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101.
Metabolism of a desert stream 总被引:8,自引:0,他引:8
SUMMARY. Rates of photosynthesis and community respiration were determined for benthic assemblages in Sycamore Creek, a Sonoran Desert stream in Arizona. Benthos in this stream can be separated into (1) mats of Cladophora glomerata and associated epiphytes and (2) assemblages of epipelic diatoms and blue-green algae. Community respiration and net photosynthesis were measured for these assemblages using submerged light-dark chambers in situ . Multiple regression analysis was used to predict (1) gross photosynthesis as a function of photosynthetically active radiation, temperature and chlorophyll-α concentration; and (2) community respiration as a function of temperature and biomass.
Calculations suggest that Sycamore Creek is autotrophic during the summer ( P/R = 1.7) and that the rates of gross photosynthesis ( P =8.5 g O2 m−2 day−1 ) and community respiration ( R = 5.1 g O2 m−2 day−1 ) are high for a small stream. Considerable difference exists between the Cladophora mat assemblages, in which mean P is 12.5gO2 m−2 day−1 and the P/R ratio is 2.3, and the epipelic assemblages in which mean P is 4.4 g O2 m−2 day−1 and P/R is 0.96. The high rate of gross photosynthesis, low litter inputs, high biomass of algae and the intermittent but severe floods that characterize Sycamore Creek indicate that this stream and other similar desert streams are net exporters of organic matter and are, thereby, truly autotrophic stream ecosystems. 相似文献
Calculations suggest that Sycamore Creek is autotrophic during the summer ( P/R = 1.7) and that the rates of gross photosynthesis ( P =8.5 g O
102.
1. The relationship between algal biomass accumulation, invertebrate colonization, and stream-water pH was investigated in seven streams in three regions of England and Wales. Possible nutrient limitation of algal production at all sites was examined with diffusion substrata. 2. Periphyton assemblages on experimental substrata after 30 days were dominated by diatoms, notably Eunotia spp., at all sites. Algal pigment concentration (chlorophyll a and phaeopigments) was not correlated with stream-water pH, and mean concentrations on control (unenriched) substrata ranged from 0.08 to 1.94 μg cm?2. 3. The growth response of periphyton to nutrient additions was site specific. Algal production was stimulated by nutrient additions at sites in the English Lake District and Llyn Brianne (south-west Wales), but not in the Ashdown Forest (southern England). 4. Larval Chironomidae were the main invertebrates retrieved from substrata at all sites. Within all three regions, larval abundance was positively related to algal pigment concentration (biomass). Abundance of the stonefly Nemurella pictetii was also positively correlated with algal biomass at the one site where it occurred. 5. Our results indicate that epilithic algal production in small, oligotrophic streams is unlikely to be determined primarily by pH. Neither do they support the view that an absence of grazers from acid streams is necessarily due to an inadequate food supply. 相似文献
103.
Interstitial Protozoa and Algae of Louisiana Salt Marshes 总被引:1,自引:0,他引:1
PRISCILLA BROWN ELLIOTT STUART S. BAMFORTH 《The Journal of eukaryotic microbiology》1975,22(4):514-519
SYNOPSIS. The majority of Louisiana salt marshes consists of stagnant pools among a vegetation of Spartina spp. and Distichlis spicata. The sediments constitute a "sulphide biome,'with Eh values reaching to –350 mV. The 200 interstitial ciliate species had definite stratification. Generally, algivores and omnivores occurred in the upper, and bactivores in the lower layers of the sediments. Compaction of particles prevented the flexible and large ciliates from inhabiting the lower layers, while Eh below –200 mV limited the distribution of some species but favored certain bactivores. The pH/Eh range and the abundance of nutrients in the sulfide biome provide habitable conditions for all the major groups of microflora. These, in turn, support nutritionally diverse predatory ciliate populations. 相似文献
104.
STUART S. BAMFORTH 《The Journal of eukaryotic microbiology》1971,18(1):24-28
SYNOPSIS. The numbers and kinds of testacea and ciliates were studied in the litters and soils of 23 sites, from temperate and subtropical coniferous and deciduous forests, and grasslands. In coniferous forests, testacea were 10 times or more abundant than ciliates, and numbered 10,000–24,000/g (wet weight) in litters and up to 8,000/g in soils. Ciliates numbered up to 1,500/g, but averaged less than 600/g in litters and less than 300/g in soils. Under deciduous vegetation, ciliates approached, equaled, or exceeded testacea, and numbered 1,000–5,000/g in litters, while remaining about the same in soils. Temperature and soil influence vegetation types, and their rates of litter decay affect the protozoa. Moisture favors numerical dominance of certain species. Among testacea, several species dominate in a particular habitat; among ciliates, the genus Colpoda dominates in almost all litter and soil habitats. 相似文献
105.
Periphyton production in Fort River, Massachusetts 总被引:4,自引:0,他引:4
SUMMARY. The primary production and general ecology of a periphyton community of a New England, lowland stream were studied over a seventeen-month period. Temperature, light, periphyton chlorophyll-α, and community structure were monitored regularly. Seasonally distinct chlorophyll peaks coincided with the light maximum in early May, just prior to the appearance of leaves of riparian trees, and again in autumn after terrestrial leaf fall. During midwinter, despite low light and temperature levels and high stream discharge, mean chlorophyll concentrations remained similar to summer values.
