Abstract
The formation of wood results from cambial activity and its anatomical properties reflect the variability of environmental conditions during the growing season. Recently, it was found that wood density variations in conifers growing under cold-limited environment result from the adjustment of cell wall thickness (CWT) to temperature. Additionally, it is known that intra-annual density fluctuations (IADFs) are formed in response to precipitation after the summer drought. Although IADFs are frequent in Mediterranean conifers no study has yet been conducted to determine if these structures result from the adjustment of lumen diameter (LD) or CWT to soil water availability. Our main objective is to investigate the intra-ring variation of wood anatomical features (LD and CWT) in Pinus pinaster Ait. growing under a water-limited environment. We compared the tracheidograms of LD and CWT for the years 2010–2013 in P. pinaster growing in the west coast of Portugal. Our results suggest a close association between LD and soil moisture content along the growing season, reinforcing the role of water availability in determining tracheid size. Compared with CWT, LD showed a higher intra- and inter-annual variability suggesting its strong adjustment value to variations in water availability. The formation of a latewood IADF appears to be predisposed by higher rates of cell production in spring and triggered by early autumn precipitation. Our findings reinforce the crucial role of water availability on cambial activity and wood formation in Mediterranean conifers, and emphasize the high plasticity of wood anatomical features under Mediterranean climate.
Highlights
IntroductionWood is formed by the vascular cambium that is controlled by intrinsic (e.g. plant hormones) and extrinsic factors (e.g. temperature and precipitation)
Wood is formed by the vascular cambium that is controlled by intrinsic and extrinsic factors
Latewood intra-annual density fluctuations (IADFs) are characterized by earlywood-like cells within latewood, we considered that an IADF was formed when the lumen diameter (LD)/cell wall thickness (CWT) ratio was 2 after the occurrence of the first latewood tracheid
Summary
Wood is formed by the vascular cambium that is controlled by intrinsic (e.g. plant hormones) and extrinsic factors (e.g. temperature and precipitation). The variability of climatic conditions during the growing season can affect cambial activity [1, 2] and tree rings properties by changing the number of xylem cells produced and/or their anatomical properties [3]. Adaptations in tracheid anatomy were observed in a continental site in Switzerland where P. sylvestris from a dry site showed narrower tree rings and lower latewood proportions compared to a mesic site [15]. These studies indicate that cellular parameters respond to environmental conditions at the time of their formation [16]
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