Résultat de la recherche
Above- and belowground linkages in Sphagnum peatland: climate warming affects plant-microbial interactions
Peatlands contain approximately one third of all soil organic carbon (SOC). Warming can alter above- and belowground linkages that regulate soil organic carbon dynamics and C-balance in peatlands. Here we examine the multiyear impact of in situ experimental warming on the microbial food web, vegetation, and their feedbacks with soil chemistry. We provide evidence of both positive and negative impacts of warming on specific microbial functional groups, leading to destabilization of the microbial food web. We observed a strong reduction (70%) in the biomass of top-predators (testate amoebae) in warmed plots. Such a loss caused a shortening of microbial food chains, which in turn stimulated microbial activity, leading to slight increases in levels of nutrients and labile C in water. We further show that warming altered the regulatory role of Sphagnum-polyphenols on microbial community structure with a potential inhibition of top predators. In addition, warming caused a decrease in Sphagnum cover and an increase in vascular plant cover. Using structural equation modelling, we show that changes in the microbial food web affected the relationships between plants, soil water chemistry, and microbial communities. These results suggest that warming will destabilize C and nutrient recycling of peatlands via changes in above- and belowground linkages, and therefore, the microbial food web associated with mosses will feedback positively to global warming by destabilizing the carbon cycle. This study confirms that microbial food webs thus constitute a key element in the functioning of peatland ecosystems. Their study can help understand how mosses, as ecosystem engineers, tightly regulate biogeochemical cycling and climate feedback in peatlands
Relationship between testate amoeba (Protist) communities and atmospheric heavy metals accumulated in Barbula indica (Bryophyta) in vietnam
We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H' was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.
Relationship Between Testate Amoeba (Protist) Communities and Atmospheric Heavy Metals Accumulated in Barbula indica (Bryophyta) in Vietnam
We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H′ was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.
Above- and belowground linkages in Sphagnum peatland: climate warming affects plant-microbial interactions
Peatlands contain approximately one third of all soil organic carbon (SOC). Warming can alter above- and belowground linkages that regulate soil organic carbon dynamics and C-balance in peatlands. Here we examine the multiyear impact of in situ experimental warming on the microbial food web, vegetation, and their feedbacks with soil chemistry. We provide evidence of both positive and negative impacts of warming on specific microbial functional groups, leading to destabilization of the microbial food web. We observed a strong reduction (70%) in the biomass of top-predators (testate amoebae) in warmed plots. Such a loss caused a shortening of microbial food chains, which in turn stimulated microbial activity, leading to slight increases in levels of nutrients and labile C in water. We further show that warming altered the regulatory role of Sphagnum-polyphenols on microbial community structure with a potential inhibition of top predators. In addition, warming caused a decrease in Sphagnum cover and an increase in vascular plant cover. Using structural equation modelling, we show that changes in the microbial food web affected the relationships between plants, soil water chemistry, and microbial communities. These results suggest that warming will destabilize C and nutrient recycling of peatlands via changes in above- and belowground linkages, and therefore, the microbial food web associated with mosses will feedback positively to global warming by destabilizing the carbon cycle. This study confirms that microbial food webs thus constitute a key element in the functioning of peatland ecosystems. Their study can help understand how mosses, as ecosystem engineers, tightly regulate biogeochemical cycling and climate feedback in peatlands.
To What Extent Do Food Preferences Explain the Trophic Position of Heterotrophic and Mixotrophic Microbial Consumers in a Sphagnum Peatland?
Although microorganisms are the primary drivers of biogeochemical cycles, the structure and functioning of microbial food webs are poorly studied. This is the case in Sphagnum peatlands, where microbial communities play a key role in the global carbon cycle. Here, we explored the structure of the microbial food web from a Sphagnum peatland by analyzing (1) the density and biomass of different microbial functional groups, (2) the natural stable isotope (delta C-13 and delta N-15) signatures of key microbial consumers (testate amoebae), and (3) the digestive vacuole contents of Hyalosphenia papilio, the dominant testate amoeba species in our system. Our results showed that the feeding type of testate amoeba species (bacterivory, algivory, or both) translates into their trophic position as assessed by isotopic signatures. Our study further demonstrates, for H. papilio, the energetic benefits of mixotrophy when the density of its preferential prey is low. Overall, our results show that testate amoebae occupy different trophic levels within the microbial food web, depending on their feeding behavior, the density of their food resources, and their metabolism (i.e., mixotrophy vs. heterotrophy). Combined analyses of predation, community structure, and stable isotopes now allow the structure of microbial food webs to be more completely described, which should lead to improved models of microbial community function.
Effects of experimental lead pollution on the microbial communities associated with Sphagnum fallax (Bryophyta)
Ecotoxicological studies usually focus on single microbial species under controlled conditions. As a result, little is known about the responses of different microbial functional groups or individual species to stresses. In an aim to assess the response of complex microbial communities to pollution in their natural habitat, we studied the effect of a simulated lead pollution on the microbial community (bacteria, cyanobacteria, protists, fungi, and micrometazoa) living on Sphagnum fallax. Mosses were grown in the laboratory with 0 (control), 625, and 2,500 mu g L-1 of Pb2+ diluted in a standard nutrient solution and were sampled after 0, 6, 12, and 20 weeks. The biomasses of bacteria, microalgae, testate amoebae, and ciliates were dramatically and significantly decreased in both Pb addition treatments after 6, 12, and 20 weeks in comparison with the control. The biomass of cyanobacteria declined after 6 and 12 weeks in the highest Pb treatment. The biomasses of fungi, rotifers, and nematodes decreased along the duration of the experiment but were not significantly affected by lead addition. Consequently, the total microbial biomass was lower for both Pb addition treatments after 12 and 20 weeks than in the controls. The community structure was strongly modified due to changes in the densities of testate amoebae and ciliates, whereas the relative contribution of bacteria to the microbial biomass was stable. Differences in responses among the microbial groups suggest changes in the trophic links among them. The correlation between the biomass of bacteria and that of ciliates or testate amoebae increased with increasing Pb loading. We interpret this result as an effect on the grazing pathways of these predators and by the Pb effect on other potential prey (i.e., smaller protists). The community approach used here complements classical ecotoxicological studies by providing clues to the complex effect of pollutant-affecting organisms both directly and indirectly through trophic effects and could potentially find applications for pollution monitoring.
