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Made available in DSpace on 2022-04-29T08:40:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-04-01 We evaluated differential expression of genes in leaf and xylem tissues for three Eucalyptus clones in the field using Illumina sequencing, under four contrasting fertilization regimes: a control combining nitrogen (N), phosphorus (P), and potassium (K) and three regimes with N, K, and P deficiency. The field results showed significantly better performance with a control fertilizing regime for height and circumference at 14 months, but no differences between clones. The number of up and down regulated DEG (differentially expressed genes) in pairwise clone comparisons was around 5900 for leaf and 6900 for xylem at FDR < 0.01. With fertilization treatment comparisons, DEG were only observed for N deficiency versus control with 45 up and down-regulated DEG for leaf and 1022 for xylem. The number of DEGs between fertilizer deficiency treatment and control varied greatly within each clone showing important clone by fertilization interaction. Gene ontology analysis showed that a great number of genes were related to stress, transport, and transcription factors. The co-expression analysis showed some significant correlations between complex network gene expression and tree growth induced by fertilization regime. For example, the co-expression of a 54 DEG network showed a significant correlation with tree height (0.84, P value: 1e−04) and DBH (0.89, P value: 7e−06) in the case of N deficiency versus control. Our results suggest that gene expression levels between different fertilization treatments and clones can provide a basis for future research on gene function in Eucalyptus under nutrient stress with the perspective of new development in Eucalyptus breeding. Departamento de Ciências Químicas E Biológicas Instituto de Biociências UNESP - Univ Estadual Paulista, SP Instituto de Biotecnologia (IBTEC) UNESP - Univ Estadual Paulista Alameda das Tecomarias s/n. Chácara Capão Bonito, SP AGAP Univ Montpellier CIRAD INRA and Montpellier SupAgro UMR AGAP DGD-RS CIRAD, Avenue Val de Montferrand FCA (Faculdade de Ciências Agronômicas Departamento de Ciência Florestal Solos e Ambiente UNESP Univ Estadual Paulista “Júlio de Mesquita Filho” Eco&Sols Univ Montpellier CIRAD INRA IRD Montpellier SupAgro UMR Ecoa&Sols CIRAD, 2 Place Viala Departamento de Ciências Químicas E Biológicas Instituto de Biociências UNESP - Univ Estadual Paulista, SP Instituto de Biotecnologia (IBTEC) UNESP - Univ Estadual Paulista Alameda das Tecomarias s/n. Chácara Capão Bonito, SP FCA (Faculdade de Ciências Agronômicas Departamento de Ciência Florestal Solos e Ambiente UNESP Univ Estadual Paulista “Júlio de Mesquita Filho”

Within agroforestry systems, trees greatly contribute to soil carbon (C) sequestration. We still know little about how this contribution varies according to tree species. Here, we quantified the soil C content derived from three main tree species, Eucalyptus robusta, Coffea arabica and Citrus clementina, used in rainfed rice-based agroforestry in the Highlands of Madagascar. A fully factorial controlled mesocosm experiment was performed, with seedlings of the tree species planted with or without rice in a Ferralsol. The natural 13C abundance in the soil was measured to assess tree- and rice-derived C. One year after planting, Eucalyptus robusta was the species exhibiting the highest tree-derived C values, with 148 g C m−2 on average. In contrast, Citrus clementina transferred only 12 g C m−2 to the soil. No significant contribution of Coffea arabica to the soil C stock was found. The presence of rice affected neither the growth of tree seedlings nor their abilities to provide C to the soil. The difference in soil C sequestration among tree species was significantly correlated with differential root biomass. Tree root biomass was significantly correlated with soil δ13C. This experimental assay highlighted the contrasting contributions of tree species to ecological processes such as soil C sequestration at the early stage of agroforestry establishment. Further studies considering tree density and spatial arrangement should be conducted under field conditions to gain further insights into tree contributions to soil C sequestration in agroforestry systems.

Made available in DSpace on 2021-06-25T11:16:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The savannas (called Cerrado) are the second-largest vegetation formation in Brazil after the Amazon rainforest, with about 2 million km2. Roots have been found in very deep soil layers in Cerrado ecosystems, which suggests a crucial role of deep rooting in the supply of water and nutrients over dry periods. The aim of our study was to gain insight into the complementarity of common Cerrado woody species in taking up mobile nutrients throughout deep soil profiles. In a closed-canopy savanna with dense woody understory, labeled nitrate was injected into the soil at six soil depths (0.1, 1.5, 3.0, 6.0, 9.0, or 12.0 m) with three plots per depth, at two dates (in rainy and dry seasons). Five months after labeled nitrate injection, young leaves were sampled and foliar δ15N was determined in each plot in the three most common woody species (Coussarea hydrangeifolia, Miconia albicans and Xylopia aromatica). The maximum depth of 15N uptake was dependent on the species. X. aromatica trees took up 15N from a maximum depth of 9 m and exploited a much larger soil volume than the two other species, with the uptake of 15N at a horizontal distance of up to 5 m between the trunk and the injection site. The behavior of M. albicans and C. hydrangeifolia was similar, with a strong uptake of 15N only in the 0–1.5 m soil layer, within 2 m horizontally from the injection site. The depth of 15N uptake over the dry season was not related to the diameter at breast height of the woody plants sampled. We show that roots can take up labeled nitrogen from a depth of 9 m in tropical wooded savannas, which suggests an important role of deep-rooted species in closing biogeochemical cycles on highly weathered tropical soils. São Paulo State University (Unesp) School of Agriculture CIRAD UMR Eco&Sols Eco&Sols Univ Montpellier CIRAD INRA IRD Montpellier SupAgro Department of Ecology University of São Paulo (USP) São Paulo State University (Unesp) Institute of Biosciences São Paulo State University (Unesp) School of Agriculture São Paulo State University (Unesp) Institute of Biosciences FAPESP: 2015/25946–0

Mixed plantations of Eucalyptus and N2-fixing trees are ecologically beneficial because they stimulate organic matter cycling and increase carbon (C) and nitrogen (N) pools in the soil. However, the microbial mechanisms that contribute to the improvement of C and N dynamics remain poorly understood in managed forest ecosystems. Here, we evaluated interactions between the bacterial community and biological functions involved in C and N cycles in the soil and litter layers resulting from pure or mixed Eucalyptus grandis and Acacia mangium plantations. We hypothesized that the mixed plantations induce changes in the bacterial community that would drive increases in C and N pools in soil and litter layers. We established a field experiment with treatments including pure E. grandis without (E) and with nitrogen fertilization (E + N), pure A. mangium (A), and mixed E. grandis and A. mangium (E + A). Soil and litter from all treatments were sampled 27 and 39 months after planting. We evaluated the soil and litter bacterial community and biological functions involved in C and N cycles (i.e., microbial and enzyme activities, functional gene abundance, and soil-litter nutrient cycling). The treatments A and E + A showed an increase in C and N contents in the organic soil fractions. We found higher bacterial diversity and OTU richness in soil and litter, and higher nifH gene abundance in the soil under A and E + A, when compared to pure E. grandis (especially E + N) plantation. Our data suggest that the total N content influences the bacterial community structure of the litter, which undergoes alterations according to the treatment and forest age. Equally, Rhizobium, Bradyrhizobium and Sphingomonas showed a positive correlation with nifH and soil N. Our study provided evidence that changes in the microbial community in mixed A. mangium and E. grandis plantations is correlated with increased C and N cycling. These findings have implications for increased productivity and environmental sustainability, besides allowing for the optimization of mineral fertilization in forest plantations.

