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Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes¹

⁰ Department of Plant Biology and The Photosynthesis Center, Arizona State University, Tempe, Arizona 85287-1601 USA

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 (P_n) and dark respiration (R_d), by growing plants for 90 d under three contrasting temperature regimes: 7°C day/7°C night, 12°C day/7°C night, and 20°C day/7°C night (18 h/6 h). These daytime temperatures represent suboptimal (7°C), near-optimal (12°C), and supraoptimal (20°C) temperatures for P_n 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 20°C had greater RGR (relative growth rate) and produced 2.2–3.3 times as much total biomass as plants grown at daytime temperatures of 12° or 7°C. Plants grown at 20°C 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 12° or 7°C. Greater RGR and biomass production at 20°C appeared primarily due to greater biomass allocation to leaf production in these plants. Rates of P_n (leaf-area basis), when measured at their respective daytime growth temperatures, were highest in plants grown at 12°C, and rates of plants grown at 20°C were only 58 (C. quitensis) or 64% (D. antarctica) of the rates in plants grown at 12°C. Thus, lower P_n per leaf area in plants grown at 20°C was more than offset by much greater leaf-area production. Rates of whole-canopy P_n (per plant), when measured at their respective daytime growth temperatures, were highest in plants grown at 20°C, and appeared well correlated with differences in RGR and total biomass among treatments. Colobanthus quitensis exhibited only a slight ability for relative acclimation of P_n (leaf-area basis) as the optimal temperature for P_n increased from 8.4° to 10.3° to 11.5°C as daytime growth temperatures increased from 7° to 12° to 20°C. There was no evidence for relative acclimation of P_n in D. antarctica, as plants grown at all three temperature regimes had a similar optimal temperature (10°C) for P_n. There was no evidence for absolute acclimation of P_n in either species, as rates of P_n in plants grown at a daytime temperature of 12°C were higher than those of plants grown at daytime temperatures of 7° or 20°C, 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 P_n, both species exhibited full acclimation of R_d, and rates of R_d 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 P_n per leaf area) and (2) their ability to acclimate R_d, such that respiratory losses per leaf area do not increase under higher temperature regimes.

Key Words: Antarctica • Colobanthus quitensis • Deschampsia antarctica • growth • photosynthesis • respiration • temperature • warming

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