Comunidade de nemátodes do solo associada a Quercus suber em declínio
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2017-12-18
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O sobreiro, Quercus suber, tem sofrido um declínio acentuado nas últimas décadas. Tendo já sido alvo de diversos estudos, as causas para este fenómeno ainda não são totalmente compreendidas. A relação entre os diversos fatores que lhe podem estar associados é complexa, interessando conhecer diferenças entre sobreiros que apresentem percentagens de declínio distintas. A comunidade de nemátodes da rizosfera pode ser utilizada como um indicador da qualidade do solo e dos seus processos, podendo demonstrar inter-relações estabelecidas nas diferentes condições. Neste trabalho pretendeu-se conhecer a comunidade de nemátodes associada a sobreiros em diferentes estados de declínio numa área predominante de sobreiro em Portugal (região de Grândola). Recolheram-se amostras de solo da rizosfera de sobreiros em diferentes estados de declínio, sujeitos a condições ambientais semelhantes, para extracção, identificação e classificação por grupos funcionais dos nemátodes (espetro colonizador-persistente), como base para o cálculo de índices ecológicos. Devido à abundância de nemátodes colonizados por fungos, procedeu-se ainda ao isolamento e identificação de fungos nematófagos através da sequenciação da região ITS. Os indicadores das comunidades de nemátodes estudadas revelaram sistemas edáficos onde predominam canais de decomposição bacteriana. Nas amostras analisadas foram detetados nemátodes fitoparasitas dos géneros: Gracilacus, Helicotylenchus, Hemicycliophora, Hoplolaimus, Longidorus, Paratrichodorus, Pratylenchoides, Pratylenchus, Psilenchus, Rotylenchus, Tylenchorhynchus, Xenocriconemella e Xiphinema. A análise estatística confirmou diferenças entre as comunidades de nemátodes e estabeleceu correlações altamente significativas entre a percentagem de declínio e diversos descritores da comunidade, destacando-se: a densidade populacional de nemátodes bacterívoros e carnívoros e a abundância de nemátodes fitoparasitas do género Xenocriconemella. As comunidades de nemátodes de sobreiros de percentagens de declínio baixa ou intermédia diferiram das comunidades de nemátodes de sobreiros de percentagem elevada. Foram obtidos quatro isolados a partir de nemátodes colonizados por fungos, tendo sido identificados dois fungos patogénicos: Cladosporium sp. e Cytospora sp. e dois fungos com actividade nematodicida: Trichoderma sp. e Penicillium bilaiae. As comunidades de nemátodes diferiram entre sobreiros em classes de declínio distintas demonstrando indícios do envolvimento do género Xenocriconemella e da comunidade bacteriana neste processo. A comunidade de nemátodes poderá vir a constituir uma ferramenta útil na previsão e avaliação do estado sanitário de sobreiros.
The cork oak, Quercus suber, has suffered from an accentuated decline for the past decades. Having been subject to many studies, the causes for this phenomenon are not yet fully understood. The connections between the diverse factors associated with cork oak decline is complex, therefore it is of utmost interest to understand differences between trees that show distinct percentages of decline. The soil nematode community can be used as an indicator of soil quality and function, being able to demonstrate interactions established in different conditions. The aim of this study was the analysis of the soil nematode communities in the rhizosphere of trees of varying percentages of decline in a major cork oak area in Portugal (Grândola region). Soil samples from the rhizosphere of cork oaks in different percentages of decline, subject to the same environmental conditions, were collected for nematode extraction, identification and classification according to functional groups (colonizer-persister spectrum), as basis for ecological index calculations. Due to an abundance in nematodes revealing fungal structures in their organisms, the isolation and identification of nematophagous fungi was attempted through ITS region sequencing. Soil nematode community indicators revealed edaphic systems where bacterial channels of decomposition predominate. In the analysed samples, the following genus of plant parasitic nematodes were detected: Gracilacus, Helicotylenchus, Hemicycliophora, Hoplolaimus, Longidorus, Paratrichodorus, Pratylenchoides, Pratylenchus, Psilenchus, Rotylenchus, Tylenchorhynchus, Xenocriconemella and Xiphinema. Statistical analysis confirmed differences between nematode communities and established high significance correlations between the percentage of decline and numerous community descriptors, from which the populational density of bacterivores and carnivores and the abundance of Xenocriconemella sp. are most noteworthy. Differences were noted between the nematode communities within the rhizosphere of cork oaks in a low or intermediate percentage of decline when compared with communities of cork oaks of higher percentage. Four fungal isolates were obtained from nematodes bearing fungal structures, having two been identified as phytopathogenic fungi: Cladosporium sp. and Cytospora sp. and two as nematicidal fungi: Trichoderma sp. and Penicillium bilaiae. Soil nematode communities were different between cork oaks of different decline classes, hinting at the involvement of the genus Xenocriconemella and the bacterial community in the phenomenon. The nematode community could become a useful tool in the prediction and evaluation of the health status of cork oaks.
The cork oak, Quercus suber, has suffered from an accentuated decline for the past decades. Having been subject to many studies, the causes for this phenomenon are not yet fully understood. The connections between the diverse factors associated with cork oak decline is complex, therefore it is of utmost interest to understand differences between trees that show distinct percentages of decline. The soil nematode community can be used as an indicator of soil quality and function, being able to demonstrate interactions established in different conditions. The aim of this study was the analysis of the soil nematode communities in the rhizosphere of trees of varying percentages of decline in a major cork oak area in Portugal (Grândola region). Soil samples from the rhizosphere of cork oaks in different percentages of decline, subject to the same environmental conditions, were collected for nematode extraction, identification and classification according to functional groups (colonizer-persister spectrum), as basis for ecological index calculations. Due to an abundance in nematodes revealing fungal structures in their organisms, the isolation and identification of nematophagous fungi was attempted through ITS region sequencing. Soil nematode community indicators revealed edaphic systems where bacterial channels of decomposition predominate. In the analysed samples, the following genus of plant parasitic nematodes were detected: Gracilacus, Helicotylenchus, Hemicycliophora, Hoplolaimus, Longidorus, Paratrichodorus, Pratylenchoides, Pratylenchus, Psilenchus, Rotylenchus, Tylenchorhynchus, Xenocriconemella and Xiphinema. Statistical analysis confirmed differences between nematode communities and established high significance correlations between the percentage of decline and numerous community descriptors, from which the populational density of bacterivores and carnivores and the abundance of Xenocriconemella sp. are most noteworthy. Differences were noted between the nematode communities within the rhizosphere of cork oaks in a low or intermediate percentage of decline when compared with communities of cork oaks of higher percentage. Four fungal isolates were obtained from nematodes bearing fungal structures, having two been identified as phytopathogenic fungi: Cladosporium sp. and Cytospora sp. and two as nematicidal fungi: Trichoderma sp. and Penicillium bilaiae. Soil nematode communities were different between cork oaks of different decline classes, hinting at the involvement of the genus Xenocriconemella and the bacterial community in the phenomenon. The nematode community could become a useful tool in the prediction and evaluation of the health status of cork oaks.
Descrição
Dissertação de Mestrado em
Engenharia Agronómica apresentada à Universidade de Trás-os-Montes e Alto Douro
Palavras-chave
bioindicadores , ecologia do solo , grupos tróficos , índices ecológicos , nemátodes fitoparasitas