Impact of Intra Annual Wood Density Fluctuation on Tree Hydraulic Function: Insights from a Continuous Monitoring Approach

Abstract

Climate change significantly impacts global forests, leading to tree decline and dieback. To cope with climate change, trees develop several functional traits, such as intra-annual density fluctuations (IADFs) in tree-rings. The formation of these traits facilitates trees to optimize resource allocation, allowing them to withstand periods of stress and eventually recover when conditions become favourable again. This study focuses on a Pinus pinaster forest in a warm, drought-prone Mediterranean area, comparing two growing seasons with different weather patterns. The innovative continuous monitoring approach used in this study combines high-resolution monitoring of sap flow, analysis of xylogenesis, and quantitative wood anatomy. Our results revealed the high plasticity of Pinus pinaster in water use and wood formation, shedding light on the link between IADFs and tree conductance. Indeed, the capacity to form large cells in autumn (such as IADFs) improves the total xylem hydraulic conductivity of this species. For the first time, a continuous sap flow measurement system captured the dynamics of bimodal sap flow during the 2022 growing season, in conjunction with the bimodal growth pattern observed through xylogenesis monitoring. These results highlight the intricate interplay between environmental conditions, water use, wood formation, and tree physiology, providing valuable insights into the acclimation mechanisms employed by Pinus pinaster to cope with weather fluctuations.