title: How fresh is maple syrup? Sugar maple trees mobilize carbon stored several years previously during early springtime sap-ascent.
abstract: While trees store substantial amounts of nonstructural carbon (NSC) for later use, storage regulation and mobilization of stored NSC in long-lived organisms like trees are still not well understood. At two different sites with sugar maple (Acer saccharum), we investigated ascending sap (sugar concentration, δ(13) C, Δ(14) C) as the mobilized component of stored stem NSC during early springtime. Using the bomb-spike radiocarbon approach we were able to estimate the average time elapsed since the mobilized carbon (C) was originally fixed from the atmosphere and to infer the turnover time of stem storage. Sites differed in concentration dynamics and overall δ(13) C, indicating different growing conditions. The absence of temporal trends for δ(13) C and Δ(14) C indicated sugar mobilization from a well-mixed pool with average Δ(14) C consistent with a mean turnover time (TT) of three to five years for this pool, with only minor differences between the sites. Sugar maple trees hence appear well buffered against single or even several years of negative plant C balance from environmental stress such as drought or repeated defoliation by insects. Manipulative investigations (e.g. starvation via girdling) combined with Δ(14) C measurements of this mobilized storage pool will provide further new insights into tree storage regulation and functioning.
authors.affiliation: Max-Planck-Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745, Jena, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Muhr
authors.affiliation: Institut des Sciences de la Forêt Tempéré (ISFORT), Université du Québec en Outaouais (UQO), 58 Rue Principale, Ripon, QC, JOV 1V0, Canada.|Center for Forest Research (CEF), Université du Québec à Montréal, PO Box 8888, Centre-ville Station, Montréal, QC, H3C 3P8, Canada.
authors.forename: Christian
authors.initials: C
authors.lastname: Messier
authors.affiliation: Center for Forest Research (CEF), Université du Québec à Montréal, PO Box 8888, Centre-ville Station, Montréal, QC, H3C 3P8, Canada.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Delagrange
authors.affiliation: Max-Planck-Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745, Jena, Germany.|Department of Earth System Science, University of California, Irvine, CA, 92697-3100, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Trumbore
authors.affiliation: Department of Earth System Science, University of California, Irvine, CA, 92697-3100, USA.
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Xu
authors.affiliation: Max-Planck-Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745, Jena, Germany.
authors.forename: Henrik
authors.initials: H
authors.lastname: Hartmann
mesh_terms: D031002:Acer / Q000502:physiology*; D002241:Carbohydrates / Q000032:analysis; D002244:Carbon / Q000378:metabolism*; D002250:Carbon Radioisotopes; D053147:Plant Exudates / Q000378:metabolism*; D055110:Radiometric Dating; D012621:Seasons; D014197:Trees / Q000502:physiology*; D052584:Xylem / Q000378:metabolism
chemical_list: D002241:Carbohydrates; D002250:Carbon Radioisotopes; D053147:Plant Exudates; D002244:Carbon
keywords: bomb-radiocarbon approach; nonstructural carbon (NSC) pool; reserve carbon (C) mobilization; springtime sap production; sugar maple (Acer saccharum)