Fertilization increases the functional specialization of fine roots in deep soil layers for young Eucalyptus grandis trees

Abstract

Functional specialization of fine roots was found for Eucalyptus grandis trees at harvesting age (6 years) on tropical soils. Aiming to elucidate whether functional specialization is a ubiquitous feature of eucalypts, we focused on its changes with ontogeny, tree nutrient status and soil depth. We studied the potential uptake of N, K and Ca by 2-year-old E. grandis trees, as a function of soil depth and NPK fertilization. We injected NO −3-15 N, Rb + (K + analogue) and Sr 2+ (Ca 2+ analogue) tracers simultaneously in a solution at depths of 10, 50, 150 and 300 cm in a sandy Ferralsol soil. A complete randomized block design was set up with three replicates of paired trees per injection depth, in fertilized and non-fertilized plots. Recently expanded leaves were sampled at 70 days after tracer injection. Determination of foliar Rb, Sr concentrations and x(15 N) allowed estimating the relative uptake potential (RUP) and the specific RUP (SRUP), defined as the ratio between RUP and fine root length density (RLD) in the corresponding soil layer. Various root traits were measured at each depth. Foliar N and K concentrations were higher in fertilized than in non-fertilized trees. The RUP of NO 3-15 N decreased sharply with soil depth and the highest values of the SRUP of NO 3-15 N were found at a depth of 50 cm. The RUP of Rb + and Sr 2+ did not change with soil depth, whilst the SRUP of Rb + and Sr 2+ were higher at the depth of 300 cm than in the topsoil, concomitant with an increase in root diameter and a decrease in root tissue density with depth. The SRUP of Rb + and Sr 2+ at a depth of 300 cm were on average 136 and 61% higher for fertilized trees than for non-fertilized trees, respectively. Fine roots of young E. grandis trees showed contrasting potential uptake rates with soil depth depending on the nutrient. Fertilization increased the uptake rate of Rb + and Sr 2+ by unit of root length in deep soil layers. Functional specialization of fine roots for cations of low mobility depending on depth previously shown at harvesting age also occurs in young E. grandis plantations and increases with fertilization application. This mechanism helps explaining very low amounts of cations lost by leaching in Eucalyptus plantations established in deep tropical soils, even in highly fertilized stands. High productivity of commercial eucalypt plantations in Brazil

Management strategies differentially affect root functional trait expression in cocoa agroforestry systems

“…These traits are generally positively related with nutrient uptake rates and root turnover: specific root length (SRL; m g −1 ), specific root tip abundance (SRTA; tips g −1 or comparable trait describing branching intensity) (Ostonen et al 2007;Eissenstat et al 2015;Chen et al 2017), as well as the nitrogen content of roots (N root ), which is associated with metabolic processes in the root (i.e., nutrient uptake) (Freschet and Roumet 2017). Other studies, however, have shown opposite trends with soil resource availability (Fort et al 2016;Bordron et al 2018) and newly emerging research has revealed functional specialization of roots for acquiring specific nutrients of different mobilities at different depths (Bordron et al 2018). Under naturally heterogeneous soil nutrient environments, cocoa intraroot system trait variation in relation to soil nutrients has been shown to be nutrient specific (Borden et al 2019) but also dependent on interactions with con-or heterospecific neighbor trees (Isaac et al 2014), thus leading to further questions on the interactive nature of soil amendments and species combination on root trait expression in tree-based agroecosystems.…”

“…Analyses of root traits and coordinated root trait variation have characterized resource acquisition strategies across soil nutrient availability gradients (Weemstra et al 2017) and, importantly, trade-offs in resource acquiring versus conserving strategies have been reported among individuals of the same species (e.g., in Cunninghamia lanceolata (Wang et al 2016) and in a crop species Coffea arabica (Isaac et al 2017)). However, additional spectra or dimensions of coordinated trait variation in roots have also been found (Kong et al 2014;Prieto et al 2015;Liese et al 2017) likely due to the complex role of roots in soil, which can vary, for example, with soil depth (Yan et al 2017;Bordron et al 2018) and with interactions with neighboring plants (Isaac et al 2017).…”

Digging Deeper for Agricultural Resources, the Value of Deep Rooting

“…Actually, for both P and K, considerable reservoirs occur at depth in most soils as pools of P and K contained in poorly weathered minerals in both temperate [33] and tropical soils [34]. Significant nutrient acquisition from more than 2 m depth has also been shown in fast-growing eucalypt plantation trees, with the evidence of a greater capacity of deep roots for cation acquisition, compared with roots in surface layers [35,36]. In agricultural systems, Sr was taken up by lucerne from below 3 m depth [12].…”

The effect of drought and intercropping on chicory nutrient uptake from below 2 m studied in a multiple tracer setup

“…Most studies making use of trace elements as tracers are focusing on the upper 1 m of soil or even shallower. Only three studies are placing trace elements deeper, of which two are focusing on eucalyptus trees (da Silva et al 2011a;Bordron et al 2019) and only one on an agricultural crop, that is lucerne (Fox and Lipps 1964). All three studies documented significant uptake of Sr, and the eucalyptus studies also of Rb at 3 m depth, demonstrating the feasibility of the method.…”