The Experts below are selected from a list of 39 Experts worldwide ranked by ideXlab platform
D. M. John - One of the best experts on this subject based on the ideXlab platform.
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taxonomic observations on some uncommon and new Gongrosira species chaetophorales sensu stricto division chlorophyta
European Journal of Phycology, 1992Co-Authors: L R Johnson, D. M. JohnAbstract:Three species of Gongrosira were isolated from freshwater habitats in England and Denmark. Developmental morphology and reproduction of the isolated strains were studied over a wide range of light and temperature regimes by means of a cross-gradient apparatus. Some of the traits traditionally used for defining infraspecific taxa (e.g. comparative development of prostrate and erect branches, position of zoosporangia) were found to be of questionable diagnostic value. New information is provided on previously described species and the isolates compared with cultures of related taxa. Gongrosira scourfieldii was collected from its type locality and culture-based observations have enabled an improved description of this little-known alga. A new species of Gongrosira is described, G. pseudoprostrata L. Johnson nov. sp., characterized by the presence of a well-defined primary prostrate axis and secondary axes. Problems of defining some of the main character traits and the possible ecological implications of the ...
Alexander M. Milner - One of the best experts on this subject based on the ideXlab platform.
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Disturbance frequency influences patch dynamics in stream benthic algal communities
Oecologia, 2008Co-Authors: Mark E. Ledger, Rebecca M. L. Harris, Patrick D. Armitage, Alexander M. MilnerAbstract:Disturbance is integral to the organisation of riverine ecosystems. Fluctuating low flows caused by supra-seasonal drought and water management periodically dewater habitat patches, potentially creating heterogeneity in the taxonomic composition and successional dynamics of benthic communities. The frequency of disturbance induced by low flows is contingent upon the topography of the river bed and thus varies among patches. We investigated whether the frequency of patch dewatering influenced the structure and temporal dynamics of benthic algal communities attached to the upper surfaces of stones in stream mesocosms (4 m2). In a 693-day disturbance experiment, we applied short dewatering disturbances (6 days) at high (33-day cycles) and low frequencies (99-day cycles) and compared algal assemblages with undisturbed controls at 21 endpoints. In the absence of disturbance, epilithic space was dominated by the green encrusting alga Gongrosira incrustans. However, drying disturbances consistently reduced the dominance of the green alga, and crust abundance decreased with increasing disturbance frequency, thereby opening space for a diversity of mat-forming diatoms. The response of mat diatoms to disturbance varied markedly during the experiment, from strong reductions in the abundance of loosely attached mats in mid-late 2000 to the exploitation of open space by closely adhering mats in 2001. Contrary responses were attributed to changes in the species composition of mat diatoms, which influenced the physiognomy and hence stress-resistance and resilience of the assemblage. Our results indicate that patchy dewatering of habitat patches during periods of low flow influences the successional dynamics of algae, thereby creating distinctive mosaics on the stream bed.
L R Johnson - One of the best experts on this subject based on the ideXlab platform.
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taxonomic observations on some uncommon and new Gongrosira species chaetophorales sensu stricto division chlorophyta
European Journal of Phycology, 1992Co-Authors: L R Johnson, D. M. JohnAbstract:Three species of Gongrosira were isolated from freshwater habitats in England and Denmark. Developmental morphology and reproduction of the isolated strains were studied over a wide range of light and temperature regimes by means of a cross-gradient apparatus. Some of the traits traditionally used for defining infraspecific taxa (e.g. comparative development of prostrate and erect branches, position of zoosporangia) were found to be of questionable diagnostic value. New information is provided on previously described species and the isolates compared with cultures of related taxa. Gongrosira scourfieldii was collected from its type locality and culture-based observations have enabled an improved description of this little-known alga. A new species of Gongrosira is described, G. pseudoprostrata L. Johnson nov. sp., characterized by the presence of a well-defined primary prostrate axis and secondary axes. Problems of defining some of the main character traits and the possible ecological implications of the ...
Zheng Yu Hu - One of the best experts on this subject based on the ideXlab platform.
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taxonomic transfer of Gongrosira fluminensis fritsch chaetophorales chlorophyceae to lithotrichon darienko et proschold ulvales ulvophyceae based on morphological observation and phylogenetic analyses
Fottea, 2019Co-Authors: Qinghua Wang, Shuyin Li, Jiao Fang-yi, Zheng Yu HuAbstract:One green algal specimen from China was identified as Gongrosira fluminensis Fritsch, due to its unique morphology that pseudoparenchymal basal stratum with rounded or polygonal cells grew into dense little-branched upright threads that reached approximately the same height with specific akinete formation and germination and formed strong cushions without calcification. Examination of the ultrastructural characteristics of plasmodesmata and pyrenoid confirmed that Gongrosira fluminensis Fritsch should be excluded from the order Chaetophorales. The phylogenetic evidence based on DNA sequence data from the nucleus (18S rDNA, ITS rDNA) and chloroplast (tufA) sequences clearly revealed that the Gongrosira fluminensis Fritsch should be classified in the Ulvales (Ulvophyceae) as the new combination species of the genus Lithotrichon Darienko et Proschold, instead of the Chaetophorales (Chlorophyceae). More specimens in conjunction with natural morphological investigation and molecular analyses are required to reevaluate the microfilamentous genus Gongrosira Kutzing and reveal hidden diversities among the Ulvophyceae.
Mark E. Ledger - One of the best experts on this subject based on the ideXlab platform.
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Disturbance frequency influences patch dynamics in stream benthic algal communities
Oecologia, 2008Co-Authors: Mark E. Ledger, Rebecca M. L. Harris, Patrick D. Armitage, Alexander M. MilnerAbstract:Disturbance is integral to the organisation of riverine ecosystems. Fluctuating low flows caused by supra-seasonal drought and water management periodically dewater habitat patches, potentially creating heterogeneity in the taxonomic composition and successional dynamics of benthic communities. The frequency of disturbance induced by low flows is contingent upon the topography of the river bed and thus varies among patches. We investigated whether the frequency of patch dewatering influenced the structure and temporal dynamics of benthic algal communities attached to the upper surfaces of stones in stream mesocosms (4 m2). In a 693-day disturbance experiment, we applied short dewatering disturbances (6 days) at high (33-day cycles) and low frequencies (99-day cycles) and compared algal assemblages with undisturbed controls at 21 endpoints. In the absence of disturbance, epilithic space was dominated by the green encrusting alga Gongrosira incrustans. However, drying disturbances consistently reduced the dominance of the green alga, and crust abundance decreased with increasing disturbance frequency, thereby opening space for a diversity of mat-forming diatoms. The response of mat diatoms to disturbance varied markedly during the experiment, from strong reductions in the abundance of loosely attached mats in mid-late 2000 to the exploitation of open space by closely adhering mats in 2001. Contrary responses were attributed to changes in the species composition of mat diatoms, which influenced the physiognomy and hence stress-resistance and resilience of the assemblage. Our results indicate that patchy dewatering of habitat patches during periods of low flow influences the successional dynamics of algae, thereby creating distinctive mosaics on the stream bed.