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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 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 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)

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

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)

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

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.

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.

[b]Background and Aims[/b][br/]Recent studies showed a positive tree response to Na addition in K-depleted tropical soils. Our study aimed to gain insight into the effects of K and Na fertilizations on leaf area components for a widely planted tree species.[br/][br/][b]Methods[/b][br/]Leaf expansion rates, as well as nutrient, polyol and soluble sugar concentrations, were measured from emergence to abscission of tagged leaves in 1-year-old Eucalyptus grandis plantations. Leaf cell size and water status parameters were compared 1 and 2 months after leaf emergence in plots with KCl application (+K), NaCl application (+Na) and control plots (C).[br/][br/][b]Results[/b][br/]K and Na applications enhanced tree leaf area by increasing both leaf longevity and the mean area of individual leaves. Higher cell turgor in treatments +K and +Na than in the C treatment resulting from higher concentrations of osmotica contributed to increasing both palisade cell diameters and the size of fully expanded leaves.[br/][br/][b]Conclusions[/b][br/]Intermediate total tree leaf area in treatment +Na compared to treatments C and +K might result from the capacity of Na to substitute K in osmoregulatory functions, whereas it seemed unable to accomplish other important K functions that contribute to delaying leaf senescence.

Made available in DSpace on 2019-09-12T16:53:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2013 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad) Universidade de São Paulo (USP) Comité Français d´Evaluation de la Coopération Universitaire avec le Brésil (COFECUB) Nutrient remobilizations in tree ligneous components have been little studied in tropical forests. A complete randomized block design was installed in Brazilian eucalypt plantations to quantify the remobilizations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) within stem wood. Three treatments were studied: control with neither K nor Na addition (C), 3 kmol ha(-1) K applied (+K), and 3 kmol ha(-1) Na applied (+Na). Biomass and nutrient contents were measured in the stem wood of eight trees destructively sampled at 1, 2, 3 and 4 years after planting in each treatment and annual rings were localized on discs of wood sampled every 3 m in half of the trees. Chemical analyses and wood density measurements were performed individually for each ring per level and per tree sampled. Nutrient remobilizations in annual rings were calculated through mass balance between two successive ages. Our results show that nutrient remobilizations within stem wood were mainly source-driven. Potassium and Na additions largely increased their concentration in the outer rings as well as the amounts remobilized in the first 2 years after the wood formation. The amount of Na remobilized in annual rings was 15 % higher in +Na than in +K the fourth year after planting despite a 34 % higher production of stem wood in +K leading to a much higher nutrient sink. A partial substitution of K by Na in the remobilizations within stem wood might contribute to enhancing Eucalyptus grandis growth in K-depleted soils. [Sette, Carlos Roberto, Jr.] Fed Univ Goias UFG, Forest Engn Dept, BR-74690900 Goiania, Go, Brazil [Sette, Carlos Roberto, Jr.; Tomazello Filho, Mario; Moreira, Rildo M.; Bouillet, Jean-Pierre] Univ Sao Paulo, ESALQ, Dept Forest Sci, BR-13418900 Piracicaba, SP, Brazil [Laclau, Jean-Paul; Bouillet, Jean-Pierre] CIRAD, UMR 111, F-34060 Montpellier, France [Laclau, Jean-Paul] Univ Estadual Paulista UNESP, BR-18610307 Botucatu, SP, Brazil [Ranger, Jacques] INRA, UR Biogeochim Ecosyst Forestiers, F-54280 Seichamps, France [Raposo Almeida, Julio Cesar] Universidade de Taubaté (Unitau)

