Kinetics of tracheid development explain conifer tree‐ring structure

Abstract

SummaryConifer tree rings are generally composed of large, thin-walled cells of light earlywood followed by narrow, thick-walled cells of dense latewood. Yet, how wood formation processes and the associated kinetics create this typical pattern remains poorly understood.We monitored tree-ring formation weekly over 3 yr in 45 trees of three conifer species in France. Data were used to model cell development kinetics, and to attribute the relative importance of the duration and rate of cell enlargement and cell wall deposition on tree-ring structure.Cell enlargement duration contributed to 75% of changes in cell diameter along the tree rings. Remarkably, the amount of wall material per cell was quite constant along the rings. Consequently, and in contrast with widespread belief, changes in cell wall thickness were not principally attributed to the duration and rate of wall deposition (33%), but rather to the changes in cell size (67%). Cell enlargement duration, as the main driver of cell size and wall thickness, contributed to 56% of wood density variation along the rings.This mechanistic framework now forms the basis for unraveling how environmental stresses trigger deviations (e.g. false rings) from the normal tree-ring structure.

Tree growth, cambial phenology, and wood anatomy of limber pine at a Great Basin (USA) mountain observatory

“…The cross-sectional surface (or lumen area) of water conduits directly reflects the hydration status of the plant at the moment of cell formation during the growing season, and it represents the final outcome of complex mechanical and physiological trade-offs between structural development and resistance to drought in the hydraulic architecture of the stem (Sperry et al 2006). Water is needed to maintain cellular turgor during tracheid expansion, affecting the duration of the enlargement phase and the final tracheid size (Cuny et al 2014). This mechanism could then lead to significant differences in cellular parameters (e.g., lumen area and cell diameter), as was found at our study sites.…”

Class I KNOX transcription factors promote differentiation of cambial derivatives into xylem fibers in the Arabidopsis hypocotyl

“…Promotion of xylem fiber differentiation by STM and KNAT1 stands in sharp contrast to their proposed function of preventing differentiation of meristematic cells in the SAM. Final radial diameter of cambial derivatives is a result of the cell expansion rate and the residence time in the expansion zone (Skene, 1969;Cuny et al, 2014). Hence, large expansion zones, as observed for example during early wood formation, correlate with big luminal areas, whereas short expansion zones are associated with smaller lumina of cambial derivatives.…”

How does climate influence xylem morphogenesis over the growing season? Insights from long-term intra-ring anatomy inPicea abies

“…Cuny et al, 2014;Rossi et al, 2014) and diel stem radial variations (e.g. King et al, 2013;Steppe et al, 2015).…”

“…However, despite the strong inter-annual variability of cambial phenology (Treml et al, 2015), this process has usually been quantified with just a few years (typically 1-5 in most studies) of continuous observations. In addition, studies monitoring xylogenesis have provided clues on how climate before and during the growing season affects the onset of cambial activity (Rossi et al, 2013) and impacts the kinetics of cell formation, influencing xylem cell morphological traits (Cuny et al, 2014). However, these observations lack the necessary long-term perspective to thoroughly assess the responses of wood formation and structure to inter-annual climate variability (Boulouf Lugo et al, 2012).…”