Responses of a beaded Arctic stream to short-term N and P fertilisation

1. Oligotrophic Arctic streams are likely to be sensitive to changes in hydrology and nutrient inputs predicted to occur as a consequence of future climate and land use change. To investigate the potential consequences of nutrient enrichment for low‐order Arctic streams, we added ammonium‐N and phosphorous to a second‐order beaded, tundra stream on Alaska's north slope. We measured responses in nutrient chemistry, chlorophyll a standing crop, and in the breakdown and macroinvertebrate colonisation of leaf litter over a 38‐day summer period. 2. During the addition, nutrient concentrations immediately downstream of the dripper averaged 6.4 μm ammonium‐N and 0.45 μm soluble reactive P. Concentrations upstream of the dripper averaged 0.54 μm ammonium‐N and 0.03 μm soluble reactive P. Uptake of both nutrients was rapid. Concentrations were reduced on average to 28% (ammonium‐N) and 15% (inorganic P) of maximum values within 1500 m. Standing crops of chlorophyll a on standardised samplers were significantly higher by the end of the experiment. Breakdown rates of senescent willow (Salix sp.) and sedge (Carex sp.) litter and associated fungal biomass were also significantly increased by nutrient addition. 3. Fertilisation resulted in four‐ to sevenfold higher macroinvertebrate abundance and two‐ to fourfold higher macroinvertebrate biomass in litter bags, as well as an increase in late‐summer body mass of larval Nemoura stoneflies. 4. Our results are consistent with those of similar studies of larger streams in the high‐Arctic region. Based on our short‐term experiment, increased inputs of nutrients into these ecosystems, whether caused by climate change or more local disturbance, are likely to have profound ecological consequences. Longer‐term effects of enrichment, and their interaction with other components of future change in climate or land use, are more difficult to assess.     

Managing precipitation use in sustainable dryland agroecosystems

In the Great Plains of North America potential evaporation exceeds precipitation during most months of the year. About 75% of the annual precipitation is received from April through September, and is accompanied by high temperatures and low relative humidity. Dryland agriculture in the Great Plains has depended on wheat production in a wheat-fallow agroecosystem (one crop year followed by a fallow year). Historically this system has used mechanical weed control practices during the fallow period, which leaves essentially no crop residue cover for protection against soil erosion and greatly accelerates soil organic carbon oxidation. This paper reviews the progress made in precipitation management in the North American Great Plains and synthesises data from an existing long-term experiment to demonstrate the management principles involved. The long-term experiment was established in 1985 to identify dryland crop and soil management systems that would maximize precipitation use efficiency (maximization of biomass production per unit of precipitation received), improve soil productivity, and increase economic return to the farmers in the West Central portion of the Great Plains. Embedded within the primary objective are sub-objectives that focus on reducing the amount of summer fallow time and reversing the soil degradation that has occurred in the wheat-fallow cropping system. The experiment consists of four variables: 1) Climate regime; 2) Soils; 3) Management systems; and 4) Time. The climate variable is based on three levels of potential evapotranspiration (ET), which are represented by three sites in eastern Colorado. All sites have annual long-term precipitation averages of approximately 400–450 mm, but vary in growing season open pan evaporation from 1600 mm in the north to 1975 mm in the south. The soil variable is represented by a catenary sequence of soils at each site. Management systems, the third variable, differ in the amount of summer fallow time and emphasize increased crop diversity. All systems are managed with no-till techniques. The fourth variable is time, and the results presented in this paper are for the first 12 yr (3 cycles of the 4-yr system). Comparing yields of cropping systems that differ in cycle length and systems that contain fallow periods, when no crop is produced, is done with a technique called “annualisation”. Yields are “annualised” by summing yields for all crops in the system and dividing by the total number of years in the system cycle. For example in a wheat-fallow system the wheat yield is divided by two because it takes 2 yr to produce one crop. Cropping system intensification increased annualised grain and crop residue yields by 75 to 100% compared to wheat-fallow. Net return to farmers increased by 25% to 45% compared to wheat-fallow. Intensified cropping systems increased soil organic C content by 875 and 1400 kg ha⁻¹, respectively, after 12 yr compared to the wheat-fallow system. All cropping system effects were independent of climate and soil gradients, meaning that the potential for C sequestration exists in all combinations of climates and soils. Soil C gains were directly correlated to the amount of crop residue C returned to the soil. Improved macroaggregation was also associated with increases in the C content of the aggregates. Soil bulk density was reduced by 0.01g cm⁻³ for each 1000 kg ha⁻¹ of residue addition over the 12-yr period, and each 1000 kg ha⁻¹ of residue addition increased effective porosity by 0.3%. No-till practices have made it possible to increase cropping intensification beyond the traditional wheat-fallow system and in turn water-use efficiency has increased by 30% in West Central Great Plains agroecosystems. Cropping intensification has also provided positive feedbacks to soil productivity via the increased amounts of crop residue being returned to the soil.     