Organized forestry in Brazil began in the late 1960s, stimulated by a government policy which subsidized afforestation programs from 1967 to 1989 to develop an internationally-competitive wood-based industry, managed by the private sector. Currently, planted forests in Brazil total about 6.9 million ha, from which 4.9 million ha is planted with eucalypt (around 25% of world plantation), 1.6 million ha with pine, and 0.42 M ha with other species. Roundwood consumption of forest plantations totaled 170.1 million m(3) in 2011, eucalypt plantation accounted for 80.6% of this total. Most eucalypt plantations are managed in short rotations (6-8 years) and are established in regions with water, nutritional and frost stresses of low to high degrees. The mean annual increment is 40 m(3) ha(-1) year(-1) roundwood, ranging from 25 to 60 m(3) ha(-1) year(-1) depending on the level of environmental stress. Improving natural resources use efficiency by breeding and matching genotypes to sites and using appropriate site management practices is a key challenge to sustain or increase productivity. The wide range of eucalypt species and hybrids with different climatic and edaphic suitability associated with the easy propagation by seeds and cloning allow the adaptation of plantations to various tropical and subtropical regions in Brazil. The possibility of using eucalypt wood in a range of purposes has led large and small enterprises to establish eucalypt forests for multiple uses. The desirable characteristics in association with the accumulated knowledge on eucalypt silviculture encourage the use of this genus in most plantations. The most important factors in the selective process for a genotype are wood characteristics, productivity level, susceptibility to pests and diseases, drought tolerance, especially in tropical regions (frost free), and frost tolerance in subtropical regions (mostly without water deficit). In regions with pronounced seasonality and moderate to long drought periods, the planting of hybrid genotypes predominates, propagated by cloning. Under subtropical conditions, the planting of single species predominates, propagated by seed. Clonal plantations with interspecific hybrids have been fundamental for eucalypt adaptation in regions under water and nutritional stresses. Given the rapid advances in eucalypt breeding, regarding adaptation to water stress and resistance to diseases and pests, and the adoption of clonal propagation techniques, genotypes are rapidly becoming obsolete and are replaced by more productive ones after harvesting. Thus, the replanting of crops has become a common procedure after the second half of the 1990s in Brazil. This paper describes the basic requirements for integrating genetic and silvicultural strategies to minimize abiotic and biotic constraints in eucalypt plantations. (c) 2013 Elsevier B.V. All rights reserved.

Background and aims Eucalyptus plantations cover 20 million hectares on highly weathered soils. Large amounts of nitrogen (N) exported during harvesting lead to concerns about their sustainability. Our goal was to assess the potential of introducing A. mangium trees in highly productive Eucalyptus plantations to enhance soil organic matter stocks and N availability. Methods A randomized block design was set up in a Brazilian Ferralsol soil to assess the effects of mono-specific Eucalyptus grandis (100E) and Acacia mangium (100A) stands and mixed plantations (50A:50E)on soil organic matter stocks and net N mineralization. Results A 6-year rotation of mono-specific A. mangium plantations led to carbon (C) and N stocks in the forest floor that were 44% lower and 86% higher than in pure E. grandis stands, respectively. Carbon and N stocks were not significantly different between the three treatments in the 0-15 cm soil layer. Field incubations conducted every 4 weeks for the two last years of the rotation estimated net soil N mineralization in 100A and 100E at 124 and 64 kg ha(-1) yr(-1), respectively. Nitrogen inputs to soil with litterfall were of the same order as net N mineralization. Conclusions Acacia mangium trees largely increased the turnover rate of N in the topsoil. Introducing A. mangium trees might improve mineral N availability in soils where commercial Eucalyptus plantations have been managed for a long time.