Made available in DSpace on 2021-06-25T10:21:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Aims: Belowground interactions are still poorly understood in mixed-species forests. We investigated the effects of soil fertility on belowground processes in mixed planted forests. Methods: The dynamics and traits of Eucalyptus and Acacia mangium fine roots (diameter < 2 mm) in plantations with 50% of each species were studied in a randomized block design established in a nutrient depleted soil. Stands with NPK fertilization applied at planting (F+) were compared to unfertilized stands (F-). Results: In the 0–15 cm soil layer, Eucalyptus root mass density (RMD) was higher than Acacia RMD by 50% in F+ and 10% in F-, considering both ages. At 34 months of age, Eucalyptus RMD was 94% higher near Acacia trees than near Eucalyptus trees in F-. In this layer, Eucalyptus specific root length (SRL) was 21% higher than Acacia SRL at 16 months of age and was 10% higher in F- than in F+ at 34 months of age. The cumulative Eucalyptus fine root length production between 16 and 34 months was 66% higher in F- than in F+ in the 0–1 m soil layer. Conclusions: Fertilization increased the competition between species and led to a partial exclusion of Acacia fine roots from the nutrient-rich topsoil. Soil exploration by Eucalyptus roots in the vicinity of Acacia trees was higher in F- than in F+, which suggests that unfertilized trees benefited from facilitation through higher soil N availability and direct N transfer from Acacia trees. ESALQ Forest Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo Université de Lorraine AgroParisTech INRAE UMR Silva School of Agriculture São Paulo State University (UNESP) Eco&Sols CIRAD INRA IRD Montpellier SupAgro Univ Montpellier CIRAD UMR Eco&Sols ESALQ Soil Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo UFES Centro de Ciências Agrárias e Engenharias Alto Universitário, S/N Guararema School of Agriculture São Paulo State University (UNESP)

Made available in DSpace on 2021-06-25T10:32:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Fertilization is commonly used to increase growth in forest plantations, but it may also affect tree water relations and responses to drought. Here, we measured changes in biomass, transpiration, sapwood-to-leaf area ratio (As:Al) and sap flow driving force (ΔΨ) during the 6-year rotation of tropical plantations of Eucalyptus grandis under controlled conditions for throughfall and potassium (K) fertilization. K fertilization increased final tree height by 8 m. Throughfall exclusion scarcely affected tree functioning because of deep soil water uptake. Tree growth increased in K-supplied plots and remained stable in K-depleted plots as tree height increased, while growth per unit leaf area increased in all plots. Stand transpiration and hydraulic conductance standardized per leaf area increased with height in K-depleted plots, but remained stable or decreased in K-supplied plots. Greater Al in K-supplied plots increased the hydraulic constraints on water use. This involved a direct mechanism through halved As:Al in K-supplied plots relative to K-depleted plots, and an indirect mechanism through deteriorated water status in K-supplied plots, which prevented the increase in ΔΨ with tree height. K fertilization in tropical plantations reduces the hydraulic compensation to growth, which could increase the risk of drought-induced dieback under climate change. CIRAD UMR Eco&Sols Eco&Sols Univ Montpellier CIRAD INRAe IRD Montpellier SupAgro Department of Forest Sciences Universidade de São Paulo “Luiz de Queiroz” College of Agriculture (USP-ESALQ) Center of Nuclear Energy in Agriculture Universidade de São Paulo (USP-CENA) Edafotec SL NIPE UNICAMP Bordeaux Sciences Agro UMR INRAe-ISPA 1391 Nicholas School of the Environment Duke University Ecologie Systématique Evolution Univ. Paris-Sud CNRS AgroParisTech Université Paris-Saclay School of Agricultural Sciences UNESP—São Paulo State University School of Agricultural Sciences UNESP—São Paulo State University

Climate change is expected to increase the frequency of droughts in most tropical regions in the coming decades. A passive phenomenon called hydraulic redistribution (HR) allows some plant species to take up water from deep and wet soil layers and redistribute it in the upper dry layers where other plants and soil biota can benefit from it. In addition, soil fertilization, particularly potassium (K), may also affect drought-adaptive mechanisms and increase water use efficiency (WUE) on poor and acidic tropical soils. The present study aimed at quantifying the role of HR and K fertilization on both wood productivity and WUE for stemwood production (WUEp) of Eucalyptus grandis plantations in Brazil under ambient and reduced (−37%) throughfall conditions. Tree transpiration was measured using trunk sap flow sensors over 21 months, and HR was estimated from the reverse sap flow (RF) observed in shallow roots over 18 months. Tree biomass, hydraulic conductance, soil water storage from surface to the water table (down to 17 m), and leaf photosynthetic capacity were also assessed. Significant HR was detected over the whole year, even during the rainy seasons. Neither potassium fertilization nor throughfall exclusion affected the velocity of water transported by HR, probably because most trees reached water table. Nonetheless, some photosynthetic capacity parameters, including the maximum photosynthetic rate (Amax), increased in treatments with K addition. This higher Amax combined with an increased sapwood area index, was associated with an increase in water uptake by 30 %–50 % and WUEp by 300 % relative to K-deficient trees. We postulate that the increase in WUEp promoted by potassium fertilization was partly driven by an increase in biomass allocation to wood, at the expense of foraging organs (leaves and roots), because K addition alleviated constraints on light and water use. Our results indicate that fertilizing E. grandis plantations with K is beneficial to both wood biomass production and WUEp.

Many studies have shown that introducing N

International audience; The selection of ideotypes combining high biomass production, high water use efficiency (WUE) and adequate wood properties is a major challenge in improving forest trees for industrial plantations. This issue was addressed in a field experiment evaluating 1130 clones of Eucalyptus urophylla * Eucalyptus grandis. Genomic selection using 3303 SNPs and the GBLUP model was carried out at age 55 months to select genitors and clones for stem volume (V55), WUE (using stable carbon isotope composition in stemwood, δ13C as a proxy, transformed into intrinsic WUE, Wi), as well as lignin (KL) and holocellulose (HCEL) contents. The variance components were mainly additive for δ13C(Wi), KL and HCEL, while they were highly non-additive for V55 (the ratio of dominance to additive variance was 130%). The narrow sense heritability was higher for Wi (h2 = 0.704) than for volume and wood traits (

Made available in DSpace on 2020-12-12T01:05:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-11-01 Centre de Coopération Internationale en Recherche Agronomique pour le Développement 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. CIRAD UMR Eco&Sols Eco&Sols Univ Montpellier CIRAD INRA IRD Montpellier SupAgro ESALQ University São Paulo CIRAD UMR BGPI BGPI Univ Montpellier CIRAD INRA IRD Montpellier SupAgro CENA University São Paulo Federal University of Ceará UNESP University São Paulo LSTM Univ Montpellier CIRAD INRA IRD Montpellier SupAgro INRA US 1426 GeT-PlaGe Genotoul UNESP University São Paulo

Made available in DSpace on 2018-12-11T17:30:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-05-01 Agence Nationale de la Recherche Centre de Coopération Internationale en Recherche Agronomique pour le Développement Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Universidade de São Paulo Background and aims: Comparing root functioning under contrasting rainfall regimes can help assessing the capacity of plant species to cope with more intense and frequent drought predicted under climate change context. While the awareness of the need to study the whole root system is growing, most of the studies of root functioning through rhizosphere analyses have been restricted to the topsoil. Our study aimed to assess whether the depth in the soil and the rainfall amount affect root functioning, and notably the fate of nutrients within the rhizosphere. Methods: We compared pH and nutrient availability within the rhizosphere and bulk soil along a 4-m deep soil profile in a 5-year-old eucalypt (Eucalyptus grandis) plantation under undisturbed and reduced rainfall treatments. Results: The exchangeable K concentration and the pH of the bulk soil were not influenced by the reduced rainfall treatment. By contrast, the H3O+ concentration in the rhizosphere was significantly greater than that of the bulk soil, only in the reduced rainfall plot. The concentrations of exchangeable K in the rhizosphere were significantly larger than those of the bulk soil in both treatments but this difference was higher in the reduced rainfall plot, notably below the depth of 2 m. Both exchangeable K and H3O+ concentration significantly increased within the rhizosphere in the reduced rainfall treatment at soil depth down to 4 m. Conclusions: The amount of K brought to the roots by mass flow was estimated and could not explain the observed increase in exchangeable K concentration within the rhizosphere. A more likely explanation was root-induced weathering of K-bearing minerals, partly related to enhanced rhizosphere acidification. Our results demonstrate that root functioning can be considerably altered as a response to drought down to large depths. CIRAD UMR Eco&Sols, 2 Place Viala INRA UMR Eco&Sols, 2 Place Viala FCA UNESP LCF ESALQ CENA ESALQ FCA UNESP Agence Nationale de la Recherche: ANR-13-AGRO-0005 FAPESP: 2013/25998-4

Made available in DSpace on 2018-11-26T16:27:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-03-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) CIRAD USP-COFECUB AGREENIUM (Plantrotem project) SOERE F-ORE-T Agence Nationale de la Recherche Adaptive strategies to improve tree water-use efficiency (WUE) are required to meet the global demand for wood in a future drier climate. A large-scale throughfall exclusion experiment was set up in Brazil to study the interaction between water status and potassium (K) or sodium (Na) availability on the ecophysiology of Eucalyptus grandis trees. This experiment focused primarily on the changes in aboveground net primary production, stand water use, phloem sap and leaf delta C-13, net CO2 assimilation and stomatal conductance. The correlations between these response variables were determined to gain insight into the factors controlling water-use efficiency in tropical eucalypt plantations. The intrinsic WUE in individual leaves (the ratio of net CO2 assimilation to stomatal conductance) was estimated at a very short time scale from the leaf gas exchange. Sap flow measurements were carried out to assess the WUE for stem wood production (the ratio of wood biomass increment to stand water use). Averaged over the two water supply regimes, the stemwood biomass 3 years after planting was 173% higher in trees fertilized with K and 79% higher in trees fertilized with Na than in trees with no K and Na addition. Excluding 37% of the throughfall reduced stemwood production only for trees fertilized with K. Total canopy transpiration between 1 and 3 years after planting increased from about 750 to 1300 mm y(-1) in response to K fertilization with a low influence of the water supply regime. K fertilization increased WUE for stemwood production by approx. 60% with or without throughfall exclusion. There was a strong positive correlation between phloem sap delta C-13 and short-term leaf-level intrinsic WUE. Whatever the water and nutrient supply regime, the gas exchange WUE estimates were not correlated with WUE for stemwood production. Phloem sap delta C-13 and leaf delta C-13 were therefore not valuable proxies of WUE for stemwood production. The allocation pattern in response to nutrient and water supply appeared to be a major driver of WUE for stemwood production. In areas with very deep tropical soils and annual rainfall

