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81.
PIERRE WACHE GERARD MAURICE MICHEL LUCIUS JEAN-FRANCOIS STOLTZ XIONG WANG 《Computer methods in biomechanics and biomedical engineering》2013,16(6):525-533
Abstract Mechanical forces influence endothelial cell's (EC) morphology and functions. In this work it was proposed a numerical analysis of steady laminar flows near a modelled monolayer of elastic ECs in order to determine the local distributions of mechanical forces on the surface and inside the cell. Numerical results showed that the flow induced non uniform mechanical stresses on cell surface and led to a cell deformation. These numerical results were compared with experimental measurements of the deformation of cultured human aortic endothelial cells under flow. It will be interesting to study eventual correlations between the distributions of biological receptors (cytoskeleton, adhesion molecules, etc.) and that of the non-uniform mechanical forces. 相似文献
82.
Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance 总被引:4,自引:0,他引:4
REIMO KINDLER KLAUS KAISER DAVID C. WALMSLEY CHRISTIAN BERNHOFER NINA BUCHMANN PIERRE CELLIER WERNER EUGSTER GERD GLEIXNER THOMAS GRŨNWALD ALEXANDER HEIM ANDREAS IBROM STEPHANIE K. JONES MIKE JONES KATJA KLUMPP WERNER KUTSCH KLAUS STEENBERG LARSEN SIMON LEHUGER BENJAMIN LOUBET REBECCA MCKENZIE EDDY MOORS BRUCE OSBORNE KIM PILEGAARD CORINNA REBMANN MATTHEW SAUNDERS MICHAEL W. I. SCHMIDT MARION SCHRUMPF JANINE SEYFFERTH UTE SKIBA JEAN‐FRANCOIS SOUSSANA MARK A. SUTTON CINDY TEFS BERNHARD VOWINCKEL MATTHIAS J. ZEEMAN MARTIN KAUPENJOHANN 《Global Change Biology》2011,17(2):1167-1185
Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH4), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ13C signature. Leaching of biogenic DIC was 8.3±4.9 g m?2 yr?1 for forests, 24.1±7.2 g m?2 yr?1 for grasslands, and 14.6±4.8 g m?2 yr?1 for croplands. DOC leaching equalled 3.5±1.3 g m?2 yr?1 for forests, 5.3±2.0 g m?2 yr?1 for grasslands, and 4.1±1.3 g m?2 yr?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m?2 yr?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO2 in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO2. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO2 in acidic forest soil solutions and large NEE. Leaching of CH4 proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems. 相似文献
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84.
DIDIER BOUCHON CATHERINE SOUTY-GROSSET JEAN-PIERRE MOCQUARD AHMED CHENTOUFI PIERRE JUCHAULT 《Invertebrate reproduction & development.》2013,57(1-3):203-212
Summary Seasonal reproduction in Crustacea is synchronized by environmental cues (e.g., temperature and photoperiod). Two types of responses occur: (1) in reptant decapods, short photoperiods and low temperatures are necessary to induce vitellogenesis; (2) in natant decapods and in most peracarids, both high temperatures and long photoperiods promote the onset of reproduction. In this context studies on the biological clocks involved in photoperiodic time measurement were performed on two crustaceans: the ditch shrimp Palaemonetes varians and the woodlouse Armadillidium vulgare, which is distributed worldwide outside polar and intertropical areas. The most important feature of the photoperiodic response curves was the same mean lag time in response to photophase length ≤ 12 h: short photophases delayed breeding but did not prevent it (i.e., “short-day effect”). On the contrary, long photophases promoted the onset of reproduction (i.e., “long-day effect”) differently in P. varians and A. vulgare. In A. vulgare strains the shape of the photoperiodic response curve depended on latitudinal origin. Results of “resonance” experiments provided evidence of involvement of an endogenous circadian component in the photoperiodic clocks of the two species according to the internal coincidence model developed for insects. Seeing that relations between reproduction and moulting were different in the two species, we proposed the hypothesis of an evolutionary change in the transition from the sea to the continental environment. 相似文献
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87.
DAMASE KHASA PATRICK POLLEFEYS AURA NAVARRO‐QUEZADA PIERRE PERINET JEAN BOUSQUET 《Molecular ecology resources》2005,5(4):920-923
Species‐specific microsatellite markers were obtained for the unambiguous recognition of five poplar species of ecological and commercial importance to eastern North America: the native species Populus balsamifera and Populus deltoides, the exotic species Populus maximowiczii, Populus nigra, Populus trichocarpa and their interspecific hybrids. Forty‐four of 71 tested primer pairs amplified simple sequence repeat (SSR) loci for all five taxa. Six of these loci showed non‐overlapping allelic diversity between species, including fixed differences. Together, they were useful to identify unambiguously the five taxa and to validate parental contributions in a group of hybrid progeny. These markers will be invaluable to detect gene flow from plantations of exotic poplar into adjacent stands of native species and between the two potentially hybridizing native species P. balsamifera and P. deltoides. 相似文献
88.
