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Plant roots exposed to water scarcity respond by modulating root functional traits, such as deep and prolific root growth, to maximize resource acquisition. Such adjustments, which include the alterations of root morphology and anatomy to optimize water uptake and/or maximize root survival, may also increase the carbon demand for soil exploration. But this altered carbon allocation to foster belowground resource acquisition limits aboveground plant development. In the present study we investigated the relationship between root physiology, root trait plasticity and whole plant growth under drought stress. We quantified shoot and root traits of nine contrasting spring barley cultivars grown in soil-filled rhizoboxes under well-watered (4 weeks, 55% of field capacity) or drought conditions (2 weeks, 55% of field capacity + 2 weeks without water). Time-lapse imaging was applied to quantify root and shoot growth rates, and combined with measurements of root distribution, morphology, anatomy as well as mycorrhizal colonization. Aboveground traits had a strong and uniform response to drought compared to belowground traits. Root traits’ plasticity were variable and differed among cultivars. The differences between cultivars were particularly pronounced for the proportion of root length and root biomass in deep soil layers as well as changes in root morphological and anatomical traits. We suggest that cultivars characterized by an increase in root conduits, a greater hierarchical structure and a reduction of specific root length and area may be good candidates to promote hydraulic lift while lowering carbon cost for root growth. Increased root length and depth, root density and specific root length in drought condition are different cultivars’ strategies that may promote soil exploration and optimize water uptake. This is directly linked to the interplay of above and belowground carbon investment, with some cultivars yielding both a high shoot biomass and enhanced resource acquisition. Based on our findings, testing new agronomic strategies to mobilize the diversity of cultivars could be key to enhance drought resistance and resilience of barley cropping systems.

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

Les racines fines jouent un role essentiel dans l'absorption de l'eau et des nutriments, favorisant ainsi la croissance des plantes, et influencent considerablement les flux de carbone. Preciser la dynamique spatio-temporelle de l'exploration du sol par les racines fines est donc un enjeu important pour la durabilite des plantations d'Eucalyptus installees dans des zones peu fertiles et soumises a de fortes contraintes hydriques saisonnieres. Au Bresil, les plantations d'Eucayptus sont les principales plantations forestieres, occupant 5,1 millions d'hectares. La gestion sylvicole en taillis des plantations d'Eucalyptus peut constituer un avantage contre le stress hydrique: les arbres beneficient ainsi d'un systeme racinaire deja developpe, capable d'explorer les couches profondes du sol, ou l'eau est plus disponible. L'objectif de cette etude est donc d'evaluer: la production des racines fines, le dioxyde de carbone (CO2), le methane (CH4) et le protoxyde d'azote (N2O) jusqu'a la nappe phreatique, avant et apres la coupe d'une plantation d'Eucalyptus grandis menee en taillis sur une experimentation de reduction des eaux de pluies. Pour cela, deux fosses de 17 metres de profondeur ont etes creusees dans deux parcelles caracterisees par les traitements suivants: une parcelle dans laquelle 37% du volume des eaux de pluies est exclu par des bâches en plastiques et une parcelle sans exclusion. Une autre fosse creusee dans une parcelle adjacente du meme âge, non recoltee, permettra d'evaluer l'effet de la coupe les arbres. La dynamique des racines fines sera etudiee en utilisant la methode des minirhizotrons: vingt-quatre tubes transparents en polyvinyle chlorure ont etes installes dans les fosses en 2014 (12 par fosse) jusqu'a 17 metres de profondeur et 7 tubes seront installes jusqu'a 4 metres de profondeur, dans la parcelle non coupee. Des images seront obtenues a l'aide d'un scanner circulaire tous les 14 jours pendant un an avant la coupe des arbres, puis pendant un an et demi apres leur coupe. Le logiciel WinRhizotron sera utilise pour estimer la croissance des racines. L'echantillonnage de gaz sera effectue toutes les deux semaines pendant 24 mois (6 mois avant et 18 mois apres la coupe des arbres) sur l'ensemble du profil de sol, jusqu'a la nappe phreatique. Les echantillons de gaz seront analyses par chromatographie gazeuse. Les series temporelles de teneurs en CO2, CH4 et N2O a la surface du sol, ainsi qu'a differentes profondeurs, seront utilisees pour calibrer un modele de transfert de gaz qui permettra d'estimer cette production a chaque profondeur. La dynamique des concentrations de gaz peut fournir des informations supplementaires sur les processus heterogenes d'echange de ces gaz selon la profondeur dans le sol et comment les flux a la surface du sol sont correles a la dynamique des racines sur l'ensemble du profil. Ameliorer notre comprehension des facteurs regissant les flux de gaz a effet de serre sur l'ensemble des profils de sol, et notamment a des fortes profondeurs, est necessaire afin de developper des modeles bases sur des processus fiables permettant la prediction a grande echelle de la production de bois par les entreprises forestieres.