Made available in DSpace on 2020-12-12T01:29:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-11-10 Silpakorn University Ministry of Science and Technology of Thailand Agence Nationale de la Recherche Many studies have shown that introducing N2-fixing trees (e.g. Acacia mangium) in eucalypt plantations can increase soil N availability as a result of biological N2 fixation and faster N cycling. Some studies have also shown improved eucalypt P nutrition. However, the effects of N2-fixing trees on P cycling in tropical soils remain poorly understood and site-dependent. Our study aimed to assess the effects of planting A. mangium trees in areas managed over several decades with eucalypt plantations on soil organic P (Po) forms and low molecular weight organic acids (LMWOAs). Soil samples were collected from two tropical sites, one in Brazil and one in the Congo. Five different treatments were sampled at each site: monospecific acacia, monospecific eucalypt, below acacias in mixed-species, below eucalypts in mixed-species as well as native vegetation. Po forms and LMWOAs were identified in sodium hydroxide soil extracts using ion chromatography and relationships between these data and available P were determined. At both sites, the concentrations of most Po forms and LMWOAs were different between native ecosystems and monospecific eucalypt and acacia plots. Also, patterns of Po and LMWOAs were clearly separated, with glucose-6-P found mainly under acacia and phytate and oxalate mainly under eucalypt. Despite the strongest changes occurred at site with a higher N2 fixation and root development, acacia introduction was able to change the profile of organic P and LMWOAs in

Made available in DSpace on 2018-12-11T16:52:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01 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−3-15N, Rb+ (K+ analogue) and Sr2+ (Ca2+ 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(15N) 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 NO3 –-15N decreased sharply with soil depth and the highest values of the SRUP of NO3 –-15N were found at a depth of 50 cm. The RUP of Rb+ and Sr2+ did not change with soil depth, whilst the SRUP of Rb+ and Sr2+ 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 Sr2+ 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 Sr2+ 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. USP-ESALQ CIRAD UMR Eco&Sols Eco&Sols Univ Montpellier CIRAD INRA IRD, Montpellier SupAgro UNESP Departamento de Solos e Recursos Ambientais Universidade Estadual Paulista ‘Júlio de Mesquita Filho’ USP-CENA INRA CIRAD IRD Montpellier SupAgro University of Montpellier UMR Eco&Sols UNESP Departamento de Solos e Recursos Ambientais Universidade Estadual Paulista ‘Júlio de Mesquita Filho’

Made available in DSpace on 2019-10-06T16:31:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Climate changes will increase the probability of drought, which is likely to dramatically increase tree mortality. The capacity of trees to withdraw water in deep soil layers is an important trait likely to account for tree survival over prolonged droughts. Our study aimed to gain insight into the maximum distance from the trunk where Eucalyptus fine roots take up water and mobile nutrients in deep sandy soils during dry periods. NO3 −-15N was injected in the soil at the end of the rainy season in commercial Eucalyptus stands planted with the same E. urophylla × E. grandis clone. The 15N tracer was applied in the middle of the inter-row (replicated in 3 plots): at 5 depths (from 0.1 to 6 m)at age 0.6 year, at 4 depths (from 0.1 to 9 m)at age 1.2 years, at 5 depths (from 0.1 to 12 m)at age 2.2 years, and at 6 depths (from 0.1 to 15 m)at age 6.4 years. δ15N was determined in leaves sampled in dominant and suppressed trees at different distances from each injection area, 4–5 months after NO3 −-15N injection (after the dry season). While dominant trees took up NO3 −-15N down to a depth of 6 m between 7 and 12 months after planting, the maximum depth of NO3 −-15N uptake for suppressed trees was between 3 and 4.5 m. From 1.5 to 6 years after planting, a foliar enrichment in 15N was mainly detected when the NO3 −-15N tracer was injected in the upper soil layers and only for a few trees at a depth of 6 m. Most of the uptake of 15N occurred within 2 m of horizontal distance from the injection site, whatever tree age and tree social status. Low amounts of NO3 −-15N were taken up for injection sites located between 2 m and 5 m from the trunk, and 15N uptake was never detected at horizontal distances greater than 6 m from the trunk. Eucalyptus fine roots can take up nitrates at depths between 6 and 8 m the first year after planting. However, the NO3 −-15N tracer injected at a depth of 6 m was only taken up by dominant trees and a 15N foliar enrichment of suppressed trees was only detected when the tracer was injected in the upper 3 m. Fertilizers must be applied within 2 m of the trunks in Eucalyptus plantations to be taken up by all trees, regardless of their social status. When fertilizations are concentrated the first months after planting in sandy soils, nutrient leaching in deep layers might increase the heterogeneity of the stands since mobile nutrients could only be taken up by dominant trees. Universidade Estadual Paulista (Unesp) Faculdade de Ciências Agronômicas CIRAD UMR Eco&Sols Eco&Sols CIRAD INRA IRD Montpellier SupAgro University of Montpellier ESALQ Universidade de São Paulo Universidade Estadual Paulista (Unesp) Centro de Isótopos Estáveis Suzano SA Company Universidade Estadual Paulista (Unesp) Faculdade de Ciências Agronômicas Universidade Estadual Paulista (Unesp) Centro de Isótopos Estáveis FAPESP: 2015/25946-0

Made available in DSpace on 2019-10-06T15:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-03-15 Mixing N-fixing trees with eucalypts is an attractive option to improve the long-term soil N status in fast-growing plantations established in tropical soils. A randomized block design was replicated at four sites in Brazil to compare the biogeochemical cycles in mono-specific stands of Eucalyptus (100E) and Acacia mangium (100A) with mixed-species plantations in a proportion of 1:1 (50A50E). Our study aimed to assess the effects of introducing A. mangium trees in Eucalyptus plantations on atmospheric N 2 fixation, N cycling and soil organic matter stocks. Litterfall and soil N mineralization were measured over the last two years of the rotation (4–6 years after planting). Aboveground N accumulation in the trees and C and N stocks in the forest floor and in the top soil were intensively sampled at harvesting age. N 2 fixation rates were estimated using the natural abundance of 15 N as well as by the difference between total N stocks in 100A and 50A50E relative to 100E (accretion method). While the 15 N natural abundance method was unsuitable, the accretion method showed consistently across the four sites that atmospheric N fixation reached about 250 and 400 kg N ha −1 rotation −1 in 50A50E and 100A, respectively. Except at one site with high mortality, N contents within trees at harvesting were approximately 40% higher in 100A than in 100E. Mean N contents in litterfall and N mineralization rates were about 60% higher in 100A than in 100E, with intermediate values in 50A50E. The amounts of N in litterfall were much more dependent on soil N mineralization rates for acacia trees than for eucalypt trees. Soil C and N stocks were dependent on soil texture but not influenced by tree species. N budgets over a 6-year rotation were enhanced by about 65 kg N ha −1 yr −1 in 100A and 40 kg N ha −1 yr −1 in 50A50E relative to monospecific eucalypt plantations. Introducing N-fixing trees in eucalypt plantations might therefore contribute to reducing the need for mineral N fertilization in the long-term. USP ESALQ Forest Science Department UNESP Departamento de Solos e Recursos Ambientais Universidade Estadual Paulista ‘Júlio de Mesquita Filho’ CIRAD UMR Eco&Sols Eco&Sols INRA CIRAD IRD Montpellier SupAgro University of Montpellier USP CENA, Av. Centenário, 303 CENIBRA Coordenação de Pesquisa Florestal, 35196-972 Belo Oriente Department of Forest Science and Wood UFES, 29550-000 Jerônimo Monteiro UNESP Departamento de Solos e Recursos Ambientais Universidade Estadual Paulista ‘Júlio de Mesquita Filho’

