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Although highly weathered soils cover considerable areas in tropical regions, little is known about exploration by roots in deep soil layers. Intensively managed Eucalyptus plantations are simple forest ecosystems that can provide an insight into the belowground growth strategy of fast-growing tropical trees. Fast exploration of deep soil layers by eucalypt fine roots may contribute to achieving a gross primary production that is among the highest in the world for forests. Soil exploration by fine roots down to a depth of 10 m was studied throughout the complete cycle in Eucalyptus grandis plantations managed in short rotation. Intersects of fine roots, less than 1 mm in diameter, and medium-sized roots, 1-3 mm in diameter, were counted on trench walls in a chronosequence of 1-, 2-, 3.5-, and 6-year-old plantations on a sandy soil, as well as in an adjacent 6-year-old stand growing in a clayey soil. Two soil profiles were studied down to a depth of 10 m in each stand (down to 6 m at ages 1 and 2 years) and 4 soil profiles down to 1.5-3.0 m deep. The root intersects were counted on 224 m(2) of trench walls in 15 pits. Monitoring the soil water content showed that, after clear-cutting, almost all the available water stored down to a depth of 7 m was taken up by tree roots within 1.1 year of planting. The soil space was explored intensively by fine roots down to a depth of 3 m from 1 year after planting, with an increase in anisotropy in the upper layers throughout the rotation. About 60% of fine root intersects were found at a depth of more than 1 m, irrespective of stand age. The root distribution was isotropic in deep soil layers and kriged maps showed fine root clumping. A considerable volume of soil was explored by fine roots in eucalypt plantations on deep tropical soils, which might prevent water and nutrient losses by deep drainage after canopy closure and contribute to maximizing resource uses.

Despite the strong ecological importance of ectomycorrhizal (ECM) fungi, their vertical distribution remains poorly understood. To our knowledge, ECM structures associated with trees have never been reported in depths below 2 meters. In this study, fine roots and ECM root tips were sampled down to 4-m depth during the digging of two independent pits differing by their water availability. A meta-barcoding approach based on Illumina sequencing of internal transcribed spacers (ITS1 and ITS2) was carried out on DNA extracted from root samples (fine roots and ECM root tips separately). ECM fungi dominated the root-associated fungal community, with more than 90% of sequences assigned to the genus Pisolithus. The morphological and barcoding results demonstrated, for the first time, the presence of ECM symbiosis down to 4-m. The molecular diversity of Pisolithus spp. was strongly dependent on depth, with soil pH and soil water content as primary drivers of the Pisolithus spp. structure. Altogether, our results highlight the importance to consider the ECM symbiosis in deep soil layers to improve our understanding of fine roots functioning in tropical soils.

Background and aims : While the role of deep roots in major ecosystem services has been shown for tropical forests, there have been few direct measurements of fine root dynamics at depths of more than 2 m. The factors influencing root phenology remain poorly understood, creating a gap in the knowledge required for predicting the effects of climate change. We set out to gain an insight into the fine root phenology of fast-growing trees in deep tropical soils. Methods : Fine root growth and mortality of Eucalyptus grandis trees were observed fortnightly using minirhizotrons down to a soil depth of 6 m, from 2 to 4 years after planting. Results : In the topsoil, the highest live root length production was during the rainy summer (20 cm m−2 d−1) whereas, below 2 m deep, it was at the end of the dry winter (51 cm m−2 d−1). The maximum root elongation rates increased with soil depth to 3.6 cm d−1 in the 5–6 m soil layer. Conclusions : Our study shows that the effect of the soil depth on the seasonal variations in fine root growth should be taken into account when modelling the carbon, water and nutrient cycles in forests growing on deep tropical soils.

This study investigated the effects of using increasing doses of thiamethoxam, a neonicotinoid insecticide, applied as seed treatment, on the physiological, biochemical and nutritional composition of Brachiaria brizantha cv. Piatã. We conducted two experiments with B. brizantha in a greenhouse, in the absence of insects. Biometric parameters and nutritional quality, for feed, were measured in the first experiment, and the root system and the leaf nitrate reductase activity were analyzed in the second experiment. The doses of: 0, 17.5, 35.0, 70.0 and 140.0 g of thiamethoxam per 100 kg of seeds, were applied in both experiments. The results show that the seed treatment with thiamethoxam resulted in a slight decrease in shoot development, but provided root growth, which led to an increase in the nitrate reductase activity that resulted in the higher crude protein content in the shoot. Our data indicate that thiamethoxam alters the metabolism and physiology of B. brizantha, and improving the feed quality is thus becoming a technological tool to be applied to crops.

No Semiárido Brasileiro, 38% das famílias residem na zona rural e geralmente não tem acesso às tecnologias de tratamento de esgoto e à água de qualidade, criando obstáculos para o desenvolvimento sustentável da região. Nesse contexto, o tratamento de esgoto para reúso agrícola se torna uma alternativa para fortalecer a convivência do homem e da mulher do campo com o Semiárido. Esse estudo tem como objetivo analisar o desenvolvimento de uma tecnologia de saneamento básico rural familiar, como alternativa para produção de água de reúso para fins agrícolas no Semiárido Brasileiro. Os resultados comprovaram que esta tecnologia promove uma satisfatória redução dos níveis de matéria orgânica, preserva os nutrientes necessários para o crescimento vegetal e diminui a concentração de microrganismos patogênicos. Com isso, temos um efluente com qualidade satisfatória para ser utilizado na irrigação de culturas forrageiras, madeireiras, cerealíferas e frutíferas. Analisam-se os investimentos nessa tecnologia à luz da abordagem cepalina do Big Push para a Sustentabilidade.