Comparative anatomy of ectomycorrhizas synthesized on Douglas fir by Rhizopogon spp. and the hypogeous relative Truncocolumella citrina

The morphology and anatomy of ectomycorrhizas of Rhizopogon parksii , Rhizopogon vinicolor and Rhizopogon subcaerulescens , and a hypogeous relative, Truncocolumella citrina , synthesized on Douglas fir in glasshouse conditions using spore slurries as inoculum, are described and compared. Mycorrhizas formed with R. parksii and R. vinicolor did not exhibit their characteristic subtuberculate morphology in these tests, but rather had a pinnate form. All species had diagnostic features of ectomycorrhizas: a well-developed Hartig net and a fungal mantle. In addition, several species exhibited crystal inclusions in the outer mantle, usually at the interface between the mantle and soil. Truncocolumella citrina had crystal-like inclusions within the mantle but external to fungal hyphae, a feature rarely described in ectomycorrhizas.     

Developmental Gene Regulation and the Evolution of Large Animal Body Plans

SYNOPSIS. A diverse assemblage of invertebrate animals, someof which basically resemble the forms found in modern oceans,appears in the fossil record soon after the advent of the Cambrianperiod, though the first large multicellular animals clearlyarose even earlier. How this occurred is among the intellectuallychallenging mysteries of biology. The solution to this mysteryis likely to emerge, in part, from an understanding of the molecularprocesses by which modern animals use their genetic informationto construct their body plans during embryonic development.We discuss a mechanistic hypothesis that was presented earlieras an explanation of the causal events underlying the "Cambrianexplosion," and thus the divergence of large animal body plans.     

Association between microtubules and symbiotic fungal hyphae in protocorm cells of the orchid species, Spiranthes sinensis

Seeds of the orchid species, Spiranthes sinensis (Pers.) Ames, were sterilized and germinated in vitro with the symbiotic fungus Ceratobasidium cornigerum (Bourdot) Rogers. Colonized embryos developed into protocorms and these were examined for changes in microtubule arrays, after initial invasion of fungal hyphae into embryos and during peloton formation and degradation. Methods utilized to detect microtubules included immunofluorescence combined with laser scanning confocal microscopy, conventional transmission electron microscopy combined with morphometric analysis, and immunogold labelling. Microtubules were regularly found in close association with intracellular hyphae and degraded hyphal masses. Cortical microtubules disappear during peloton formation but reappear in cells that show fungal lysis. With conventional transmission electron microscopy and immunogold labelling the microtubules associated with fungal hyphae and degenerated hyphal masses were located close to the perifungal membrane that separates fungal hyphae from protocorm cytoplasm.     

Genetic differentiation in Philippine bats of the genera Cynopterus and Haplonycteris

Genetic variation and differentiation in six island populations of two species ( Cynopterus brachyotis Müller and Haplonycteris fischeri Lawrence) of Philippine fruit bats (Chiroptera, Pteropodidae) were analysed using allozyme electrophoresis. Cynopterus is eurytopic and widespread in southeast Asia; Haplonycteris is stenotopic and endemic to the Philippines. Genetic variability within populations is consistently higher in Cynopterus , but differentiation between populations is much more pronounced in Haplonycteris. Genetic variation is not significantly correlated with island size in either species, but a positive trend is present in both. Levels of gene flow are sufficiently low to allow differentiation by genetic drift alone in Haplonycteris ( Nm = 0.05), but not in Cynopterus ( Nm = 7.5). There is no significant association between genetic distance and distance between sampling sites; however, between-population differentiation is positively related to degree of geographic isolation during Pleistocene periods of low sea level and to vagility and consequent levels of gene flow among populations. Significant effects of population size on genetic differentiation were not found. Genetic distance matrices for the two species share a common structure that is similar to patterns of mammalian faunal similarity for the Philippines as a whole, suggesting similar effects of geographic and/or environmental factors.     

