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1.
Phytoplankton biomass values in Tavropos Reservoir, ranging from 92 to 1071 mg m–3, are within a range characteristic of oligotrophic waters. The seasonal sequence of biomass shows three annual peaks, differing from the monoacmic pattern seen in oligotrophic lakes. This sequence was profoundly affected by changes in water withdrawal and inflow rates. Diatoms, cryptophytes, chrysophytes and dinoflagellates, in that order, were the major constituents of the reservoir phytoplankton. The succession, from diatoms and chrysophytes in late winter-spring, to centric diatoms in late spring-summer and again to diatom-chrysophytes in late autumn was similar to that in oligotrophic lakes. 相似文献
2.
Jesper H. Andersen Jacob Carstensen Daniel J. Conley Karsten Dromph Vivi Fleming‐Lehtinen Bo G. Gustafsson Alf B. Josefson Alf Norkko Anna Villnäs Ciarán Murray 《Biological reviews of the Cambridge Philosophical Society》2017,92(1):135-149
Much of the Baltic Sea is currently classified as ‘affected by eutrophication’. The causes for this are twofold. First, current levels of nutrient inputs (nitrogen and phosphorus) from human activities exceed the natural processing capacity with an accumulation of nutrients in the Baltic Sea over the last 50–100 years. Secondly, the Baltic Sea is naturally susceptible to nutrient enrichment due to a combination of long retention times and stratification restricting ventilation of deep waters. Here, based on a unique data set collated from research activities and long‐term monitoring programs, we report on the temporal and spatial trends of eutrophication status for the open Baltic Sea over a 112‐year period using the HELCOM Eutrophication Assessment Tool (HEAT 3.0). Further, we analyse variation in the confidence of the eutrophication status assessment based on a systematic quantitative approach using coefficients of variation in the observations. The classifications in our assessment indicate that the first signs of eutrophication emerged in the mid‐1950s and the central parts of the Baltic Sea changed from being unaffected by eutrophication to being affected. We document improvements in eutrophication status that are direct consequences of long‐term efforts to reduce the inputs of nutrients. The reductions in both nitrogen and phosphorus loads have led to large‐scale alleviation of eutrophication and to a healthier Baltic Sea. Reduced confidence in our assessment is seen more recently due to reductions in the scope of monitoring programs. Our study sets a baseline for implementation of the ecosystem‐based management strategies and policies currently in place including the EU Marine Strategy Framework Directives and the HELCOM Baltic Sea Action Plan. 相似文献
3.
Single Cell Analysis Linking Ribosomal (r)DNA and rRNA Copy Numbers to Cell Size and Growth Rate Provides Insights into Molecular Protistan Ecology 下载免费PDF全文
Ribosomal (r)RNA and rDNA have been golden molecular markers in microbial ecology. However, it remains poorly understood how ribotype copy number (CN)‐based characteristics are linked with diversity, abundance, and activity of protist populations and communities observed at organismal levels. Here, we applied a single‐cell approach to quantify ribotype CNs in two ciliate species reared at different temperatures. We found that in actively growing cells, the per‐cell rDNA and rRNA CNs scaled with cell volume (CV) to 0.44 and 0.58 powers, respectively. The modeled rDNA and rRNA concentrations thus appear to be much higher in smaller than in larger cells. The observed rRNA:rDNA ratio scaled with CV0.14. The maximum growth rate could be well predicted by a combination of per‐cell ribotype CN and temperature. Our empirical data and modeling on single‐cell ribotype scaling are in agreement with both the metabolic theory of ecology and the growth rate hypothesis, providing a quantitative framework for linking cellular rDNA and rRNA CNs with body size, growth (activity), and biomass stoichiometry. This study also demonstrates that the expression rate of rRNA genes is constrained by cell size, and favors biomass rather than abundance‐based interpretation of quantitative ribotype data in population and community ecology of protists. 相似文献
4.
C. Lu F.G. Acién Fernández E. Cañizares Guerrero D.O. Hall E. Molina Grima 《Journal of applied phycology》2002,14(5):331-342
The outdoor production of Monodus subterraneus wasstudied in bubble column and helical reactors, mainly analysing the influenceofdilution rate, air flow rate and solar irradiance on growth rate andbiochemicalcomposition. Photoinhibition and photo-oxidation phenomena were also analysed.The cultures were stressed at high solar irradiance and dissolved oxygenconcentrations. A clear relationship between stress of the cultures and thefluorescence from PSII measurements was observed, the Fv/Fm ratio being lowerinthe helical reactor than in the bubble column. Growth rate and biomassproductivity were both a function of the average irradiance and the Fv/Fmratio;maximum values of 0.040 h–1 and 0.54 gL–1 d–1 were measured. The influenceofphotoinhibition and average irradiance was modelled, the model also fitting theexperimental data reported by another author. The chlorophyll contenthyperbolically decreased, whereas the carotenoid content decreased linearlywiththe average irradiance. The higher the dilution rate the higher the protein andcarbohydrate content of the biomass, and the lower the lipid content. Theeicosapentaenoic acid (EPA) content ranged from 2.3 to 3.2% d.wt, the higherthe dilution rate, the lower EPA content, although the higher the EPAproportion. Maximum EPA productivity was only 9 mg L–1d–1, due to the stress to which the cultures wereexposed. 相似文献
5.