Average wood density of 38-year-old Cariniana legalis (Mart.) Kuntze, a Brazilian native forest species, was found to increase with faster growth and lower stocking, while decreasing from pith to bark. A complete randomised block design was planted with five blocks. Ten trees were harvested in each of three spacing treatments. We hypothesised that the stand stemwood production would not significantly differ depending on tree spacing. However, tree growth would be higher in the wider spacing and wood density would be higher in the narrower spacing. The diameter growth of trees was higher at 3 m × 2.5 m than at 3 m × 2 m and 3 m × 1.5 m. Nevertheless, this higher individual tree growth at 3 m × 2.5 m did not compensate for the greater tree stock density at 3 m × 1.5 m with stand stemwood production at 38 years of 530 m3 ha−1 and 649 m3 ha−1, respectively. These results suggest that C. legalis, which can produce up to 17 m3 ha−1 y−1 of medium- to high-density timber – about 800 kg m−3 – is a promising native species for forest plantations in Brazil.Keywords: Brazilian native wood, management of tropical timber, X -ray densitometry

Made available in DSpace on 2018-12-11T16:39:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-01-01 Unlike Eucalyptus monocultures, nitrogen fixing trees are likely to improve the soil nutrient status through the decomposition of N-enriched litter. The Home Field Advantage (HFA) hypothesis states that plants can create conditions that increase the decomposition rates of their own litter. However, there may not be any HFA when most of the decomposers are generalists. A reciprocal transplant decomposition experiment of fine roots and leaves of Acacia mangium and Eucalyptus grandis was undertaken in monocultures of these two species to test the HFA hypothesis using a complete randomized design with three blocks. Three litterbags containing leaf or fine root residues of each species were collected every 3 months from each plot over 12 months for fine roots and 24 months for leaves. The litter mass and C, N and P concentrations were measured at each sampling date. The concentrations of C-compounds were measured 0, 12 and 24 months from the start of the experiment. There was no evidence of HFA for either the leaves or the fine roots of either species. The decomposition rates were slower for Acacia litter than for Eucalyptus litter even though initial N concentrations were 1.9-2.9 times higher and P concentrations were 1.5-3.3 times higher in the Acacia residues. N:P ratios were greater than 20-30 for the residues of both species, with the highest values for Acacia. Litter decomposition depended partly on the C quality of the litter, primarily in terms of water soluble compounds and lignin content. As shown recently in tropical rainforests, these results suggest that the activity of decomposers is limited by energy starvation in tropical planted forests. Decomposer activity may also have been limited by P availability which may not have been directly related to the P concentrations or C:P ratios in the residues. USP CENA, 303 Av. Centenario USP ESALQ, 11 Av. Padua Dias CIRAD UMR Eco and Sols, 2 Place Viala INRA UR BEF, Rue de l'Arboretum CIRAD UMR AGAP, Avenue Agropolis UNESP Ciência Florestal, 1780 Rua José Barbosa de Barros UNESP Ciência Florestal, 1780 Rua José Barbosa de Barros

Made available in DSpace on 2018-12-11T17:17:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-03-01 Key message: Inter-specific interactions with eucalypts in mixed plantations increased N2fixation rate of acacia trees compared to monocultures. N2fixation was higher during the wet summer than during the dry winter both in acacia monocultures and in mixed plantations. Context: Introducing N-fixing trees in fast-growing tropical plantations may contribute to reducing the long-term requirements of N fertilizers. Management practices established in forest monocultures should be revisited in mixed-species plantations. Aims: This field experiment aimed to compare N2 fixation rates of Acacia mangium Wild in monospecific stands and in mixed-species stands with Eucalyptus grandis W. Hill ex Maiden. A secondary objective was to gain insight into the seasonal variations of N2 fixation. Methods: 15N was applied to acacia and eucalypt monocultures and mixed-species with a 1:1 ratio at mid rotation. Leaves were collected in autumn, winter, spring, and summer to determine the foliar N concentrations and 15N atom fraction. The N content in the above-ground biomass was estimated as well as the percentage of N derived from atmospheric N2 (%Ndfa) using eucalypts in monoculture as reference plants. Results: %Ndfa values averaged over the year were 14% in monoculture and 44% in mixed-species stands. While the stocking density of acacia trees was twice as high in monoculture as in mixture, the amounts of N fixed in above-ground biomass of acacia trees were close (35–39 kg N ha−1) at 39 months after planting. %Ndfa values were higher during the wet summer than the dry winter both in acacia monocultures and in mixed plantations. Conclusion: The stocking density of acacia trees can be reduced in mixed plantations with eucalypts in comparison to acacia monocultures with a low influence on the input of N to soil through biological fixation. USP ESALQ Departamento de Ciências Florestais, Av. Pádua Dias, 11, Piracicaba UFES Departamento de Ciências Florestais e da Madeira, Av. Governador Carlos Lindemberg, 316, Jerônimo Monteiro Eco&Sols INRA CIRAD IRD Montpellier SupAgro University of Montpellier USP CENA Divisão de Desenvolvimento de Técnicas Analíticas e Nucleares, Av. Centenário, 303, Piracicaba Embrapa Solos, Rua Jardim Botânico, 1024 UNESP Departamento de Solos e Recursos Ambientais, Rua José Barbosa de Barros, 1780, Botucatu UNESP Departamento de Solos e Recursos Ambientais, Rua José Barbosa de Barros, 1780, Botucatu

Although vast areas in tropical regions have weathered soils with low potassium (K) levels, little is known about the effects of K supply on the photosynthetic physiology of trees. This study assessed the effects of K and sodium (Na) supply on the diffusional and biochemical limitations to photosynthesis in Eucalyptus grandis leaves. A field experiment comparing treatments receiving K (+K) or Na (+Na) with a control treatment (C) was set up in a K-deficient soil. The net CO2 assimilation rates were twice as high in +K and 1.6 times higher in +Na than in the C as a result of lower stomatal and mesophyll resistance to CO2 diffusion and higher photosynthetic capacity. The starch content was higher and soluble sugar was lower in +K than in C and +Na, suggesting that K starvation disturbed carbon storage and transport. The specific leaf area, leaf thickness, parenchyma thickness, stomatal size and intercellular air spaces increased in +K and +Na compared to C. Nitrogen and chlorophyll concentrations were also higher in +K and +Na than in C. These results suggest a strong relationship between the K and Na supply to E. grandis trees and the functional and structural limitations to CO2 assimilation rates.

Summary 1.Climate models predict that the frequency, intensity and duration of drought events will increase in tropical regions. Although water withdrawal from deep soil layers is generally considered to be an efficient adaptation to drought, there is little information on the role played by deep roots in tropical forests. Tropical Eucalyptus plantations managed in short rotation cycles are simple forest ecosystems that may provide an insight into the water use by trees in tropical forests. 2.The contribution made by water withdrawn from deep soil layers to the water required for evapotranspiration was quantified daily from planting to harvesting age for a E. grandis stand using a soil water transfer model coupled with an ecophysiological forest model (MAESPA). The model was parameterized using an extensive dataset and validated using time series of the soil water content down to a depth of 10 m and water table level, as well as evapotranspiration measured using eddy-covariance. 3.Fast root growth after planting provided access to large quantities of water stored in deep soil layers over the first two years. Eucalyptus roots reached the water table at a depth of 12 m after 2 years. Although the mean water withdrawal from depths of over 10 m amounted to only 5% of canopy transpiration from planting to a harvesting age of 5 years, the proportion of water taken up near the water table was much higher during dry periods. The water table rose from 18 m to 12 m below ground over 2 years after the harvest of the previous stand, and then fell until harvesting age as evapotranspiration rates exceeded the annual rainfall. 4.Deep rooting is an efficient strategy to increase the amount of water available for the trees, allowing the uptake of transient gravitational water and possibly giving access to a deep water table. Deep soil layers have an important buffer role for large amounts of water stored during the wet season that is taken up by trees during dry periods. Our study confirms that deep rooting could be a major mechanism explaining high transpiration rates throughout the year in many tropical forests. This article is protected by copyright. All rights reserved.

Our knowledge of the rhizosphere bacterial communities in deep soils and the role of Eucalyptus and Acacia on the structure of these communities remains very limited. In this study, we targeted the bacterial community along a depth profile (0 to 800 cm) and compared community structure in monospecific or mixed plantations of Acacia mangium and Eucalyptus grandis. We applied quantitative PCR (qPCR) and sequence the V6 region of the 16S rRNA gene to characterize composition of bacterial communities. We identified a decrease in bacterial abundance with soil depth, and differences in community patterns between monospecific and mixed cultivations. Sequence analysis indicated a prevalent effect of soil depth on bacterial communities in the mixed plant cultivation system, and a remarkable differentiation of bacterial communities in areas solely cultivated with Eucalyptus. The groups most influenced by soil depth were Proteobacteria and Acidobacteria (more frequent in samples between 0 and 300 cm). The predominant bacterial groups differentially displayed in the monospecific stands of Eucalyptus were Firmicutes and Proteobacteria. Our results suggest that the addition of an N2-fixing tree in a monospecific cultivation system modulates bacterial community composition even at a great depth. We conclude that co-cultivation systems may represent a key strategy to improve soil resources and to establish more sustainable cultivation of Eucalyptus in Brazil.

