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101.
Paleoecological records suggest that growing season length and/or cloudiness may affect peatland carbon accumulation and testate amoeba-based environmental reconstructions, highlighting a need to understand how light intensity affects microbial communities. We shaded plots on two peatlands for two years to examine effects on testate amoeba communities, the relative abundance of mixotrophic and heterotrophic testate amoebae, transfer-function performance, and δ13C values of two species of mixotrophic testate amoebae. Surprisingly, relative abundance of mixotrophic species increased in shade, although compositional changes did not affect transfer-function performance. Shading did not affect δ13C values of Hyalosphenia papilio and Heleopera sphagni, which ranged from −23.5 to −19.6‰ and −23.2 to −19.2‰, respectively. These δ13C values were higher than those of potential food sources and lower than literature-derived values for Chlorella, the zoochlorellae inhabiting mixotrophic testate amoebae. δ13C values thus suggest that these mixotrophic species obtain some carbon from Chlorella, although coupled dietary and isotope studies are needed to quantify this contribution. More research is needed to assess impacts of light variability on peatland microbial communities; however, carbon sources are recorded by δ13C values of testate amoebae, indicating potential for studies of carbon cycling and how mixotrophy varies temporally and spatially. 相似文献
102.
A study on the decomposition process of Pistia stratiotes L. was carried out in Cisne Reservoir, Uruguay. For this purpose, leaves and roots were considered separately, and the process was studied in the littoral and the pelagic zone. The litter bag technique was used to estimate dry weight losses at different times. Leaves decomposed faster than roots in both zones. Pistia decomposed faster in the pelagic zone due to better oxygen conditions and a more intensive water movement that removes material from within the bags. Phosphorus, potassium, sodium and magnesium were leached rapidly during the first week. Nitrogen content in the leaves initially increased, reaching its maximum in the littoral zone that coincided with that of bacterial numbers colonizing the litter. The number of macroinvertebrates, dominated by Chironomidae, was low. A rough estimation of the phosphorus impact on the littoral zone associated to the decomposition process shows that after 24 h between 13.9 and 16.8 μg-at.1−1 have been released to the water. 相似文献
103.
Nitrogen stable isotopic composition of leaves and soil: Tropical versus temperate forests 总被引:25,自引:5,他引:20
L.A. Martinelli M.C. Piccolo A.R. Townsend P.M. Vitousek E. Cuevas W. McDowell G.P. Robertson O.C. Santos K. Treseder 《Biogeochemistry》1999,46(1-3):45-65
Several lines of evidence suggest that nitrogen in most tropical forests is relatively more available than N in most temperate forests, and even that it may function as an excess nutrient in many tropical forests. If this is correct, tropical forests should have more open N cycles than temperate forests, with both inputs and outputs of N large relative to N cycling within systems. Consequent differences in both the magnitude and the pathways of N loss imply that tropical forests should in general be more15N enriched than are most temperate forests. In order to test this hypothesis, we compared the nitrogen stable isotopic composition of tree leaves and soils from a variety of tropical and temperate forests. Foliar 15N values from tropical forests averaged 6.5 higher than from temperate forests. Within the tropics, ecosystems with relatively low N availability (montane forests, forests on sandy soils) were significantly more depleted in15N than other tropical forests. The average 15N values for tropical forest soils, either for surface or for depth samples, were almost 8 higher than temperate forest soils. These results provide another line of evidence that N is relatively abundant in many tropical forest ecosystems. 相似文献
104.
An Exotic Tree Alters Decomposition and Nutrient Cycling in A Hawaiian Montane Forest 总被引:1,自引:1,他引:0
We evaluated the effects of the exotic tree Fraxinus uhdei on decomposition dynamics and nutrient turnover in a montane Hawaiian rainforest. We used reciprocal transplants of litterbags between forests dominated by Fraxinus and by the native Metrosideros polymorpha to distinguish between endogenous (litter quality) and exogenous (for example, microclimate, nutrient availability, microbial and invertebrate communities) effects of Fraxinus on mass loss and nutrient dynamics of decomposing litter. Fraxinus produced greater quantities of litter that was thinner, had higher N and P concentrations, and lower concentrations of lignin and soluble polyphenols. Microbes decomposing Fraxinus litter produced fewer enzymes involved in N and P acquisition and more of those involved in cellulose degradation. Differences in litter quality and microbial activity resulted in a strong effect of litter type on rates of mass loss, whereby Fraxinus litter decomposed and released nutrients at nearly twice the rate of Metrosideros litter (k=0.82 versus 0.48), regardless of site of decomposition. Although site of decomposition had no effect on rates of litter mass loss, Fraxinus litter decomposed under a Fraxinus canopy mineralized approximately 20% less P after one year than Fraxinus litter decomposed under a Metrosideros canopy. Furthermore, Fraxinus litter decomposed under a Fraxinus canopy immobilized greater amounts of N and P in the early stages of decay, suggesting that the large amounts of N and P in Fraxinus litterfall have raised nutrient availability to decomposers in the forest floor. Greater immobilization of N and P under a Fraxinus canopy may act as a governor on rates of nutrient cycling, limiting the degree to which Fraxinus invasion accelerates N and P cycling in this system. 相似文献
105.