The debate about drag and reconfiguration of freshwater macrophytes: comparing results obtained by three recently discussed approaches 总被引:1,自引:0,他引:1
BERNHARD STATZNER NICOLAS LAMOUROUX VLADIMIR NIKORA PIERRE SAGNES 《Freshwater Biology》2006,51(11):2173-2183
1. The paper by Sand‐Jensen (2003 , Freshwater Biology, 48 , 271–283) on drag and reconfiguration of freshwater macrophytes stimulated comments and a reply about the use of variables in assessments of the drag coefficient (Cd) or the Reynolds number (Re) of such plants. Although the physical argument in this debate starts from the same equations, it diverges into approaches that address differently the dynamic behaviour of flexible plants in the boundary layer flow (the typical condition experienced by lotic macrophytes). 2. We compared three (potentially among many more) such different approaches using some preliminary experiments with Egeria densa by measuring drag (and other physical variables of interest) on (1) a single shoot exposed to varying flume flows; (2) a single shoot exposed to a constant flume flow, from which we subsequently pruned off pieces from the distal end; and (3) multiple shoots exposed to a constant flume flow after they had experienced replicated flow disturbances (causing shoot reconfiguration). 3. These experiments illustrated that the three approaches can produce opposite trends in the relationship between Cd and Re and that, for a given plant and flow, the Cd values obtained by these approaches can differ by about two orders of magnitude. Thus, conventions about the use of variables are required for experiments on drag and reconfiguration of freshwater macrophytes, otherwise the field will be plagued by a multitude of incomparable results. 相似文献
89.
NATHALIE RAUFASTE ANNIE ORTH KHALID BELKHIR DAVID SENET CAROLE SMADJA STUART J. E. BAIRD † FRANÇOIS BONHOMME BARBARA DOD PIERRE BOURSOT 《Biological journal of the Linnean Society. Linnean Society of London》2005,84(3):593-616
We analysed the patterns of allele frequency change for ten diagnostic autosomal allozyme loci in the hybrid zone between the house mouse subspecies Mus musculus domesticus and M. m. musculus in central Jutland. After determining the general orientation of the clines of allele frequencies, we analysed the cline shapes along the direction of maximum gradient. Eight of the ten clines are best described by steep central steps with coincident positions and an average width of 8.9 km (support limits 7.6–12.4) flanked by tails of introgression, indicating the existence of a barrier to gene flow and only weak selection on the loci studied. We derived estimates of migration from linkage disequilibrium in the centre of the zone, and by applying isolation by distance methods to microsatellite data from some of these populations. These give concordant estimates of σ = 0.5–0.8 km generation . The barrier to gene flow is of the order of 20 km (support limits 14–28), and could be explained by selection of a few per cent at 43–120 underdominant loci that reduces the mean fitness in the central populations to 0.45. Some of the clines appear symmetrical, whereas others are strongly asymmetrical, and two loci appear to have escaped the central barrier to gene flow, reflecting the differential action of selection on different parts of the genome. Asymmetry is always in the direction of more introgression into musculus , indicating either a general progression of domesticus into the musculus territory, possibly mediated by differential behaviour, or past movement of the hybrid zone in the opposite direction, impeded by potential geographical barriers to migration in domesticus territory. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 593–616. 相似文献
90.
1. We surveyed 62 Canadian Shield lakes (<50 ha) to determine the relationship between factors related to isolation and extinction and the occurrence of brook trout (BT) (Salvelinus fontinalis), for which local extinctions have been documented over the last century in half of the lakes. 2. Logistic regression and information–theoretic model selection were used to determine the importance for the occupancy of BT of (i) isolation factors (degree of lake connectivity and the proximity of source populations of BT in neighbouring bodies of water) and (ii) extinction factors (lake morphometry and trophic status, as proxies of the risk of lake anoxia; predation and competition; and flooding caused by beaver (Castor canadensis) dams, which could potentially increase the risk of anoxia). 3. Isolation factors were the best predictors of the absence of BT in these lakes. Among extinction factors, only the impact of beaver dams (as measured by an index of increased water level and mortality of shrubs and trees in the littoral zone) improved model fits. Beaver dams were present at the outlets of all study lakes, but extensive mortality of riparian trees and shrubs was more common in lakes where BT populations were extinct. 4. Taken together, these results suggest that recolonization is a major factor determining the occurrence of BT while flooding caused by beaver dams might contribute to BT extinction by increasing the likelihood of winterkill in these small lakes. 相似文献