title: In situ 13CO2 pulse labelling of field-grown eucalypt trees revealed the effects of potassium nutrition and throughfall exclusion on phloem transport of photosynthetic carbon.
abstract: 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 (13)CO2 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 (13)C 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 (0.20-0.82 m h(-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 -2.2 MPa). 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 (13)C 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.
authors.affiliation: UMR 1137, Ecologie et Ecophysiologie Forestières, Faculté des Sciences, Université de Lorraine, F-54500 Vandoeuvre-les-Nancy, France INRA, UMR 1137, Ecologie et Ecophysiologie Forestières, Centre de Nancy, F-54280 Champenoux, France CIRAD, UMR Eco&sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agro-écosystèmes, F-34060 Montpellier, France daniel.epron@univ-lorraine.fr.
authors.forename: Daniel
authors.initials: D
authors.lastname: Epron
authors.affiliation: Embrapa Meio Ambiente, CEP 13820-000, Jaguariúna, São Paulo, Brazil.
authors.forename: Osvaldo Machado Rodrigues
authors.initials: OM
authors.lastname: Cabral
authors.affiliation: CIRAD, UMR Eco&sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agro-écosystèmes, F-34060 Montpellier, France Universidade Estadual de São Paulo, Botucatu, CEP 18610-300 São Paulo, Brazil Departamento de Ciências Florestais, ESALQ, Universidade de São Paulo, ESALQ, CEP 13418-900 Piracicaba, São Paulo, Brazil.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Laclau
authors.affiliation: Laboratory of Forest Utilization, Department of Forest and Biomaterial Science, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Dannoura
authors.affiliation: Embrapa Meio Ambiente, CEP 13820-000, Jaguariúna, São Paulo, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Packer
authors.affiliation: UMR 1137, Ecologie et Ecophysiologie Forestières, Faculté des Sciences, Université de Lorraine, F-54500 Vandoeuvre-les-Nancy, France INRA, UMR 1137, Ecologie et Ecophysiologie Forestières, Centre de Nancy, F-54280 Champenoux, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Plain
authors.affiliation: Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, CEP 13400-970 Piracicaba, São Paulo, Brazil.
authors.forename: Patricia
authors.initials: P
authors.lastname: Battie-Laclau
authors.affiliation: Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, CEP 13400-970 Piracicaba, São Paulo, Brazil.
authors.forename: Marcelo Zacharias
authors.initials: MZ
authors.lastname: Moreira
authors.affiliation: Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, CEP 13400-970 Piracicaba, São Paulo, Brazil.
authors.forename: Paulo Cesar Ocheuze
authors.initials: PC
authors.lastname: Trivelin
authors.affiliation: CIRAD, UMR Eco&sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agro-écosystèmes, F-34060 Montpellier, France Departamento de Ciências Florestais, ESALQ, Universidade de São Paulo, ESALQ, CEP 13418-900 Piracicaba, São Paulo, Brazil.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bouillet
authors.affiliation: UMR 1137, Ecologie et Ecophysiologie Forestières, Faculté des Sciences, Université de Lorraine, F-54500 Vandoeuvre-les-Nancy, France INRA, UMR 1137, Ecologie et Ecophysiologie Forestières, Centre de Nancy, F-54280 Champenoux, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Gérant
authors.affiliation: CIRAD, UMR Eco&sols, Ecologie Fonctionnelle & Biogéochimie des Sols & Agro-écosystèmes, F-34060 Montpellier, France Departamento de Ciências Atmosféricas, IAG, Universidade de São Paulo, ESALQ, CEP 05508-900 São Paulo, Brazil.
authors.forename: Yann
authors.initials: Y
authors.lastname: Nouvellon
mesh_terms: D000345:Affinity Labels; D001693:Biological Transport, Active; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D005052:Eucalyptus / Q000378:metabolism*; D052585:Phloem / Q000378:metabolism*; D010788:Photosynthesis; D011188:Potassium / Q000378:metabolism*; D014197:Trees / Q000378:metabolism*
chemical_list: D000345:Affinity Labels; D002247:Carbon Isotopes; D002244:Carbon; D011188:Potassium
keywords: Eucalyptus grandis; carbon isotope; carbon transfer; drought; fertilization