Publicação
Structural and functional diversity of the diazotrophic community in xeric ecosystems: response to nitrogen availability
| Resumo: | The effects of increased nitrogen (N) input in the ecosystems have brought concern for some time, however, the long-term consequences of this input to Mediterranean ecosystems are poorly studied. The Mediterranean ecosystem is considered a hotspot of biodiversity; the Mediterranean basin was considered one of the places in the world with most biodiversity. Taking in consideration that these ecosystems are regarded as environments under N limitation, changes in N availability will alter the relationships between the organisms. The research presented here was carried out on the Mediterranean basin and it is part of an ongoing study over the last 10 years, in which fields were fertilized with different quantities and forms of N. To understand the consequences of this fertilization, diazotrophic bacteria were isolated from rhizospheric soil of Ulex densus subjected to different N addition and characterized in terms of the structural and functional diversity of the communities, using this community as an ecological marker for comparing the different treatments. The methodology applied to understand the ecological consequences was the isolation of the rhizospheric bacteria in N free media and characterization of this collection of isolates, in terms of diversity (phenotypic and genotypic), morphophysiology (distribution of the isolates by different morphotypes), structure (identification of the genera associated with the treatments), functionality (ability to perform ammonification, nitrification and/or denitrification) and metabolic plasticity (ability to use different carbon sources). The N fixation of these isolates was confirmed by their growth in solid and liquid N free media and by isotopic characterization of the ratio of 15N over 14N; a search for the nifH gene was also performed. For this community there were no differences in diversity nor at the morphophysiological level between the different treatments. However, a higher number of isolates was detected in the treatments with higher NH4+ inputs (40A, and 80AN). The ability to perform N fixation was confirmed through multiple passages in solid and liquid N-free media and nifH gene was detected through PCR and dot-blot hybridization, though this was not possible for every representative isolate. Differences with genera associated with the form and quantity of N added to the soil were observed, with some genera only appearing in certain treatments. Every isolate presented more than one function in the N cycle and a decrease in nitrification together with an increase of denitrification was observed along with the increase of bioavailable N. Isolates belonging to genera detected exclusively in treatment 80AN presented higher N content and higher denitrification rates. The variation of the metabolic plasticity between the treatments increased with N fertilization, since the control treatment had the more consistent response for metabolic plasticity. The increase on the isolates number followed the same pattern as the proliferation of U. densus, showing that the potential for N fixation was not inhibited by NH4+ addition. The differences in genera associated with the treatments evidenced a change in the structure of the community. The results of multifunctionality showed a shift in the diazotrophic community, since nitrification and denitrification presented specificity towards different forms of fertilization. The higher variation of the metabolic plasticity associated with N fertilization can be related to changes in carbon source availability in the soil. From the work presented here and future work can arise a platform to direct alterations on the agriculture and ecological guidelines. These alterations are essential to protect this kind of ecosystem, which is extremely important due to the unique biodiversity associated with it. |
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| Autores principais: | Almeida, Carolina Cristiano de |
| Assunto: | Fixação de N Ecossistemas mediterrânicos Fertilização com N Multifuncionalidade no ciclo do N Diversidade diazotrófica Teses de mestrado - 2019 |
| Ano: | 2019 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | The effects of increased nitrogen (N) input in the ecosystems have brought concern for some time, however, the long-term consequences of this input to Mediterranean ecosystems are poorly studied. The Mediterranean ecosystem is considered a hotspot of biodiversity; the Mediterranean basin was considered one of the places in the world with most biodiversity. Taking in consideration that these ecosystems are regarded as environments under N limitation, changes in N availability will alter the relationships between the organisms. The research presented here was carried out on the Mediterranean basin and it is part of an ongoing study over the last 10 years, in which fields were fertilized with different quantities and forms of N. To understand the consequences of this fertilization, diazotrophic bacteria were isolated from rhizospheric soil of Ulex densus subjected to different N addition and characterized in terms of the structural and functional diversity of the communities, using this community as an ecological marker for comparing the different treatments. The methodology applied to understand the ecological consequences was the isolation of the rhizospheric bacteria in N free media and characterization of this collection of isolates, in terms of diversity (phenotypic and genotypic), morphophysiology (distribution of the isolates by different morphotypes), structure (identification of the genera associated with the treatments), functionality (ability to perform ammonification, nitrification and/or denitrification) and metabolic plasticity (ability to use different carbon sources). The N fixation of these isolates was confirmed by their growth in solid and liquid N free media and by isotopic characterization of the ratio of 15N over 14N; a search for the nifH gene was also performed. For this community there were no differences in diversity nor at the morphophysiological level between the different treatments. However, a higher number of isolates was detected in the treatments with higher NH4+ inputs (40A, and 80AN). The ability to perform N fixation was confirmed through multiple passages in solid and liquid N-free media and nifH gene was detected through PCR and dot-blot hybridization, though this was not possible for every representative isolate. Differences with genera associated with the form and quantity of N added to the soil were observed, with some genera only appearing in certain treatments. Every isolate presented more than one function in the N cycle and a decrease in nitrification together with an increase of denitrification was observed along with the increase of bioavailable N. Isolates belonging to genera detected exclusively in treatment 80AN presented higher N content and higher denitrification rates. The variation of the metabolic plasticity between the treatments increased with N fertilization, since the control treatment had the more consistent response for metabolic plasticity. The increase on the isolates number followed the same pattern as the proliferation of U. densus, showing that the potential for N fixation was not inhibited by NH4+ addition. The differences in genera associated with the treatments evidenced a change in the structure of the community. The results of multifunctionality showed a shift in the diazotrophic community, since nitrification and denitrification presented specificity towards different forms of fertilization. The higher variation of the metabolic plasticity associated with N fertilization can be related to changes in carbon source availability in the soil. From the work presented here and future work can arise a platform to direct alterations on the agriculture and ecological guidelines. These alterations are essential to protect this kind of ecosystem, which is extremely important due to the unique biodiversity associated with it. |
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