Functional specialization of Eucalyptus fine roots: contrasting potential uptake rates for nitrogen, potassium and calcium tracers at varying soil depths

Abstract

Summary 1.Little is known about the role of deep roots in the nutrition of forest trees and their ability to provide a safety-net service taking up nutrients leached from the topsoil. 2. To address this issue, we studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (6 years of age -25 m mean height), in Brazil, as a function of soil depth, texture and water content. We injected NO ) tracers simultaneously in a solution through plastic tubes at 10, 50, 150 and 300 cm in depth in a sandy and a clayey Ferralsol soil. A complete randomized design was set up with three replicates of paired trees per injection depth and soil type. Recently expanded leaves were sampled at various times after tracer injection in the summer, and the experiment was repeated in the winter. Soil water contents were continuously monitored at the different depths in the two soils. 3. Determination of foliar Rb and Sr concentrations and 15 N atom % made it possible to estimate the relative uptake potential (RUP) of tracer injections from the four soil depths and the specific RUP (SRUP), defined as RUP, per unit of fine root length density in the corresponding soil layer. 4. The highest tracer uptake rates were found in the topsoil, but contrasting RUP distributions were observed for the three tracers. Whilst the RUP was higher for NO À 3 -15 N than for Rb + and Sr 2+ in the upper 50 cm of soil, the highest SRUP values for Sr 2+ and Rb + were found at a depth of 300 cm in the sandy soil, as well as in the clayey soil when gravitational solutions reached that depth. 5. Our results suggest that the fine roots of E. grandis trees exhibit contrasting potential uptake rates with depth depending on the nutrient. This functional specialization of roots might contribute to the high growth rates of E. grandis trees, efficiently providing the large amounts of nutrients required throughout the development of these fast-growing plantations.

Acquisition of phosphorus and other poorly mobile nutrients by roots. Where do plant nutrition models fail?

“…The model efficiency amounted to 0.66 for the low P treatment and 0.97 for the high P treatment, showing substantial underestimation of the observed P uptake at low P supply (from Mollier et al (2008), reprinted with permission from Elsevier BV) architecture, in spite of its importance in resource exploitation efficiency (Fitter et al 1991). In particular, the contribution of very deep roots on water and nutrient uptake in natural and agroecosystems established on highly weathered tropical soils is still poorly known (Battie-Laclau and Laclau 2009; Christina et al 2011;Jackson et al 2000;Schenk and Jackson 2002;Silva et al 2011). Nevertheless, root architecture models have proved useful for predicting water uptake (Doussan et al 1998(Doussan et al , 1999(Doussan et al , 2003(Doussan et al , 2006Pagès et al 2004;Pierret et al 2007), localizing nutrient uptake zones or describing situations of heterogeneous distribution of nutrients in the soil profile (Ge et al 2000;Liao et al 2001;Lynch and Brown 2001;Rubio et al 2003).…”

Chemical composition of soil solution under eucalyptus plantation in Southern Brazil

“…The differences in nutrients concentrations in the soil profile can be related to the uptake rates and the trees growth. Silva et al (2011) evaluating Eucalyptus grandis plantations observed that the fine roots exhibit contrasting potential uptake rates with depth depending on the nutrient. These authors suggest that, the roots specialization might contribute to the high growth rates of the trees and efficiently providing the nutrients required in their development.…”

“…In fast-growing plantations the potential uptake rates depends on the functional specialization of roots (SILVA et al, 2011). Mareschal et al (2013) studied the effect to eucalyptus plantations managed in short rotations after afforestation of an African savanna.…”

Potasio y Boro en plantaciones dendroenergéticas, en dos suelos marginales de la Región de Biobío, Chile

“…El aumento generalizado de potasio en la profundidad 0-20 cm observado en la Figura 1 podría estar relacionado por un lado a la capacidad mostrada por las raíces profundas de Eucalyptus spp, las cuales presentan grandes potencialidades en la absorción del potasio (Da Silva et al, 2011) lo por lo que la especie podría estar extrayendo potasio en profundidad y depositándolo, vía hojarasca, en la parte superior del suelo, este sería un motivo por el cual una adecuada preparación de sitio, como la realizada en este caso, podría promover el desarrollo radicular en profundidad siendo esta una estrategia para la obtención de potasio, por los árboles, en estas plantaciones.…”