title: Combining stable isotope and carbohydrate analyses in phloem sap and fine roots to study seasonal changes of source-sink relationships in a Mediterranean beech forest.
abstract: Carbon isotope composition (δ(13)C) and carbohydrate content of phloem sap and fine roots were measured in a Mediterranean beech (Fagus sylvatica L.) forest throughout the growing season to study seasonal changes of source-sink relationships. Seasonal variations of δ(13)C and content of phloem sap sugars, collected during the daylight period, reflected the changes in soil and plant water status. The correlation between δ(13)C and content of phloem sap sugars, collected from plants belonging to different social classes, was significantly positive only during the driest month of July. In this month, δ(13)C of phloem sap sugars was inversely related to the increment of trunk radial growth and positively related to δ(13)C of fine roots. We conclude that the relationship between δ(13)C and the amount of phloem sap sugars is affected by a combination of causes, such as sink strength, tree social class, changes in phloem anatomy and transport capacity, and phloem loading of sugars to restore sieve tube turgor following the reduced plant water potential under drought conditions. However, δ(13)C and sugar composition of fine roots suggested that phloem transport of leaf sucrose to this belowground component was not impaired by mild drought and that sucrose was in a large part allocated towards fine roots in July, depending on tree social class. Hence, fine roots could represent a functional carbon sink during the dry seasonal periods, when transport and use of assimilates in other sink tissues are reduced. These results indicate a strict link between above- and belowground processes and highlight a rapid response of this Mediterranean forest to changes in environmental drivers to regulate source-sink relationships and carbon sink capacity.
authors.affiliation: Istituto di Biologia Agroambientale e Forestale (IBAF), Consiglio Nazionale delle Ricerche (CNR), Via Salaria km 29,300, 00016 Monterotondo Scalo (RM), Italy Istituto di Biologia Agroambientale e Forestale (IBAF), Consiglio Nazionale delle Ricerche (CNR), Viale G. Marconi 2, 05010 Porano (TR), Italy andrea.scartazza@ibaf.cnr.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Scartazza
authors.affiliation: Istituto di Biologia Agroambientale e Forestale (IBAF), Consiglio Nazionale delle Ricerche (CNR), Viale G. Marconi 2, 05010 Porano (TR), Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Moscatello
authors.affiliation: Istituto di Biologia Agroambientale e Forestale (IBAF), Consiglio Nazionale delle Ricerche (CNR), Via Salaria km 29,300, 00016 Monterotondo Scalo (RM), Italy Istituto per i Sistemi Agricoli e Forestali del Mediterraneo (ISAFoM), Consiglio Nazionale delle Ricerche (CNR), Via Cavour 4/6, 87036 Rende (CS), Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Matteucci
authors.affiliation: Istituto di Biologia Agroambientale e Forestale (IBAF), Consiglio Nazionale delle Ricerche (CNR), Viale G. Marconi 2, 05010 Porano (TR), Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Battistelli
authors.affiliation: Istituto di Biologia Agroambientale e Forestale (IBAF), Consiglio Nazionale delle Ricerche (CNR), Viale G. Marconi 2, 05010 Porano (TR), Italy Present address: Dipartimento Scienze del Sistema Terra e Tecnologie per l'Ambiente, Consiglio Nazionale delle Ricerche (CNR), Piazzale Aldo Moro 7, 00185 Roma (RM), Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Brugnoli
mesh_terms: D001692:Biological Transport; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000032:analysis; D002247:Carbon Isotopes / Q000032:analysis; D055864:Droughts; D029964:Fagus / Q000502:physiology*; D065928:Forests; D052585:Phloem / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D018517:Plant Roots / Q000502:physiology*; D012621:Seasons; D014867:Water / Q000502:physiology
chemical_list: D002241:Carbohydrates; D002247:Carbon Isotopes; D014867:Water
keywords: Fagus sylvatica; carbon allocation; carbon isotope composition; non-structural carbohydrates; water stress; water-use efficiency