ORCID IDs: 0000-0003-3830-0415 (J.-G.H.); 0000-0001-5248-9096 (M.B.).Nonstructural carbohydrates (NSCs) play a crucial role in xylem formation and represent, with water, the main constraint to plant growth. We assessed the relationships between xylogenesis and NSCs in order to (1) verify the variance explained by NSCs and (2) determine the influence of intrinsic (tissue supplying carbon) and extrinsic (water availability and temperature) factors. During 2 years, wood formation was monitored in saplings of black spruce (Picea mariana) subjected to a dry period of about 1 month in June and exposed to different temperature treatments in a greenhouse. In parallel, NSC concentrations were determined by extracting the sugar compounds from two tissues (cambium and inner xylem), both potentially supplying carbon for wood formation. A mixed-effect model was used to assess and quantify the potential relationships. Total xylem cells, illustrating meristematic activity, were modeled as a function of water, sucrose, and D-pinitol (conditional r 2 of 0.79). Water availability was ranked as the most important factor explaining total xylem cell production, while the contribution of carbon was lower. Cambium stopped dividing under water deficit, probably to limit the number of cells remaining in differentiation without an adequate amount of water. By contrast, carbon factors were ranked as most important in explaining the variation in living cells (conditional r 2 of 0.49), highlighting the functional needs during xylem development, followed by the tissue supplying the NSCs (cambium) and water availability. This study precisely demonstrates the role of carbon and water in structural growth expressed as meristematic activity and tissue formation.

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.

HighlightNight and day warming combined with drought affect wood anatomy and survival, reflecting the importance of carbon–water relations for the survival process in Picea mariana saplings.

The aim of the study was to qualify and quantify non-structural carbohydrates (NSC) in stems of black spruce (Picea mariana (Mill.) B.S.P) seedlings. The effects of temperatures and water deficit on the seasonal NSC amount within the stem were also investigated. Weekly secondary growth observations of the stem was correlated to the sugars variations in order to define the most important sugars involved in wood formation in different environmental conditions (water deficit and warmer temperatures). The carbohydrates found in cambium and xylem were mainly composed of sucrose, pinitol, glucose, fructose, raffinose and starch. Water deficit decreased sucrose, while raffinose rose. Temperature had no effect on carbohydrates but amplified the effect of water deficit. Sucrose, pinitol and raffinose were correlated to cambium activity and xylem development, but changes in those carbohydrates quantities only had a little effect on cell development in the stem.