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61.
1. Decades of introductions of exotic sportfish to mountain lakes around the world have impoverished them biologically, and this may be exacerbated by global warming. We assessed the current status of invasive salmonids and native zooplankton communities in 34 naturally fishless lakes along an elevational gradient, which served as an environmental proxy for the expected effects of climate change. 2. Our main goal was to explore how climate‐related variables influence the effects of stocked salmonids on the total biomass, species richness and taxonomic composition of zooplankton. We predicted that warmer conditions would dampen the negative predatory effects of exotic brook trout (Salvelinus fontinalis) on zooplankton communities because more temperate lakes contain a greater diversity of potentially tolerant species. 3. Instead, we discovered that the persistence of stocked brook trout in the warmer lakes significantly amplified total zooplankton biomass and species richness. In colder and deeper lakes, zooplankton were relatively unaffected by S. fontinalis, which however persisted better in alpine lakes than at lower elevations after stocking practices were halted over two decades ago. Warmer lake conditions and higher concentrations of dissolved organic carbon (DOC) were significant primary drivers of zooplankton species turnover, both favouring greater species diversity. 4. Our findings of an ecological surprise involving potential synergistic positive effects of climate warming and exotic trout on native zooplankton communities presents a conundrum for managers of certain national mountain parks. Present mandates to eradicate non‐native trout and return the mountain lakes to their naturally fishless state may conflict with efforts to conserve biodiversity under a rapidly changing climate. 相似文献
62.
CLAIRE COONEY-SOVETTS ROLF SATTLER 《Botanical journal of the Linnean Society. Linnean Society of London》1986,94(3):327-371
Phylloclades are traditionally defined as flattened, determinate, leaf-like stems primarily on the basis of their axillary position. However, because the literature is replete with controversy over the morphological interpretation of these organs, a study of phylloclade development in comparison with leaf and stem development was undertaken in four closely related species of the Asparagaceae: Ruscus aculeatus, Danae racemosa, Semele androgyna and Asparagus densiflorus. Results reveal a continuum in phylloclade development from very leaf-like forms, such as those of Danae , via the more intermediate types of Ruscus , to the gradually more shootlike forms of Semele and Asparagus. This continuum results from a differential expression of stem (or shoot) and leaf characteristics in an axillary position. When stem (or shoot) and leaf features are combined, as in the fertile phylloclade of Ruscus , an intermediate organ is formed. Phylloclades are a form of evolutionary novelty that exemplifies the phenomenon of homoeosis, which is the transference of features from one organ to another. Developmentally, this means that leaf features are expressed by the axillary meristem. 相似文献
63.
JOSE A. CERISOLA CARLOS E. DEL PRADO ROLF ROHWEDDER JUAN P. BOZZINI 《The Journal of eukaryotic microbiology》1971,18(3):503-506
SYNOPSIS. Blastocrithidia triatomae n. sp. found in the digestive tract of T. infestans in Argentina is described. Cysts attached to the flagellum, a conspicuous characteristic of the new species, are described and shown in photomicrographs. Since T. infestans may harbor both T. cruzi and B. triatomae, or either one independently, it is essential that they be distinguished in xenodiagnosis. 相似文献
64.
ROLF A. OLSEN 《Physiologia plantarum》1975,33(1):75-82
Addition of aescin to mycelia of Ophiobolus graminis and Neurospora crassa induced leakage of ribonucleotide material together with pentose phosphate or pentose. In O. graminis a rapid release of mono- and dinucleotides together with nucleosides and pentose occurred. In addition some oligonucleotides were released during the first 30 min of the treatment. A slow leakage of polynucleotides was also observed. In N. crassa aescin induced only slight leakage during the first hour, and the mono- and dinucleotide leakage was actually decreasing. From that time on, however, a rapid release of mono- and dinucleotides together with nucleosides and pentose phosphate or pentose was observed. Only small amounts of poly- and oligonucleotides leaked and the cell content of oligonucleotides seemed to be released only during the last hour of the treatment period. In Aspergillus niger, which was insensitive to the inhibitor, aescin only induced leakage of pentose or pentose phosphate and small amounts of mono- and dinucleotides. Loss of viability in mycelia of O. graminis and N. crassa seemed to be correlated with the loss of oligonucleotides from the cells. 相似文献
65.
