RESUMO
This research evaluated the effects of coffee cultivation with two different water regimes associated or not with liming and the presence/absence of brachiaria as intercrop on the activities of the soil enzymes ß-glucosidase, arylsulfatase and acid phosphatase. The study was carried out at the experimental farm of Embrapa Cerrados, using the cultivar IAC 144 (Coffea arabica L.), under a clayey dystrophic Cerrado Oxisol. Two water regimes (WR) were considered, WR1 with irrigation shifts throughout the year and WR3 with controlled water stress, for about 70 days, in the dry season. In each water regime, effects of lime application (with/without) and the presence/absence of brachiaria cultivated between the lines of coffee plants were evaluated. The activities of the enzymes ß-glucosidase, arylsulfatase and acid phosphatase were evaluated during the rainy and dry seasons. Liming and intercropped brachiaria positively affected the activities of the three enzymes assessed in this study at varying degrees, depending on season and/or the WR. Our findings evidenced that intercropped brachiaria in coffee rows was the factor that most positively impacted soil enzymes activities.
O objetivo desse trabalho foi avaliar os efeitos do cultivo do café sobre a atividade das enzimas do solo ß-glicosidase, arilsulfatase e fosfatase ácida em função de dois diferentes regimes hídricos associados ou não à calagem e ao cultivo de braquiária nas entrelinhas. Esse estudo foi realizado em um experimento conduzido no campo experimental do Centro de Pesquisa Agropecuária dos Cerrados, utilizando a cultivar IAC 144 (Coffea arabica L.), sob um Latossolo Vermelho distrófico argiloso. Foram considerados dois regimes hídricos (RH), RH1 com irrigação plena em turnos de rega ao longo do ano e RH3 com estresse hídrico controlado, por cerca de 70 dias, na época seca. Em cada regime hídrico foram avaliadas a aplicação ou não de calcário em cobertura e a presença ou ausência de braquiária cultivada nas entrelinhas das plantas do cafezal. As atividades das enzimas ß-glicosidase, arilsulfatase e fosfatase ácida foram avaliadas durante as estações chuvosa e seca. A calagem e a presença de braquiária nas entrelinhas tiveram efeito positivo sobre a atividade das três enzimas avaliadas nesse estudo, em graus variáveis, dependendo da época de coleta das amostras e/ou do RH. Nossos resultados evidenciam que a braquiária nas entrelinhas do café foi o fator de maior impacto positivo sobre a atividade enzimática do solo.
Assuntos
Arilsulfatases/análise , Fosfatase Ácida/análise , Acidez do Solo/análise , Coffea , Glicosídeo Hidrolases/análise , BrachiariaRESUMO
BACKGROUND AND AIMS: The large monophyletic genus Mimosa comprises approx. 500 species, most of which are native to the New World, with Central Brazil being the main centre of radiation. All Brazilian Mimosa spp. so far examined are nodulated by rhizobia in the betaproteobacterial genus Burkholderia. Approximately 10 Mya, transoceanic dispersal resulted in the Indian subcontinent hosting up to six endemic Mimosa spp. The nodulation ability and rhizobial symbionts of two of these, M. hamata and M. himalayana, both from north-west India, are here examined, and compared with those of M. pudica, an invasive species. METHODS: Nodules were collected from several locations, and examined by light and electron microscopy. Rhizobia isolated from them were characterized in terms of their abilities to nodulate the three Mimosa hosts. The molecular phylogenetic relationships of the rhizobia were determined by analysis of 16S rRNA, nifH and nodA gene sequences. KEY RESULTS: Both native Indian Mimosa spp. nodulated effectively in their respective rhizosphere soils. Based on 16S rRNA, nifH and nodA sequences, their symbionts were identified as belonging to the alphaproteobacterial genus Ensifer, and were closest to the 'Old World' Ensifer saheli, E. kostiensis and E. arboris. In contrast, the invasive M. pudica was predominantly nodulated by Betaproteobacteria in the genera Cupriavidus and Burkholderia. All rhizobial strains tested effectively nodulated their original hosts, but the symbionts of the native species could not nodulate M. pudica. CONCLUSIONS: The native Mimosa spp. in India are not nodulated by the Burkholderia symbionts of their South American relatives, but by a unique group of alpha-rhizobial microsymbionts that are closely related to the 'local' Old World Ensifer symbionts of other mimosoid legumes in north-west India. They appear not to share symbionts with the invasive M. pudica, symbionts of which are mostly beta-rhizobial.