Depth matters: Microbial eukaryote diversity and community structure in the eastern North Pacific revealed through environmental gene libraries     

Astrid Schnetzer  Stefanie D. MoorthiPeter D. Countway  Rebecca J. GastIlana C. Gilg  David A. Caron 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(1):16-26

Protistan community structure was examined from 6 depths (1.5, 20, 42, 150, 500, 880 m) at a coastal ocean site in the San Pedro Channel, California. A total of 856 partial length 18S rDNA protistan sequences from the six clone libraries were analyzed to characterize diversity present at each depth. The sequences were grouped into a total of 259 Operational Taxonomic Units (OTUs) that were inferred using an automated OTU calling program that formed OTUs with approximately species-level distinction (95% sequence similarity). Most OTUs (194 out of 259) were observed at only one specific depth, and only two were present in clone libraries from all depths. OTUs were obtained from 21 major protistan taxonomic groups determined by their closest BLAST matches to identified protists in the NCBI database. Approximately 74% of the detected OTUs belonged to the Chromalveolates, with Group II alveolates making up the largest single group. Protistan assemblages at euphotic depths (1.5, 20 and 42 m) were characterized by the presence of clades that contained phototrophic species (stramenopiles, chlorophytes and haptophytes) as well as consumers (especially ciliates). Assemblages in the lower water column (150, 500 and 800 m) were distinct from communities at shallow depths because of strong contributions from taxa belonging to euglenozoans, acantharians, polycystines and Taxopodida (Sticholonche spp. and close relatives). Species richness (Chao I estimate) and diversity (Shannon index) were highest within the euphotic zone and at 150 m, and lowest for protistan assemblages located in the oxygen minimum zone (500 and 880 m). Multivariate analyses (Bray-Curtis coefficient) confirmed that protistan assemblage composition differed significantly when samples were grouped into shallow (≤150 m) and deep water assemblages (≥150 m).  相似文献   

Spatio-temporal variation in soil seed banks under contrasting grazing regimes following low and high seasonal rainfall in arid Namibia     

N. Dreber  K.J. Esler 《Journal of Arid Environments》2011,75(2):174-184

In arid rangelands, soil seed bank characteristics vary with rainfall patterns, livestock pressure and habitat heterogeneity. We investigated this issue by assessing spatio-temporal patterns in soil seed bank density and richness in a degraded (heavy grazing) and non-degraded (light grazing) Nama Karoo ecosystem. To account for variation in seed distribution, different microsites were compared, and the effect of diaspore size on the patterning analyzed. Long-term heavy grazing increased seed densities and species richness of the soil seed bank by favoring small-seeded and tiny-seeded annual species. The spatial patterning of the soil seed bank was, however, similar to that found under sustainable grazing. The overall seed distribution was dictated by the small-scale environmental heterogeneity, which interacted with diaspore size. Our results suggest that the degraded environment is still efficient in controlling secondary dispersal and retaining seeds. This is through low stature barriers like surface rocks, which replace the function of grazing-sensitive perennial grasses in trapping and storing small diaspores. Soil seed banks were persistent and accumulated readily-germinable seeds over time. Observed temporal pattern across the study sites indicates that both condition and sequence of preceding rainfall seasons are likely to have a profound effect on soil seed banks of subsequent years.  相似文献   

The role of human interventions in tree dynamics and environmental rehabilitation in the Sahel zone of Niger     

M. Larwanou  M. Saadou 《Journal of Arid Environments》2011,75(2):194-200

A study was conducted in 15 village territories of 3 regions in Niger. Among these sites, 4 were control and 11 had interventions comprising of farmer-managed tree natural regeneration (FMNR), water harvesting techniques (WHT) and windbreaks. The objective of the study was to determine the state of tree vegetation in terms of species diversity and harvestable volume and evaluate the environmental trend in the sites. An inventory of the vegetation was carried out during the rainy season using radial transects from the village centre, outwards, in addition to surveys with local communities.The results showed that tree diversity is enhanced in sites with interventions, and soil rehabilitation techniques and farmer-managed tree natural regeneration favor the rehabilitation and development of trees. The number of resprouts/seedlings varied with site, soil type and intervention. The number of harvestable trees depended on factors like caring, monitoring of cutting, types of intervention and ecological zone.Harvestable volume is a function of high regeneration rate, number of harvestable individual trees and site. Vegetation is improving in all the sites and local communities using tree products for their various needs. This study contributed to setting up a reference database for these sites.  相似文献   

