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1.
An igapó forest near the confluence of Rio Tarumã Mirim (Tarumãzinho) and Rio Negro has been studied. It is a typical ectotroph forest with a raw humus layer and suppressed litter decomposing activity by Higher (i.e., carpophore-producing) Fungi. The number of the latter is about one-fifth of that observed in the (anectotrophic) terra firme forest. All ectotrophically mycorrhizal fungi observed belonged in three families:Amanitaceae, Boletaceae, Russulaceae. Leguminosae are dominant, and of theseAldina latifolia andSwartzia cf.polyphylla were demonstrably ectomycorrhizal. The scarcity of mineral nutrients in the soils of igapó, campinarana and campina is overcome by direct cycling through ectomycorrhizae. This is in contrast to other black- and white-water inundated forest communities in Amazonia.Litter Decomposition and Ectomycorrhiza in Amazonian Forests3. Previous contributions seeSinger & Araujo (1979) andSinger & al. (1983). 相似文献
2.
Assignment of orthologous relationships among mammalian alpha-globin genes by examining flanking regions reveals a rapid rate of evolution 总被引:1,自引:0,他引:1
In order to study the relationships among mammalian alpha-globin genes, we
have determined the sequence of the 3' flanking region of the human alpha 1
globin gene and have made pairwise comparisons between sequenced
alpha-globin genes. The flanking regions were examined in detail because
sequence matches in these regions could be interpreted with the least
complication from the gene duplications and conversions that have occurred
frequently in mammalian alpha-like globin gene clusters. We found good
matches between the flanking regions of human alpha 1 and rabbit alpha 1,
human psi alpha 1 and goat I alpha, human alpha 2 and goat II alpha, and
horse alpha 1 and goat II alpha. These matches were used to align the
alpha-globin genes in gene clusters from different mammals. This alignment
shows that genes at equivalent positions in the gene clusters of different
mammals can be functional or nonfunctional, depending on whether they
corrected against a functional alpha-globin gene in recent evolutionary
history. The number of alpha-globin genes (including pseudogenes) appears
to differ among species, although highly divergent pseudogenes may not have
been detected in all species examined. Although matching sequences could be
found in interspecies comparisons of the flanking regions of alpha- globin
genes, these matches are not as extensive as those found in the flanking
regions of mammalian beta-like globin genes. This observation suggests that
the noncoding sequences in the mammalian alpha-globin gene clusters are
evolving at a faster rate than those in the beta-like globin gene clusters.
The proposed faster rate of evolution fits with the poor conservation of
the genetic linkage map around alpha-globin gene clusters when compared to
that of the beta-like globin gene clusters. Analysis of the 3' flanking
regions of alpha-globin genes has revealed a conserved sequence
approximately 100-150 bp 3' to the polyadenylation site; this sequence may
be involved in the expression or regulation of alpha-globin genes.
相似文献
3.
Litter quality and nutrient cycling affected by grazing-induced species replacements along a precipitation gradient 总被引:10,自引:0,他引:10
María Semmartin Martín R. Aguiar Roberto A. Distel Alicia S. Moretto Claudio M. Ghersa 《Oikos》2004,107(1):148-160
One of the potential mechanisms for the impact of herbivores on nutrient cycling is the effect of selective grazing on litter quality through changes in species composition. However, the scarce evidence collected on this mechanism is controversial and seemingly influenced by site-specific variables. In this paper, we explored the consequences of grazing-induced changes in species composition on litter quality and nitrogen cycling with a regional perspective. Along a 900-mm of mean annual rainfall gradient, we selected species promoted and diminished by grazing from three natural rangelands of Argentina, analyzed their litter quality, and determined their decomposition and nutrient release kinetics under common greenhouse conditions. Litter quality and decomposition rates were strongly associated with plant response to grazing. However, the magnitude and direction of these differences depended on the ecosystem considered. In the wettest site, the species promoted by grazing (forbs) had higher nitrogen and phosphorus contents, faster decomposition rates, and higher release of nitrogen to the soil than species diminished by grazing (C3 and C4 grasses). In the intermediate and dry sites, species promoted by grazing had lower nitrogen and phosphorus contents, and slower decomposition rates than those diminished by grazing (C3 grasses in both cases). Decomposition of the entire group of species was not correlated with mean annual rainfall, but when litter of the species diminished by grazing was analyzed, it was negatively correlated with precipitation. Nitrogen was immobilized more often than mineralized, even after one year of incubation. Immobilization was negatively correlated with precipitation. All these results indicate that grazing may significantly alter nutrient cycling by affecting litter quality through changes in species composition. These effects seem to be larger when species replacements induced by grazing either involve functional groups, as it was the case in our wettest site, or change root to shoot ratios. Therefore, the functional groups involved in the replacement of species as well as shifts between belowground and aboveground allocation should play a key role in grazing-induced changes on nitrogen cycling. 相似文献
4.
