Transpiration, tracheids and tree rings : linking stem water flow and wood formation in high-elevation conifers

• Main Author: Peters, Richard Louis
• Other Authors: Kahmen, Ansgar, Fonti, Patrick, Hoch, Günter
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Arctic
• Online Access: http://edoc.unibas.ch/diss/DissB_12926; https://edoc.unibas.ch/67835/; https://edoc.unibas.ch/67835/1/PhD_Thesis-Richard_Louis_Peters_Unibas.pdf; https://doi.org/10.5451/unibas-007085812

Conifers show a biogeographical distribution across a wide range of contrasting environmental conditions, stretching from the Arctic Circle to the equator and Southern Hemisphere. In mountainous ecosystems, conifers can dominate at high elevations with low temperatures severely limiting tree growth and survival. Conifers growing at sites with temperature limiting conditions are highly sensitive to ongoing climatic change, where warmer and drier conditions will impact their growth. Understanding how high-elevation conifers will respond to these changes in climate is critical, as they play a role in regulating terrestrial carbon storage (facilitated by the formation of woody tissue) and water balance (by releasing water to the atmosphere via transpiration). The environmental regulation of wood formation (i.e., tracheid development in conifers), which dictates annual ring-width patterns, is commonly associated with the tree’s photosynthetic activity, while other growth-limiting factors might also be relevant. For example, tree growth requires turgidity in the cambium to exert the pressure necessary for cell expansion, assimilates to lengthen and thicken cell walls, warmth to allow the metabolic reactions to take place, and time for these processes to be completed. Yet, an in-depth study on how important tree hydraulics (i.e., transpiration dynamics) are in regulating “turgor-driven” growth in high elevation forests is lacking. As part of the LOTFOR project, the general objective of this work is to develop a better mechanistic understanding on how tree hydraulics and environmental factors interact in regulating wood formation and shaping tree rings in high-elevation conifer trees. More specifically, the coupling between stem hydrological cycles and structural carbon dynamics is investigated in the context of increasing temperature and water scarcity. This thesis combines multi-annual records of both intra-annual wood formation data and high-resolution hydraulic measurements within a mechanistic growth model to ...