The introduction of nitrogen fixing species (NFS) in fast-growing tree plantations is an alternative option to reduce fertilizer inputs. However, the success of mixed-species plantations depends on the balance between positive interactions among species (resulting from facilitation and/or complementarity) and the negative effects of interspecific competition. Using a carbon budget approach and coupling measurements of standing biomass, aboveground litterfall and soil CO2 efflux, we assessed the influence of replacing half of eucalypt trees by Acacia mangium on total belowground carbon flux (TBCF), net primary production (NPP) and its partitioning between above- and belowground growth at two tropical sites in Brazil (Itatinga) and in Congo (Kissoko) exhibiting contrasting climates, edaphic conditions and wood productions. Annual soil CO2 efflux (F-S) was significantly lower in the acacia monocultures than in eucalypt monocultures and mixed-species stands at both sites. Annual F-S was significantly lower at Itatinga compared to Kissoko for all stands while TBCF was significantly lower in the eucalypt stands only. In the eucalypt monocultures we found a significantly lower aboveground NPP (ANPP) and wood production (wood NPP) at Kissoko compared to Itatinga that was almost fully balanced by a significantly higher belowground NPP (BNPP), leading to similar NPP. Similarly, acacia monocultures exhibited significantly higher ANPP and wood NPP at Itatinga than at Kissoko. The mixed-species stands exhibited a significantly lower wood NPP and ANPP than the eucalypt monocultures at the Brazilian site while NPP of the mixture was not significantly different than the average NPP of the two monocultures. At the Congolese site, NPP of the mixture was significantly higher than the average NPP of the two monocultures. NPP was similar in the mixed-species stand and the eucalypt monoculture with a significantly lower partitioning of NPP to belowground production, leading to a one third higher wood biomass at harvest in the mixed-species stand. A positive effect of growing eucalypts with the nitrogen fixing acacia trees on stand wood production occurred at Kissoko but not at Itatinga. Mixed-species plantations with NFS can be advocated at sites where the productive gains resulting from nitrogen fixation are not compromised by other resource limitations. (c) 2012 Elsevier B.V. All rights reserved.

The objectives of the study were to assess changes in fine root anisotropy and specific root lengths throughout the development of Eucalyptus grandis (W. Hill ex Maiden) plantations and to establish a predictive model of root length density (RLD) from root intercept counts on trench walls. Fine root densities (

La présente étude a été réalisée dans la chênaie verte du Moyen Atlas central marocain (Tafachna et Reggada), avec pour objectif la détermination du stock de carbone organique dans les différentes couches des sols, de la litière et des différentes composantes de l'arbre (bois du tronc, écorce, branches, rameaux et feuilles). " en ressort que le stock de carbone total (SCOT) dans cet écosystème est de 145 tC/ha pour Tafachna et 114 tC/ha pour Reggada. Le stock de carbone organique des sols (SCOS) représente plus de 50% du SCOT. Le SCOS varie considérablement avec la densité du peuplement, avec 80 tC/ha pour Tafachna (51.92 piedsiha) et 56 tC/ha pour Reggada (1584 pieds/ha). Au contraire, le stock de carbone dans la biomasse arborée (aérienne et racinaire) est plus important dans Tafachna que dans Reggada (64 tC/ha pour Tafachna et 58 tC/ha pour Reggada). Plus de 80% du stock de carbone organique des sols sont emmagasinés dans les trente premiers centimètres, où il est de l'ordre de 63 t/ha (43% du SCOT) pour Tafachna et 47 tlha (410/0 du SCOT) pour Reggada.

Introducing N-fixing species in the understorey of fast-growing plantations might be an attractive option to improve soil N status. Intensive fine root sampling was performed in a complete randomized block design to investigate the ability of Eucalyptus grandis and Acacia mangium seedlings in monospecific stands and mixed-species plantations to take up complementary resources from niche exploration of soil layers. The same soil layers were explored by the two species down to a depth of 2 m in monospecific stands. Whilst the development of E. grandis fine roots was not affected by A. mangium trees in mixed-species plantations, A. mangium fine roots were excluded from the upper soil layer from 18 months after planting onwards, despite the paramount importance of that horizon for tree nutrition in highly weathered soils, and were only found deeper and close to A. mangium trees 30 months after planting.

