不同环境条件下土壤微生物对模拟大气氮沉降的响应

研究了林内及林缘两个生境中,在有苔藓覆盖和无苔藓覆盖条件下,人工加氮对土壤理化性质及土壤微生物群落的影响。结果显示加氮使土壤pH下降,有效态氮和有效态磷的含量上升,但不同生境及有无苔藓植物覆盖在一定程度上影响土壤理化性质及其对加氮的反应。苔藓植物覆盖可以缓解加氮引起的土壤酸化及有效氮含量上升压力,促进有效态磷含量上升。不同生境中,土壤微生物对氮沉降的响应亦不同。低氮使林缘生境土壤微生物的胁迫程度减小,中高氮使其胁迫程度上升,而任何加氮均增加林内生境中土壤微生物的胁迫程度。两个生境中,苔藓植物覆盖均可以缓解过量氮沉降对土壤微生物造成的压力,降低过量氮沉降对土壤微生物的伤害,提高土壤微生物的代谢活性。     

Invertebrate communities delineate hydro-ecoregions and respond to anthropogenic disturbance in East-Amazonian streams

Many tropical regions lack models predicting the biological and environmental conditions expected in any given area, thus precluding the implementation of reference condition-based water policies. We focused on streams of French Guiana, and tested two predictions: geomorphology determines ecological sub-regions that have typical invertebrate communities, and diversity declines as anthropogenic pressure increases. Sixty-five stream sites were sampled for benthic invertebrates and physical–chemical variables across various watersheds. We used the Self-Organizing Map algorithm (neural network) to model relationships between invertebrate communities and environmental variables. Sites characterized by invertebrate communities clustered into two major subsets matching French Guiana’s hydro-ecoregions: the coastal alluvial plain characterized by recent sediment and low elevations, and the Guiana Shield characterized by an eroded rocky substrate and dense rainforests. Changes in community composition, and to a lesser extent taxonomic richness within each sub-region revealed ecological impacts of gold mining and logging, further clustering hydro-ecoregions into subsets of reference and impaired sites. Further analyses would, however, be needed to identify tipping points between natural and disturbed states, especially in remote headwater streams where gold mining had the harsher impact upon freshwater diversity, making upstream communities resembling the most downstream impacted ones.     

Effect of isolation on the structure and nutrient content of oak epiphyte communities

Because isolated trees in pasture experience greater exposure than forest trees, the epiphytes on them should be more drought and sun-tolerant. In Veracruz, Mexico, we compared the structure and nutrient content of the epiphyte community on five forest oaks (FO) in a fragment of lower montane cloud forest to that of five isolated oaks in pasture (IO). IO supported fewer epiphyte species than FO; 62.8% of the 35 epiphyte species were recorded only in one habitat (51.4% on FO and 11.4% on IO). Polypodium plebeium and Tillandsia spp. seedlings were more abundant on FO, while T. kirchhoffiana and T. punctulata were more abundant on IO. Evenness was lower on IO, which supported higher epiphyte biomass. pH, Ca, Mg, N, K, and Na concentrations were similar for FO and IO, with only P_extractable being lower on IO than FO. We concluded that when an epiphyte community is isolated (IO), the populations of some species expand while those of other diminish or disappear, a phenomenon that changes the structure of the epiphyte community becoming less even.     

Invertebrate communities of Prairie-Pothole wetlands in the age of the aquatic Homogenocene

Hydrobiologia - Simplification of communities is a common consequence of anthropogenic modification. However, the prevalence and mechanisms of biotic homogenization among wetland systems require...     

Invertebrate communities associated with macrophytes in Lake Ladoga: effects of environmental factors

Littoral invertebrate communities (meio- and macrobenthos and zooplankton) were studied in seven types of macrophyte associations commonly encountered in Lake Ladoga: in reed (Phragmites) beds on sand, soft and hard bottoms, in associations with the prevalence of Potamogeton spp., Carex spp., and Equisetum fluviatile, and in diverse vegetation stands with e.g. Polygonum amphibium, Cicuta virosa, Typha latifolia and Eleocharis acicularis. Some of the studied habitats were affected by sewage pollution, others were in comparatively undisturbed areas. Statistically significant differences between invertebrate communities in the different macrophyte associations were found. In stepwise multiple linear regression analysis the following factors were identified as determinants of abundance of aquatic invertebrates in macrophyte associations: shoot density, plant dry weight biomass, periphyton biomass, periphyton chlorophyll a, periphyton primary production, and concentrations of Sr, Mg, Ca, P, Mn, Zn, Pb and Cu. Pollution was shown to have a minor effect on the composition of littoral invertebrate communities. It is not possible to determine one single principle factor responsible for the structure and density of invertebrates in macrophyte communities.     

