hypsithermal prevailed in the area from 6250 to 4115 yr BP. The stable, open Great Lakes – St. Lawrence type forest that developed here at the beginning of the Hypsithermal continues to prevail to the present. The periodic colonization of the lake by beavers (Castor canadensis) acted as a control on water-level and eutrophication through the Holocene. Evidence of eutrophication was indicated in the core samples by the abundance of high levels of the alga Pediastrum and the arcellacean Cucurbitella tricuspis. Eutrophication periodically developed when beavers dammed a site, causing the rate of flow in drainage streams to slow and stagnant conditions occurred. When the site became depleted of the nearby trees, which were preferred by beaver (Betula, Alnus and Populus), the dam would be abandoned, causing the water-level to drop. Stagnant conditions were reduced as flow levels increased, reducing eutrophication and resulting in recovering forest stands. In addition, the lowering water levels would result in encroachment of the forest along the lake shore. This cycle occurred many times in the history of this lake as indicated by fluctuations in the size of arcellacean populations.     

Effects of nitrogen nutritional stress on the morphological and yield parameters of tomato (Solanum lycopersicum L.)

This investigation was carried out to better understand the effects of nitrogen stress on the growth and yield of tomato(Solanum lycopersicon L.). Seeds of S. lycopersicon(Ife No. 1 variety) were collected from the Osun–State Ministry of Agriculture, Oshogbo, Nigeria and planted in analyzed top soil. The plants were grown for a period of five weeks within which they were supplied with water and kept under optimum environmental conditions that enhanced normal growth. After this period, the plants were subjected to different levels of nitrogen stress which include: plants supplied with distilled water only(n), plants supplied with complete nutrient solution(N), plants supplied with nutrient solution in which nitrogen concentration sources was increased by a factor of 5(N5), and plants supplied with nutrient solution in which nitrogen concentration sources was increased by a factor of 10(N10). Analysis of Variance(ANOVA) results shows that there is no significant effect of stress on the growth and morphological parameters of tomato plants. However, there was a significant effect of nitrogen stress on the yield parameters. Nitrogen stress also caused an increase in the number and size of fruits produced in plants subjected with high nitrogen concentration.     

Gas exchange responses of a desert herbaceous perennial to variable sunlight in contrasting microhabitats

Over the course of a day, aridland plants experience a range of incident photosynthetic photon flux (PPF) spanning three orders of magnitude. Rapid photosynthetic responses to changes in PPF have large effects on individual plant carbon gain and water use patterns, hence are important to plant distribution and success. We investigated the response over time of photosynthesis (A), stomatal conductance (g), and inter-cellular CO₂ concentration (C_i) to step changes in PPF in a long-lived aridland perennial that typically occurs in two contrasting microhabitats, shade under shrubs of other species and unshaded inter-shrub spaces. An initial rapid response in A and C_i for plants in both microhabitats occurred after abrupt changes in PPF. This was followed by slower changes in these parameters during the rest of the light or dark period. Stomatal conductance responded more gradually to step changes in PPF. The initial increase in A after a dark cycle was significantly greater for plants under shrubs than for plants in inter-shrub spaces, but other changes in A, g and C_i did not differ. We attribute the similar responses in plants from different microhabitats to natural variations in solar radiation and limited selection for differentiation due to population gene pools dominated by plants in the open. Our results support the hypothesis that variable light regimes select for photosynthetic gas exchange processes that closely track changes in incident PPF. Our data also support the hypothesis that gas exchange responses to variable light regimes in aridland plants minimize trade-offs between carbon gain and water loss.     

Geographical patterns of tree-limits of Norway spruce and Scots pine in the southern Swedish Scandes

The tree-limit altitudes of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) from 180 sites (within an area of 95?km?×?165?km) in the southern Scandes were correlated with the geographical variables latitude, longitude and distance to the sea. The results were compared with a similar investigation of the tree-limit of mountain birch (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) in the same area. The three tree-limit altitudes showed good negative correlation with latitude, poor correlation with longitude and good positive correlation with the distance to the sea, suggesting that on a regional scale the altitudes are controlled by macroclimate. At some sites, local topoclimatic features, some of which were partially aspect-dependent, may cause deviations in the regional pattern of tree-limit altitude that is set primarily by summer temperature. Tree-limit responses to potential future climate warming will probably differ substantially in magnitude from site to site in relation to local topography and associated ecological constraints.     