Made available in DSpace on 2018-11-26T17:49:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-03-01 Agence national de la recherche Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Ecofor Allenvi French National Research Infrastructure ANAEE-F Fine-root functioning is a major driver of plant growth and strongly influences the global carbon cycle. While fine-root over-yielding has been shown in the upper soil layers of mixed-species forests relative to monospecific stands, the consequences of tree diversity on fine-root growth in very deep soil layers is still unknown. Our study aimed to assess the consequences of mixing Acacia mangium and Eucalyptus grandis trees on soil exploration by roots down to the water table at 17 m depth in a tropical planted forest. Fine roots (diameter < 2 mm) were sampled in a randomized block design with three treatments: monospecific stands of Acacia mangium (100A), Eucalyptus grandis (100E), and mixed stands with 50% of each species (50A50E). Root ingrowth bags were installed at 4 depths (from 0.1 m to 6 m) in the three treatments within three different blocks, to study the fine-root production over 2 periods of 3 months. Down to 17 m depth, total fine-root biomass was 1127 g m(-2) in 50A50E, 780 g m(-2) in 100A and 714 g m(-2) in 100E. Specific root length and specific root area were 110-150% higher in 50A50E than in 100A for Acacia mangium trees and 34% higher in 50A50E than in 100E for Eucalyptus grandis trees. Ingrowth bags showed that the capacity of fine roots to explore soil patches did not decrease down to a depth of 6 m for the two species. Belowground interactions between Acacia mangium and Eucalyptus grandis trees greatly increased the exploration of very deep soil layers by fine roots, which is likely to enhance the uptake of soil resources. Mixing tree species might therefore increase the resilience of tropical planted forests through a better exploration of deep soils. Univ Estadual Paulista, Dept Solos & Recursos Ambientais, BR-18610300 Botucatu, SP, Brazil Univ Montpellier, Eco&Sols, INRA, CIRAD,IRD,Montpellier SupAgro, Montpellier, France Univ Sao Paulo, ESALQ, BR-13400970 Piracicaba, SP, Brazil CIRAD, Eco&Sols, Montpellier, France Univ Fed Espirito Santo, Dept Ciencias Florestais & Madeira, BR-2955000 Jeronimo Monteiro, ES, Brazil Univ Estadual Paulista, Dept Solos & Recursos Ambientais, BR-18610300 Botucatu, SP, Brazil Agence national de la recherche: ANR-2010-STRA-004-03 FAPESP: 2015/24911-8 FAPESP: 2011/20510-8

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

International audience; While the number of studies dealing with fine root dynamics in deep soils layers (depth > 1 m) has increased sharply recently, the phenology, the morphology, the anatomy and the role of deep fine roots are still poorly known in forest ecosystems. This review summarizes the current knowledge on fine root production, mortality and longevity in deep soil layers, mycorrhizal association with deep roots, and the role of deep fine roots on carbon, water and nutrient cycling in forest ecosystems. Plant species are known to be more deeply rooted in tropical ecosystems than in temperate and boreal ecosystems, but deep-rooted species are common in a wide range of climates. Deep fine roots are highly plastic in response to changes in environmental conditions and soil resources. Recent studies show that functional traits can be different for deep and shallow roots, with a possible functional specialization of deep fine roots to take up nutrients. With higher vessel diameter and larger tracheid, the anatomy of deep fine roots is also oriented toward water acquisition and transport by increasing the hydraulic conductivity. Deep fine roots can have a great impact on the biogeochemical cycles in many forests (in particular in tropical areas where highly weathered soils are commonly very deep), making it possible to take up water and nutrients over dry periods and contributing to store carbon in the soil. The biogeochemical models in forest ecosystems need to consider the specificity of deep root functioning to better predict carbon, water and nutrient cycling as well as net ecosystem productivity.

Made available in DSpace on 2019-10-06T17:08:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-08-01 Centre de Coopération Internationale en Recherche Agronomique pour le Développement Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Improving our understanding of the spatiotemporal dynamics of fine roots in deep soil layers is of utter importance to manage tropical planted forests in a context of climate change. Our study aimed to assess the effect of clear-cutting and drought on fine-root dynamics down to the water table in Brazilian ferralsol under eucalypt plantations conducted in coppice. Fine roots (i.e. diameter 13 m)and, surprisingly, root mortality remained extremely low whatever the depth and the treatment. Total fine-root biomass in coppice down to 17 m depth was 1266 and 1017 g m−2 in +W and −W, respectively, at 1.5 year after the clear-cut and was 1078 g m−2 in NH 7.5 years after planting. Specific root length and specific root area were about 15% higher in −W than in +W. Proliferation of fine roots at great depths could be an adaptive mechanism for tree survival, enhancing the access to water stored in the subsoil. The root system established before clear-cutting provides access to water stored in very deep layers that probably contribute to mitigate the risk of tree mortality during prolonged drought periods when the eucalypt plantations is conducted in coppice after the clear-cut. UNESP-São Paulo State University School of Agricultural Sciences Eco&Sols Univ Montpellier CIRAD INRA IRD Montpellier SupAgro CIRAD UMR Eco&Sols ESALQ Forest Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo ESALQ Soil Science Department Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo IRD UMR Eco&Sols LMI IESOL, BP 1386 UNESP-São Paulo State University School of Agricultural Sciences FAPESP: 2015/24911-8

Background and Aims Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of root dynamics have principally been observed in shallow soil horizons (2.5 m) root growth occurred at two distinct periods, at bud break in spring and throughout the winter i.e., after leaf fall. In contrast, shallow roots grew mainly during the spring-summer period. Maximum root elongation rates ranged from 1 to 2 cm day−1 depending on soil depth. Most root mortality occurred in upper soil layers whereas only 10 % of fine roots below 4 m died over the study period. Fine root lifespan was longer in thicker and in deeper roots with the lifespan of the thinnest roots (0.0–0.5 mm) increasing from 129 days in the topsoil to 190 at depths > 2.5 m. Conclusions The unexpected growth of very deep fine roots during the winter months, which is unusual for a deciduous tree species, suggests that deep and shallow roots share different physiological strategies and that current estimates based on the shortest root growth periods (i.e., during spring and summer) may be underestimating root production. Although high fine root turnover rates might partially result from the minirhizotron approach used, our results help gain insight into some of the factors driving soil organic carbon content.