The consequences of diversity on belowground processes are still poorly known in tropical forests. The distributions of very fine roots (diameter < 1 mm) and fine roots (diameter < 3 mm) were studied in a randomized block design close to the harvest age of fast-growing plantations. A replacement series was set up in Brazil with mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and a mixture with the same stocking density and 50 % of each species (50A:50E). The total fine root (FR) biomass down to a depth of 2 m was about 27 % higher in 50A:50E than in 100A and 100E. Fine root over-yielding in 50A:50E resulted from a 72 % rise in E. grandis fine root biomass per tree relative to 100E, whereas A. mangium FR biomass per tree was 17 % lower than in 100A. Mixing A. mangium with E. grandis trees led to a drop in A. mangium FR biomass in the upper 50 cm of soil relative to 100A, partially balanced by a rise in deep soil layers. Our results highlight similarities in the effects of directional resources on leaf and FR distributions in the mixture, with A. mangium leaves below the E. grandis canopy and a low density of A. mangium fine roots in the resource-rich soil layers relative to monospecific stands. The vertical segregation of resource-absorbing organs did not lead to niche complementarity expected to increase the total biomass production.

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 -15N, Rb+ (analogue of K+) and Sr2+ (analogue of Ca2+) 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 15N 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 -15N than for Rb+ and Sr2+ in the upper 50 cm of soil, the highest SRUP values for Sr2+ 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. (Resume d'auteur)

The sustainability of fast-growing tropical Eucalyptus plantations is of concern in a context of rising fertilizer costs, since large amounts of nutrients are removed with biomass every 6–7 years from highly weathered soils. A better understanding of the dynamics of tree requirements is required to match fertilization regimes to the availability of each nutrient in the soil. The nutrition of Eucalyptus plantations has been intensively investigated and many studies have focused on specific fluxes in the biogeochemical cycles of nutrients. However, studies dealing with complete cycles are scarce for the Tropics. The objective of this paper was to compare these cycles for Eucalyptus plantations in Congo and Brazil, with contrasting climates, soil properties, and management practices. The main features were similar in the two situations. Most nutrient fluxes were driven by crown establishment the two first years after planting and total biomass production thereafter. These forests were characterized by huge nutrient requirements: 155, 10, 52, 55 and 23 kg ha−1 of N, P, K, Ca and Mg the first year after planting at the Brazilian study site, respectively. High growth rates the first months after planting were essential to take advantage of the large amounts of nutrients released into the soil solutions by organic matter mineralization after harvesting. This study highlighted the predominant role of biological and biochemical cycles over the geochemical cycle of nutrients in tropical Eucalyptus plantations and indicated the prime importance of carefully managing organic matter in these soils. Limited nutrient losses through deep drainage after clear-cutting in the sandy soils of the two study sites showed the remarkable efficiency of Eucalyptus trees in keeping limited nutrient pools within the ecosystem, even after major disturbances. Nutrient input–output budgets suggested that Eucalyptus plantations take advantage of soil fertility inherited from previous land uses and that long-term sustainability will require an increase in the inputs of certain nutrients.

Nitrogen fertilizer inputs increased sharply over the last decade in Brazilian eucalypt plantations. Due to the economic and potential environmental cost of fertilizers, mixed plantations with N-fixing species might be an attractive option to improve the long-term soil N status. A randomized block design was set up in southern Brazil, including a replacement series and an additive series design, as well as a nitrogen fertilization treatment. The development of mono-specific stands of Eucalyptus grandis (0A:100E) and Acacia mangium (100A:0E) was compared with mixed plantations in proportions of 1:1 (50A:50E), and other stands with different densities of acacia for the same density of eucalypts. The objective was to assess the effect of inter-specific interactions on the early development of the two species. Aboveground biomass was measured 6, 12, 18 and 30 months after planting, sampling 6–10 trees of each species per treatment at each age, and allometric equations were established in 0A:100E, 100A:0E, 50A:50E and 50A:100E. The height and basal area of E. grandis seedlings were enhanced by 12% and 30%, respectively by N fertilization at age 1 year. Inter-specific competition led to a stratified canopy, with suppression in acacia growth earlier for basal area than for height. The mean number of stems per acacia tree at 36 months after planting was significantly higher in pure stands (3.7), than in 50A:50E (2.7) and in the additive series (between 1.6 and 1.8). H / D ratios were highly sensitive to inter-tree competition for the two species. The suppressed acacia understorey in mixed-species stands did not influence biomass production and partitioning within eucalypts. This pattern led to biomass accumulation combining the two species in 50A:100E that was about 10% higher than in 0A:100E, from age 12 months onwards. Aboveground net primary production (ANPP) amounted to 25 Mg ha −1 and 37 Mg ha −1 from age 18 to 30 months in 100A:0E and 0A:100E, respectively. Acacia ANPP in 50A:100E amounted to 2 Mg ha −1 over the same period, as a result of substantial inter-specific competition. An increment in biomass production in these very fast-growing eucalypt plantations was achieved introducing acacia as an understorey and not in the 50A:50E design, as observed in other studies.

The introduction of N-2-fixing tree species in fast growing tree plantations is a sustainable management option aiming to reduce the risk of nitrogen (N) deficiency due to a large and frequent exportation of nutrients at harvest. Differences in soil mineral N preferences between Eucalyptus urophylla x grandis and Acacia mangium may, in addition to facilitation related to atmospheric N-2 fixation, contribute to the success of mixed-species plantations of the two species on nutrient-poor soils of the coastal Congolese plains. We tested whether these two species differ in their preference for nitrate or ammonium by supplying either ammonium or nitrate enriched in N-15 to six-month-old potted trees growing in an open-air nursery. Although the uptake of nitrate tended to be higher than that of ammonium by both species, the difference was not significant and there was no significant difference between the species regarding their preferred form of soil mineral N. Despite much lower N contents in foliage, stems, and roots of eucalypt compared to acacia, the specific rates of N uptake were up to three times higher for eucalypt than acacia, which suggests that atmospheric N-2 was the major source of N in the six-month-old acacias. We conclude that N-2 fixation rather than complementarity for soil mineral nitrogen alleviates the competition between species in successful mixed eucalypt and acacia plantations.

Sustainable wood production requires appropriate management of commercial forest plantations. Establishment of industrial eucalypt plantations on poor sandy soils leads to a high loss of nutrients including nitrogen (N) after wood harvesting. An ecological intensification of eucalypt plantations was tested with the replacement of half of the Eucalyptus urophylla × E. grandis by Acacia mangium in the eucalypt monoculture to sustain soil fertility through enhancement of the N biological cycle. A randomised block design was set up on ferralitic arenosol in the Congolese coastal plains to assess differences in soil N mineralisation, N fluxes in litterfall, and N stocks in forest floor litter and soil between pure acacia (100A), pure eucalypt (100E) and mixed-species treatments (50A50E). Soil N mineralisation was enhanced under acacia, reaching on average 0.17 and 0.15 mg kg−1 soil d−1 in 100A and 50A50E, respectively, compared with 0.09 mg kg−1 soil d−1 in 100E. Higher amounts of N returning to the soil through harvest residues and litterfall were observed under acacia than under eucalypt. However, N stock in mineral soil was not increased in 100A and exhibited a limited increase only in the top soil layer of 50A50E. Our results suggest a much faster N turnover under acacia than under eucalypt. Although A. mangium is an exotic N2-fixing tree in central Africa, it appears to be well adapted to the climatic and edaphic conditions of the Congo, showing an efficient growth strategy. Eucalypt trees could benefit from the increase in soil N availability in mixed-species stands.Keywords: ammonium, arenosol, Congo, ecological intensification, forest plantation, mixed species, N2 fixation, nitrate

