ABSTRACT
Development and activity of plant roots exhibit high adaptive variability. Although it is well-documented, that physicochemical soil properties can strongly influence root morphology and root exudation, particularly under field conditions, a comparative assessment is complicated by the impact of additional factors, such as climate and cropping history. To overcome these limitations, in this study, field soils originating from an unique experimental plot system with three different soil types, which were stored at the same field site for 10 years and exposed to the same agricultural management practice, were used for an investigation on effects of soil type on root development and root exudation. Lettuce (Lactuca sativa L. cv. Tizian) was grown as a model plant under controlled environmental conditions in a minirhizotrone system equipped with root observation windows (rhizoboxes). Root exudates were collected by placing sorption filters onto the root surface followed by subsequent extraction and GC-MS profiling of the trapped compounds. Surprisingly, even in absence of external stress factors with known impact on root exudation, such as pH extremes, water and nutrient limitations/toxicities or soil structure effects (use of sieved soils), root growth characteristics (root length, fine root development) as well as profiles of root exudates were strongly influenced by the soil type used for plant cultivation. The results coincided well with differences in rhizosphere bacterial communities, detected in field-grown lettuce plants cultivated on the same soils (Schreiter et al., this issue). The findings suggest that the observed differences may be the result of plant interactions with the soil-specific microbiomes.
ABSTRACT
Este trabalho apresenta os níveis de contaminação do solo por metais pesados, decorrentes de 16 anos de operação da Estação de Tratamento de Esgotos, por escoamento à superfície, localizada no município de Populina (São Paulo). As análises realizadas para esta avaliação envolveram o pH e os seguintes metais pesados cobre, zinco, alumínio, cádmio, mercúrio, molibdênio, níquel e chumbo. Os resultados mostraram que a grande maioria dos metais apresentou comportamento semelhante, com concentrações consideráveis até 30 e 50 m de distância do ponto de lançamento, nos primeiros 20 cm de profundidade. Deverão ser realizadas novas pesquisas devido aos valores elevados de Hg, Ni, Pb e Al registrados a 20 m de distância do ponto de lançamento dos esgotos, pois se isto for confirmado existem grandes riscos de contaminação dos lençóis subterrâneos.
This assay presents the soil contamination levels by heavy metals, from 16 years of a sewage plant operation, by overland flow, in Populina City, São Paulo State, Brazil. The analyses carried out for this evaluation were the pH and the following heavy metals: copper, zinc, aluminum, cadmium, mercury, molybdenum, nickel and lead. The results showed that the majority of the metals presented similar behavior, with considerable concentration up to 30 and 50m of distance from the launching spot, concentrated on the first 20cm of depth. The dumping from gas stations on the sewage collecting system seems to contribute to the increase of the lead levels. New researches should be carried out due to the high values of Hg, Ni, Pb and Al registered 20m far from the sewage launching spots, because if it is confirmed there will be high contamination risks to the table waters.
