Augmentation de la capacité photosynthétique avec l’altitude: mesures d’échanges gazeux à pressions partielles de CO2 ambiante et constante

Abstract

Abstract• Because all microclimatic variables change with elevation, it is difficult to compare plant performance and especially photosynthetic capacity at different elevations. Indeed, most previous studies investigated photosynthetic capacity of low-and high-elevation plants using constant temperature, humidity and light but varying CO 2 partial pressures (P CO2 ).• Using gas exchange measurements, we compared here maximum assimilation rates (A max ) at ambient and constant-low-elevation P CO2 for two temperate tree species along an altitudinal gradient (100 to 1600 m) in the Pyrénées mountains.• Significant differences in A max were observed between the CO 2 partial pressure treatments for elevations above 600 m, the between-treatment differences increasing with elevation up to 4 µmol m −2 s −1 . We found an increase in A max with increasing elevation at constant-low-elevation P CO2 but not at ambient P CO2 for both species. Given a 10% change in P CO2 , a proportionally higher shift in maximum assimilation rate was found for both species.• Our results showed that high elevation populations had higher photosynthetic capacity and therefore demonstrated that trees coped with extreme environmental conditions by a combination of adaptation (genetic evolution) and of acclimation. Our study also highlighted the importance of using constant CO 2 partial pressure to assess plant adaptation at different elevations. Mots-clés :adaptation / acclimatation / gradient altitudinal / pression partielle / capacité photosynthétique Résumé -Augmentation de la capacité photosynthétique avec l'altitude : mesures d'échanges gazeux à pressions partielles de CO 2 ambiante et constante.• Les conditions microclimatiques étant très variables avec l'altitude, il est difficile de comparer les performances d'une espèce végétale à différentes altitudes, particulièrement la capacité photosynthé-tique. En effet, la plupart des études antérieures ont estimé le taux maximal d'assimilation à basses et hautes altitudes en maintenant la température, l'humidité de l'air et la lumière constantes mais en laissant varier la pression partielle de CO 2 (P CO2 ).• Afin de comparer le taux maximum d'assimilation (A max ) à pressions partielles de CO 2 constantes de basse altitude et variables, nous avons effectué des mesures d'échanges gazeux sur deux espèces d'arbres tempérés le long d'un gradient altitudinal de 1600 m de dénivelé dans les Pyrénées françaises.• La différence entre les deux traitements de P CO2 est significative au-dessus de 600 m d'altitude et atteint un maximum de 4 µmol m −2 s −1 . Pour les deux espèces, nous avons mis en évidence une augmentation de A max avec l'altitude à P CO2 constantes mais pas à P CO2 ambiantes. Pour une modification de P CO2 de 10 %, le changement du taux maximum d'assimilation est proportionnellement supérieur chez les deux espèces.• Nos résultats montrent que les populations de hautes altitudes possèdent une capacité photosynthétique supérieure, démontrant que les arbres font face aux conditions environnement...

Adaptive variation in physiological traits of beech provenances in Central Europe

“…Körner (2007) suggested that trees carry out a relatively high level of photosynthesis to compensate for extreme environmental conditions and short growing season at high altitudes. This hypothesis was confirmed also by Bresson et al (2009), who noted that the CO2 assimilation rate increased significantly with increasing altitude, approximately 2.8 µmol CO2 m -2 s -1 per 1000 m for beech. The small increase in maximum assimilation rate at high altitude may be attributed to a slight increase in stomatal conductance, implying an increase in CO2 diffusion into the leaf.…”

“…Several studies reported changes in stomatal traits with increasing altitude in various plant species including beech; PCI, guard cell length or stomatal density were observed to increase with altitude (Hovenden & Brodribb 2000, Kouwenberg et al 2007, Bresson et al 2009, Paridari et al 2013, presumably compensating for a decrease of CO2 partial pressure, which limits photosynthetic potential across altitudinal gradients, shorter growing seasons and/or increasing UV radiation (Woodward & Bazzaz 1988, Kouwenberg et al 2007. The increase in stomatal density and index with altitude could be also result of opening up of the higher altitude landscape, which increases the amount of intercepted radiation (Hovenden & Brodribb 2000).…”

“…and morphological traits of leaves (stomatal density, leaf mass per area, thickness of leaf lamina, etc.) along an altitudinal gradient, as well as the morphologically and physiologically distinctiveness of high-altitude populations in comparison to related populations at lower altitudes (Ackerly et al 2000, Still et al 2005, Bresson et al 2009, Holland & Richardson 2009, Paridari et al 2013, Chen et al 2016.…”

Effect of altitude and age of stands on physiological response of three dominant plants in forests of the Western Carpathians

“…Also, it was not possible to prove the effect of altitudinal gradients between the areas G1-G6 (750-1110 m a.s.l.) on P n , while, for example, Bresson et al (2009) …”

Driving forces of mid-Holocene vegetation shifts on the upper Tibetan Plateau, with emphasis on changes in atmospheric CO2 concentrations

“…Earlier plant physiological modelling studies concluded that the pressure reduction is largely mitigated by physical mechanisms such as faster molecular gas diffusion and parallel lowered O 2 , which competes with CO 2 at the Rubisco reaction site (Terashima et al, 1995). However, experimental investigations have shown that the photosynthetic capacity of upland population increases to the same extent as the partial CO 2 pressure is artificially raised (Körner and Diemer, 1987;Bresson et al, 2009). Transferred to the central Tibetan Plateau (w4500 m), this finding implies that alpine vegetation suffers from 40% lower carbon availability compared to sealevel.…”