FRANK HAGEDORN DIETER SPINNLER† MAYA BUNDT PETER BLASER ROLF SIEGWOLF‡ 《Global Change Biology》2003,9(6):862-872
The aim of this study was to estimate (i) the influence of different soil types on the net input of new C into soils under CO2 enrichment and (ii) the stability and fate of these new C inputs in soils. We exposed young beech–spruce model ecosystems on an acidic loam and calcareous sand for 4 years to elevated CO2. The added CO2 was depleted in 13C, allowing to trace new C inputs in the plant–soil system. We measured CO2‐derived new C in soil C pools fractionated into particle sizes and monitored respiration as well as leaching of this new C during incubation for 1 year. Soil type played a crucial role in the partitioning of C. The net input of new C into soils under elevated CO2 was about 75% greater in the acidic loam than in the calcareous sand, despite a 100% and a 45% greater above‐ and below‐ground biomass on the calcareous sand. This was most likely caused by a higher turnover of C in the calcareous sand as indicated by 30% higher losses of new C from the calcareous sand than from the acidic loam during incubation. Therefore, soil properties determining stabilization of soil C were apparently more important for the accumulation of C in soils than tree productivity. Soil fractionation revealed that about 60% of the CO2‐derived new soil C was incorporated into sand fractions. Low natural 13C abundance and wide C/N ratios show that sand fractions comprise little decomposed organic matter. Consistently, incubation indicated that new soil C was preferentially respired as CO2. During the first month, evolved CO2 consisted to 40–55% of new C, whereas the fraction of new C in bulk soil C was 15–23% only. Leaching of DOC accounted for 8–23% of the total losses of new soil C. The overall effects of CO2 enrichment on soil C were small in both soils, although tree growth increased significantly on the calcareous sand. Our results suggest that the potential of soils for C sequestration is limited, because only a small fraction of new C inputs into soils will become long‐term soil C. 相似文献
66.
SI‐QIN GE MAURO DACCORDI ROLF GEORG BEUTEL JING REN JUN‐ZHI CUI WEN‐ZHU LI XING‐KE YANG 《Systematic Entomology》2012,37(2):332-345
The leaf beetle genera Ambrostoma Motschulsky, 1860 and Parambrostoma Chen, 1934 have been revised and now include 14 species. Two new species from Nepal are described, Parambrostoma kippenbergi sp.n. and P. medvedevi sp.n. Three new synonymies are established: Ambrostoma rugosopunctatum Chen = Ambrostoma (Parambrostoma) laosensis Kimoto & Gressitt, syn.n. , Ambrostoma rugosopunctatum Chen = Ambrostoma daccordii Medvedev, syn.n., Ambrostoma fortunei (Baly) = Ambrostoma quadriimpressum chusanica Gruev, syn.n . One species was transferred from Chrysomela Linnaeus to Ambrostoma Motschulsky: A. superbum (Thunberg), comb.n . All the species now included are described and illustrated. Microcomputer tomography was applied for the first time in a study on chrysomelid beetles. A cladistic analysis based on morphological characters of adults was conducted to reconstruct the intergeneric and interspecific phylogeny of Ambrostoma and Parambrostoma. The results show that the monophyly of both genera is well supported. Ambrostoma is widespread in East Asia, whereas Parambrostoma is restricted to the southern slope of the Himalayas, where a relatively recent and modest speciation took place. 相似文献
67.
68.
MICHAEL R. CHRISTENSEN MARK D. GRAHAM ROLF D. VINEBROOKE DAVID L. FINDLAY† MICHAEL J. PATERSON† MICHAEL A. TURNER† 《Global Change Biology》2006,12(12):2316-2322
The number of combinations of anthropogenic stressors affecting global change is increasing; however, few studies have empirically tested for their interactive effects on ecosystems. Most importantly, interactions among ecological stressors generate nonadditive effects that cannot be easily predicted based on single‐stressor studies. Here, we corroborate findings from an in situ mesocosm experiment with evidence from a whole‐ecosystem manipulation to demonstrate for the first time that interactions between climate and acidification determine their cumulative impact on the food‐web structure of coldwater lakes. Interactions among warming, drought, and acidification, rather than the sum of their individual effects, best explained significant changes in planktonic consumer and producer biomass over a 23‐year period. Further, these stressors interactively exerted significant synergistic and antagonistic effects on consumers and producers, respectively. The observed prevalence of long‐ and short‐term ecological surprises involving the cumulative impacts of multiple anthropogenic stressors highlights the high degree of uncertainty surrounding current forecasts of the consequences of global change. 相似文献
69.
Diffusive fractionation complicates isotopic partitioning of autotrophic and heterotrophic sources of soil respiration 总被引:1,自引:0,他引:1
ANDREW B. MOYES SARAH J. GAINES ROLF T. W. SIEGWOLF DAVID R. BOWLING 《Plant, cell & environment》2010,33(11):1804-1819
Carbon isotope ratios (δ13C) of heterotrophic and rhizospheric sources of soil respiration under deciduous trees were evaluated over two growing seasons. Fluxes and δ13C of soil respiratory CO2 on trenched and untrenched plots were calculated from closed chambers, profiles of soil CO2 mole fraction and δ13C and continuous open chambers. δ13C of respired CO2 and bulk carbon were measured from excised leaves and roots and sieved soil cores. Large diel variations (>5‰) in δ13C of soil respiration were observed when diel flux variability was large relative to average daily fluxes, independent of trenching. Soil gas transport modelling supported the conclusion that diel surface flux δ13C variation was driven by non‐steady state gas transport effects. Active roots were associated with high summertime soil respiration rates and around 1‰ enrichment in the daily average δ13C of the soil surface CO2 flux. Seasonal δ13C variability of about 4‰ (most enriched in summer) was observed on all plots and attributed to the heterotrophic CO2 source. 相似文献
70.