Structure and ecology of epiphyte communities of a cloud forest in central Veracruz,Mexico

Abstract. 39 species of vascular epiphytes were found in a 625-m² plot in a cloud forest in Veracruz, Mexico. Epiphyte biomass was estimated for all species in six zones distinguished on each tree > 10 cm in DBH: stem base, lower stem, upper stem, branches > 20 cm, branches from 5 — 20 cm and branches < 5 cm diameter. Branches were additionally separated according to their position in the upper, middle or lower canopy. Total dry matter of green organs was 318 kg/ha. Dominance/diversity curves fitted best to the lognormal model. Principal Coordinate Analysis showed that canopy height and branch thickness are both important factors and also that the stem base was the most distinct zone. Microhabitat preferences and niche overlap of the frequent species proved some degree of resource partitioning within the canopy. Ecophysiological characters possibly responsible for these preferences and implications for conservation are discussed.     

Invertebrate grazing during the regenerative phase affects the ultimate structure of macrophyte communities

1. Although the biomass of freshwater macrophytes consumed by invertebrate herbivores (excluding crayfish) is usually low, there is growing evidence that invertebrates do exert a structuring effect on macrophyte communities. To explain this, we postulated that the effect of invertebrates may be concentrated on macrophytes during their regenerative phase.
2. We tested this hypothesis by means of a mesocosm-based experiment, in which we investigated the effects of different densities of pond snails [ Lymnaea stagnalis (L.)] on macrophytes regenerating from the natural sediment propagule bank.
3. After 2 months, a diverse macrophyte community had established in the absence of snails, mainly from sexual propagules. Under moderate snail grazing (4 individuals m⁻²), the ultimate biomass of macrophytes was similar, but its species composition differed dramatically. Only a few unpalatable taxa, such as Ceratophyllum demersum and Nymphaeaceae, persisted. Moreover, the relative success of macrophytes regenerating from vegetative rather than sexual propagules improved. Under higher snail grazing (20 m⁻²), all macrophytes disappeared before the end of the experiment.
4. These results confirm that snails at natural densities can have a strong effect on the ultimate structure of macrophyte communities by selectively consuming some species at a juvenile stage. Therefore, the regenerative phase can be seen as a window of opportunity for invertebrate grazers, which can have a qualitative effect on communities that is disproportionate to the biomass consumed.     

Extinctions in a spatial model of fossil communities subject to correlated environmental disturbance

We present a spatial model to study the behaviour of species communities subjected to environmental stress in the form of coloured noise, focusing on long-time changes of time scales larger than 1 ka. The sensitivity to environmental change is introduced by assigning each species with an optimal value of a certain environmental variable like e.g., the temperature, and with a fitness function having the form of a Gaussian. Each species is represented by a point on a surface and competes with neighbours. Species can evolve to new species with a different optimal value, or they can migrate to regions with better environmental conditions. We find that coloured noise can prompt sudden extinctions in similarity with the fossil record. The model also reproduces the well-known fact that that eurytopic species (generalists) are favoured during environmental stresses, and shows that a strong environmental gradient may ameliorate the species performance.     

Composition and ecology of vascular epiphyte communities along an altitudinal gradient in central Veracruz,Mexico

Abstract. Vascular epiphytes were studied in forests at altitudes from 720 to 2370 m on the Atlantic slope of central Veracruz, Mexico. The biomass of all trees of each species > 10 cm diameter at breast height within plots between 625 and 1500 m² was estimated. The number of species per plot ranged between 22 and 53, and biomass between 9 and 249 g dry weight/m². The highest values, both of species and biomass, were found at an intermediate altitude (1430 m). Habitat diversity may contribute to epiphyte diversity in humid forests, but the importance of this effect could not be distinguished from the influence of climate. A remarkably high number of bromeliads and orchids grew in relatively dry forests at low altitudes. In wet upper montane forests, bromeliads were replaced by ferns, while orchids were numerous at all sites, except for a pine forest. The number of epiphytic species and their biomass on a tree of a given site were closely related to tree size. According to Canonical Correspondence Analysis, the factor determining the composition of the epiphytic vegetation of a tree was altitude and to some extent tree size, whereas tree species had practically no influence. The only trees which had an evidently negative effect on epiphytes were pines, which were particularly hostile to orchids and to a lesser degree to ferns, and Bursera simaruba, which generally had few epiphytes due to its smooth and defoliating bark.     