The Distribution of Zinc-65 in Agrostis tenuis sibth. and A. stolonifera L. Tissues4

The distribution of ⁶⁵Zn in zinc-tolerant and copper-tolerantplants of Agrostis spp. from toxic mine-tailings in Enflandand Wales was compared with zinc distribution in non-tolerantplants. Isotope was applied in culture solution in which theplants were growing. No differences could be demonstrated betweenthe plants were growing. No differences could be demonstratedbetween the plants by whole-plant radioautography, or by zincanalyses of the tops. Root/shoot ratios calculated from specificactivity values varied with population, the non-tolerant plantshaving the lowest and the zinc-tolerant plants the highest ratio.After solvent (80 per cent ethanol and water) extractions, theroot residue of zinc-tolerant plants contained a higher percentageof ⁶⁵Zn than that of non-tolerant plants. Chemical fractionationof the roots revealed that the main high difference was thatthe amount of ⁶⁵Zn in the pectate extract of the cell wall washigh in zinc-tolerant plants and low in non-tolerant plants.The ⁶⁵Zn distribution in the copper-tolerant plants was similarto that in the non-tolerant plants, indicating that the tolerancemechanisms for the elements are different. Soluble protein andRNA preparations were made but they contained low levels of⁶⁵Zn. An exception was the relatively high value for RNA fromzinc-tolerant A. stolonifera shoots. An anionic complex of ⁶⁵Znin the soluble fraction was investigated. This complex accountedfor most of the radioactivity in A. tennis extracts of shootsbut the concentration of the complex was low in A. stoloniferashoots, and in root extracts of all plants examined.     

油杉叶锈研究

油杉叶锈寄生在油杉叶上,作者研究了此菌的模式标本、同引模式标本和后来在模式地区采得的标本;并和柱锈属、金锈属、鞘锈属、栅锈属等11属锈菌作了比较研究。证明这种锈菌冬孢子堆为带状或扁平柱状,无细胞组织垫座,无被;冬孢子可互相撕离而不破裂,孢壁薄而无色,无柄。这些性状说明它不同于柱锈而近于金锈属。因此作者将其转归金锈属,改定为Chrysomyxa keteleeriae(Tai)Wang et Peterson新组合,(基础异名Cronartium keteleeriae Tai)。这种锈菌与其它生在云杉、铁杉叶上的4种短生金锈属锈菌一样,冬孢子堆都生在针叶上,窄带状到扁平柱状或圆形有短柄,鲜桔色或桔红色。虽然油杉叶锈冬孢子堆高达 6mm,但这只是同一属内的种间差别,也象Coleosporium crowellii Cumm。与同属内其它种的区别一样,属于种间的差别。云南粗杉金锈的冬孢子可以从10—20细胞组成的有柄孢子分离产生,正如鞘柄锈冬孢子的互相分离产生一样。冷杉金锈,特别是变形金锈的冬孢子的产生方式也是这样。生在同种油杉寄主枝上的Peridermium kunmingense Jen和油杉叶锈有无关系,需在接种试验后才能肯定。从寄主与寄主菌共同进化关系看,这种锈菌的寄主——油杉在分类系统上与金锈属寄主——云杉、铁杉等属近缘,传统分类学家多认为它同冷杉、银杉、黄杉等属同归冷杉亚科。但也有学者认为油杉有许多原始性状,与冷杉亚科无关。作者在油杉上发现金锈可能支持了传统植物分类系统。     

Response of plant roots to elevated atmospheric carbon dioxide

Plant root response to atmospheric CO₂ enrichment can be great. Results from this controlled environment investigation demonstrate substantial effects on root system architecture, micromorphology and physiology. The most pronounced effects were an increase in root length (110%) and root dry weight (143%). Root diameter, stele diameter, cortex width, root/shoot and root weight ratios all increased; root numbers did not increase. The long-term implications for belowground processes could be enormous.     

A survey of angiosperm species to detect hypodermal Gasparian bands. III. Rhizomes

PERUMALLA, C. J., CHMIELEWSKI, J. G. & PETERSON, C A., 1990. A survey of angiosperm species to detect hypodermal Casparian bands. III. Rhizomes. Rhizomes of ten species of the class Magnoliopsida (Dicotyledoneae) and five species of the class Liliopsida (Monocotyledoneae) were studied to determine whether Casparian bands exist in their hypodermes. The hypodermal walls of rhizomes of all species surveyed appeared autofluorescent under violet light. In sections cleared with NaOH and stained with Chelidonium majus root extract, the radial walls and sometimes the tangential walls of the hypodermis showed bright fluorescence. When the rhizomes were treated with the apoplastic dye, Cellufluor, the dye was initially blocked by the cuticle. When the continuity of the cuticle was disrupted with a needle before treating with Cellufluor, the dye penetrated all the walls of the epidermis and the outer tangential walls of the hypodermis but was blocked by the radial walls of the hypodermis. The walls of the hypodermis stained positively for suberin or suberin and lignin and were resistant to treatment with concentrated sulphuric acid. On the basis of the above tests, it is concluded that Casparian bands are present in the hypodermis of rhizomes of all species surveyed.