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41.
Mineralization, pore water chemistry and phosphorus release from peaty sediments in the eutrophic Loosdrecht lakes, The Netherlands 总被引:3,自引:0,他引:3
ANJA J. C. SINKE ADI A. CORNELESE PEER KEIZER ONNO F. R. VAN TONGEREN THOMAS E. CAPPENBERG 《Freshwater Biology》1990,23(3):587-599
SUMMARY. 1. Pore water chemistry in peaty sediment was monitored for a year at two representative locations of the eutrophic shallow Loosdrecht lakes. The Netherlands. Phosphorus fluxes over the sediment-water interface were calculated using measured concentration gradients in the pore water and compared to fluxes measured under laboratory conditions. Results were analysed with Redundancy Analysis to detect patterns of variation in pore water chemistry and in measured and calculated fluxes, that could be ascribed to environmental variables.
2. It was demonstrated that phosphorus fluxes measured in long-term laboratory incubations were not correlated to any of the pore water characteristics.
3. Initial phosphorus fluxes measured in sediment columns, which varied between −7.7 and 1330 μmol m−2 : day−1 , were correlated significantly to the calculated phosphorus flux over the sediment-water interface.
4. The high correlation between calculated fluxes of ammonia, phosphorus and methane and measured initial flux of phosphorus, conclusively pointed to mineralization of organic matter as the driving force for phosphorus release from the sediment.
5. Redundancy Analysis demonstrated that the rates of mineralization and phosphorus release were only weakly related to temperature. They appeared to be especially stimulated by the autumnal decrease in temperature which was probably related to an extra input of organic matter. 相似文献
2. It was demonstrated that phosphorus fluxes measured in long-term laboratory incubations were not correlated to any of the pore water characteristics.
3. Initial phosphorus fluxes measured in sediment columns, which varied between −7.7 and 1330 μmol m
4. The high correlation between calculated fluxes of ammonia, phosphorus and methane and measured initial flux of phosphorus, conclusively pointed to mineralization of organic matter as the driving force for phosphorus release from the sediment.
5. Redundancy Analysis demonstrated that the rates of mineralization and phosphorus release were only weakly related to temperature. They appeared to be especially stimulated by the autumnal decrease in temperature which was probably related to an extra input of organic matter. 相似文献
42.
DAVID A. MORRISON GEOFFREY J. CARY STUART M. PENGELLY DAVID G. ROSS BRUCE J. MULLINS COLLETTE R. THOMAS TIMOTHY S. ANDERSON 《Austral ecology》1995,20(2):239-247
Abstract Fire frequency is the number of fires experienced by a particular community within a given time period. This concept can potentially be resolved into a number of interacting variables, including: time since the most recent fire, the length of the inter-fire intervals, and the variability of the length of the inter-fire intervals. We estimated the effects of these three variables on the floristic composition of 65 samples from dry sclerophyll vegetation with different fire histories in Brisbane Water, Ku-ring-gai Chase and Royal National Parks near Sydney. Our analyses suggest that fire frequency may account for about 60% of the floristic variation among our samples. They confirm the hypothesis that the recent (<30 years) fire frequency produces effects on floristic composition of fire-prone communities that can recognizably be attributed both to the time since the most recent fire and to the length of the intervals between fires. These effects are equal in magnitude but are different in the nature of the floristic variation they are associated with. Increasing time-since-fire is associated with a decline in the evenness of fire-tolerant species, indicating that fewer of these species come to dominate the community in the prolonged absence of fire. Herbs and small shrubs decrease in abundance, while larger shrubs increase in abundance. Inter-fire intervals of decreasing length are associated with a decrease in the evenness of the fire-sensitive species, particularly those large Proteaceae shrubs that often dominate the community biomass in dry sclerophyll shrublands of southeastern Australia. Furthermore, the variation associated with inter-fire intervals is not necessarily solely related to the shortest inter-fire interval, but is related to combinations of inter-fire intervals through time. Thus, increasing variability of the length of the inter-fire intervals is associated with an increase in the species richness of both fire-sensitive and fire-tolerant species, implying that it may be variation of the inter-fire intervals through time that is primarily responsible for maintaining the presence of a wide variety of plant species in a particular community. Our results also suggest that the floristic variation associated with different inter-fire intervals decreases with increasing time-since-fire. 相似文献
43.