Fire behavior characteristics of buffelgrass-fueled fires and native plant community composition in invaded patches     

C.J. McDonald  G.R. McPherson 《Journal of Arid Environments》2011,75(11):1147-1154

Buffelgrass invasions have been documented in Australia to North America, pointing to an end result of large-scale wildfires. In heavily populated areas such as Nogales, Sonora and Tucson and Phoenix, Arizona buffelgrass populations are growing exponentially. Although much research has been conducted on buffelgrass, relatively little is known about fire behaviors produced by a buffelgrass-fueled fire. To determine which abiotic and biotic characteristics best predict fire behavior, fire-behavior characteristics were measured in four prescribed fires in southern Arizona. Given that buffelgrass is known to decrease native plant richness in other ecosystems, the relationship between buffelgrass abundance and native plant cover was evaluated. Buffelgrass fires are more intense than fires in surrounding ecosystems, even in communities with comparable fuels. There is a strong negative relationship between buffelgrass cover and native plant cover. In addition, buffelgrass appears to be invading favorable microsites rather than species-poor communities and is radiating from the former sites. Historically, fire was rare in arid regions, but with the increase in fuels and because arid regions have weather that promotes intense fire behavior, as observed in this study, managers will increasingly observe and need to mitigate hazardous fires.  相似文献   

Effects of iron limitation on intracellular cadmium of cultured phytoplankton: Implications for surface dissolved cadmium to phosphate ratios     

Erin S. Lane  David M. Semeniuk  Robert F. Strzepek  Jay T. Cullen  Maria T. Maldonado   《Marine Chemistry》2009,115(3-4):155-162

This study compares intracellular Cd content (Cd:C) of cultured marine phytoplankton grown under various Fe levels, with estimated particulate Cd:P ratios derived from regression slopes of Cd versus PO₄³⁻ relationships from a global dataset. A 66-fold difference in Cd:C ratios was observed among the seven species grown under identical Fe concentrations, with oceanic diatoms having the highest Cd quotas and prymesiophytes the lowest. Interestingly, all species significantly increased their Cd:C ratios under Fe-limitation (on average 2-fold). The global data set also showed that the mean estimated Cd:P ratio of surface water particulates in HNLC (high nutrient low chlorophyll) regions were approximately 2-fold higher than non-HNLC regions. A sequence of events are proposed to explain high Cd:P ratios in HNLC waters. First, the seasonal relief from Fe-limitation in HNLC regions leads to blooms of large chain forming diatoms with high intrinsic Cd:P ratios. These large blooms may, in theory, deplete surface water CO₂ and Zn concentrations, which ultimately, would result in increased Cd uptake. Eventually these blooms will run out of Fe, which has been shown to further increase intercellular Cd via growth biodilution and increased Cd uptake through non-specific Fe(II) transporters. Ultimately, Fe-limited diatoms with enhanced Cd quotas will sink out of surface waters leading to pronounced regional differences in Cd:P ratios between HNLC and non-HNLC waters in the global ocean.  相似文献   

察尔汗盐湖区生物种类调查及生态环境保护建议          下载免费PDF全文

余冬梅 《盐湖研究》2022,30(2)

随着察尔汗盐湖资源开发活动强度的不断增加,各种人工设施和水利工程数量日渐增加,对生态环境的影响也逐步明显,因此本研究对盐湖区生态多样性和生态景观格局的变化趋势开展系统调查。主要通过梳理文献和对察尔汗盐湖周边的重点补给河流格尔木河的干支流及附属人工防洪堤水库水体开展生物多样性调查与评估,主要查明生物种类、分布、数量,评估生物多样性现状,并从保护生物多样性的角度为盐湖区生态环境保护提供建议。  相似文献   

美国全球变化研究的法律基础   总被引：1，自引：0，他引：1  

罗宗俊  刘闯  王正兴 《地球科学进展》2003,18(3):464-470

自1990年以来，美国全球变化研究计划（USGCRP）已经实施了10多年，并取得了丰硕的成果，这在很大程度上归因于相对完善的法律体系。一方面，《1990年全球变化研究法案》全面协调该计划在国内和国际的实施，使计划在实施的10年里获得了大量的基础科学数据和丰富的研究成果；另一方面，美国《信息自由法》、《版权法》及相关数据政策促进了全球变化研究数据和信息的共享，避免了在获取科学数据方面的重复建设，提高了数据的使用效率。在全球变化研究法案的强制要求下，美国的全球变化研究计划稳定发展、不断完善。  相似文献   