Changes in nitrogen resorption traits of six temperate grassland species along a multi-level N addition gradient 总被引:1,自引:0,他引:1
Ju-Ying Huang Xiao-Guang Zhu Zhi-You Yuan Shi-Huan Song Xin Li Ling-Hao Li 《Plant and Soil》2008,306(1-2):149-158
Nitrogen (N) resorption from senescing leaves is an important mechanism of N conservation for terrestrial plant species, but
changes in N-resorption traits over wide-range and multi-level N addition gradients have not been well characterized. Here,
a 3-year N addition experiment was conducted to determine the effects of N addition on N resorption of six temperate grassland
species belonging to three different life-forms: Stipa krylovii Roshev. (grass), Cleistogenes squarrosa (T.) Keng (grass), Artemisia frigida Willd. (semishrub), Melissitus ruthenica C.W.Wang (semishrub and N-fixer), Potentilla acaulis L. (forb) and Allium bidentatum Fisch.ex Prokh. (forb). Generally, N concentrations in green leaves increased asymptotically for all species. N concentrations
in senescent leaves for most species (5/6) also increased asymptotically, except that the N concentration in senescent leaves
of A. bidentatum was independent of N addition. N-resorption efficiency decreased with increasing N addition level only for S. krylovii and A. frigida, while no clear responses were found for other species. These results suggest that long-term N fertilization increased N
uptake and decreased N-resorption proficiency, but the effects on N-resorption efficiency were species-specific for different
temperate grassland species in northern China. These inter-specific differences in N resorption may influence the positive
feedback between species dominance and N availability and thus soil N cycling in the grassland ecosystem in this region. 相似文献
6.
E. B. Kirichenko Yu. V. Orlova D. V. Kurilov 《Russian Journal of Plant Physiology》2008,55(6):846-853
Abstrac The composition of essential oil of Artemisia lerchiana Web. plants growing in Volgograd oblast was studied. Sampling was performed from plots contrasting in climatic and soil characteristics.
Essential oil was obtained by hydrodistillation. The content of essential oil in shoot biomass increased gradually during
shoot formation, flower bud formation, and flowering beginning and then decreased. The highest content of essential oil varied
from 1.1 to 1.5% of plant dry weight at the stage of flower bud formation. More than thirty compounds were identified by gas
chromatography-mass spectrometry. The following major components were found: camphor, borneol, bornylacetate, camphene, and
1,8-cineole. Some of compounds (sesquiterpenes and sesquiterpenoids) were identified for the first time. The time-course of
accumulation of essential oil components strongly depended on habitat edaphic factors and climatic conditions during the year
of sampling. The results permit a conclusion that A. lerchiana is a valuable producer of essential oils.
Original Russian Text ? E.B. Kirichenko, Yu.V. Orlova, D.V. Kurilov, 2008, published in Fiziologiya Rastenii, 2008, Vol. 55,
No. 6, pp. 934–941. 相似文献
7.
南昌市不同植物类群叶片氮磷浓度及其化学计量比 总被引:11,自引:2,他引:9
对南昌大学前湖校区89种主要植物叶片的N、P浓度及其化学计量比进行了研究,结果表明:乔灌、常绿、针叶、种子、裸子和单子叶植物类群的N浓度分别低于相对应的草本、落叶、阔叶、蕨类、被子和双子叶植物类群,而C3和C4植物差异不显著;乔灌、常绿和裸子植物类群的P浓度含量分别低于相对应的草本、落叶和被子植物类群,而针叶和阔叶、蕨类和种子、单子叶和双子叶、C3和C4植物类群间差异不显著;乔木、阔叶、被子和双子叶植物类群叶片N/P分别高于相对应的灌草、针叶、裸子和单子叶植物类群,而常绿和落叶、蕨类和种子、C3和C4植物类群之间差异不显著.可见,不同类型植物对N和P的吸收利用存在差异,且对不同养分供应采取不同的适应对策.结合研究区土壤养分现状,建议优先选择常绿、针叶、裸子和单子叶植物类群作为城市园林植物. 相似文献
8.