Ecosystem responses to changes in plant functional type composition: An example from the Patagonian steppe 总被引:2,自引:0,他引:2
Abstract. Grass cover along a grazing intensity gradient in Patagonia decreases, whereas bare soil and shrub cover increases. Our objective was to study the effect of a change in the dominant plant functional type on soil water balance, primary production, herbivore biomass, roughness, and albedo. Using a soil water balance model, we found increases in evaporation and deep drainage, and a decrease in total transpiration along the grazing intensity gradient. Above-ground primary production, estimated from transpiration, decreased along the grazing intensity gradient because shrubs did not fully compensate for the decrease in grass production. Using a statistical model, we calculated herbivore biomass from estimates of above-ground primary production. Estimated herbivore biomass was lowest in the shrub-dominated extreme of the grazing gradient. Roughness increased from the grass-dominated to the shrub-dominated community. Albedo had a maximum at an intermediate position along the gradient. Our results suggest that changes in plant functional type composition, independent of changes in biomass, affect ecosystem functioning and the exchange of energy and material with the atmosphere. Grasses and shrubs proved to be appropriate plant functional types to link structure and function of ecosystems. 相似文献
5.
E. Martinez J. Morales J. Aguiar Y. Pineda M. Izquierdo G. Ferbeyre 《Biotechnology letters》1992,14(2):83-86
Summary The gene coding for the major surface antigen of the hepatitis B virus was integrated into the genome ofKluyveromyces
lactis and expressed up to levels of 0.4% of the total soluble protein. 相似文献
6.
Ana O. Fagundes Maira R. Aguiar Claudia S. Aguiar Giselli Scaini Monique U. Sachet Nayara M. Bernhardt Gislaine T. Rezin Samira S. Valvassori João Quevedo Emilio L. Streck 《Neurochemical research》2010,35(11):1675-1680
Methylphenidate is commonly used for the treatment of attention deficit/hyperactivity disorder. There are still few works
regarding the effects of methylphenidate on brain energy metabolism. Thus, in the present study we evaluated the effect of
chronic administration of methylphenidate on the activities of mitochondrial respiratory chain complexes I and III in the
brain of young rats. The effect of acute administration of methylphenidate on mitochondrial respiratory chain complexes I,
II, III and IV in the brain of young rats was also investigated. For acute administration, a single injection of methylphenidate
was given to rats on postnatal day 25. For chronic administration, methylphenidate injections were given starting at postnatal
day 25 once daily for 28 days. Our results showed that complexes I and III were not affected by chronic administration of
methylphenidate. Moreover, the acute administration of methylphenidate decreased complex I activity in cerebellum and prefrontal
cortex, whereas complexes II, III and IV were not altered. 相似文献
7.
Ivan?BernezEmail author Maria?Teresa?Ferreira Antonio?Albuquerque Francisca?Aguiar 《Hydrobiologia》2005,550(1):121-130
We examined the variability of macroinvertebrate assemblage structure, species identities, and functional feeding group composition in relation to stream size, tributary position, and in-stream factors in a boreal watershed in Finland. Our study included three riffle sites in each of three stream sections in each of three stream size classes. Multi-response permutation procedure, indicator value method, and canonical correspondence analysis revealed clear differences in assemblage structure among the stream size classes, with a gradual increase of species richness as the stream size increased. Significant differences in assemblage structure were also found among the tributary river systems. The functional feeding group composition broadly followed the river continuum concept, i.e., headwaters were dominated by shredders, gatherers, or filterers, whereas scrapers increased in relative abundance with stream size. There was, however, considerable variation in the functional feeding group composition both among and within the headwater stream sections. Our findings refer to a strong influence of stream size on macroinvertebrate assemblages, but also factors prevailing at the scale of individual riffles should be considered in biodiversity conservation of lotic ecosystems. 相似文献
8.
Bone marrow stromal cells produce nerve growth factor and glial cell line-derived neurotrophic factors 总被引:19,自引:0,他引:19
García R Aguiar J Alberti E de la Cuétara K Pavón N 《Biochemical and biophysical research communications》2004,316(3):753-754
Bone marrow stromal cells (BMSC) have attracted interest through their possible use for cell therapy in neurological diseases. Recent reports demonstrated that these cells are able to migrate and have potential for neuronal differentiation after transplantation into brain parenchyma. The objective of this work was determine whether rat BMSC express NGF and GDNF, in order to study its potential application for treatment of neurodegenerative diseases. BMSC were harvested from male rats and cultured in DMEM supplemented with 20% fetal bovine serum. At passage 6 the total RNA was isolated using TriZol reactive. RT-PCRs to evaluate the expression of NGF and GDNF using specific primers were carried out. Our results indicate that rat BMSC have potential to produce NGF and GDNF. We have not found any report in favor of GDNF or NGF production from rat BMSC. 相似文献
9.
10.
da Silva Mateus V. C. Souza Amanda B. de Castro Heizir F. Aguiar Leandro G. de Oliveira Pedro C. de Freitas Larissa 《Bioprocess and biosystems engineering》2020,43(4):615-623
Bioprocess and Biosystems Engineering - This study investigated the synthesis of 2-ethylhexyl oleate catalyzed by Candida antarctica lipase immobilized on magnetic poly(styrene-co-divinylbenzene)... 相似文献