ABSTRACT. Experimental transmission of two bacterial endosymbionts to symbiont-free isolates of Acanthamoeba spp. was studied to determine specificity of the host-symbiont relationship. Both symbionts originated from amoebic isolates displaying an identical mitochondrial DNA Eco RI fingerprint (group AcUW II). Symbioses were readily established in one amoebic isolate which displayed a homologous mtDNA fingerprint (group AcUW II). Exposure of a heterologous amoebic isolate (group AcUW IV) to the two symbionts resulted in either cell death or encystation without the establishment of symbioses. While symbioses were established with an amoebic isolate from a second heterologous group (AcUW I), a unique membranous sheath appeared and persisted around one of the symbionts which did not exist in the original host. An isolate representing a third heterologous amoebic group (AcUW VI) was variable in its susceptibility with one symbiont unable to infect the host and the other becoming established only after an initial reaction in which trophozoites rounded-up and floated off the substrate. These studies suggest that a specific recognition system exists between particular isolates of Acanthamoeba and their symbionts, and that the appearance of a killer phenotype is related to contact between mismatched, though recognized, pairs. 相似文献
44.
Effects of nitrogen on the response of loblolly pine to drought 总被引:3,自引:1,他引:2
45.
Monitoring the persistence of Laccaria bicolor as an ectomycorrhizal symbiont of nursery-grown Douglas fir by PCR of the rDNA intergenic spacer 总被引:2,自引:0,他引:2
B. HENRION C. DI BATTISTA D. BOUCHARD D. VAIRELLES B. D. THOMPSON † F. LE TACON F. MARTIN 《Molecular ecology》1994,3(6):571-580
The large-scale inoculation of selected beneficial ectomycorrhizal fungi in forest nurseries has generated renewed interest in the ecology of these symbiotic fungi. However, information on the dissemination and persistence of introduced symbionts is scarce due to the limitation of the current identification methods. To identify ectomycorrhizal fungi on single root tips, we investigated the polymorphism of the PCR-amplified ribosomal DNA intergenic spacer (IGS) from a wide range of ectomycorrhizal fungi. To investigate the reliability of this molecular approach in large-scale surveys, the dissemination and persistence on Douglas fir seedlings of the introduced Laccaria bicolor S238N were assessed in a forest nursery in the Massif Central (France). Several hundred ectomycorrhizas and fruiting bodies were sampled from plots where control and L. bicolor inoculated-Douglas fir seedlings were grown for 1.5 years. PCR typing of mycorrhizas indicated that trees inoculated with L. bicolor S238N remained exclusively colonized by that isolate (or sexually derived isolates) for the entire test period. In contrast, control seedlings were infected by indigenous isolates of Laccaria laccata and Thelephora terrestris. The molecular evidence for the persistence of the introduced mycobiont despite the competition from indigenous isolates of the same species provides further illustration of the potential of exotic species for large-scale microbial application. 相似文献
46.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
47.
Abstract Androdioecy (the presence of males and hermaphrodites in a breeding population) is a rare reproductive system in plants, with Datisca glomerata (Datiscaceae) representing the only well-documented example. Recent reports of high outcrossing rates, inbreeding depression, and high male pollen production satisfy theoretical predictions for the continued maintenance of androdioecy in populations of this species. However, in prior studies pollen production was measured indirectly in terms of numbers of anthers per flower—based on the assumption that male and hermaphroditic plant have equal numbers of flowers and that anthers from the two sexual morphs produce equivalent amounts of pollen. Herein, we demonstrate that male and hermaphrodite plants do not differ significantly in terms of flower number, but that pollen production in anthers from hermaphroditic plants is 12.6% higher than in anthers from male plants, thus refining the estimate of relative pollen fecundity of male versus hermaphrodite plants. The differential lowers the frequency of males predicted by theory, but is still consistent with the maintenance of androdioecy in this species. 相似文献
48.
Mitochondrial DNA sequence diversity and the colonization of Scandinavia by house mice from East Holstein 总被引:3,自引:0,他引:3
49.
50.
THOMAS D. SHAHADY 《Freshwater Biology》1993,30(2):279-287
- 1 In reservoirs of the south-eastern United States, Daphnia typically decline in abundance during the summer months. Current understanding suggests that adult shad (Dorosoma spp.), the dominant planktivore in these reservoirs, plays a limited role in Daphnia midsummer declines. The impact of shad larvae is beginning to be documented.
- 2 To examine the impact of larval shad on Daphnia seasonal dynamics, larval dynamics were studied over two seasons and stomach contents were analysed during one season.
- 3 Initial Daphnia panwla declines correlated with abundance of shad larvae. During the decline, shad stomach contents consisted of 97—100%D. parvula. After D. parvula declined, Bosmina and Diaphanosoma accounted for up to 97% of larval diets. When shad diets included other cladocerans, D. parvula abundance increased in the reservoir.
- 4 When this predation pattern was incorporated into a predictive model, larval shad predation accounted for an initial, temporary decline in D. parvula abundance. However, when other crustaceans were incorporated into the shad diet, D. parvula populations increased.
- 5 These results suggest that larval shad have a temporary, strong influence on the structure and abundance of D. parvula populations in south-eastern reservoirs of the United States.