Invertebrate communities in dry-season pools of a large subtropical river: patterns and processes

In order to develop an optical model to map the extent of coastal waters, the authors analyzed variations in bio-optical constituents and submarine optical properties along a transect from the nutrient-enriched coastal bay, Himmerfjärden, out into the open Baltic Sea. The model is a simple implementation of the “ecosystem approach,” because the optical constituents are proxies for important components of ecosystem state. Yellow substance or colored dissolved organic matter (CDOM) is often a marker for terrestrial freshwater or decay processes in the littoral zone. Phytoplankton pigments, especially chlorophyll a, are used as a proxy for phytoplankton biomass that may be stimulated by fluvial or coastal inputs of anthropogenic nutrients. Suspended particulate matter (SPM) is placed in suspension by tidal or wind-wave stirring of shallow seabeds, and is therefore an indicator for physical forcing. It is the thesis of this article that such constituents, and the optical properties that they control, can be used to provide an ecological definition of the extent of the coastal zone. The spatial distribution of the observations was analyzed using a steady-state model that assumes diffusional transport of bio-optical variables along an axis perpendicular to the coast. According to the model, the resulting distribution along this axis can be described as a low-order polynomial (of order 1–3) when moving from a “source” associated with land to the open-sea “sink.” Order 1 implies conservative mixing, and the higher orders imply significant biological or chemical processes within the gradient. The analysis of the transect data confirmed that the trend of each optical component could be described well using a low-order polynomial. Multiple regression analysis was then used to weigh the contribution of each optical component to the spectral attenuation coefficient K _d(490) along the transect. The results showed that in this Swedish Baltic case study, the inorganic fraction of the SPM may be used to distinguish between coastal and open-sea waters, as it showed a clear break between coastal and open-sea waters. Alternative models may be needed for coastal waters in which fronts interrupt the continuity of mixing.     

Linking forest harvest and landscape factors to benthic macroinvertebrate communities in the interior of British Columbia

Detecting the magnitude of human-induced disturbance events, such as forest harvest, on biological communities is often confounded by other environmental gradients and scales at which these effects are examined. In this study, benthic invertebrates were collected from 43 streams across four basins and two geographic regions to (1) determine whether invertebrate abundance and community structure are best explained by historic forest harvest, landscape variables or a combination of both, and (2) evaluate associations among harvest, landscape variables, in-stream physical habitat, and invertebrates. Nonmetric multidimensional scaling showed that invertebrate community structure was primarily explained by watershed area and elevation, and basin and region but not by measures of forest harvest. Model selection using an information-theoretic approach and Akaike’s information criterion indicated that watershed area was the most important variable explaining clinger and long-lived taxa richness, while basin was the most important variable explaining total abundance, and total, Ephemeroptera, Plecoptera, and Trichoptera taxa richness. Forest harvest ranked lower than landscape variables in relative importance in all models. These results suggest that landscape characteristics were relatively more important in predicting invertebrate community structure than forest harvest, and should therefore be considered when assessing the impacts of both reach and watershed scale forest harvest on benthic communities. Perhaps, the levels of forest harvest examined in this study had only marginal effects on benthic invertebrates because these ecosystems are naturally resilient as a result of frequent disturbance from forest fires.     

Detection of QTL affecting harvest traits in a commercial Atlantic salmon population

Genetic variation in performance and quality traits measured at harvest has previously been demonstrated in Atlantic salmon aquaculture populations. To map major loci underlying this variation, we utilized data from 10 families from a commercial breeding programme. Significant QTL were detected affecting harvest weight and length traits on linkage group 1, and affecting waste weight on linkage group 5. In total, 11 of the 29 linkage groups examined showed at least suggestive evidence for a QTL. These data suggest that major loci affecting economically important harvest characteristics are segregating in commercial salmon populations.     

Exploring the effect of host tree identity on epiphyte bryophyte communities in different Canarian subtropical cloud forests

This study explores the host tree preferences of epiphyte bryophyte communities in two key types of evergreen cloud forests on La Gomera (Canary Islands, Spain): ericaceous versus broadleaved laurel forest. By comparing two pairs of tree species (Erica arborea and Myrica faya vs. Ilex canariensis and Laurus novocanariensis) that occur in both forest types, we quantitatively examined whether epiphyte-host relationships change with the type of forest. In 51 ancient forest stands, the low-trunk bryophyte composition on the two host tree groups was analysed with both non-parametric procedures and ordination analyses. Our results highlight that the influence of local environmental conditions on the structuring of epiphyte communities may be different depending on the host tree identity. Whilst the epiphyte composition of the host tree group formed by I. canariensis and L. novocanariensis differed significantly between forest types depending on solar exposure, we failed to find variations for the other host tree group, excepting in those localities wherein mist precipitation was extremely high. Our findings highlight the importance of the natural diversity of tree species along environmental gradients, as well as of water availability at different spatial scales for epiphytic bryophytes in montane cloud forests.     

