title: Impact of warming and drought on carbon balance related to wood formation in black spruce.
abstract: OBJECTIVE
  Wood formation in trees represents a carbon sink that can be modified in the case of stress. The way carbon metabolism constrains growth during stress periods (high temperature and water deficit) is now under debate. In this study, the amounts of non-structural carbohydrates (NSCs) for xylogenesis in black spruce, Picea mariana, saplings were assessed under high temperature and drought in order to determine the role of sugar mobilization for osmotic purposes and its consequences for secondary growth.
  
  
  METHODS
  Four-year-old saplings of black spruce in a greenhouse were subjected to different thermal conditions with respect to the outside air temperature (T0) in 2010 (2 and 5 °C higher than T0) and 2011 (6 °C warmer than T0 during the day or night) with a dry period of about 1 month in June of each year. Wood formation together with starch, NSCs and leaf parameters (water potential and photosynthesis) were monitored from May to September.
  
  
  RESULTS
  With the exception of raffinose, the amounts of soluble sugars were not modified in the cambium even if gas exchange and photosynthesis were greatly reduced during drought. Raffinose increased more than pinitol under a pre-dawn water potential of less than -1 Mpa, presumably because this compound is better suited than polyol for replacing water and capturing free radicals, and its degradation into simple sugar is easier. Warming decreased the starch storage in the xylem as well the available hexose pool in the cambium and the xylem, probably because of an increase in respiration.
  
  
  CONCLUSIONS
  Radial stem growth was reduced during drought due to the mobilization of NSCs for osmotic purposes and due to the lack of cell turgor. Thus plant water status during wood formation can influence the NSCs available for growth in the cambium and xylem.
authors.affiliation: Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555 boulevard de l'Université, Chicoutimi, QC G7H2B1, Canada adeslaur@uqac.ca.
authors.forename: Annie
authors.initials: A
authors.lastname: Deslauriers
authors.affiliation: Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555 boulevard de l'Université, Chicoutimi, QC G7H2B1, Canada.
authors.forename: Marilène
authors.initials: M
authors.lastname: Beaulieu
authors.affiliation: Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555 boulevard de l'Université, Chicoutimi, QC G7H2B1, Canada.
authors.forename: Lorena
authors.initials: L
authors.lastname: Balducci
authors.affiliation: Laboratorio di Xilogenesi, IVaLSA-CNR, via Madonna de Piano, 50019 Sesto Fiorentino, (FI), Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Giovannelli
authors.affiliation: Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555 boulevard de l'Université, Chicoutimi, QC G7H2B1, Canada.
authors.forename: Michel J
authors.initials: MJ
authors.lastname: Gagnon
authors.affiliation: Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555 boulevard de l'Université, Chicoutimi, QC G7H2B1, Canada.
authors.forename: Sergio
authors.initials: S
authors.lastname: Rossi
mesh_terms: D058506:Cambium / Q000502:physiology; D002241:Carbohydrates / Q000032:analysis; D002244:Carbon / Q000378:metabolism*; D055864:Droughts; D005740:Gases / Q000378:metabolism; D057232:Global Warming; D010788:Photosynthesis; D028222:Picea / Q000254:growth & development* / Q000378:metabolism*; D018515:Plant Leaves / Q000502:physiology; D011792:Quebec; D012621:Seasons; D012995:Solubility; D018709:Statistics, Nonparametric; D013696:Temperature; D014867:Water; D014934:Wood / Q000254:growth & development* / Q000378:metabolism*; D052584:Xylem / Q000166:cytology / Q000502:physiology
chemical_list: D002241:Carbohydrates; D005740:Gases; D014867:Water; D002244:Carbon
keywords: Cambium; Picea mariana; black spruce; climate change; drought; global warming; non-structural carbohydrate; raffinose; soluble sugars; starch; wood formation; xylogenesis