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941.
Although arbuscular mycorrhizal fungi (AMF) form spatially complex communities in terrestrial ecosystems, the scales at which this diversity manifests itself is poorly understood. This information is critical to the understanding of the role of AMF in plant community composition. We examined small-scale (submetre) variability of AMF community composition (terminal restriction fragment length polymorphism fingerprinting) and abundance (extraradical hyphal lengths) in two 1 m(2) plots situated in a native grassland ecosystem of western Montana. Extraradical AMF hyphal lengths varied greatly between samples (14-89 m g soil(-1)) and exhibited spatial structure at scales <30 cm. The composition of AMF communities was also found to exhibit significant spatial autocorrelation, with correlogram analyses suggesting patchiness at scales <50 cm. Supportive of overall AMF community composition analyses, individual AMF ribotypes corresponding to specific phylogenetic groups exhibited distinct spatial autocorrelation. Our results demonstrate that AMF diversity and abundance can be spatially structured at scales of <1 m. Such small-scale heterogeneity in the soil suggests that establishing seedlings may be exposed to very different, location dependent AMF communities. Our results also have direct implications for representative sampling of AMF communities in the field. 相似文献
942.
Local adaptation in response to fine-scale spatial heterogeneity is well documented in terrestrial ecosystems. In contrast, in marine environments local adaptation has rarely been documented or rigorously explored. This may reflect real or anticipated effects of genetic homogenization, resulting from widespread dispersal in the sea. However, evolutionary theory predicts that for the many benthic species with complex life histories that include both sexual and asexual phases, each parental habitat patch should become dominated by the fittest and most competitive clones. In this study we used genotypic mapping to show that within headlands, clones of the sea anemone Actinia tenebrosa show restricted distributions to specific habitats despite the potential for more widespread dispersal. On these same shores we used reciprocal transplant experiments that revealed strikingly better performance of clones within their natal rather than foreign habitats as judged by survivorship, asexual fecundity, and growth. These findings highlight the importance of selection for fine-scale environmental adaptation in marine taxa and imply that the genotypic structure of populations reflects extensive periods of interclonal competition and site-specific selection. 相似文献
943.
Currat M Ruedi M Petit RJ Excoffier L 《Evolution; international journal of organic evolution》2008,62(8):1908-1920
Despite hundreds of reports involving both plants and animals, the mechanisms underlying introgression remain obscure, even if some form of selection is frequently invoked. Introgression has repeatedly been reported in species that have recently colonized a new habitat, suggesting that demographic processes should be given more attention for understanding the mechanisms of introgression. Here we show by spatially explicit simulations that massive introgression of neutral genes takes place during the invasion of an occupied territory if interbreeding is not severely prevented between the invading and the local species. We also demonstrate that introgression occurs almost exclusively from the local to the invading species, especially for populations located far away from the source of the invasion, and this irrespective of the relative densities of the two species. This pattern is strongest at markers experiencing reduced gene flow, in keeping with the observation that organelle genes are often preferentially introgressed across species boundaries. A survey of the literature shows that a majority of published empirical studies of introgression during range expansions, in animals and in plants, follow the predictions of our model. Our results imply that speciation genes can be identified by comparing genomes of interfertile native and invading species pairs. 相似文献
944.
We investigated soil exploration by roots and plant growth in a heterogeneous environment to determine whether roots can selectively
explore a nutrient-rich patch, and how nutrient heterogeneity affects biomass allocation and total biomass before a patch
is reached. Lolium perenne L. plants were grown in a factorial experiment with combinations of fertilization (heterogeneous and homogeneous) and day
of harvest (14, 28, 42, or 56 days after transplanting). The plant in the heterogeneous treatment was smaller in its mean
total biomass, and allocated more biomass to roots. The distributions of root length and root biomass in the heterogeneous
treatment did not favor the nutrient-rich patch, and did not correspond to the patchy distribution of inorganic nitrogen.
