Minimum Leaf Conductance (gmin) Is Higher in the Treeline of Pinus uncinata Ram. in the Pyrenees: Michaelis Hypothesis Revisited

• Published in: Frontiers in Plant Science
• Main Authors: Bueno, A., Alonso Forn, David, Peguero Pina, José Javier, de Souza, Aline Xavier, Ferrio Díaz, Juan Pedro, Sancho Knapik, Domingo, Gil Pelegrín, Eustaquio
• Format: Book
• Language: Spanish
• Published: 2023
• Subjects: Pinus uncinata; Bosques; Transpiración; Sequía; Tundra
• Online Access: http://hdl.handle.net/10532/6388

The search for a universal explanation of the altitudinal limit determined by the alpine treeline has given rise to different hypotheses. In this study, we revisited Michaelis’ hypothesis which proposed that an inadequate “ripening” of the cuticle caused a greater transpiration rate during winter in the treeline. However, few studies with different explanations have investigated the role of passive mechanisms of needles for protecting against water loss during winter in conifers at the treeline. To shed light on this, the cuticular transpiration barrier was studied in the transition from subalpine Pinus uncinata forests to alpine tundra at the upper limit of the species in the Pyrenees. This upper limit of P. uncinata was selected here as an example of the ecotones formed by conifers in the temperate mountains of the northern hemisphere. Our study showed that minimum leaf conductance in needles from upper limit specimens was higher than those measured in specimens living in the lower levels of the sub-alpine forest and also displayed lower cuticle thickness values, which should reinforce the seminal hypothesis by Michaelis. Our study showed clear evidence that supports the inadequate development of needle cuticles as one of the factors that lead to increased transpirational water losses during winter and, consequently, a higher risk of suffering frost drought. The work of DA-F was supported by an FPI-INIA contract BES2017-081208. AS was a recipient of a doctoral fellowship from the Brazilian National Council for Scientific and Technological Development (CNPq). DA-F, JF, JP-P, DS-K, and EG-P acknowledge the financial contribution by Reference Group H09_20R (Gobierno de Aragón, Spain) cuticular waxes minimum leaf conductance Michaelis’ hypothesis treeline Pinus uncinata In press