A mathematical expression relating periphyton photosynthesis per unit chlorophyll-α to temperature, light and periphyton density was established with submersible light-dark chambers in situ . Survey data collected over the study period were employed in the empirical equation to estimate seasonal variations in periphyton primary production. Weekly mean daily estimates of periphyton gross production ranged from < 0.1 g O2 m−2 , during midwinter, to 6.5 g O2 m−2 during early May. Estimated annual periphyton gross production and respiration were 0.58 and 1.27 kg O2 m−2 , respectively. Factors influencing seasonal variations of Fort River periphyton standing crop are discussed. 相似文献
A mathematical expression relating periphyton photosynthesis per unit chlorophyll-α to temperature, light and periphyton density was established with submersible light-dark chambers in situ . Survey data collected over the study period were employed in the empirical equation to estimate seasonal variations in periphyton primary production. Weekly mean daily estimates of periphyton gross production ranged from < 0.1 g O
106.
The fate of extranuclear chromatin bodies (ECBs) formed by exclusion of macronuclear material at the time of karyokinesis was followed quantitatively in Tetrahymena pyriformis strain GL-I. In a logarithmic growth phase culture, 51% of the dividing cells produced one (43%) or more (8%) ECBs. Most of these gradually disappear before the next cell division, but ? 13% are retained and carried into subsequent cell cycles. The random distribution of ECBs into anterior or posterior daughter cells, their staining and morphological characteristics, and their rapid loss in cells in starvation medium, all indicate that ECBs play no more of a role in cellular activity than that of an internally produced food vacuole. 相似文献
107.
108.
BRUCE A. HUNGATE CHRISTOPHER P. LUND HOLLY L. PEARSON F. STUART CHAPIN III 《Biogeochemistry》1997,37(2):89-109
We examined the effects of growth carbon dioxide (CO2)concentration and soil nutrient availability on nitrogen (N)transformations and N trace gas fluxes in California grasslandmicrocosms during early-season wet-up, a time when rates of Ntransformation and N trace gas flux are high. After plant senescenceand summer drought, we simulated the first fall rains and examined Ncycling. Growth at elevated CO2 increased root productionand root carbon:nitrogen ratio. Under nutrient enrichment, elevatedCO2 increased microbial N immobilization during wet-up,leading to a 43% reduction in gross nitrification anda 55% reduction in NO emission from soil. ElevatedCO2 increased microbial N immobilization at ambientnutrients, but did not alter nitrification or NO emission. ElevatedCO2 did not alter soil emission of N2O ateither nutrient level. Addition of NPK fertilizer (1:1:1) stimulatedN mineralization and nitrification, leading to increased N2Oand NO emission from soil. The results of our study support a mechanisticmodel in which elevated CO2 alters soil N cycling and NOemission: increased root production and increased C:N ratio in elevatedCO2 stimulate N immobilization, thereby decreasingnitrification and associated NO emission when nutrients are abundant.This model is consistent with our basic understanding of how C availabilityinfluences soil N cycling and thus may apply to many terrestrial ecosystems. 相似文献
109.
On the basis of the evidence that insect fungivory has the potential to affect fungal reproductive fitness, we investigated the effects of two specialist ciid beetles ( Octotemnus glabriculus and Cis boleti ) on the reproductive potential of their host fungus, Coriolus versicolor . We found, from field data, a negative correlation between the number of individuals of O. glabriculus inhabiting C. versicolor fruit bodies and the percentage of the fungal spore-producing surface (hymenium) that was functional. By contrast, the number of C. boleti inhabiting C. versicolor fruit bodies did not correlate with the percentage of functional hymenium. Experimentally, O. glabriculus and C. boleti reduced the reproductive potential of C. versicolor by 58% and 30%, respectively, whereas the combined trophic activity of both beetles caused a reduction of 64%. This latter effect was not significantly different from that caused by O. glabriculus alone. These findings disagree with previous assertions that insect fungivory on fruit bodies has only neutral effects on fungal fitness. We conclude that in the short-term, fungivory by ciids significantly decreases the area of functional hymenium of C. versicolor and is likely to reduce fungal reproductive fitness. Within this perspective the evolution of certain fungal characteristics (i.e. chemical composition, consistency and phenology) can be interpreted as being driven by fungivory. 相似文献
110.
XIE Feng Michael Wai Neng LAU Simon N STUART Janice S CHANSON Neil A COX Debra L FISCHMAN 《中国科学C辑(英文版)》2007,50(2)
The conservation status of all the amphibians in China is analyzed, and the country is shown to be a global priority for conservation in comparison to many other countries of the world. Three Chinese regions are particularly rich in amphibian diversity: Hengduan, Nanling, and Wuyi mountains. Salamanders are more threatened than frogs and toads. Several smaller families show a high propensity to become seriously threatened: Bombinatoridae, Cryptobranchidae, Hynobiidae and Salamandridae. Like other parts of the world, stream-breeding, high-elevation forest amphibians have a much higher likelihood of being seriously threatened. Habitat loss, pollution, and over-harvesting are the most serious threats to Chinese amphibians. Over-harvesting is a less pervasive threat than habitat loss, but it is more likely to drive a species into rapid decline. Five conservation challenges are mentioned with recommendations for the highest priority research and conservation actions. 相似文献