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

Abstract

High-alpine environments have been proposed as particularly vulnerable to global warming. The interaction of variables
such as water deficit and temperature conditions may restrict gas exchange in high-alpine areas. Due to different abiotic
constraints that occur at different elevations in the Andes of central Chile we hypothesize that the temperature increases will
positively affect the photosynthesis of the high-Andean plant Phacelia secunda at high elevation but it will be negatively
affected by warming at lower elevations. In this study we evaluated the effect of increased environmental temperature on
the gas exchange of P. secunda at two contrasting elevations: 2900 m and 3600 m a.s.l. At each elevation we exposed six
individuals of P. secunda to a passive warming system with “Open Top Chamber” (OTC) that increased air temperature on
ca. 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 both
elevations air temperature was on average 3.5°C higher inside the OTC. In contrast, OTC reduced 28% the soil and xylem
water 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 by
changes in stomatal conductance. This suggests that the effects of global warming on the photosynthesis of P. secunda at
two contrasting altitudes are related with the concomitant changes on drought at each elevation.