Specific root length (length/biomass) was higher and root elongation was more extensive both laterally and vertically in the
heterogeneous treatment. These characteristics may enable plants to acquire nutrients efficiently and increase the probability
of encountering nutrient-rich patches in a heterogeneous soil. However, heterogeneity of soil nutrients would hold back plant
growth before a patch was reached. Therefore, although no significant selective root placement in the nutrient-rich patch
was observed, plant growth before reaching nutrient-rich patches differed between heterogeneous and homogeneous environments. 相似文献
945.
Protopanaxadiol 6-hydroxylase and its role in regulating the ginsenoside heterogeneity in Panax notoginseng cells 总被引:1,自引:0,他引:1
Various structure-similar plant secondary metabolites like ginseng saponins (ginsenosides) possess different or even totally opposite biological activities. Intentional manipulation of the ginsenoside heterogeneity in cellular biosynthesis is of great interest and significance [Zhong and Yue (2005); Adv Biochem Eng Biotechnol 100:53-88]. In this work, CO-binding spectra of microsomes prepared from the suspended cells of Panax notoginseng showed increases in absorption at 450 nm compared with the control without CO sparging, and protopanaxadiol 6-hydroxylase (P6H), a new enzyme catalyzing the conversion of ginsenoside aglycone protopanaxadiol into protopanaxatriol, was found. P6H was dependent on NADPH and molecular oxygen. The enzymatic reaction was inhibited by carbon monoxide and partially reversible upon illumination with blue light, and sensitive to cytochrome P450 inhibitors. The results supported the contention that P6H was a cytochrome P450-dependent hydroxylase, whose catalytic product was confirmed to be protopanaxatriol by HPLC-MS. Induction of P6H activity by phenobarbital, a cytochrome P450 inducer, was observed. A maximal activity of P6H was obtained with addition of 0.5 mM phenobarbital on day 4 of shake-flask cultivation. The maximum content of protopanaxatriol-type ginsenosides (Rg(1) and Re, Rg group) and the maximum ratio of the content of protopanaxatriol: protopanaxadiol reached 6.88 +/- 0.21 mg g(-1) dry weight and 7.0, respectively, which was about 1.4 and 2.0-fold that of respective controls (without addition of phenobarbital). Oxidative burst was also observed in the cell cultures with addition of phenobarbital. P6H was concluded as a key enzyme in regulating Rg-group ginsenoside biosynthesis in P. notoginseng cells. 相似文献
946.
This review summarizes results of biochemical and immunohistochemical studies indicating the existence of functional heterogeneity of hepatocytes depending on their localization in the hepatic acinus; this determines characteristic features of metabolism of carbohydrates, lipids, and xenobiotics. The physiological significance of hepatocyte heterogeneity is discussed. According to the proposed model of intercellular communication, the metabolic specialization of hepatocytes is determined by secretory activity of hepatic resident macrophages (Kupffer cells) localized mainly in the periportal zone of the liver acinus. Macrophages participate in secretion of a wide spectrum of intercellular mediators (cytokines, prostaglandins, growth factors) and also in metabolism of numerous blood metabolites and biologically active substances (hormones, lipoproteins, etc.). In the sinusoid and in the space of Disse (also known as perisinusoidal space) they form a concentration gradient of regulatory factors and metabolites inducing the phenotypic differences between hepatocytes. 相似文献
947.
