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91.
DIANA H. WALL MARK A. BRADFORD MARK G. ST. JOHN JOHN A. TROFYMOW VALERIE BEHAN‐PELLETIER DAVID E. BIGNELL J. MARK DANGERFIELD WILLIAM J. PARTON JOSEF RUSEK WINFRIED VOIGT VOLKMAR WOLTERS HOLLEY ZADEH GARDEL FRED O. AYUKE RICHARD BASHFORD OLGA I. BELJAKOVA PATRICK J. BOHLEN ALAIN BRAUMAN STEPHEN FLEMMING JOH R. HENSCHEL DAN L. JOHNSON T. HEFIN JONES MARCELA KOVAROVA J. MARTY KRANABETTER LES KUTNY KUO‐CHUAN LIN MOHAMED MARYATI DOMINIQUE MASSE ANDREI POKARZHEVSKII HOMATHEVI RAHMAN MILLOR G. SABARÁ JOERG‐ALFRED SALAMON MICHAEL J. SWIFT AMANDA VARELA HERALDO L. VASCONCELOS DON WHITE XIAOMING ZOU 《Global Change Biology》2008,14(11):2661-2677
Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 43°S to 68°N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region‐ or biome‐scale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity. 相似文献
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Seedlings of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, and ponderosa pine, Pinus ponderosa Dougl. ex Laws., were grown in a controlled environment and fertilized with nutrient solutions containing 150 ppm (+N), or
0 ppm nitrogen (−N). These treatments greatly altered seedling growth, and the concentrations of N and carbohydrates in their
tissues. Metabolically active tissues, such as roots, incubated with a limited supply of O2 became hypoxic faster and synthesized more ethanol than less active tissues, such as needles. All tissues that were incubated
for 4 h in N2 synthesized ethanol. Needles incubated in N2 and light had much lower quantities of ethanol than needles in N2 and dark, suggesting that O2 from photosynthetsis limited internal anoxia. Most tissues from +N seedlings synthesized greater quantities of ethanol in
N2 anoxia than tissues from −N seedlings, probably because they were able to produce more enzymes with a greater availability
of N. However, this increase in ethanol synthesis between N treatments was most pronounced in the phloem. Ethanol and soluble
sugar concentrations were negatively related in needles and positively related in roots of N+ seedlings, but not −N seedlings.
Starch concentrations had no effect on the amount of ethanol produced by any tissue. Regardless of N treatments, all tissues
from ponderosa pine produced more N2-induced ethanol than Douglas-fir, in part because its tissues contained different concentrations of soluble sugars and N
as a consequence of phenological differences between the species. However, ponderosa pine tissues may also maintain greater
quantities of anaerobic enzymes, or their isozymes than Douglas-fir.
Received: 22 February 1998 / Accepted 23 June 1998 相似文献
96.
CD11/CD18 cell surface adhesion glycoproteins: Discordance of monocyte function and expression in response to stimulation 总被引:4,自引:0,他引:4
D. G. Hassall P. M. W. Bath A-M. Gladwin J. E. Beesley 《Experimental cell research》1991,196(2):346-352
The adherence of blood leukocytes to vascular endothelium precedes their diapedesis into the extravascular space. These processes require the expression of adherence glycoproteins on the cell surface of the leukocyte. The relative importance of these adherence molecules is so far poorly understood. However, there is evidence to suggest that a disparity exists between the surface receptor expression of these glycoproteins and leukocyte adherence to vascular endothelial cells in culture. We have investigated the importance of each of the adhesion glycoproteins CD11a, CD11b, and CD11c in mediating the adherence of human monocytes to endothelial cells in culture. We have also investigated the chronological relationship between changes in monocyte adherence to endothelial cells and the surface expression of CD11a, CD11b, and CD11c following stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP). The increase in adherence occurred within 1 minute, but declined if monocytes were preincubated with fMLP for up to 30 minutes. The surface expression of adherence molecules demonstrated a significant increase in CD11a and CD11b in the presence of fMLP after 10 min and was maintained while monocyte adherence to endothelium declined. These changes in surface receptor expression were quantitated using an immunolabeling technique. It is suggested that fMLP stimulation of monocyte adherence is unlikely to be solely dependent on increased surface receptor expression of adhesion molecules. 相似文献
97.
TEYKER ROBERT H.; DALLMEIR KENNETH A.; AUBIN GREGORY R. ST.; LAMBERT ROBERT J. 《Journal of experimental botany》1991,42(1):97-102
Two experiments were conducted to evaluate the effects of phenotypicrecurrent selection for high and low post-anthesis leaf-laminain vivo NRA on nitrate uptake, nitrate partitioning and in vitroNRA of seedling roots and leaves. In Experiment 1, intact plantsof cycle 0, 4, and 6 of the high and low NRA strains were grownon NH4-N for 11 d, then exposed to 1.0 mol m3 KNO3, andcultures sampled at 6 h and 28 h (induction and post-inductionperiods). Nitrate uptake, tissue nitrate concentration and invitro NRA were determined. The pattern of response to selectionin seedling leaf NRA was similar to that observed for in vivoNRA of field grown plants. Leaf NRA increased between 6 h and28 h. Root NRA was not affected by selection or sampling time.Treatments differed in total fresh weight but not in reductionor uptake of nitrate per unit weight, indicating a lack of correspondencebetween NRA and reduction and supporting the idea that concomitantreduction by NR is not obligatorily linked to nitrate influxin the intact plant. In Experiment 2, dark-grown plants of cycle 0, and 6 of thehigh and low NRA strains were cultured without N, detopped onday 6, transferred the following day to 0-75 mol m3 KNO3and sampled at 6 h and 28 h. In contrast to Experiment 1, selectionpopulations differed in nitrate reduction and root NRA, whichby 28 h reached higher average levels than root NRA of intactplants. Translocation and reduction were inversely related amongstrains within each sampling time. The high level of translocationin detopped plants of the low NRA strain was difficult to reconcilewith its low leaf NRA level of Experiment 1. It is suggestedthat nitrate transport in detopped roots is altered relativeto the intact system in a way which permits greater NRA inductionand nitrate reduction. The results indicate that nitrate partitioningby detopped root systems should be interpreted with caution. Key words: Zea, nitrate reductase activity, nitrate uptake, nitrate reduction, nitrate partitioning, selection 相似文献
98.
HOLLISTER LE ELKINS H HILER EG ST PIERRE R 《Annals of the New York Academy of Sciences》1957,67(10):789-98; discussion 798-800
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F. B. ST. C. PALMER 《The Journal of eukaryotic microbiology》1974,21(1):160-163
The incorporation of radioactivity from [1,2-34C]choline, [1,2-34C]ethanolamine, [3-14C]serine and [methyl-14C]methionine into lipids was studied in growing cultures of Crithidia fasciculata. Lecithin was formed both from choline and by the methylation of phosphatidylethanolamine. Mono- and dimethylphosphatidylethanolamines were present in no more than trace amounts. Growth of the protozoa in media containing choline (1 mM) did not decrease synthesis by the methylation pathway. Phosphatidylethanolamine was formed from ethanolamine. Radioactivity from serine also was present in both phosphatidylethanolamine and lecithin; however, the presumed intermediate, phosphatidylserine, could not be detected. 相似文献