Made available in DSpace on 2018-12-11T16:42:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-08-15 The invasive potential of a species is related to the interaction between genetic and environmental characteristics, as climatic conditions and native vegetation, reflecting the species adaptation to local conditions. An ecologically-adapted alien species can alter diversity and structure of forest ecosystems. This study assessed the invasiveness potential of eight commercially important Eucalyptus species in the germination and early establishment phases in southeastern Brazil. The first experiment evaluated seed germination under controlled temperature and air humidity conditions testing six substrate water potentials. The second experiment was conducted in pots to evaluate seed germination and seedling mortality under rainfed and irrigated regimes. Nine field trials were set up in the third experiment in six locations. In each trial, 80 plots of 1 m2 were installed with half the plots undisturbed and half where preexisting plants and litter were removed. In the first experiment, Eucalyptus taxa differed significantly in seed germination for substrate water potential ≥-0.6 MPa. No germination was found for any taxa at -0.8 MPa substrate water potential. In the second experiment, differences in germination between species and water treatments were observed 21 days after sowing. No mortality was found in the irrigated treatments. No seedling mortality was observed in the rainfed treatments when the relative air humidity was higher than 85%, even during a dry period of 45 days. By contrast, seedling mortality was observed for all taxa in all the rainfed treatments when relative air humidity fell under 80%. In the third experiment, germination and seedling establishment of Eucalyptus species was always very low. The non-Eucalyptus species showed differences in germination between trials and soil exposures. Our results showed that soil and air moisture were major drivers of eucalypt germination and initial establishment in controlled conditions. However, under field conditions additional factors such as competition of non-Eucalyptus species and seedlings predation drastically limited eucalypt establishment suggesting low ecological adaptation of Eucalyptus sp. as an invasive species. IPEF - Instituto de Pesquisas e Estudos Florestais, Avenida Pádua Dias 11, Caixa Postal 530 UNESP-Universidade Estadual Julio de Mesquita Filho/FCAV-Faculdade de Ciencias Agrarias e Veterinarias, Via de Acesso Prof. Donato Castellane S/N CIRAD UMR EcoandSols USP-ESALQ Departamento de Ciências Florestais, Av. Pádua Dias, 11 Caixa Postal 9 UNESP-Universidade Estadual Julio de Mesquita Filho/FCAV-Faculdade de Ciencias Agrarias e Veterinarias, Via de Acesso Prof. Donato Castellane S/N

Made available in DSpace on 2022-04-28T19:03:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-08-11 Potassium (K) is an important limiting factor of tree growth, but little is known of the effects of K supply on the long-distance transport of photosynthetic carbon (C) in the phloem and of the interaction between K fertilization and drought. We pulse-labelled 2-year-old Eucalyptus grandis L. trees grown in a field trial combining K fertilization (+K and -K) and throughfall exclusion (+W and -W), and we estimated the velocity of C transfer by comparing time lags between the uptake of 13CO2 and its recovery in trunk CO2 efflux recorded at different heights. We also analysed the dynamics of the labelled photosynthates recovered in the foliage and in the phloem sap (inner bark extract). The mean residence time of labelled C in the foliage was short (21-31 h). The time series of 13C in excess in the foliage was affected by the level of fertilization, whereas the effect of throughfall exclusion was not significant. The velocity of C transfer in the trunk (0.20-0.82mh-1) was twice as high in +K trees than in -K trees, with no significant effect of throughfall exclusion except for one +K-W tree labelled in the middle of the drought season that was exposed to a more pronounced water stress (midday leaf water potential of -2.2MPa). Our results suggest that besides reductions in photosynthetic C supply and in C demand by sink organs, the lower velocity under K deficiency is due to a lower cross-sectional area of the sieve tubes, whereas an increase in phloem sap viscosity is more likely limiting phloem transport under drought. In all treatments, 10 times less 13C was recovered in inner bark extracts at the bottom of the trunk when compared with the base of the crown, suggesting that a large part of the labelled assimilates has been exported out of the phloem and replaced by unlabelled C. This supports the 'leakage-retrieval mechanism' that may play a role in maintaining the pressure gradient between source and sink organs required to sustain high velocity of phloem transport in tall trees. UMR 1137 Ecologie et Ecophysiologie Forestières Facult des Sciences Universit de Lorraine INRA UMR 1137 Ecologie et Ecophysiologie Forestières Centre de Nancy CIRAD UMR Ecoandsols Ecologie Fonctionnelle and Biogochimie des Sols and Agro-cosystèmes Embrapa Meio Ambiente Universidade Estadual de São Paulo Departamento de Ciências Florestais ESALQ Universidade de São Paulo ESALQ Laboratory of Forest Utilization Department of Forest and Biomaterial Science Graduate School of Agriculture Kyoto University Centro de Energia Nuclear Na Agricultura Universidade de São Paulo Departamento de Ciências Atmosfricas IAG Universidade de São Paulo ESALQ Universidade Estadual de São Paulo

Cette communication expose des méthodes, basées sur la modélisation, pour estimer les stocks de carbone dans l'écosystème et les produits forestiers, et la façon dont ces stocks répondent à quelques variations de sylviculture. Une application à la distinction entre forêts anciennes et récentes est proposée.

For open canopies, the partitioning of energy and water fluxes between the upper canopy and the under-storey is key to understand the competition mechanisms between layers. We monitored stand evapo-transpiration by eddy-covariance (E), tree transpiration (T) by heat-dissipative sapflow, soil (G) and stand (J) heat storage during 3 years in a typical coconut palm row-plantation of the humid tropics, displaying a constant leaf area index (LAI = 3) and a grass under-storey. A two-level flux experiment yielded cross-validation of the evapo-transpiration of the under-storey (Eu) with E - T, through energy balance closure for E and sapflow calibration in the laboratory for T. On a yearly time step, E represented 40% of rainfall, the sensible heat flux (H) was 26% of net radiation and the Bowen ratio was 0.39, all indicating that water availability was close-to-optimum. T represented 68% of E, close to the 75% of soil coverage by palms. The inter-annual variability was low for potential evapo-transpiration (ETo), energy and water fluxes. The seasonal variability was more pronounced, driven by radiation and vapour pressure deficit (VPD). The canopy conductance of coconut palms appeared to be strongly controlled by VPD. Given its constant LAI, its continuous growth and its simple architecture, the coconut palm appears to be an ideal candidate for physiological work and agroforestry modelling. © 2006 Elsevier B.V. All rights reserved.

Clonal plantations of Eucalyptus have been introduced since 1978 on savanna soils of the coastal plains of Congo. Atmospheric deposition, canopy exchange and transfer through the soil were estimated on the whole rooting depth (6 m) over 3 years, in an experimental design installed in a native savanna and an adjacent 6-year-old Eucalyptus plantation. Complementary measurements after planting the experimental savanna made it possible to establish input–output budgets of nutrients for the whole Eucalyptus rotation and to compare them with the native savanna ecosystem. In this highly-weathered soil, atmospheric deposits and symbiotic N fixation by a legume species balanced the nutrient budgets in savanna, despite large losses during annual burnings. After afforestation, weeding in the Eucalyptus stands eliminated the leguminous species responsible for a N input by symbiotic fixation of about 20 kg ha−1 year−1. Whereas the budgets of P, K, Ca and Mg were roughly balanced, the current silviculture led to a deficit of about 140 kg N ha−1 in the soil, throughout a 7-year rotation. This deficit was large relative to the pool of total N in the upper soil layer (0–50 cm), which was about 2 t ha−1. Therefore, the sustainability of Congolese plantations will require an increase in N fertilizer inputs over successive rotations to balance the N budget. These results were consistent with field trials of fertilization. Practical consequences of these budgets were identified, in order to: (i) direct field trials of fertilization, (ii) select appropriate methods of soil preparation, weed control and harvest, (iii) highlight the importance of fire prevention in this area, and (iv) support the implementation of field trials aiming at introducing a biological nitrogen fixing understorey in Eucalyptus stands.

In the context of global change, potential estimations of carbon storage by the oil palm ecosystem in different ecologies have been calculated for the major productive countries in Africa, Asian and American continents. Comparisons were done with other types of planted ecosystems as eucalyptus and coconut as well as different types of natural forests. Carbon budget components as NPP, autotrophic and heterotrophic soil respiration, litter and fine litter contributions were discussed in regards to the very high rate of carbon sequestration by oil palm ecosystem : from 250 to 940 C m-2 yr-1 (estimations including harvested bunches). (Resume d'auteur)

The dynamics of nutrients were compared over three years in a clonal Eucalyptus plantation and in a native savanna in Congo. This paper focuses on the changes in the chemical composition of solutions during their transfer through the soil in both ecosystems. The main characteristics of the soil (Ferralic Arenosol) were similar in the two ecosystems, and the low inter-stand variability allowed reliable comparisons of the influence of afforestation on the soil solution chemistry. Rainfall amounted to about 1400 mm per year during the experimental period. In both ecosystems, an enrichment was observed for most elements during the transfer of solutions through the foliage, but N uptake occurred. Concentrations of H+ and dissolved organic carbon (DOC) in solutions increased through the litter layer in both stands. In the Eucalyptus ecosystem, a quick uptake of nutrients by a dense root mat inside the forest floor likely explained why the concentrations of gravitational waters were not enhanced markedly for ‘base cations’, despite the mineralization of high amounts of nutrients during the litter decay. Soil solutions were collected by zero tension lysimeters (ZTL) at a depth of 15 cm, but these lysimeters were inefficient at collecting gravitational solutions beyond this depth. By contrast, tension lysimeters (TL) maintained at a suction of −60 kPa, collected soil solutions at the depths of 15, 50 cm, 1, 2, 3, 4 m in both ecosystems and 6 m in the plantation. In the topsoil of both stands, the nutrient concentration decreased sharply when the time of residence of solutions increased. This pattern highlighted the crucial role of the inputs by throughfall, stemflow and mineralization of the litter layer for the nutrition of these stands. A combination of high nutrient requirements of the stands and low availability of exchangeable cations in this highly weathered soil might account for the extremely low nutrient concentrations in solutions collected by TL, regardless of the depth.

