Avaliação do pH da rizosfera de genótipos de café em resposta à toxidez de alumínio no solo

Abstract

RESUMOFoi realizado um experimento em casa de vegetação com o objetivo de avaliar a relação entre pH da rizosfera e tolerância ao Al de cinco genótipos de café, na presença e na ausência de calagem. As plantas de café foram desenvolvidas em caixas plásticas, com as raízes próximas da tampa. Após 90 dias as tampas foram removidas e uma fina camada de agar contendo indicador foi derramada sobre a superfície. Também foram avaliados a produção de biomassa seca da parte aérea e das raízes, o comprimento e a superfície de raízes. Quando o solo foi corrigido observou-se o desenvolvimento da coloração amarela próximo às raízes, indicando o abaixamento do pH em H2O. O resultado foi confirmado pela avaliação do pH do solo e da rizosfera com variações de 0,2 e 0,3 unidades de pH. Por outro lado, na presença de Al não houve diferença entre o pH do solo e o da rizosfera, indicando que a alteração no pH desta não parece ser o mecanismo de tolerância ao Al em cafeeiros, uma vez que os genótipos sensíveis e tolerantes apresentaram o mesmo comportamento. Palavras-chave: café, alumínio, pH da rizosfera, tolerância, técnica do agar-indicador. ABSTRACT RHIZOSPHERE pH EVALUATION OF COFFEE GENOTYPES IN RESPONSE TO SOIL ALUMINUM TOXICITYThis work was carried out in greenhouse aiming to evaluate the relationship between rhizospherepH and aluminum tolerance of five coffee genotypes, grown with or without soil liming. Coffee plants were grown in plastic boxes, with roots developing near the cover. After 90 days the lids were removed and a solid agar layer with pH indicator was placed on the surface of soil and roots. It was also evaluated roots and shoots dry biomass production and roots length and surface. When the soil was limed, it was observed the development of yellow color near the roots indicating a pH decrease. This result was confirmed by observing soil and rhizosphere-pH changes, varying between 0.2 and 0.3 units of pH. On the other hand, in the presence of Al it was not observed differences among soil and rhizosphere-pH, indicating that the change of pH induced by roots is not the mechanism of Al tolerance in coffee plants, since sensible and tolerant genotypes showed the same behavior.

Tolerance of arabica coffee cultivars for aluminum in nutritive solution

“…However, with aluminum, there was no alteration. These results suggested that pH variation was dependent on the absence or presence of aluminum in the medium, and that the different cultivars did not interfere in this variation, confirming the results of Braccini et al (2000b). Many studies have shown that root growth inhibition is the most rapid visible symptom of aluminum toxicity in the plants, resulting in root system reduction and injuries, likely leading to mineral deficiency and water stress (Degenhardt et al, 1998).…”

Tolerance to aluminum toxicity by tropical leguminous plants used as cover crops

“…Degenhardt et al (1998) presented the first evidence of an Al-tolerance mechanism based on pH increase in rizosphere of an Arabidopsis thaliana mutant, tolerant to Al toxicity. On the other hand, Braccini et al (2000a) demonstrated that rizosphere pH-changes of coffee plants were not related to higher capacity of this specie to tolerate excess Al in soil. Since the mechanisms to Al toxicity so far have elucidated excluded organic compounds in rizosphere, one may consider that the cultivation of plant materials in the same nutrient solution, as in the present experiment, may influence the plant reaction to Al toxicity.…”

Toxic effect of elements on the germination and initial development of barley seeds (Hordeum vulgare L.)

“…We can observe that Al at all concentrations affected the initial development of barley seedlings for all parameters evaluated. Under conditions of Al extress, plant tolerance has been associated with the control of pH in the rhizosphere and the exclusion of Al by the plasma membrane of plant roots, as presented by Braccini et al (2000) and Souza et al (2011). The same was observed for the Cu element, except for the PDM parameter, which did not demonstrate a significant difference between the other treatments.…”