Pre-climax epiphyte communities of bryophytes and lichens in Mediterranean forests from the Central Plateau (Spain)

The pre-climax epiphytic communities of forests from the Spanish Mediterranean region (Central Plateau) were studied by numerical and traditional floristic methods. One hundred phytosociological relevés were analyzed through a classical numerical approach based on hard partitions improved by PCoA — Principal Coordinates Analysis — ordinations. Two groups easily related to two different suballiances included in Frullanion dilatatae Lecointe 1975, Ulotenion crispae (Barkman 1958) Lecointe 1975 and Fabronienion pusillae Barkman 1958 were detected. Two new syntaxa within the ass. Ortotrichetum lyellii (Allorge 1922) Lecointe 1975 are proposed. Phytogeography, syntaxonomy and ecology of these communities are discussed.     

Strategies for restoring the structure and function of lichen‐moss biocrust communities

Biological soil crusts (biocrusts) are crucial components of dryland ecosystems, but they are slow to recover following disturbance. Herein, we evaluated several methods for restoring lichen‐moss biocrusts that included factorial applications of moss fragments in a water‐slurry (1) with and without lichen fragments (to restore biocrust taxonomic structure), (2) with and without clay (to facilitate establishment), and (3) with and without jute ground cloth (to facilitate establishment). Three and four years after inoculation, moss and lichen cover was up to five and eight times higher on jute ground cloth than on bare ground, respectively. Lichen cover was six times higher in plots where lichen fragments were added. Clay amendments did not increase moss or lichen establishment. To understand the effects of biocrust recovery on soil properties, we measured soil inorganic nitrogen, microbial biomass carbon, and soil water availability in restoration and control plots. Restored biocrusts decreased inorganic NH₄‐N availability by 67% when compared to controls 3 years after inoculation, but did not influence the availability of inorganic NO₃‐N, soil water, or microbial biomass carbon. Our results demonstrate that adding a biocrust inoculant to jute ground cloth can expedite recovery of lichen‐moss biocrust and reestablish its influence on soil properties within a few years.     

Responses of crustose corallines to epiphyte and canopy cover

Although a dense cover of epiphytes is generally considered to be harmful for some coralline algae (Corallinaceae, Rhodophyta), crustose corallines in the littoral zone seem to be preserved from bleaching when covered by canopy plants and epiphytes during summer. This study aimed to test the responses of coralline crusts to epiphytes and canopy algae and their interaction with grazing limpets. Growth rates and color changes were followed in two crust species in areas with or without canopy algae in the Isle of Man, British Isles. Limpets were excluded, to allow epiphytes to grow upon crusts. Responses were measured both on pieces of crusts upon acrylic plates and on crusts growing naturally on the shore. Fucus canopy and epiphytic Enteromorpha significantly influenced the crusts' growth, depending on season. Epiphytes reduced the light levels beneath by up to 78%, more than the canopy algae (62%). Crusts exposed outside the canopy bleached in summer, but gradually restored their color once they were covered by epiphytes. The fast-growing Phymatolithon lenormandii (Aresch.) Adey recovered its coloration more quickly than the slow-growing P. purpureum (P. et H. Crouan) Woelkerling et Irvine. However, neither crust species could restore its color when epiphytes were reduced by grazing limpets, Patella vulgata L. Bleaching did not kill the crusts, but seemed to interfere with crusts' growth. Restoration of pigmentation was quantified for the first time on bleached coralline crusts. Epiphyte and canopy algae were experimentally shown to be beneficial, probably by providing shade and also protecting crusts from desiccation.     

Microbial communities in iron-silica-rich microbial mats at deep-sea hydrothermal fields of the Southern Mariana Trough

The abundance, diversity and composition of bacterial and archaeal communities in the microbial mats at deep-sea hydrothermal fields were investigated, using culture-independent 16S rRNA and functional gene analyses combined with mineralogical analysis. Microbial mats were collected at two hydrothermal areas on the ridge of the back-arc spreading centre in the Southern Mariana Trough. Scanning electron microscope and energy dispersive X-ray spectroscopic (SEM-EDS) analyses revealed that the mats were mainly composed of amorphous silica and contained numerous filamentous structures of iron hydroxides. Direct cell counting with SYBR Green I staining showed that the prokaryotic cell densities were more than 10⁸ cells g⁻¹. Quantitative polymerase chain reaction (Q-PCR) analysis revealed that Bacteria are more abundant than Archaea in the microbial communities. Furthermore, zetaproteobacterial cells accounted for 6% and 22% of the prokaryotic cells in each mat estimated by Q-PCR with newly designed primers and TaqMan probe. Phylotypes related to iron-oxidizers, methanotrophs/methylotrophs, ammonia-oxidizers and sulfate-reducers were found in the 16S rRNA gene clone libraries constructed from each mat sample. A variety of unique archaeal 16S rRNA gene phylotypes, several pmoA , dsrAB and archaeal amoA gene phylotypes were also recovered from the microbial mats. Our results provide insights into the diversity and abundance of microbial communities within microbial mats in deep-sea hydrothermal fields.