Macrophyte beds in a subtropical reservoir shifted from a nutrient sink to a source after drying then rewetting 总被引:1,自引:0,他引:1 下载免费PDF全文
Jing Lu Stephen J. Faggotter Stuart E. Bunn Michele A. Burford 《Freshwater Biology》2017,62(5):854-867
- Macrophytes play a key role in assimilating and storing nutrients in shallow aquatic ecosystems, but their capacity to act as a long‐term nutrient sink can be affected by water level fluctuations. Water level drawdown in reservoirs followed by rewetting may mobilise a significant nutrient pool. These nutrients can be stored in the littoral zone in dead or dormant macrophytes, and in the desiccated sediments within the macrophyte beds. However, the contribution of desiccated macrophyte beds to nutrient release upon rewetting has not been well quantified.
- Our study examined the effect of rewetting the previously desiccated waterlily Nymphoides indica (Menyanthaceae) in treatments (1) without sediments (N.i.?Sed), and (2) with sediments in N. indica beds (N.i.+Sed) on water quality.
- We found that longer drying duration increased dissolved nutrients (nitrate/nitrite, ammonium and total dissolved organic nitrogen/phosphorus) and organic carbon release from N.i.+Sed and N.i.?Sed treatments after rewetting. In the N.i.+Sed treatment with <4 weeks of desiccation, all N. indica plants regenerated from roots after subsequent rewetting. In addition, the resulting nutrient/carbon release was not significantly different to the control treatment which did not have desiccation. A significant increase in dissolved nutrient and carbon concentrations in the water column was found in treatments with more than 10 weeks of desiccation followed by rewetting. This coincided with the sediment reaching its minimum moisture content. Furthermore, chlorophyll a (Chl‐a) concentrations in the overlying water also increased with more than 10 weeks of desiccation, presumably in response to the increased nutrient availability and the removal of competition for nutrients from macrophytes.
- On the basis of our laboratory experiments, we calculated the potential effect of desiccated and rewetted N. indica beds on water quality in a local N. indica‐dominated reservoir after water level drawdown. We also separated the contribution of N. indica plants from their macrophyte beds on water quality changes. Fourteen days after rewetting, the total dissolved nutrients released from N. indica alone (N.i.?Sed) could contribute 0.5% of the total nitrogen and 29% of total phosphorus to the water column concentrations in the whole reservoir. In contrast, N. indica beds (N.i.+Sed) contributed more total dissolved nitrogen (4.3%) but less total dissolved phosphorus (0.3%) release into the water column. The higher nitrogen release for the N.i.+Sed treatment was likely due to the organic matter decomposition in the sediment in macrophyte beds. In contrast, the less dissolved phosphorus release, compared with the N. indica alone, was likely the result of phosphate adsorption by previously desiccated soil particles and/or assimilation by phytoplankton, since the phytoplankton biomass (as measured by Chl‐a concentrations) was significantly higher in the N.i.+Sed treatment.
- This study highlights the importance of managing both the duration and rate of water level drawdown in reservoirs to prevent rooted macrophytes, like N. indica, from becoming a source of nutrients, which may cause deterioration in water quality.
9.
A polymorphism in the porcine miR‐208b is associated with microRNA biogenesis and expressions of SOX‐6 and MYH7 with effects on muscle fibre characteristics and meat quality 下载免费PDF全文
MicroRNAs (miRNAs) encoded by the myosin heavy chain (MHC) genes are muscle‐specific miRNAs (myomiRs) and regulate the expression of MHC isoforms in skeletal muscle. These miRNAs have been implicated in muscle fibre types and their characteristics by affecting the heterogeneity of myosin. In pigs, miR‐208b and miR‐499 are embedded in introns of MYH7 and MYH7b respectively. Here, we identified a novel single nucleotide polymorphism (SNP) in intron 30 of MYH7 by which porcine miR‐208b is encoded. Based on the association study using a total of 487 pigs including Berkshire (n = 164), Landrace (n = 121) and Yorkshire (n = 202), the miR‐208b SNP (g.17104G>A) had significant effects on the proportions of types I and IIb fibre numbers (P < 0.010) among muscle fibre characteristics and on drip loss (P = 0.012) in meat quality traits. Moreover, the SNP affected the processing of primary miR‐208b into precursor miR‐208b with a marginal trend towards significance (P = 0.053), thereby leading to significant changes in the levels of mature miR‐208b (P = 0.009). These SNP‐dependent changes in mature miR‐208b levels were negatively correlated with the expression levels of its target gene, SOX‐6 (P = 0.038), and positively associated with the expression levels of its host gene, MYH7 (P = 0.046). Taken together, our data suggest that the porcine miR‐208b SNP differentially represses the expression of SOX‐6 by regulating miRNA biogenesis, thereby affecting the expression of MYH7 and the traits of muscle fibre characteristics and meat quality. 相似文献