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Abstract Detail

Physiology & Ecophysiology

Mocko, Kerri [1], Chong, Caroline [2], Jones, Cynthia [3].

Traits underlying seasonal photosynthetic performance in co-occurring congeners of a highly diverse South African clade.

Seasonal variation in functional traits among co-occurring congeners and the extent to which these traits predict changes in physiology during a single growing season are relatively unexplored. The Leaf Economics Spectrum establishes that high LMA leaves have lower rates of photosynthesis but exhibit greater leaf longevity (LL) due to increased time needed to amortize initial carbon investments – a trend that is strong for evergreen species but weak for deciduous species which shed leaves during unfavorable seasonal conditions. In Mediterranean ecosystems, where growing conditions transition from cool and wet to hot and dry over the course of the season, it’s assumed yet rarely tested that optimal photosynthesis for deciduous species coincides with water availability, even though temperatures are cool. We were interested in knowing whether optimal photosynthetic performance in cool, wet winter versus warm, dry spring conditions links to differences in functional traits or trait combinations, and used 23 deciduous, co-occurring species of Pelargonium, a diverse genus across xeric and mesic sites within the winter rainfall region of South Africa, to track photosynthesis, functional leaf traits and environmental conditions over the course of one growing season. Specifically, we asked: Do relationships among LL, LMA and photosynthesis change seasonally? What functional leaf traits, climate and micro-environmental variables influence seasonal shifts in photosynthesis? We found that Pelargonium species represent 52% and 27% of the worldwide ranges of LL and LMA in deciduous species. Moreover, winter to spring photosynthetic rates declined as much as 67% in some species but increased as much as 39% in other species. Climate variables had no influence on shifts in photosynthetic rates, but micro-environmental traits reflecting greater access to resources (canopy openness and water) together with greater LL and LMA resulted in more positive photosynthetic responses over the season. Photosynthesis expressed on a mass basis was associated with functional traits in winter whereas area-based photosynthesis was strongly associated with functional traits in spring, suggesting that relationships between functional traits and photosynthesis shift from an emphasis on structural carbon gain during peak winter conditions to an emphasis on how traits influence flux dominated processes in the spring.

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1 - University Of Connecticut, Ecology And Evolutionary Biology, U-3043, 75 N. Eagleville Rd, Storrs, CT, 06269, United States
2 - Australian National Botanic Gardens, National Seed Bank, Clunies Ross Street, Acton, ACT, 2601, Australia
3 - University Of Connecticut, Department Of Ecology & Evolutionary Biology, Unit 3043, 75 N. Eagleville Rd., Storrs, CT, 06269, United States

leaf longevity
functional traits
Leaf Economics Spectrum
South Africa

Presentation Type: Oral Paper
Session: 39, Ecophysiology
Location: 114/Mayo Civic Center
Date: Wednesday, July 25th, 2018
Time: 8:15 AM
Number: 39002
Abstract ID:795
Candidate for Awards:None

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