Evidences of different drought sensitivity in xylem cell developmental processes in south siberia scots pines

Abstract

Research Highlights: This study emphasized the importance of multi-parameter analyses along ecological gradients for a more holistic understanding of the complex mechanism of tree-ring formation. Background and Objectives: The analysis of climatic signals from cell anatomical features measured along series of tree-rings provides mechanistic details on how environmental drivers rule tree-ring formation. However, the processes of cell development might not be independent, limiting the interpretation of the cell-based climatic signal. In this study, we investigated the variability, intercorrelations and climatic drivers of wood anatomical parameters, resulting from consequent cell developmental processes. Materials and Methods: The study was performed on thin cross-sections from wood cores sampled at ~1.3 m stem height from mature trees of Pinus sylvestris L. growing at five sampling sites along an ecological gradient from cold and wet to hot and dry within continental Southern Siberia. Tracheid number per radial file, their diameters and wall thicknesses were measured along the radial direction from microphotographs for five trees per site. These parameters were then averaged at each site for earlywood and latewood over the last 50 tree rings to build site chronologies. Their correlations among themselves and with 21-day moving climatic series were calculated. Results: Our findings showed that wood formation was not simply the result of environmentally driven independent subprocesses of cell division, enlargement and wall deposition. These processes appear to be interconnected within each zone of the ring, as well as between earlywood and latewood. However, earlywood parameters tend to have more distinctive climatic responses and lower intercorrelations. On the other hand, there are clear indications that the mechanisms of cell division and enlargement share similar climatic drivers and are more sensitive to water limitation than the process of wall deposition. Conclusions: Indications were provided that (i) earlywood formation left a legacy on latewood formation, (ii) cell division and enlargement shared more similar drivers between each other than with wall deposition, and (iii) the mechanism of cell division and enlargement along the gradient switch from water to heat limitations at different thresholds than wall deposition.