PARENT SESSION
Oral Session # 24: Photosynthesis and Respiration.
Presiding: A Leakey
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.
Photosynthetic variation in young and old conifers across an alpine-treeline ecotone.
Germino, Matthew*,1, Smith, William2, Craig, Brodersen2, Johnson, Dan2, 1 Idaho State University, Pocatello, ID2 Wake Forest University, Winston-Salem, NC
ABSTRACT- Whether reduced carbon assimilation contributes to exclusion of trees from subalpine and alpine meadows is currently debated, yet there have been few or no reports of photosynthesis in treeline conifers across the gradient from forest to alpine. Moreover, most studies of factors affecting treeline have focused on responses of adult trees to high-elevation climates, even though young seedlings may represent a critical life stage for determining conifer establishment above forest elevation limits. Microclimate, photosynthetic carbon uptake, chlorophyll fluoresence, and plant water potential were measured in newly-germinated seedlings (germinants), 3-10 yr old seedlings, and adult Picea engelmannii from subalpine forest across the treeline ecotone up to the alpine of the Snowy Range of Wyoming, USA. Mean photosynthesis was greater for adult trees, marginally lower for seedlings, and ~50% lower for germinants near the alpine compared to lower elevation sites. Similarly, predawn Fv/Fm (an indicator of photosynthetic light-use efficiency) did not vary in adults along the gradient, but was over 18% lower in germinants in the alpine compared to lower sites. Mean Fv/Fm remained above 0.75 for adults, but became as low as 0.55 for germinants, indicating greater photoinhibition in the colder, brighter alpine compared to more-forested sites, as well as in the younger compared to older individuals. These results indicate that young, establishing seedlings may be more likely than mature trees to experience carbon limitations above the forest elevation limit.
Key words: photosynthesis, seedling, treeline, conifer