Document: MAT-3-37-10

Importance of plant form and microsite to the avoidance of low-temperature photoinhibition in different life stages of conifers in the alpine treeline.

GERMINO, M.J.* 1,2 and W.K.SMITH 1,2

University of Wyoming, Laramie WY 82071-7325 USA 1
Wake Forest University, Winston-Salem NC 27109-7325 USA 2

Abstract:
Relationships between plant form, microsite frost and high sunlight exposure, and photosynthesis were evaluated in current-year germinants, seedlings (ca. 5th year), and adult trees of Englemann spruce (Picea englemannii) and subalpine fir (Abies lasiocarpa) in the Snowy Range of Wyoming, USA. The ratio of sunlit to total leaf area (STAR) was highest in germinants (0.25 for P. englemannii, 0.33 for A. lasiocarpa), about 40% lower in seedlings than germinants, and > 75% lower in adults than germinants for both species (ANOVA, P < 0.05). These data indicated much greater structural optimization of sunlight and temperature for older plants. The occurrence of individuals in microsites with high sky exposure, where frost and sunlight exposure is greatest, was considerably lower for seedlings than for adults or germinants. Seasonal depressions in the ratio of maximal to variable fluoresence (Fv/Fm), as a result of low-temperatures and high sunlight exposure, were greatest in cotyledons of germinants (from ca. 0.81 to 0.19 for P. englemannii and 0.07 for A. lasiocarpa), at least 35% lower in primary needles of seedlings, and at least 60% lower in adult needles (ANOVA, P < 0.01). Smaller depressions in Fv/Fm for older plants indicated less low-temperature photoinhibition (LTP) than in the germinants. The absence of avoidance strategies for LTP in germinants may contribute to their high mortality. In contrast, reduced STAR in adults, and reduced STAR and microsite selection in seedlings may be important for avoiding LTP.

Keywords: Alpine-treeline ecotone, low-temperature photoinhibition, life history of conifers

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This abstract is being presented at: 4:00 PM in session:
Oral Session #10: Light Relations in Plants.