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排序方式: 共有92条查询结果,搜索用时 31 毫秒
31.
32.
Matthew A. Bowker Fernando T. Maestre David Eldridge Jayne Belnap Andrea Castillo-Monroy Cristina Escolar Santiago Soliveres 《Biodiversity and Conservation》2014,23(7):1619-1637
Model systems have had a profound influence on the development of ecological theory and general principles. Compared to alternatives, the most effective models share some combination of the following characteristics: simpler, smaller, faster, general, idiosyncratic or manipulable. We argue that biological soil crusts (biocrusts) have unique combinations of these features that should be more widely exploited in community, landscape and ecosystem ecology. In community ecology, biocrusts are elucidating the importance of biodiversity and spatial pattern for maintaining ecosystem multifunctionality due to their manipulability in experiments. Due to idiosyncrasies in their modes of facilitation and competition, biocrusts have led to new models on the interplay between environmental stress and biotic interactions and on the maintenance of biodiversity by competitive processes. Biocrusts are perhaps one of the best examples of micro-landscapes—real landscapes that are small in size. Although they exhibit varying patch heterogeneity, aggregation, connectivity and fragmentation, like macro-landscapes, they are also compatible with well-replicated experiments (unlike macro-landscapes). In ecosystem ecology, a number of studies are imposing small-scale, low cost manipulations of global change or state factors in biocrust micro-landscapes. The versatility of biocrusts to inform such disparate lines of inquiry suggests that they are an especially useful model system that can enable researchers to see ecological principles more clearly and quickly. 相似文献
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Question: Are soil lichen communities structured by biotic interactions? Location: Gypsum outcrops located next to Belmonte del Tajo, central Spain. Methods: We sampled a total of 68 (50 cm × 50 cm) plots in gypsum outcrops from central Spain. Each plot was divided into 100 (5 cm × 5 cm) sampling quadrats, and the presence of all lichen species in every quadrat was recorded (6800 quadrats in total). We used two realistic null models to generate random communities unstructured by biotic interactions, and used them to test the hypothesis that soil lichen species co‐occur less often than expected by chance. Results: We found fewer species combinations and less co‐occurrence than expected by chance. However, the latter result was dependent on the null model selected. The number of checkerboard pairs did not differ significantly from the null expectation. Conclusions: Overall, our results suggest that gypsiferous soil lichen communities are structured by competitive interactions. They are consistent with studies conducted with a wide variety of taxa, and fill a gap in our knowledge of the factors driving the small‐scale distribution of these important organisms. 相似文献
35.
36.
Investigations using fibrinogen coupled to colloidal gold (Fgn/Au) have shown that glycoprotein IIb-IIIa (GPIIb-IIIa) receptors are mobile and undergo centripetal reorganization on spread platelets following surface activation. The assembly of cytoplasmic actin and its constriction into an inner filamentous zone have been proposed as the mechanism driving the Fgn/Au receptor complexes across the plasma membrane. The present study has used cytochalasin B (CB), an agent known to inhibit actin assembly and cause breakdown of newly formed actin filaments to test that hypothesis. At a concentration which inhibited pseudopod formation and spreading, CB did not block movement of Fgn/Au receptor complexes toward platelet centers or into the open canalicular system (OCS). Channels of the OCS filled with Fgn/Au receptor complexes were evident in over 90% of the CB-treated, surface-activated platelets. The findings do not support the concept that assembly of cytoplasmic actin and its contraction move receptor-ligand complexes on the platelet plasma membrane. 相似文献
37.
Platelet membrane responses to surface and suspension activation 总被引:5,自引:0,他引:5
Exposure of blood platelets to foreign surfaces or to potent agonists in suspension results in dramatic changes in physical appearance and conversion from a nonsticky state. The transformation to the sticky state is associated with exposure of the fibrinogen receptor, GPIIB-IIIa, which is hidden in resting, discoid platelets. Recent studies employing fibrinogen coupled to gold (Fgn-Au) as an electron-dense probe have suggested that GPIIb-IIIa receptors not only become exposed in surface-activated platelets, but undergo a reorganization not observed in suspension-activated cells. Discoid platelets do not bind Fgn-Au; however, the bodies and extended pseudopods of dendritic forms are covered with Fgn-Au particles. Conversion of dendritic platelets to spread forms is accompanied by movement of receptor-ligand complexes away from peripheral margins into a concentrated mass in cell centers over the inner filamentous zone of the cytoplasm. Movement of the Fgn-Au particles to cell centers during spreading was considered due to the transmembrane action of the newly assembled actin filaments. We have carried out similar experiments on surface- and suspension-activated platelets with Fgn-Au and latex particles. GPIIb-IIIa receptors move Fgn-Au particles on outer membranes of surface- and suspension-activated platelets to channels of the open canalicular system. Treatment with cytochalasin B prevents assembly of actin filaments in surface- and suspension-activated platelets, and dissociates residual actin from the cell membranes, circumferential microtubules and organelles with which they interact. However, cytochalasin B does not prevent removal of Fgn-Au to channels of the open canalicular system. Thus, reorganization of fibrinogen receptors on surface- and suspension-activated platelets is due to the particles, and not to the fibrinogen, although fibrinogen is required to link gold to the receptor. The surface membrane has its own detergent and cytochalasin B-resistant cytoskeleton for directed transport of ligand-receptor complexes, independent of the internal assembly and contraction of actin into an inner filamentous zone. 相似文献
38.