Relationship between atmospheric pollution characterized by NO2 concentrations and testate amoebae density and diversity
To assess the potential use of testate amoebae as biomonitors of atmospheric pollution we studied the relationship between atmospheric nitrogen dioxide (NO2) pollution and testate amoebae density, diversity, and community structure (Protista: Rhizopoda) in (zone 1) and around (zone 2) the city of Besançon, France. NO2 concentrations were on average significantly lower in the city zone (mean: 34.8±9.5 µg/m3) than in the periphery zone (mean: 14.6±4.7 µg/m3). The density of living amoebae was correlated with that of empty tests (0.001
Effect of lead pollution on testate amoebae communities living in Sphagnum fallax: An experimental study
We studied the effects of lead pollution on testate amoebae communities living on Sphagnum fallax by growing this moss under controlled conditions. A progressive series of lead (Pb) concentration was used in the growing solution of the mosses: 0 (control), 625 and 2500 μg L−1. The mosses were sampled and analysed for accumulated Pb and testate amoeba communities after 0, 6, 12, and 20 weeks. Species richness, total density and total biomass of testate amoebae declined in response to the Pb treatment and changed over time. The Pb×Time cross-effect was significant for species richness, and total density but not for the total biomass and Shannon diversity. Furthermore, the testate amoebae species richness and the total density were negatively correlated to the Pb concentrations actually accumulated in the moss at the end of the experiment. Species-specific responses of testate amoebae to Pb pollution were identified. Our results thus confirm the sensitivity of testate amoebae to lead pollution.
Effects of Experimental Lead Pollution on the Microbial Communities Associated with Sphagnum fallax (Bryophyta)
Ecotoxicological studies usually focus on single microbial species under controlled conditions. As a result, little is known about the responses of different microbial functional groups or individual species to stresses. In an aim to assess the response of complex microbial communities to pollution in their natural habitat, we studied the effect of a simulated lead pollution on the microbial community (bacteria, cyanobacteria, protists, fungi, and micrometazoa) living on Sphagnum fallax. Mosses were grown in the laboratory with 0 (control), 625, and 2,500 μg L−1 of Pb2+ diluted in a standard nutrient solution and were sampled after 0, 6, 12, and 20 weeks. The biomasses of bacteria, microalgae, testate amoebae, and ciliates were dramatically and significantly decreased in both Pb addition treatments after 6, 12, and 20 weeks in comparison with the control. The biomass of cyanobacteria declined after 6 and 12 weeks in the highest Pb treatment. The biomasses of fungi, rotifers, and nematodes decreased along the duration of the experiment but were not significantly affected by lead addition. Consequently, the total microbial biomass was lower for both Pb addition treatments after 12 and 20 weeks than in the controls. The community structure was strongly modified due to changes in the densities of testate amoebae and ciliates, whereas the relative contribution of bacteria to the microbial biomass was stable. Differences in responses among the microbial groups suggest changes in the trophic links among them. The correlation between the biomass of bacteria and that of ciliates or testate amoebae increased with increasing Pb loading. We interpret this result as an effect on the grazing pathways of these predators and by the Pb effect on other potential prey (i.e., smaller protists). The community approach used here complements classical ecotoxicological studies by providing clues to the complex effect of pollutant-affecting organisms both directly and indirectly through trophic effects and could potentially find applications for pollution monitoring.
To What Extent Do Food Preferences Explain the Trophic Position of Heterotrophic and Mixotrophic Microbial Consumers in a Sphagnum Peatland?
Although microorganisms are the primary drivers of biogeochemical cycles, the structure and functioning of microbial food webs are poorly studied. This is the case in Sphagnum peatlands, where microbial communities play a key role in the global carbon cycle. Here, we explored the structure of the microbial food web from a Sphagnum peatland by analysing (1) the density and biomass of different microbial functional groups, (2) the natural stable isotope (δ13C and δ15N) signatures of key microbial consumers (testate amoebae), and (3) the digestive vacuole contents of Hyalosphenia papilio, the dominant testate amoeba species in our system. Our results showed that the feeding type of testate amoeba species (bacterivory, algivory, or both) translates into their trophic position as assessed by isotopic signatures. Our study further demonstrates, for H. papilio, the energetic benefits of mixotrophy when the density of its preferential prey is low. Overall, our results show that testate amoebae occupy different trophic levels within the microbial food web, depending on their feeding behavior, the density of their food resources, and their metabolism (i.e., mixotrophy vs. heterotrophy). Combined analyses of predation, community structure, and stable isotopes now allow the structure of microbial food webs to be more completely described, which should lead to improved models of microbial community function.