Grimm NB Gergel SE McDowell WH Boyer EW Dent CL Groffman P Hart SC Harvey J Johnston C Mayorga E McClain ME Pinay G 《Oecologia》2003,137(4):485-501
Although biogeochemistry is an integrative discipline, terrestrial and aquatic subdisciplines have developed somewhat independently of each other. Physical and biological differences between aquatic and terrestrial ecosystems explain this history. In both aquatic and terrestrial biogeochemistry, key questions and concepts arise from a focus on nutrient limitation, ecosystem nutrient retention, and controls of nutrient transformations. Current understanding is captured in conceptual models for different ecosystem types, which share some features and diverge in other ways. Distinctiveness of subdisciplines has been appropriate in some respects and has fostered important advances in theory. On the other hand, lack of integration between aquatic and terrestrial biogeochemistry limits our ability to deal with biogeochemical phenomena across large landscapes in which connections between terrestrial and aquatic elements are important. Separation of the two approaches also has not served attempts to scale up or to estimate fluxes from large areas based on plot measurements. Understanding connectivity between the two system types and scaling up biogeochemical information will rely on coupled hydrologic and ecological models, and may be critical for addressing environmental problems associated with locally, regionally, and globally altered biogeochemical cycles.We dedicate this paper to the memory of Catherine Lisa Dent, a member of our working group who contributed much to the ideas presented herein, and to the joy of developing them together.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper. 相似文献
106.
Ibarra C Grillo MP Lo Bello M Nucettelli M Bammler TK Atkins WM 《Archives of biochemistry and biophysics》2003,414(2):303-311
In addition to glutathione (GSH) conjugating activity, glutathione S-transferases (GSTs) catalyze "reverse" reactions, such as the hydrolysis of GSH thiol esters. Reverse reactions are of interest as potential tumor-directed pro-drug activation strategies and as mechanisms for tissue redistribution of carboxylate-containing drugs. However, the mechanism and specificity of GST-mediated GSH thiol ester hydrolysis are uncharacterized. Here, the GSH thiol esters of ethacrynic acid (E-SG) and several nonsteroidal antiinflammatory agents have been tested as substrates with human GSTs. The catalytic hydrolysis of these thiol esters appears to be a general property of GSTs. The hydrolysis of the thiol ester of E-SG was studied further with GSTA1-1 and GSTP1-1, as a model pro-drug with several possible fates for the hydrolysis products: competitive inhibition, covalent enzyme adduction, and sequential metabolism. In contrast to hydrolysis rates, significant isoform-dependent differences in the subsequent fate of the products ethacrynic acid and GSH were observed. At low [E-SG], only the GSTP1-1 efficiently catalyzed sequential metabolism, via a dissociative mechanism. 相似文献
107.
Growth and nutrient dynamics of soft-stem bulrush in constructed wetlands treating nutrient-rich wastewaters 总被引:16,自引:0,他引:16
The growth characteristics and nutritional status ofSchoenoplectus tabernaemontani (C.C. Gmelin)Palla (soft-stem bulrush or lake clubrush) wereinvestigated during the second and third growthseasons in four equivalent subsurface-flow, gravel-bedconstructed treatment wetlands. Each wetland wassupplied with a different hydraulic loading rate ofagricultural wastewater, covering the range commonlyapplied to such systems. Harvest and demographictechniques were combined to determine seasonalpatterns and gradients of growth and nutrientallocation, and net annual primary productivity(NAPP). Marked seasonal patterns of early springemergence, summer growth and autumn senescence wereobserved, with little over-wintering of liveabove-ground biomass. Starch, the dominant long-termstorage substance, comprised 20% of rhizome dryweight (DW) in autumn. Mobilization during springreduced concentrations by around half, with a trend ofincreasing depletion in the higher loaded wetlands.NAPP, including above-ground mortality, during thesecond growth season ranged between 2.5 and 3.5 kg DWm-2, with 10-23% allocated to below-groundgrowth. Mean above-ground live and dead biomass rangedbetween 1.75 and 2.65 kg DW m-2 by mid-summer,with below to above-ground biomass ratios similar inall wetlands at between 0.6 and 0.7. Rhizomes, whichcomprised around 80% of the below-ground biomass,were generally restricted to the upper 10 cm of thesubstratum and over half the root biomass alsooccurred in this zone, with very few roots penetratingbelow 30 cm depth. High culm concentrations of N,P, Mg and Zn in spring declined markedly over thegrowth season, while S and Ca showed generalincreases, and K, Fe and Cu remained relativelystable. Gradients of decreasing tissue concentrationof most macronutrients were noted with increasingdistance from wastewater inflows. Plant accumulationof N rose by 20-35 g m-2 and P by 4-9 g m-2with seasonal re-growth of above-ground shoots. Netplant N and P uptake rates rose to maximum values of0.3 g N m-2 d-1 and 0.1 g P m-2d-1 in early summer, declining markedly duringlate summer and autumn. Mass balance assessments of Nand P accumulation in plants at near maximum seasonalbiomass, after three growth seasons, showed that only6 to 11% of the N removal and 6 to 13% of the Premoval recorded from wastewaters applied to thewetlands could be ascribed to plant uptake andaccumulation. 相似文献
108.