Soil organic matter and the indigenous nitrogen supply of intensive irrigated rice systems in the tropics 总被引:7,自引:0,他引:7
K. G. Cassman A. Dobermann P. C. Sta Cruz G. C. Gines M. I. Samson J. P. Descalsota J. M. Alcantara M. A. Dizon D. C. Olk 《Plant and Soil》1996,182(2):267-278
Soil organic matter (SOM) has been proposed as an index of N supply in paddy soils although field validations are few. We evaluated the relationship between the indigenous N supply (N
i
) of the soil-floodwater system and soil organic carbon (SOC) or total N (N
t
) in surface soil of long-term fertility experiments (LTFEs) at 11 sites, in 42 farmer's fiels with similar soil type, and in the same field in ten consecutive rice (Oryza sativa L.) crops. The N
i
was estimated by crop N uptake from plots without applied N (N
o
plots) under otherwise favorable growth conditions. There was a tight linear correlation between yields and N uptake in N
o
plots and tremendous variation in both parameters among LTFE sites, farmer's fields, and in the same field over time. Correlation between N
i
and SOC or N
t
explained little of this variation. Factors likely to contribute to the poor correlation were: (1) inputs of N from sources other than N mineralization of SOM in surface soil, (2) degree of congruence between soil N supply and crop demand, which is sensitive to soil drying, length of fallow, crop rotation, and residue management, and (3) differences in SOM quality related to intensive cropping in submerged soil. Better understanding of the processes governing the N
i
of tropical lowland rice systems would contribute to the development of crop management practices that optimize utilization of indigenous N resources. 相似文献
39.
Letizia Albarran Alejandro Berna-Erro Natalia Dionisio Pedro C. Redondo Esther Lopez Jose J. Lopez Gines M. Salido Jose M. Brull Sabate Juan A. Rosado 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2014
Cytosolic-free Ca2 + plays a crucial role in blood platelet function and is essential for thrombosis and hemostasis. Therefore, cytosolic-free Ca2 + concentration is tightly regulated in this cell. TRPC6 is expressed in platelets, and an important role for this Ca2 + channel in Ca2 + homeostasis has been reported in other cell types. The aim of this work is to study the function of TRPC6 in platelet Ca2 + homeostasis. The absence of TRPC6 resulted in an 18.73% decreased basal [Ca2 +]c in resting platelets as compared to control cells. Further analysis confirmed a similar Ca2 + accumulation in wild-type and TRPC6-deficient mice; however, passive Ca2 + leak rates from agonist-sensitive intracellular stores were significantly decreased in TRPC6-deficient platelets. Biotinylation studies indicated the presence of an intracellular TRPC6 population, and subcellular fractionation indicated their presence on endoplasmic reticulum membranes. Moreover, the presence of intracellular calcium release in platelets stimulated with 1-oleoyl-2-acetyl-sn-glycerol further suggested a functional TRPC6 population located on the intracellular membranes surrounding calcium stores. However, coimmunoprecipitation assay confirmed the absence of STIM1–TRPC6 interactions in resting conditions. This findings together with the absence of extracellular Mn2 + entry in resting wild-type platelets indicate that the plasma membrane TRPC6 fraction does not play a significant role in the maintenance of basal [Ca2 +]c in mouse platelets. Our results suggest an active participation of the intracellular TRPC6 fraction as a regulator of basal [Ca2 +]c, controlling the passive Ca2 + leak rate from agonist-sensitive intracellular Ca2 + stores in resting platelets. 相似文献
40.
Pathways regulating decreased soil respiration with warming in a biocrust‐dominated dryland 下载免费PDF全文
Pablo García‐Palacios Cristina Escolar Marina Dacal Manuel Delgado‐Baquerizo Beatriz Gozalo Victoria Ochoa Fernando T. Maestre 《Global Change Biology》2018,24(10):4645-4656
A positive soil carbon (C)‐climate feedback is embedded into the climatic models of the IPCC. However, recent global syntheses indicate that the temperature sensitivity of soil respiration (RS) in drylands, the largest biome on Earth, is actually lower in warmed than in control plots. Consequently, soil C losses with future warming are expected to be low compared with other biomes. Nevertheless, the empirical basis for these global extrapolations is still poor in drylands, due to the low number of field experiments testing the pathways behind the long‐term responses of soil respiration (RS) to warming. Importantly, global drylands are covered with biocrusts (communities formed by bryophytes, lichens, cyanobacteria, fungi, and bacteria), and thus, RS responses to warming may be driven by both autotrophic and heterotrophic pathways. Here, we evaluated the effects of 8‐year experimental warming on RS, and the different pathways involved, in a biocrust‐dominated dryland in southern Spain. We also assessed the overall impacts on soil organic C (SOC) accumulation over time. Across the years and biocrust cover levels, warming reduced RS by 0.30 μmol CO2 m?2 s?1 (95% CI = ?0.24 to 0.84), although the negative warming effects were only significant after 3 years of elevated temperatures in areas with low initial biocrust cover. We found support for different pathways regulating the warming‐induced reduction in RS at areas with low (microbial thermal acclimation via reduced soil mass‐specific respiration and β‐glucosidase enzymatic activity) vs. high (microbial thermal acclimation jointly with a reduction in autotrophic respiration from decreased lichen cover) initial biocrust cover. Our 8‐year experimental study shows a reduction in soil respiration with warming and highlights that biocrusts should be explicitly included in modeling efforts aimed to quantify the soil C–climate feedback in drylands. 相似文献