International audience; Studies on stem profile of teak (Tectona grandis) hardly exist. This can be possibly attributed to the occurrence of forks that is prevalent on teak trees. Stem profile model was therefore developed for teak in West Africa, which took into account the occurrence of forks. Trees were destructively sampled from Moist Evergreen Forest (MEF), Moist Semi-deciduous Forest (MSDF), Dry Semi-deciduous Forest (DSDF) and Savannah ecological zones in both Ghana and Côte d’Ivoire for the study. A single set of parameters could be used explicitly to predict stem profileof any teak tree, irrespective of country, eco-climatic zone, edaphic variables, site index, tree age, stand density and tree competition. The model efficiency and root mean square error (in relative diameter) were calculated to be 0.97 and 0.053, respectively. The relative position of the forks along the stem bole, with respect to total tree height, was highly variable and did not follow any particular trend, except higher value for the first fork in the Moist Evergreen Forest zone. However, average tree height to the first fork decreased along the ecological gradient from MEF, MSDF and DSDF to Savannah. The extent of diameter reduction due to the forks could be predicted. Relative tree form for zero-forked, one-forked and two-forked trees was calculated to be 0.39, 0.36 and 0.33, respectively. Relative loss of stem volume due to one fork and two forks was estimated to be 6.5 and 13.9%, respectively. The measured stem volume when related to the corresponding predicted value yielded coefficient and intercept not significantly different from unity and zero, respectively, with an r2 value of 0.97.

For 20 years, there has been 42,000 ha estate of clonal Eucalyptus plantations around Pointe-Noire in Congo on sandy soils that have very low reserves of available nutrients. These plantations have been based on a natural hybrid (E. PF1). This hybrid is being replaced by E. urophylla × E. grandis (UG), a more productive hybrid developed by the breeding program of UR2PI. A study of biogeochemical cycles showed that nutrient removal by harvesting is the main nutrient output in the E. PF1 ecosystem. It is therefore important to quantify the nutrient content (NC) in both hybrids to compare corresponding nutrient removal values. The work dealt with four UG clones and the most planted clone of E. PF1. Twelve trees per clone were sampled at the logging age (8 years) in a clonal test for UG clones and in a nearby stand for E. PF1. Tables were established to predict, from girth at breast height (C1.30 m), the biomass and nutrient content of stemwood, bark, dead and living branches, leaves, and were applied to the inventory of the different stands to evaluate corresponding biomass, NC and nutrient use efficiency (NUE) on a per-hectare basis. Total biomass differed between the two hybrids and among UG clones: 109 t ha−1 for E. PF1 and 108–155 t ha−1 for UG clones. In E. PF1 trees, total NC was globally lower for N, K, and Mg, but greater for P and Ca. In stemwood, nitrogen content was similar for both hybrids. By contrast, in UG clones, NC was much lower for P (−72%) and Ca (−40% to −55%). The same trends were observed for NUE: equivalent for both hybrids for N, but higher in UG clones for P (+72%) and Ca (+43% to +59%). A marked variability among clones was observed for K and Mg. UG clones allocated proportionally more nutrients in leaves than E. PF1. These results show that clones should not be selected only on growth traits but also on NUE and on the concentration of nutrients in tree components removed by harvesting. It will be then possible to limit the cost of fertilising needed to maintain stand growth and soil fertility.

The dynamics of the main nutrient fluxes of the biological cycle were quantified in a clonal Eucalyptus plantation throughout the whole planted crop rotation: current annual requirements of nutrients, uptake from the soil, internal translocations within trees, return to soil (litterfall and crown leaching) and decomposition in the forest floor. As reported for other species, two growth periods were identified in these short‐rotation plantations: (1) a juvenile phase up to canopy closure, during which the uptake of nutrients from the soil reserves supplied most of the current requirements; and (2) a second phase up to harvest, characterized by intense nutrient recycling processes. Internal translocation within trees supplied about 30 % of the annual requirements of N and P from 2 years of age onwards, and about 50 % of the K requirement. The mineralization of large amounts of organic matter returned to the soil with litterfall during stand development represented a key process providing nutrients to the stand at the end of the rotation. The importance of the recycling processes was clearly shown by the small amounts of nutrients permanently immobilized in the ligneous components of trees, compared with the total requirements accumulated over the stand rotation which were two to four times higher. Small pools of nutrients circulating quickly in the ecosystem made it possible to produce high amounts of biomass in poor soils. The sustainability of these plantations will require fertilizer inputs that match the changes in soil fertility over successive rotations, mainly linked to the dynamics of organic matter in this tropical soil.

