Effect of the increase in temperature in the photosynthesis of a high-andean species at two elevations

High-alpine environments have been proposed as particularly vulnerable to global warming. The interaction of variablessuch as water deficit and temperature conditions may restrict gas exchange in high-alpine areas. Due to different abioticconstraints that occur at different elevations in the Andes of central Chile we hypothesize that the temperature increases willpositively affect the photosynthesis of the high-Andean plant Phacelia secunda at high elevation but it will be negativelyaffected by warming at lower elevations. In this study we evaluated the effect of increased environmental temperature onthe gas exchange of P. secunda at two contrasting elevations: 2900 m and 3600 m a.s.l. At each elevation we exposed sixindividuals of P. secunda to a passive warming system with “Open Top Chamber” (OTC) that increased air temperature onca. 3oC. Other six individuals we selected in open areas and maintained as control on each elevation. At both elevations,on each selected individual (i.e. within and outside OTCs) we measured gas exchange and xylem water potential. At bothelevations air temperature was on average 3.5°C higher inside the OTC. In contrast, OTC reduced 28% the soil and xylemwater potential only at 2900 m. The increased temperature inside the OTC reduced 40.7% gas exchange rates at 2900 m,but increased it 24.4% at 3600 m. These differential effects of warming on photosynthetic rates were accompanied bychanges in stomatal conductance. This suggests that the effects of global warming on the photosynthesis of P. secunda attwo contrasting altitudes are related with the concomitant changes on drought at each elevation.