Integrating ecology with biogeography using landscape characteristics: a case study of subtidal habitat across continental Australia 总被引:1,自引:0,他引:1
Aim We aimed to redress a current limitation of local ecological studies (i.e. piecemeal information on specific taxa) by integrating existing ecological knowledge with quantifiable patterns in primary habitat (i.e. composition, distribution and cover) from local to continental scales. By achieving this aim, we sought to provide a biogeographical framework for the interpretation of variation in the ecology of, and threats to, subtidal rocky landscapes. Location The subtidal rocky coast of continental Australia, with longitudinal comparisons spanning > 4000 km of southern coast (115°03′ E–153°60′ E) between latitudes of 33°05′ S and 35°36′ S, and latitudinal comparisons across 26°40′ S to 37°08′ S of eastern Australia. Methods The frequency and size of patches of major benthic habitat were quantified to indicate contemporary function (ecology) and to establish patterns that may result from contrasting regional‐scale processes (biogeography). This was achieved by quantifying the composition and patchiness of key subtidal habitats across the continent and relating them to the known ecology of subsets of locations in each region. A nested design of several spatial scales (1000s, 100s, 10–1 km) was adopted to distinguish patterns at local through to biogeographical scales. Results We show biogeography (in terms of longitude and latitude) to have a fundamental influence on the patterns of abundance and composition of subtidal habitats across regional (1000s of kilometres) to local (10s of kilometres to metres) scales. Across the continent, the most fundamental patterns related to (1) the proportion of rock covered by kelp forests, as related to particular functional groups of herbivores, and (2) the small‐scale heterogeneity (metres) that characterizes these forests. Main conclusions We interpret these results within a framework of alternative processes known to maintain habitat heterogeneity across these regions (e.g. productivity versus consumption as shapers of habitat structure). These interpretations illustrate how regional differences in ecological patterns and processes can create contradictory outcomes for the management of natural resources. We suggest that researchers and managers of natural resources alike may benefit from understanding local issues (e.g. the effects of fishing and its synergies with water pollution) in their biogeographical contexts. 相似文献
948.
Models for forest ecosystem management: a European perspective 总被引:1,自引:0,他引:1
BACKGROUND: Forest management in Europe is committed to sustainability. In the face of climate change and accompanying risks, however, planning in order to achieve this aim becomes increasingly challenging, underlining the need for new and innovative methods. Models potentially integrate a wide range of system knowledge and present scenarios of variables important for any management decision. In the past, however, model development has mainly focused on specific purposes whereas today we are increasingly aware of the need for the whole range of information that can be provided by models. It is therefore assumed helpful to review the various approaches that are available for specific tasks and to discuss how they can be used for future management strategies. SCOPE: Here we develop a concept for the role of models in forest ecosystem management based on historical analyses. Five paradigms of forest management are identified: (1) multiple uses, (2) dominant use, (3) environmentally sensitive multiple uses, (4) full ecosystem approach and (5) eco-regional perspective. An overview of model approaches is given that is dedicated to this purpose and to developments of different kinds of approaches. It is discussed how these models can contribute to goal setting, decision support and development of guidelines for forestry operations. Furthermore, it is shown how scenario analysis, including stand and landscape visualization, can be used to depict alternatives, make long-term consequences of different options transparent, and ease participation of different stakeholder groups and education. CONCLUSIONS: In our opinion, the current challenge of forest ecosystem management in Europe is to integrate system knowledge from different temporal and spatial scales and from various disciplines. For this purpose, using a set of models with different focus that can be selected from a kind of toolbox according to particular needs is more promising than developing one overarching model, covering ecological, production and landscape issues equally well. 相似文献
949.
We conducted RAPD analyses at multiple spatial scales to contribute to the conservation and future restoration of New Zealand's seagrass, Zostera muelleri Irmisch ex Asch. (Zosteraceae). Initially we focused on fine-scale genetic variation within two estuaries on the North Island, one on the East coast the other on the West coast. Within each estuary individuals were genetically similar, however, there was clear genetic separation between the two sites (genetic distance D = 0.2965). Genetic variation within a sampling location (m scale) was similar to that observed among sampling locations (km scale) within a site (21% and 28%, respectively) and smaller than that observed between sites (51%). We then expanded our sampling to include a further six populations distributed across almost the entire latitudinal (ca. 15°) gradient of the North and South Islands. At this scale genetic differences were closely correlated with coastal currents. There was a clear separation between North Island and South Island populations and further separation between the East and West coast populations of each Island. Sites located along the same section of coastline were more genetically similar than those from the opposite coast and other Island. Genetic similarity was highest within each of the sites, indicating a low degree of gene flow between populations. We recommend that any future restoration and conservation projects use only locally eco-sourced materials for population augmentations. 相似文献
950.