Plant functional traits and microbes vary with position on striped periglacial patterned ground at Glacier National Park,Montana

The retreating snowfields and glaciers of Glacier National Park, Montana, USA, present alpine plants with changes in habitat and hydrology. The adjacent and relic periglacial patterned ground consists of solifluction terraces of green, vegetation-rich stripes alternating with sparsely vegetated brown stripes. We established georeferenced transects on striped periglacial patterned ground for long-term monitoring and data collection on species distribution and plant functional traits at Siyeh Pass and at Piegan Pass at Glacier National Park. We documented species distribution and calculated the relative percent cover (RPC) of qualitative functional traits and used 16S rRNA from soil samples to characterize microbial distribution on green and brown stripes. Plant species distribution varied significantly and there were key differences in microbial distribution between the green and brown stripes. The rare arctic-alpine plants Draba macounii, Papaver pygmaeum, and Sagina nivalis were restricted to brown stripes, where the RPC of xeromorphic taprooted species was significantly higher at the leading edge of the Siyeh Pass snowfield. Brown stripes had a higher percentage of the thermophilic bacteria Thermacetogenium and Thermoflavimicrobium. Green stripes were co-dominated by the adventitiously-rooted dwarf shrubs Salix arctica and the possibly N-fixing Dryas octopetala. Green stripes were inhabited by Krummholz and seedlings of Abies lasiocarpa and Pinus albicaulus. Prosthecobacter, a hydrophilic bacterial genus, was more abundant on the green stripes, which had 6,524 bacterial sequences in comparison to the 1,183 sequences from the brown stripes. While further research can determine which functional traits are critical for these plants, knowledge of the current distribution of plant species and their functional traits can be used in predictive models of the responses of alpine plants to disappearing snowfields and glaciers. This research is important in conservation of rare arctic-alpine species on periglacial patterned ground.

     

Two field and greenhouse diseases ofProsopis(mesquite)

Canker and tip-dieback diseases have been found in field and greenhouse plantings ofProsopisbeing examined in agroforestry trials in South Texas. Several fungal species were associated with the field cankers, most notably aLasiodiplodiaand aPestalotiopsis. In the greenhouse, a tip-dieback as well as a canker disease that began at pruning cuts on the stock plants was seen.Pestalotiopsiswas most commonly isolated from these plants. Isolated cultures of theLasiodiplodiaand thePestalotiopsistogether with several other often associated fungi, (includingAlternariaFusarium) were tested for pathogenicity on young mesquite plants. OnlyLasiodiplodiaandPestalotiopsisproduced cankers under the conditions tested when spores were applied using wound inoculation techniques.Pestalotiopsisrequired high wound inoculation techniques.Pestalotiopsisrequired high humidity and proved much less damaging compared toLasiodiplodia, which closely mimicked the field symptoms. Benlate was found to give the greatest growth inhibition of these fungal pathogens inin vitrofungicide tests.     

Fruit polymorphism in ephemeral species of Namaqualand: IV. Growth analyses of plants cultivated from the dimorphic diaspores

Growth analyses were conducted on two polymorphic annual species, Dimorphotheca sinuata and Arctotis fastuosa of Namaqualand, Republic of South Africa. Plants cultivated from disc diaspores of D. sinuata produced significantly more inflorescences, produced bigger mature plants and allocated more biomass to reproduction than plants cultivated from ray diaspores. Plants of both D. sinuata and A. fastuosa growing on less disturbed sites in the field allocated more biomass to reproduction than plants growing on more disturbed sites. Reproductive allocation of A. fastuosa increased with a decrease in plant size, whereas reproductive allocation was not affected by plant size in the case of D. sinuata.     

Notiser

The author introduces a locality in Sandviki by Lake Totak in Telemark, Southern Norway, the highest place known for elms in Scandinavia (830 m a.s.l.). With the elms are several other thermophilous plants, rarely seen in the surrounding country, supporting the idea of a relict dating back to the post-glacial warmth period. The occurrence of elm in Sandviki was protected by law, 29 October 1971.     

Charcoal morphotypes in lake sediments from British Columbia (Canada): an assessment of their utility for the reconstruction of past fire and precipitation

Quantitative analysis of variations in morphological types of charcoal were undertaken in sediment cores from three lakes on the Interior Plateau (BC, Canada) over the period AD 1919–2000. Seven distinct morphological types of charcoal were identified based on particle shape and structural features and were compared with seasonal precipitation and recorded area burned within 20 km-radius of study lakes. Fragile-type charcoal fragments, termed type M, displayed significant relationships to recorded area burned in sediment cores from Prosser (r ² = 0.5; p = 0.0001) and Opatcho (r ² = 0.2; p = 0.02) lakes. However, nonsignificant correlations (p > 0.05) were found between total charcoal and area burned. Robust and highly elongated morphotypes C and F were correlated to recorded spring precipitation (r ² = 0.5; p = 0.002) in Opatcho Lake. Charcoal from a sediment core from Big Lake, the lake with the largest watershed, was significantly but inversely related to past fires (r ² = 0.44; p = 0.0003), suggesting important contributions from secondary transportation and deposition. Models were developed to infer relative area burned and precipitation for the study lakes. Our results suggest that charcoal morphotypes are related to the biogeoclimatic and lake watershed characteristics. This study also suggest that charcoal morphotypes can provide insights on past fire and climate, which was not possible based on traditional analysis of total charcoal.     

Holocene palaeoecology of southwest Greenland inferred from macrofossils in sediments of an oligosaline lake

We retrieved a lake sediment record from an oligosaline, meromictic lake in southwest Greenland. The record spans the last 8,200 cal. years and was radiocarbon dated and analysed for macroscopic remains of plants and animals. The record extends the known history of several invertebrate species back in time, and provides minimum ages for their immigration to Greenland after the last deglaciation. Shells of the ostracod Ilyocypris bradyi were found in sediments dated to the time interval c. 7,000–6,500 cal. years BP. Shells of this species were found previously in a nearby oligosaline lake, where its occurrence was dated to about the same short time interval. The species is a thermophilous, non-arctic taxon that is absent from the present day Greenland fauna, and we suggest that its former occurrence in west Greenland marks the peak of the Holocene thermal maximum. This is in agreement with other records from Greenland.     