Despite the continuous nature of growth of eucalyptus hybrids in Congo, taper functions fitted to stem profiles of one clone throughout stand development, combined with annual tree measurements, made it possible to locate accurately the position of annual rings in stems. Annual rings were identified on discs of wood sampled every 4 m in four trees cut from 1-, 2-, 3-, 4-, 5-, 6- and 7-year-old stands. Chemical analysis, performed individually for each ring per level and per tree sampled, made it possible to quantify the changes in nutrient content of the rings during stand development. Nutrient translocation in stemwood was thus calculated in a stepwise manner between trees of two successive ages. The cumulated nutrient translocations in stemwood from the 1-year-old stage to the 6-year-old stage amounted to 18·5 kg ha −1 N, 4·2 kg ha −1 P, 38·8 kg ha −1 K, 1·5 kg ha −1 Ca and 3·2 kg ha −1 Mg. They represented 11, 18, 121, 6, and 15% of the amounts of N, P, K, Ca and Mg accumulated in stemwood, respectively, at the 7-year-old stage (logging age). Negative translocations of N, P, Ca and Mg in stemwood between 6 and 7 years might indicate an improvement in the nutritive status of the stand at the end of the rotation. Much translocation of K in stemwood suggests that this process might be involved in the high use efficiency of this element.

Summary In a recent survey of Eucalyptus clones in the Republic of Congo, Central Africa, a serious wilt and die-back disease of two different hybrid clones was observed. Affected trees ranged in age from approximately 6 months to 4 years. Isolations from symptomatic plant material consistently yielded a Ceratocystis species. On the basis of morphology and sequence data this fungus was identified as Ceratocystis fimbriata, a well-known wilt and canker pathogen of many economically important plants. The Eucalyptus isolates were compared with other Ceratocystis spp. based on sequence data generated from the ITS and 5.8S region of the rRNA operon. The results confirmed the identity of the Ceratocystis isolates from Eucalyptus as C. fimbriata and showed that they group with other C. fimbriata isolates from Brazil, South Africa and Europe. Inoculations on young Eucalyptus plants were conducted in the greenhouse and all three of the Congolese isolates tested, produced typical lesions in the bark and xylem. This study represents the first report of C. fimbriata as a pathogen of Eucalyptus in Africa. This is a serious new disease that will require considerable study in order to ensure that losses, caused by C. fimbriata, do not continue.

