In situ (CO2)-C-13 pulse labelling of field-grown eucalypt trees revealed the effects of potassium nutrition and throughfall exclusion on phloem transport of photosynthetic carbon

Author(s):Show less -

Epron, Daniel ^{[1, 2, 3]} ; Cabral, Osvaldo Machado Rodrigues ^[4] ; Laclau, Jean-Paul ^{[5, 6, 1]} ; Dannoura, Masako ^[7] ; Packer, Ana Paula ^[4] ; Plain, Caroline ^{[2, 3]} ; Battie-Laclau, Patricia ^[8] ; Moreira, Marcelo Zacharias ^[8] ; Trivelin, Paulo Cesar Ocheuze ^[8] ; Bouillet, Jean-Pierre ^{[6, 1]} ; Gerant, Dominique ^{[2, 3]} ; Nouvellon, Yann ^{[1, 9]}

Affiliation

^[1] CIRAD, UMR Eco & Sols, Ecol Fonct & Biogeochim Sols & Agroecosyst, F-34060 Montpellier - France

^[2] Univ Lorraine, Fac Sci, Ecol & Ecophysiol Forestieres, UMR 1137, F-54500 Vandoeuvre Les Nancy - France

^[3] INRA, UMR 1137, Ecol & Ecophysiol Forestieres, Ctr Nancy, F-54280 Champenoux - France

^[4] Embrapa Meio Ambiente, BR-13820000 Jaguariuna, SP - Brazil

^[5] Univ Estadual Sao Paulo, BR-18610300 Botucatu, SP - Brazil

^[6] Univ Sao Paulo, ESALQ, Dept Ciencias Florestais, BR-13418900 Piracicaba, SP - Brazil

^[7] Kyoto Univ, Grad Sch Agr, Dept Forest & Biomat Sci, Lab Forest Utilizat, Kyoto 6068502 - Japan

^[8] Univ Sao Paulo, Ctr Energia Nucl Agr, BR-13400970 Piracicaba, SP - Brazil

^[9] Univ Sao Paulo, Dept Ciencias Atmosfer, IAG, ESALQ, BR-05508900 Sao Paulo - Brazil

• Document type: Journal article
• Source: TREE PHYSIOLOGY; v. 36, n. 1, p. 6-21, JAN 2016.
• Web of Science Citations: 17

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 (CO2)-C-13 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 (21-3 h). The time series of C-13 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 h(-1)) was twice as high in +K trees than in -K trees, with no significant effect of throughfall exclusion except for one +Ka'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 C-13 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. (AU)

• FAPESP's process: 11/23706-0 - Pulse labeling experiment with 13C-CO2 in eucalyptus trees
• Grantee: Osvaldo Machado Rodrigues Cabral
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• FAPESP's process: 11/09727-5 - Drought mediated changes in carbon allocation in eucalyptus plantations: a labelling experiment to assess the effects of K fertilisation
• Grantee: Osvaldo Machado Rodrigues Cabral
• Support Opportunities: Regular Research Grants