Made available in DSpace on 2018-12-11T16:39:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-12-01 The short-term belowground transfer of nitrogen from nitrogen-fixing trees to companion trees has never been studied in the field. A 15N pulse-labeling study was conducted in a mixed plantation of Acacia mangium and Eucalyptus grandis at the peak of leaf area, 26 months after planting. 15N-NO3 - was injected into the stem of one big Acacia tree in three plots. 15N was traced over 2 months in the labeled Acacia tree as well as in neighboring Eucalyptus trees. For both species, young leaves were sampled, as well as fine roots and the rhizosphere at a distance of 0.75 m and 2.25 m from the labeled tree. The 15N atom% was also determined in the wood, bark, branches and total foliage of the 3 labeled Acacia trees and 9 Eucalyptus trees, 60 days after labeling. Most of the leaves, fine roots and rhizosphere samples of both species were 15N enriched from 5 days after labeling. The δ15N values were higher at a distance of 0.75 m than at 2.25 m in Acacia roots, but were similar at both distances in Eucalyptus roots and the rhizospheres. The wood and bark of Eucalyptus trees sampled at a distance of 6.2 m from the labeled Acacia trees were 15N enriched. This shows belowground N transfer from Acacia to Eucalyptus trees in the field during the first few days after labeling. This facilitation process may provide a significant amount of the nitrogen requirements of trees close to N-fixing trees in mixed forests. USP-ESALQ Departamento de Ciências Florestais, Av. Pádua Dias, 11 CIRAD UMR Eco andSols Écologie Fonctionnelle and oBiogéochimie des Sols and Agroécosystèmes, 2 Place Viala USP-CENA Divisão de Desenvolvimento de Técnicas Analíticas e Nucleares, Av. Centenário, 303 INRA UR 1138 Biogéochimie des Ecosystèmes Forestiers CIRAD UMR AGAP, Avenue Agropolis INRA UMR Eco andSols Écologie Fonctionnelle and Biogéochimie des Sols and Agroécosystèmes, 2 Place Viala UNESP Departamento de Ciência Florestal Julio de Mesquita Filho UNESP Departamento de Ciência Florestal Julio de Mesquita Filho

Global climate change is expected to increase the length of drought periods in many tropical regions. Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water deficit on the physiological mechanisms governing plant growth. A process-based model (MAESPA) parameterized in a split-plot experiment in Brazil was used to gain insight into the combined effects of K deficiency and water deficit on absorbed radiation (aPAR), gross primary productivity (GPP), and light-use efficiency for carbon assimilation and stem biomass production (LUEC and LUEs ) in Eucalyptus grandis plantations. The main-plot factor was the water supply (undisturbed rainfall vs. 37% of throughfall excluded) and the subplot factor was the K supply (with or without 0.45 mol K m(-2 ) K addition). Mean GPP was 28% lower without K addition over the first 3 years after planting whether throughfall was partly excluded or not. K deficiency reduced aPAR by 20% and LUEC by 10% over the whole period of growth. With K addition, throughfall exclusion decreased GPP by 25%, resulting from a 21% decrease in LUEC at the end of the study period. The effect of the combination of K deficiency and water deficit was less severe than the sum of the effects of K deficiency and water deficit individually, leading to a reduction in stem biomass production, gross primary productivity and LUE similar to K deficiency on its own. The modeling approach showed that K nutrition and water deficit influenced absorbed radiation essentially through changes in leaf area index and tree height. The changes in gross primary productivity and light-use efficiency were, however, driven by a more complex set of tree parameters, especially those controlling water uptake by roots and leaf photosynthetic capacities.

Clonal Eucalyptus plantations in the Pointe-Noire region have been established on sandy and nutrient poor soils, and carry potential risk of depleting water and nutrient. To assess these risks, water and nutrient budgets should be calculated. However, the accuracy of hydrological models is strongly dependent on a realistic description of root distribution in soil. The spatial distribution of root systems in a chronosequence of clonal stands was then studied, using root intersect counting. The stands were 3 months, 6 months, 1 year, 2 years and 9 years old. For each stand we studied three vertical profiles perpendicular to the planting row at different spacing from a representative tree. The profiles were divided into square grid cells of 25 cm 2 , and the number of roots belonging to three diameter classes (between 0.1 and 1, 1 and 10 mm, and over 10 mm) were counted in each grid cell. The profiles were 2.50 m wide (half the distance between the planting rows) and 3 m deep, except for the two youngest stands (1.5 m deep). Spatial statistical analyses and analysis of variance were carried out to describe root distributions and their spatial and temporal changes. We observed that: (1) The trees quickly developed an extensive root system. One year after planting the root system extended to depth beyond 3 m deep and up to the middle of the inter-row. (2) Root density decreased sharply with depth, with most fine roots in the surface layers. The number of fine root intersects in the 0–25 cm surface soil layer represented 16–53% of the total throughout the profile depending on stand age and the type of profile. (3) The percentage of root intersects in surface layers increased with stand age: this may reflect the greater concentration of nutrients in surface layers. (4) High variability in root densities was observed in the surface soil layers but no gradient of decrease from the planting row to the middle of the inter-row could be underscored. However, the highest root densities were generally observed under the stump.

Since 1978, 42,000 ha of clonal Eucalyptus plantations have been established around Pointe-Noire. These plantations are growing on sandy and acidic soils with small reserves of available nutrients; therefore, risks of nutrient deficiencies exist in the medium or long-term. The effects of slash and litter management practices on soil properties, tree nutrition and growth were quantified to evaluate harvesting methods with respect to sustainable management of the replanted sites. The experimental design was a randomized complete block with four replications and six treatments: R, all aboveground organic residues removed; WTH, whole-trees harvested and removed; SBH, stemwood and bark removed; SH, stemwood-only removed; DS, double slash retained; B, stemwood-only removed and all organic residues burned. After 12 months removal of all slash material (R) had a marked negative effect on total biomass (5.9 t ha-1 vs a mean of 7.2 t ha-1 for the other treatments). During the first 18 months of the study no significant differences among treatments were detected (P < 0.05), but at 24 months, tree growth was significantly reduced where all organic residues were removed (R), compared to DS (12.9 m3 ha-1 per year vs 22.2 m3 ha-1 per year). The best growth was measured in plots with the highest organic residues (treatments DS and SH). Nutrient content in the aboveground biomass of the I-year-old stand was strongly dependent on the type of slash and litter management. Differences in tree nutrient concentrations in various treatments demonstrated the ability of trees to store available nutrients in aboveground biomass. The rate of decomposition of organic residues during the first 8 months after harvesting ranged from 36% (WTH) to 56% (SH). Between 7 and 24 months, the annual production of inorganic nitrogen in the top soil (0-13 cm layer) was 71.6, 66.7, and 85.7 kg ha-1 per year for R, SH, and DS, respectively. The rate of soil nitrification was high, and therefore nitrogen leaching may have occurred in the early development stage when trees are not able to take up all the available nitrogen.

