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81.
Anthropogenic N deposition and the fate of 15NO
3
−
in a northern hardwood ecosystem 总被引:5,自引:1,他引:4
Donald R. Zak Kurt S. Pregitzer William E. Holmes Andrew J. Burton Gregory P. Zogg 《Biogeochemistry》2004,69(2):143-157
Human activity has substantially increased atmospheric NO
3
–
deposition in many regions of the Earth, which could lead to the N saturation of terrestrial ecosystems. Sugar maple (Acer saccharum Marsh.) dominated northern hardwood forests in the Upper Great Lakes region may be particularly sensitive to chronic NO
3
–
deposition, because relatively moderate experimental increases (three times ambient) have resulted in substantial N leaching over a relatively short duration (5–7 years). Although microbial immobilization is an initial sink (i.e., within 1–2 days) for anthropogenic NO
3
–
in this ecosystem, we have an incomplete understanding of the processes controlling the longer-term (i.e., after 1 year) retention and flow of anthropogenic N. Our objectives were to determine: (i) whether chronic NO
3
–
additions have altered the N content of major ecosystem pools, and (ii) the longer-term fate of 15NO
3
–
in plots receiving chronic NO
3
–
addition. We addressed these objectives using a field experiment in which three northern hardwood plots receive ambient atmospheric N deposition (ca. 0.9 g N m–2 year–1) and three plots which receive ambient plus experimental N deposition (3.0 g NO3
–-N m–2 year–1). Chronic NO
3
–
deposition significantly increased the N concentration and content (g N/m2) of canopy leaves, which contained 72% more N than the control treatment. However, chronic NO
3
–
deposition did not significantly alter the biomass, N concentration or N content of any other ecosystem pool. The largest portion of 15N recovered after 1 year occurred in overstory leaves and branches (10%). In contrast, we recovered virtually none of the isotope in soil organic matter (SOM), indicating that SOM was not a sink for anthropogenic NO
3
–
over a 1 year duration. Our results indicate that anthropogenic NO
3
–
initially assimilated by the microbial community is released into soil solution where it is subsequently taken up by overstory trees and allocated to the canopy. Anthropogenic N appears to be incorporated into SOM only after it is returned to the forest floor and soil via leaf litter fall. Short- and long-term isotope tracing studies provided very different results and illustrate the need to understand the physiological processes controlling the flow of anthropogenic N in terrestrial ecosystems and the specific time steps over which they operate. 相似文献
82.
Martina DrobnyMartina Schnölzer Sabine FiedlerUlrich Lüttge Elke Fischer-SchliebsAnna-Luise Christian Rafael Ratajczak 《生物化学与生物物理学报:生物膜》2002,1564(1):243-255
The model plant tobacco (Nicotiana tabacum L.) was chosen for a survey of the subunit composition of the V-ATPase at the protein level. V-ATPase was purified from tobacco leaf cell tonoplasts by solubilization with the nonionic detergent Triton X-100 and immunoprecipitation. In the purified fraction 12 proteins were present. By matrix-assisted laser-desorption ionization mass spectrometry (MALDI-MS) and amino acid sequencing 11 of these polypeptides could be identified as subunits A, B, C, D, F, G, c, d and three different isoforms of subunit E. The polypeptide which could not be identified by MALDI analysis might represent subunit H. The data presented here, for the first time, enable an unequivocal identification of V-ATPase subunits after gel electrophoresis and open the possibility to assign changes in polypeptide composition to variations in respective V-ATPase subunits occurring as a response to environmental conditions or during plant development. 相似文献
83.
84.
Effects of salt treatment and osmotic stress on V-ATPase and V-PPase in leaves of the halophyte Suaeda salsa. 总被引:22,自引:0,他引:22
The Chenopodiaceae Suaeda salsa L. was grown under different salt concentrations and under osmotic stress. The fresh weight was markedly stimulated by 0.1 M NaCl, 0.4 M NaCl and 0.1 M KCl and reduced by osmotic stress (PEG iso-osmotic to 0.1 M NaCl). Treatment with 0.4 M KCl severely damaged the plants. Membrane vesicle fractions containing tonoplast vesicles were isolated by sucrose gradient from leaves of the S. salsa plants and modulations of V-ATPase and V-PPase depending on the growth conditions were determined. Western blot analysis revealed that V-ATPase of S. salsa consists of at least nine subunits (apparent molecular masses 66, 55, 52, 48, 36, 35, 29, 18, and 16 kDa). This polypeptide pattern did not depend on culture conditions. V-PPase is composed of a single polypeptide (69 kDa). An additional polypeptide (54 kDa) was detected in the fractions of NaCl-, KCl- and PEG-treated plants. It turned out that the main strategy of salt-tolerance of S. salsa seems to be an up-regulation of V-ATPase activity, which is required to energize the tonoplast for ion uptake into the vacuole, while V-PPase plays only a minor role. The increase in V-ATPase activity is not obtained by structural changes of the enzyme, but by an increase in V-ATPase protein amount. 相似文献
85.
Microbial community composition and function beneath temperate trees exposed to elevated atmospheric carbon dioxide and ozone 总被引:11,自引:0,他引:11
We hypothesized that changes in plant growth resulting from atmospheric CO2 and O3 enrichment would alter the flow of C through soil food webs and that this effect would vary with tree species. To test this idea, we traced the course of C through the soil microbial community using soils from the free-air CO2 and O3 enrichment site in Rhinelander, Wisconsin. We added either 13C-labeled cellobiose or 13C-labeled N-acetylglucosamine to soils collected beneath ecologically distinct temperate trees exposed for 3 years to factorial CO2 (ambient and 200 µl l-1 above ambient) and O3 (ambient and 20 µl l-1 above ambient) treatments. For both labeled substrates, recovery of 13C in microbial respiration increased beneath plants grown under elevated CO2 by 29% compared to ambient; elevated O3 eliminated this effect. Production of 13C-CO2 from soils beneath aspen (Populus tremuloides Michx.) and aspen-birch (Betula papyrifera Marsh.) was greater than that beneath aspen-maple (Acer saccharum Marsh.). Phospholipid fatty acid analyses (13C-PLFAs) indicated that the microbial community beneath plants exposed to elevated CO2 metabolized more 13C-cellobiose, compared to the microbial community beneath plants exposed to the ambient condition. Recovery of 13C in PLFAs was an order of magnitude greater for N-acetylglucosamine-amended soil compared to cellobiose-amended soil, indicating that substrate type influenced microbial metabolism and soil C cycling. We found that elevated CO2 increased fungal activity and microbial metabolism of cellobiose, and that microbial processes under early-successional aspen and birch species were more strongly affected by CO2 and O3 enrichment than those under late-successional maple. 相似文献
86.
87.
88.
89.
90.
1. Dissociation of riboflavin from flavoprotein and from the flavoprotein-antibody complex occurs under the same conditions. 2. The precipitated apoprotein-antibody complex retains 15% of the apoprotein capacity to bind riboflavin. After solubilization of the complex in 0.3 M-KCl or 1 M-urea, the binding of riboflavin amounts to 80 - 90% of its capacity. 3. The apoprotein modified by oxidation of 50% of tryptophan residues loses the ability to bind riboflavin but its immunological reactivity with the anti-flavoprotein antibody is similar to that of native apoprotein. The apoprotein with all tryptophan residues oxidized shows much lower immunoreactivity. 4. The obtained results suggest that in riboflavin flavoprotein the region around the riboflavin-binding site does not show the properties of an antigenic determinant. 相似文献