Characterizing the potential distribution of the invasive Asian longhorned beetle (Anoplophora glabripennis) in Worcester County,Massachusetts     

《Applied geography (Sevenoaks, England)》2013

The Asian longhorned beetle (ALB) (Anoplophora glabripennis) is an invasive insect pest that has established populations in Worcester County, Massachusetts as of 2008. ALB predominantly targets red maple (Acer rubrum), sugar maple (Acer saccharum), which are prominent in New England hardwood forests, and Norway maple (Acer platanoides), which was planted in built environments as street trees in response to severe weather and invasive insect and pathogen disturbances. Mahalanobis Typicality models related presence locations of ALB presence-only locations in Worcester County towns from 2008 to 2012 to biotic, abiotic, and anthropogenic variables to predict the potential distribution of ALB and to determine locations most characteristic of infestation. k-fold cross-validation and a continuous Boyce Index were employed to validate model performance and to identify threshold values at which continuous models of typicality could be reclassified into categorical maps. Distance-to-roads (r² = 0.19) and probability of maple presence (r² = 0.13) were the most important predictor variables in the ALB model. Locations that were most consistently susceptible to ALB infestation had significant high maple presence (p < 0.001) and significant low distance-to-roads (p < 0.001) compared to the whole study area, suggesting that ALB in Worcester County, MA, prefers maple-dominant edge habitats at the current stage of invasion. The localized ALB potential distribution model was consistently accurate (Boyce Continuous Index = 0.84) despite the lack of absence locations and incomplete knowledge of ALB niche breadth in both native and invaded ranges. The results from this study could be used as a baseline for effective adaptive management policies that could help prioritize the need for early detection/eradication measures and address the potential ecological and social ramifications of the current ALB outbreak in Worcester County. It is hoped that the model employed could be further tested for future outbreaks as they are discovered in the USA.  相似文献   

Factors shaping submerged bryophyte communities: A conceptual model for small mountain streams in Germany     

Horst Tremp  Dorothea KampmannRalf Schulz 《Limnologica》2012,42(3):242-250

Several models explaining species composition of aquatic bryophytes are available for specific regions. However, a more general, conceptual model applicable to a broader range of regions is lacking.We present a conceptual model ranking environmental factors determining submerged bryophyte communities in small mountain streams. It was tested on a dataset of 54 stream sections after removing the effect of stream size and altitude. Species responses were modeled with pH as predictor variable based on 97 stream sites covering six mountain regions all over Germany. Multiple regressions revealed the importance of primary growth factors (light, Ep(CO₂)) and substrate for the total submerged bryophyte coverage.The known distinction of hard- and softwater bryoflora was clearly supported. The floristic composition of headwaters was predominantly determined by the bicarbonate/ionic strength complex. Species response to pH values supported this result and thus our conceptual model. The primary growth resources light, Ep(CO₂) and availability of coarse streambed material explained one third (R_adjusted² = 0.34) of total submerged bryophyte cover. Disturbances, predominantly spates, reduce biomass but do not affect the basic floristic structure.In conclusion, conceptual models and monitoring methods focusing on aquatic bryophytes need to clearly distinguish “aquatic” from “submersed by chance”. All “aquatic bryophytes” found in Germany can also occur at least temporarily at non-submerged sites. Therefore, a distinction between primary growth factors and additional resources is recommended to disentangle factors determining aquatic bryophyte communities.  相似文献   

Forest biodiversity assessment in Peruvian Andean Montane cloud forest     

Alicia Ledo  Sonia Condés  Iciar Alberdi 《山地科学学报》2012,9(3):372-384

Cloud forests are unusual and fragile habitats, being one of the least studied and least understood ecosystems. The tropical Andean dominion is considered one of the most significant places in the world as regards biological diversity, with a very high level of endemism. The biodiversity was analysed in an isolated remnant area of a tropical montane cloud forest known as the "Bosque de Neblina de Cuyas", in the North of the Peruvian Andean range. Composition, structure and dead wood were measured or estimated. The values obtained were compared with other cloud forests. The study revealed a high level of forest biodiversity, although the level of biodiversity differs from one area to another: in the inner areas, where human pressure is almost inexistent, the biodiversity values increase. The high species richness and the low dominance among species bear testimony to this montane cloud forest as a real enclave of biodiversity.  相似文献