Apesar do N ser o nutriente requerido em maiores quantidades pelas plantas superiores, vários pesquisadores tem observado que raramente as plantações de Eucalyptus respondem a fertilização nitrogenada nas regiões sob condições tropicais e subtropicais. Esta falta de resposta, provavelmente, é porque dentre as fontes de N, a mineralização do N orgânico, ao longo do ciclo da cultura, seja a fonte principal e suficiente para atender a demanda das árvores. Porém, devido ao esgotamento das reservas de N orgânico potencialmente mineralizável, espera-se que as florestas manejadas intensivamente respondam à fertilização nitrogenada após vários ciclos de cultivo. O presente estudo teve como objetivo avaliar (a) o teor de N potencialmente mineralizável (N0) em solos usados para plantações de eucalipto em São Paulo; (b) a resposta à fertilização nitrogenada em diferentes estádios de desenvolvimento dessas plantações; (c) a relação de N0 com a resposta à fertilização nitrogenada; (d) a eficiência do uso de atributos edáficos correlacionados com N0 para predizer a resposta à fertilização nitrogenada. Onze experimentos de fertilização, incluindo taxas de aplicadas de até 240 kg ha-1 de N foram estabelecidos em plantações experimentais de E. grandis ou E. grandis x urophylla de diversos sítios, em diferentes estádios de crescimento, no estado de São Paulo, Brasil. Os sítios possuem precipitação média anual entre 1200 a 1500 mm por ano, concentradas principalmente no verão-outono, com temperatura média anual de 20-21ºC. A maioria dos experimentos está sob os solos Latossolo Vermelho e Vermelho-Amarelo e Neossolo Quartzarênico, compreendendo uma ampla faixa de teores de matéria orgânica (18 a 55 g kg-1) e de argila (80 a 670 g kg-1), na camada de 0-20 cm. A mineralização de N foi mensurada em laboratório, pelo método químico de incubação anaeróbia, a fim de estimar o N0. A fertilização com N acelerou o crescimento das árvores em até 12% até os dois anos de idade. Numa idade intermediária, entre 3 e 4 anos, essa resposta caiu para 6%. Na idade de corte, não foi observada resposta à fertilização. As Produtividades Relativas (PR) nos povoamentos jovens e de idade média não se correlacionaram com a razão N0/Nt. Isso indica que o N disponível existente no solo é suficiente para atender a demanda das árvores. O N total (Nt) representou 3 a 5% da MO. As razões entre as concentrações de N0 e de Nt variaram, na sua grande maioria, entre 10 a 16%. O N0 encontrado, na camada superficial (0-20 cm), foi positivamente correlacionado com os teores de MO, de Nt e de argila, mostrando-se um bom indicador da disponibilidade de N nos solos. Os estoques de N0 da camada superficial (0-20 cm) são suficientes para 4 a 5 rotações de cultivo (7 anos cada), se levado em consideração a saída média de N do sistema via exportação pela colheita (apenas madeira), e as entras via fertilização e deposição atmosférica. In spite of N being a nutrient required in greater quantities by superior plants, many researchers have observed that rarely the eucalyptus crops response to nitrogen fertilization in tropical or subtropical regions. This lack of response is probably caused because from the N sources, the mineralization of organic N, along the crop cycle, is the main and enough source to supply the trees needs. However, due to the shortage of organic N reserves with mineralization potential, it is expected that the intensive managed forests react to nitrogen fertilization after several crop cycles. The objective of this research work is to evaluate (a) the content of potentially mineralizable N (N0) in soils used in eucalyptus crops in Sao Paulo; (b) the response to nitrogen fertilization in different development stages of those crops; (c) the relation between N0 and the nitrogen fertilization effect; (d) the edaphic attributes use efficiency correlated to N0 to predict the response to nitrogen fertilization. Eleven fertilization experiments, including rates applied until 240 kg ha-1 of N were established in experimental crops of E. grandis or E. grandis x urophylla of varied areas, in different growth stages in Sao Paulo state, Brazil. Those areas have a mean annual rain precipitation between 1200 and 1500 mm per year concentrated on summer and fall seasons, and a mean annual temperature of 20-21 ºC. The most of the experiments are under Oxisols and Quartzipsamments comprising a wide range content of organic matter (18 a 55 g kg-1) and clay (80 a 670 g kg-1), on 0-20 cm depth. The N mineral exploration was measured in laboratory using a chemical method of anaerobic incubation to estimate the N0. The nitrogen fertilization accelerated the trees growth in almost 12% until two years old. In middle ages, between three and four years, the response decreased until 6%. There was no observed response to fertilization at the cut age. Likewise there was no correlation between the Relative Productivity (RP) and the N0/Nt inside young and middle-aged crops. This shows that the existing available N in soil is enough to supply the trees needs. The total N (Nt), represents 3% to 5% of organic matter. The reasons between N0 and Nt concentrations vary in a great majority, between 10% and 16%. The founded N0 in 0-20 cm depth was positive correlated with the organic matter, Nt and clay contents, appearing as a great indicator of the possibilities of N in soils. The N0 stocks in 0-20 cm depth are enough to up to 4 to 5 crop rotations (7 years each one) if considering the mean system exit of N, by exportation because of harvesting (wood only), and the entrance by fertilization and atmospheric deposition.