Article,
Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes
Am. J. Bot., 87 (5): 700--710 (May 1, 2000)
Abstract
Air temperatures have risen over the past 50 yr along the Antarctic Peninsula, and it is unclear what impact this is having on Antarctic plants. We examined the growth response of the Antarctic vascular plants Colobanthus quitensis (Caryophyllaceae) and Deschampsia antarctica (Poaceae) to temperature and also assessed their ability for thermal acclimation, in terms of whole-canopy net photosynthesis (Pn) and dark respiration (Rd), by growing plants for 90 d under three contrasting temperature regimes: 7degreesC day/7degreesC night, 12degreesC day/7degreesC night, and 20degreesC day/7degreesC night (18 h/6 h). These daytime temperatures represent suboptimal (7degreesC), near-optimal (12degreesC), and supraoptimal (20degreesC) temperatures for Pn based on field measurements at the collection site near Palmer Station along the west coast of the Antarctic Peninsula. Plants of both species grown at a daytime temperature of 20degreesC had greater RGR (relative growth rate) and produced 2.2-3.3 times as much total biomass as plants grown at daytime temperatures of 12degrees or 7degreesC. Plants grown at 20degreesC also produced 2.0-4.1 times as many leaves, 3.4-5.5 times as much total leaf area, and had 1.5-1.6 times the LAR (leaf area ratio; leaf area:total biomass) and 1.1-1.4 times the LMR (leaf mass ratio; leaf mass:total biomass) of plants grown at 12degrees or 7degreesC. Greater RGR and biomass production at 20degreesC appeared primarily due to greater biomass allocation to leaf production in these plants. Rates of Pn (leaf-area basis), when measured at their respective daytime growth temperatures, were highest in plants grown at 12degreesC, and rates of plants grown at 20degreesC were only 58 (C. quitensis) or 64\% (D. antarctica) of the rates in plants grown at 12degreesC. Thus, lower Pn per leaf area in plants grown at 20degreesC was more than offset by much greater leaf-area production. Rates of whole-canopy Pn (per plant), when measured at their respective daytime growth temperatures, were highest in plants grown at 20degreesC, and appeared well correlated with differences in RGR and total biomass among treatments. Colobanthus quitensis exhibited only a slight ability for relative acclimation of Pn (leaf-area basis) as the optimal temperature for Pn increased from 8.4degrees to 10.3degrees to 11.5degreesC as daytime growth temperatures increased from 7degrees to 12degrees to 20degreesC. There was no evidence for relative acclimation of Pn in D. antarctica, as plants grown at all three temperature regimes had a similar optimal temperature (10degreesC) for Pn. There was no evidence for absolute acclimation of Pn in either species, as rates of Pn in plants grown at a daytime temperature of 12degreesC were higher than those of plants grown at daytime temperatures of 7degrees or 20degreesC, when measured at their respective growth temperatures. The poor ability for photosynthetic acclimation in these species may be associated with the relatively stable maritime temperature regime during the growing season along the Peninsula. In contrast to Pn, both species exhibited full acclimation of Rd, and rates of Rd on a leaf-area basis were similar among treatments when measured at their respective daytime growth temperature. Our results suggest that in the absence of interspecific competition, continued warming along the Peninsula will lead to improved vegetative growth of these species due to (1) greater biomass allocation to leaf-area production (as opposed to improved rates of Pn per leaf area) and (2) their ability to acclimate Rd, such that respiratory losses per leaf area do not increase under higher temperature regimes.