The impact of shade on establishment of shrubs adapted to the high light irradiation of semi-arid environments

Light may be an important limiting resource that influences community structure of chenopod shrublands. As part of a larger study that aimed to determine the factors that influence chenopod community structure, the focus of this study was the influence of plant canopy on the growth and establishment of smaller plants. We therefore measured the height and cover of three chenopods (Enchylaena tomentosa, Maireana brevifolia and Maireana georgei) when growing within and outside of the canopy of Atriplex bunburyana under field conditions. All three chenopods had lower cover and E. tomentosa was taller when growing within the canopy of A. bunburyana in comparison to those growing outside of the canopy. The chenopods were then grown under three artificial shade regimes. Plant height, cover, biomass, relative leaf area and photosynthetic surface area measurements showed that each species responded differently to shade. E. tomentosa biomass was facilitated by shade. This was inferred by an increase in total plant biomass. M. brevifolia, in contrast, tolerated shade by increasing above-ground biomass allocation. M. georgei was adversely affected by the shade regimes: root biomass decreased in response to shade. Competition for light is, therefore, likely to influence chenopod community structure of semi-arid and arid environments.     

China＇s regional transport dominance： Density, proximity, and accessibility

Transport infrastructure plays an important role in shaping the configuration of spatial socio-economic structures and influences regional accessibility. This paper defines transport dominance from three aspects: quality, quantity, and advantage, measured by density, proximity, and accessibility indices. County is the basic unit for analysis. The results reveal: (1) Transport dominance statistically follows a partial normal distribution. A very few counties, 1.4% of the total, have extremely high transport dominance which strongly supports the socio-economic development in these areas. In contrast, one eighth of all counties have poor transport dominance which impedes local socio-economic development to some extent. The remaining areas, about 70% of the counties, have median transport dominance. (2) Transport dominance is spatially unevenly distributed, with values decreasing gradually from the coastal area to the inland area. Areas in the first-highest level of transport dominance are mainly concentrated in the Yangtze River Delta, the Greater Beijing area, and the Pearl River Delta. Areas in the second-highest level are focused in Chengdu, Chongqing, and Wuhan metropolitan areas. Provincial capitals and a few other counties belong to the third-highest level.     

Reproductive and recruitment traits as indicators of the invasive potential of Kalanchoe daigremontiana (Crassulaceae) and Stapelia gigantea (Apocynaceae) in a Neotropical arid zone

Populations of two ornamental exotic species, Kalanchoe daigremontiana and Stapelia gigantea, have been recently detected inside a protected area containing arid ecosystems in Venezuela. We indirectly tested their invasive potential by characterizing their reproductive biology and recruitment patterns and comparing our estimates against Baker's Law and reproductive profiles reported for invasive plants. K. daigremontiana is autogamous, produces >16,000 seeds per plant and also reproduces clonally. Despite low seed viability (17.9%) and germination rates (11.9%), seeds were present in the seed bank. Plantlets of asexual origin showed high survival (75–100%) compared to seedlings of sexual origin (10%). S. gigantea is self-incompatible, xenogamous and produces close to 1500 seeds per m² of plant tissue. Seed viability (77%) and germination rates (62%) were high, but this species is not represented in the seed bank. It has a vegetative growth. A combination of reproductive and recruitment attributes, which match those considered in Baker's Law and others reported for invasive plants, confer K. daigremontiana and S. gigantea the potential to invade Neotropical arid zones; the former mainly through selfing and production of numerous asexual plantlets, and the latter through an association with a locally abundant pollinator and production of wind dispersed seeds.     

Adaptive evolution of rbcL in Reaumuria soongarica (Tamaricaceae)

In the field of phylogenetic analyses, the rbcL gene encoded large subunit Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco, EC4.1.1.39), which plays a crucial role in the process of photosynthesis for most terrestrial plants, has been considered to be conserved; however, recent controversy regarding rbcL conservation has appeared since it was proposed to be under natural selection within all principal lineages of land plants. In this study, by examining the variation of DNA and protein sequences among 17 species in the family Tamaricaceae, three nonsynonymous mutations were identified to be under positive selection. The favored sites were located in the alph-helix domains of Rubisco, with decreased hydrophobicity and increased entropy, which could facilitate CO₂ penetration into the active site of Rubisco. We also found that the expression level of rbcL in different genotypes of Reaumuria soongarica shifted in response to various stresses such as drought, temperature, salt, and light. This study not only sheds light on the functional/structural features of Rubisco in the evolution scenarios from C₃-like into C₄ in Tamaricaceae but also provides useful information on directing genetic performance to enhance photosynthesis efficiency of desert plants for sustaining fragile desert ecosystems; furthermore, it promotes the ability to cope with desert aridification and global warming.