Smith VH 《Antonie van Leeuwenhoek》2002,81(1-4):99-106
The supplies of nutrients, and their elemental stoichiometry, can have significant impacts upon the structure and function
of microbial communities. This review focuses on the effects of nutrient supplies on the biodegradation of organic matter,
and on the dynamics of host-pathogen interactions. Analyses of data from the literature suggest significant effects of nitrogen:phosphorus
supply ratios on the microbial decomposition of organic matter, and it is argued that these stoichiometric effects may have
important implications for the fate and fluxes of carbon in natural ecosystems. In addition, it is shown that the supplies
of nitrogen and phosphorus to the host can strongly influence the outcome of infections in both terrestrial and aquatic plants,
suggesting that resource availability and resource supply ratios potentially may have significant effects on the health of
many plant communities.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
109.
Paerl HW Dyble J Twomey L Pinckney JL Nelson J Kerkhof L 《Antonie van Leeuwenhoek》2002,81(1-4):487-507
The impacts of growing coastal pollution and habitat alteration accompanying human encroachment are of great concern at the
microbial level, where much of the ocean's primary production and biogeochemical cycling takes place. Coastal ecosystems are
also under the influence of natural perturbations such as major storms and flooding. Distinguishing the impacts of natural
and human stressors is essential for understanding environmentally-induced change in microbial diversity and function. The
objective of this paper is to discuss the applications and merits of recently developed molecular, ecophysiological and analytical
indicators and their utility in examining anthropogenic and climatic impacts on the structure and function of coastal microbial
communities. The nitrogen-limited Neuse River Estuary and Pamlico Sound, North Carolina are used as examples of ecosystems
experiencing both anthropogenic (i.e., accelerating eutrophication) and climatic stress (increasing frequencies of tropical
storms and hurricanes). Additional examples are derived from a coastal monitoring site (LEO) on the Atlantic coast of New
Jersey and Galveston Bay, on the Gulf of Mexico. In order to assess structure, function, and trophic state of these and other
coastal ecosystems, molecular (DNA and RNA-based) characterizations of the microbial taxa involved in carbon, nitrogen and
other nutrient transformations can be combined with diagnostic pigment-based indicators of primary producer groups. Application
of these methods can reveal process-level microbial community responses to environmental variability over a range of scales.
Experimental approaches combined with strategic monitoring utilizing these methods will facilitate: (a) understanding organismal
and community responses to environmental change, and (b) synthesizing these responses in the context of ecosystem models that
integrate physical, chemical and biotic variability with environmental controls.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
110.
Regulation of photosynthesis during Arabidopsis leaf development in continuous light 总被引:7,自引:0,他引:7
Previous investigations in our laboratory have shown that leaf developmental programming in tobacco is regulated by source
strength. One hypothesis to explain how source strength is perceived is that hexokinase acts as a sensor of carbohydrate flux
to regulate the expression of photosynthetic genes, possibly as a result of sucrose cycling through acid invertase and hexokinase.
We have turned to Arabidopsis as a model system to study leaf development and have examined various photosynthetic parameters during the ontogeny of a
single leaf on the Arabidopsis rosette grown in continuous light. We found that photosynthetic rates, photosynthetic gene expression, pigment contents and
total protein amounts attain peak levels early in the expansion phase of development, then decline progressively as development
proceeds. In contrast, the flux of 14CO2 into hexoses increases modestly until full expansion is attained, then falls in the fully expanded leaf. Partitioning of
carbon into hexoses versus sucrose increases until full expansion is attained, then falls. The in vitro activities of hexokinase, vacuolar acid invertase, and cell wall acid invertase do not change until the late stages of senescence,
when they increase markedly. At this time there are also dramatic increases in hexose pool sizes and in senescence-associated
gene (SAG) expression. Taken together, our results suggest that invertase and hexokinase activities do not control the partitioning
of label into hexoses during development. We conclude that our data are not readily compatible with a simple model of leaf
development, whereby alterations in photosynthetic rates are mediated directly by hexose flux or by hexose pool sizes. Yet,
these factors might contribute to the control of gene expression.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献