Spatial statistical analyses were performed to describe root distribution and changes in soil strength in a mature clonal plantation of Eucalyptus spp. in the Congo. The objective was to analyze spatial variability in root distribution. Relationships between root distribution, soil strength and the water and nutrient uptake by the stand were also investigated. We studied three, 2.35-m-wide, vertical soil profiles perpendicular to the planting row and at various distances from a representative tree. The soil profiles were divided into 25-cm2 grid cells and the number of roots in each of three diameter classes counted in each grid cell. Two profiles were 2-m deep and the third profile was 5-m deep. There was both vertical and horizontal anisotropy in the distribution of fine roots in the three profiles, with root density decreasing sharply with depth and increasing with distance from the stump. Roots were present in areas with high soil strength values (> 6000 kPa). There was a close relationship between soil water content and soil strength in this sandy soil. Soil strength increased during the dry season mainly because of water uptake by fine roots. There were large, areas with low root density, even in the topsoil. Below a depth of 3 m, fine roots were spatially concentrated and most of the soil volume was not explored by roots. This suggests the presence of drainage channels, resulting from the severe hydrophobicity of the upper soil. (Resume d'auteur)

A basic understanding of nutrition effects on the mechanisms involved in tree response to drought is essential under a future drier climate. * A large-scale throughfall exclusion experiment was set up in Brazil to gain an insight into the effects of potassium (K) and sodium (Na) nutrition on tree structural and physiological adjustments to water deficit. * Regardless of the water supply, K and Na supply greatly increased growth and leaf area index (LAI) of Eucalyptus grandis trees over the first 3 yr after planting. Excluding 37% of throughfall reduced above-ground biomass accumulation in the third year after planting for K- supplied trees only. E. grandis trees were scarcely sensitive to drought as a result of the utilization of water stored in deep soil layers after clear-cutting the previous plantation. Trees coped with water restriction through stomatal closure (isohydrodynamic behavior), osmotic adjustment and decrease in LAI. Additionally, droughted trees showed higher phloem sap sugar concentrations. * K and Na supply increased maximum stomatal conductance, and the high water requirements of fertilized trees increased water stress during dry periods. Fertilization regimes should be revisited in a future drier climate in order to find the right balance between improving tree growth and limiting water shortage.

Background and aims The introduction of Acacia mangium in Eucalyptus urophylla x grandis stands improves wood production on poor sandy soils of coastal plains of the Congo. We assessed the impact of A. mangium plantations in pure stands and in mixture with eucalypt trees on the physico-chemical properties of the soil after one rotation. Methods Bulk densities, N, C, available P and pH were determined on soil sampled in the pure acacia (100A), pure eucalypt (100E) and mixed-species (50A:50E) stands. N and P were determined in aboveground litters and in leaves, bark and wood of trees. Results N and C concentrations were higher in 50A:50E than in 100A and 100E in the top soil layer. The pH was lower in 100A and higher in 100E than in 50A:50E. The available P was lower in 50A:50E than in 100A and 100E. Leaf N was lower in 50A:50E than in 100A for acacia, and higher than in 100E for eucalypt. Leaf P was similar for acacia but higher for eucalypt in 50A:50E than in 100E. In contrast to P, the amount of N in aboveground litterfall increased with the proportion of acacia in the stand. Conclusions The introduction of acacia trees in eucalypt plantations increased C and N contents of the soil but decreased the available P content in the mixed-species stand. This may be related to a higher uptake of P needed to maintain the N:P stoichiometry in eucalypt leaves.

International audience; The association of N-2-fixing species (NFS) could be an attractive option for achieving a sustainable increase of Eucalyptus plantations (EP) productivity through a positive balance between facilitative effects and competition between species. A randomised block design was replicated at four sites (Cenibra, USP, Suzano and IP) in Southern Brazil and at one site in Congo. The development of mono-specific stands of Acacia mangium (100A) and Eucalyptus grandis or urophylla x grandis (100E), was compared with N fertilisation treatment (100E + N) and with mixed-species plantations in a 1:1 ratio (50A:50E), and in an additive series with varying densities of acacia for the same density of eucalypt (25A:100E, 50A:100E, 100A:100E). The objectives were to assess the effect of mixtures on tree growth and stand production, and the behaviour of the two species in contrasting soil and climatic conditions. Tree growth was monitored over stand rotation and the biomass of aboveground tree components estimated at mid-rotation and at harvesting age. Eucalyptus height was 13% higher in Brazil than in Congo. Favourable ecological conditions in Congo and Cenibra led to 50% higher Acacia tree height than at the other sites. A depressive effect of Eucalyptus neighbour trees on Acacia height and circumference growth, lower in Congo than in Brazil, was observed in the mixtures from age 1-2 years onwards. Depressive effects of acacia on eucalypt height and circumference growth were low in USP, Suzano and IP, high in Cenibra, and not observed in Congo, in 50A:50E and 25A:100E. A positive though insignificant response to N fertilisation was only found in USP and Congo. Complementarity for light and soil resource capture between Eucalyptus and Acacia trees resulted in mean annual increments in total stand stemwood biomass (MAI) that were 7-15%, 6-12%, and 40% higher in the additive series than for 100E in Cenibra, LISP and Congo, respectively at mid-rotation. Whilst lasting complementarity and facilitation in Congo led to 17-34% higher MAI in mixtures than for 100E at harvesting age, MAIs were not significantly higher in mixtures than for 100E in Brazil. Mixed-species plantations of Eucalyptus and A. mangium might enhance aboveground stand production on poor nutrient soils in warm and humid tropical climates with low water limitations

Soil microorganisms and microbial processes are influenced by the quality and quantity of plant waste entering the soil, by its seasonal and spatial distribution, by the ratio of above- to below-ground inputs, and by changes in nutrient inputs. Soil management strategies sometimes promote mixed-species plantations to mitigate the loss of soil nutrients and improve biogeochemical cycling. The objective of this study was to explore changes in microbiological and chemical attributes of soils and litter in the early stages of the second rotation of mixed and pure plantations of Eucalyptus grandis and Acacia mangium, and to look for correlations between attributes. Soil samples at 0-10 cm depth were collected two, seven, 14, and 20 months after planting in the following treatments: monocultures of A. mangium and E. grandis, a monoculture of E. grandis with N-fertilizer, and an intercropped plantation with E. grandis and A. mangium. Microbial soil attributes varied dramatically between treatments 20 months after planting. Total C, N and P contents in litter showed the strongest correlations with microbial biomass C and N (C-mic and N-mic), microbial respiration, and dehydrogenase activity in all sampling periods. Lower C/N and C/P ratios in litter and lower C/N and C-mic/tC ratios in soils after 20 months in the intercropped plantation illustrated the system's capacity for supplying inputs of high-quality organic matter rich in N and P, but this did not result in higher contents of these elements or greater microbial activity in soils. An implication of this finding is that, at least in the initial growth phase of these plantations, chemical attributes of the litter and variation in those attributes govern microbial processes and, consequently, are mostly responsible for plant development. Canonical discriminant analysis revealed changes in the microbiological and chemical attributes of soil in the intercropped plantation due to the plants growth and the leaf litter accumulation. Twenty months after planting, the different plantations could be discriminated by differences in litter chemistry (C, N, and P), total soil C, N-mic, and dehydrogenase activity, which were very similar in intercropped plantations and E. grandis with N-fertilizer. These results from the early stages of plantation development are important for understanding the dynamics of soil attributes in these systems, and especially in intercropped plantations. In intercropped areas the cumulative effect of microbial attributes reflects a more sustainable system. Long-term studies are needed to identify patterns that develop after 20 months, during the growth period of these plantations. (C) 2012 Elsevier B.V. All rights reserved.

African savannas developed an efficient strategy of nutrient uptake and control of nitrification making it possible to avoid large losses of nutrient by drainage. The conversion of native savanna into commercial forest plantations is an important global change driver that potentially impacts element cycles. Afforestation of native Congolese savannas by Eucalyptus started 30 years ago. Large amounts of nutrients are removed through biomass harvesting every 6-7 years. Losses of nutrients by deep drainage might be a serious threat for the sustainability of these plantations, established on sandy soils with high hydraulic conductivities. We compared the soil N-mineralisation, the nutrient fluxes and deep drainage beneath savanna and Eucalyptus plantation in Congo. Then, we discussed the strategy of nutrient recycling. The water fluxes at a depth of 400 cm were approximately 20% higher in the savanna than in Eucalyptus plantation. Although the nitrification rate and solution chemistry exhibited strong modifications during the first year following both savanna afforestation and the harvesting of the Eucalyptus stand, the losses of nutrients by deep drainage remained unexpectedly low. The largest fluxes of drainage at a depth of 6 m were found for NH4+-N, which reached a maximum of 0.4 g m(-2) yr(-1) in the second year following savanna afforestation and I g m(-2) yr(-1) in the first year after clear cutting. The deep drainage of NO3--N, Mg2+, Ca2+ and K+ did not exceed 0.2 g m(-2) yr(-1) in the savanna and at any stage of plantation development. These results are discussed regarding (i) the roots distribution in the soil of each ecosystem and (ii) the nutrient accumulation in biomass. The limited changes between the nutrient fluxes in both ecosystems were the result of fast root growth in the deep soil layers after planting, combined with an intense uptake of the tree roots to satisfy the large nutrient and water requirements for the development of tree crowns. Intense uptake and cycling of nutrients mitigated the risk due to clear cut and N fertilisation in this forest plantation. Nevertheless, forest managers must carefully fit fertilisation regimes to the nutrient requirements of new clone selected by breeding programmes and reduce as much as possible the delay between harvesting and re-planting to avoid high losses by deep drainage. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.