The influence of a thermal discharge caused by the cooling system of a nuclear power station on benthic diatom communities was assessed at the lower Ebro River (in Spain), and the information generated could be useful...The influence of a thermal discharge caused by the cooling system of a nuclear power station on benthic diatom communities was assessed at the lower Ebro River (in Spain), and the information generated could be useful to understand the effects of increasing temperature on large Mediterranean rivers. Surveys conducted at sites before and after the effluent and collected from natural and artificial substrate were analyzed and, Non-metrical Multidimensional Scaling (NMDS), Similarity Percentage Analysis (SIMPER) and 1-way Analysis of Similarities (ANOSIM) were performed to assess changes in community structure. The relationship between diatom assemblages and environmental variables was assessed with a multivariate distance-based linear regression model (DISTLM) and the model was visualized through a redundancy analysis (dbRDA). NMDS ordination was obtained with a stress of 0.18 and 0.17 for natural and artificial substrates, respectively. ANOSIM showed significant differences between Control and Impacted sites (p 0.05). Simper analysis showed that the mean dissimilarity between Control and Impacted sites was of 42.22% for natural substrate and of 39.97% for artificial substrate. DISTLM selected a set of explanatory variables (dissolved oxygen, Tº?difference, total phosphorus, pH and chlorophyll) with a 67.24% of fitted variation. Diatoms showed sensitivity to thermal changes, even though when these did not exceed 3℃. The factors that seemed to influence benthic assemblages the most were seasonal variation and the thermal increase caused by the nuclear power station.展开更多
Aims Seed bank strongly influences composition and structure of above-ground vegetation.Little attention has been paid to the role of allel-opathy driving soil seed bank dynamics,even though allelochemicals released b...Aims Seed bank strongly influences composition and structure of above-ground vegetation.Little attention has been paid to the role of allel-opathy driving soil seed bank dynamics,even though allelochemicals released by allelopathic plants might determine whether a species can or cannot germinate from the soil seed bank and,therefore,to co-exist in the neighborhood of the allelopathic species.Hence,the effects of allelopathic plants on community organization through the effects of allelochemicals on soil seed bank remain largely unknown.In this study,we assessed spatial heterogeneities in soil seed bank caused by the presence of allelopathic plants,and evaluated allelo-pathic effects on seed bank germination and seedling mortality.Methods We examined the effects of the allelopathic shrub Artemisia herba-alba Asso on the spatial structure(in terms of species richness and seed density)of the soil seed bank of a semi-arid ecosystem in NE Spain.Specifically,we evaluated seed bank richness and density at three microsites:under the canopy of A.herba-alba individuals,under the canopy of Salsola vermiculata L.(a non-allelopathic shrub)individuals,and in bare soil.In addition,we assessed the effects of aqueous extract of A.herba-alba on soil seed bank germination(seed-ling emergence and emergence timing)and seedling mortality.Important Findings We found that seed bank richness and density were higher under shrub canopy than they were in bare soil.A.herba-alba and S.vermiculata microsites had similar seed bank richness.However,seed bank density was higher under A.herba-alba because of the high abundance of A.herba-alba seeds.Aqueous extract reduced seedling emergence from the seed bank by 50%,and affected mortality of some emerged seedlings.On the other hand,aqueous extract did not influence the emergence timing of seedlings.We conclude that,although the presence of allelo-pathic plants does not cause relevant changes in seed bank struc-ture relative to similar non-allelopathic shrubs,their presence can actually result in a reduction of seedling emergence from the seed bank,which leads to low plant species richness and density nearby.To our knowledge,this is the first study to examine the effect of an allelopathic plant on the structure and germination in an entire soil seed bank.展开更多
基金funded by the Secretaria de Educacion Superior,Ciencia,Tecnologia e Innovacion(SENESCYT)of Ecuador,which provided a doctoral research fellowship to the first author.
文摘The influence of a thermal discharge caused by the cooling system of a nuclear power station on benthic diatom communities was assessed at the lower Ebro River (in Spain), and the information generated could be useful to understand the effects of increasing temperature on large Mediterranean rivers. Surveys conducted at sites before and after the effluent and collected from natural and artificial substrate were analyzed and, Non-metrical Multidimensional Scaling (NMDS), Similarity Percentage Analysis (SIMPER) and 1-way Analysis of Similarities (ANOSIM) were performed to assess changes in community structure. The relationship between diatom assemblages and environmental variables was assessed with a multivariate distance-based linear regression model (DISTLM) and the model was visualized through a redundancy analysis (dbRDA). NMDS ordination was obtained with a stress of 0.18 and 0.17 for natural and artificial substrates, respectively. ANOSIM showed significant differences between Control and Impacted sites (p 0.05). Simper analysis showed that the mean dissimilarity between Control and Impacted sites was of 42.22% for natural substrate and of 39.97% for artificial substrate. DISTLM selected a set of explanatory variables (dissolved oxygen, Tº?difference, total phosphorus, pH and chlorophyll) with a 67.24% of fitted variation. Diatoms showed sensitivity to thermal changes, even though when these did not exceed 3℃. The factors that seemed to influence benthic assemblages the most were seasonal variation and the thermal increase caused by the nuclear power station.
基金This work was supported by the Spanish Ministry of Education,Culture and Sport(AP-2012-4126 grant to A.I.A.,FPU Program)and by the Spanish Ministry of Economy and Competitiveness and FEDER(CGL-2012-37508 project).We especially thank to A.Foronda for the help with the experiment maintenance tasks.
文摘Aims Seed bank strongly influences composition and structure of above-ground vegetation.Little attention has been paid to the role of allel-opathy driving soil seed bank dynamics,even though allelochemicals released by allelopathic plants might determine whether a species can or cannot germinate from the soil seed bank and,therefore,to co-exist in the neighborhood of the allelopathic species.Hence,the effects of allelopathic plants on community organization through the effects of allelochemicals on soil seed bank remain largely unknown.In this study,we assessed spatial heterogeneities in soil seed bank caused by the presence of allelopathic plants,and evaluated allelo-pathic effects on seed bank germination and seedling mortality.Methods We examined the effects of the allelopathic shrub Artemisia herba-alba Asso on the spatial structure(in terms of species richness and seed density)of the soil seed bank of a semi-arid ecosystem in NE Spain.Specifically,we evaluated seed bank richness and density at three microsites:under the canopy of A.herba-alba individuals,under the canopy of Salsola vermiculata L.(a non-allelopathic shrub)individuals,and in bare soil.In addition,we assessed the effects of aqueous extract of A.herba-alba on soil seed bank germination(seed-ling emergence and emergence timing)and seedling mortality.Important Findings We found that seed bank richness and density were higher under shrub canopy than they were in bare soil.A.herba-alba and S.vermiculata microsites had similar seed bank richness.However,seed bank density was higher under A.herba-alba because of the high abundance of A.herba-alba seeds.Aqueous extract reduced seedling emergence from the seed bank by 50%,and affected mortality of some emerged seedlings.On the other hand,aqueous extract did not influence the emergence timing of seedlings.We conclude that,although the presence of allelo-pathic plants does not cause relevant changes in seed bank struc-ture relative to similar non-allelopathic shrubs,their presence can actually result in a reduction of seedling emergence from the seed bank,which leads to low plant species richness and density nearby.To our knowledge,this is the first study to examine the effect of an allelopathic plant on the structure and germination in an entire soil seed bank.
