PARENT SESSION
Oral Session #10: Elevated CO2.
Presiding: D. Hileman
Monday, August 5. 8:00 AM to 11:30 AM. Grand Ballroom East, Radisson.
Photosynthetic responses of a Mojave Desert drought-deciduous shrub under carbon dioxide enrichment.
Hamerlynck, Erik*,1, Huxman, Travis2, Charlet, Therese3, Smith, Stanley3, 1 Department of Biological Sciences, Newark, NJ2 Department of Ecology and Evolutionary Biology, Tucson, AZ3 Department of Biological Sciences, Las Vegas, NV
ABSTRACT- The productivity of cool-season drought-deciduous shrubs in the warm deserts of southwestern North America is constrained by low leaf areas when seasonal photosynthetic capacity is high. Elevated CO2 could alleviate this limitation by decreasing allocation to photosynthetic demand, but this would depend on the specific responses of short-shoots that only provide early-season leaf area display, and long-shoots which determine annual growth increment in these plants. We measured plant water relations, photosynthetic gas exchange, and growth in short- and long-shoots of the drought-deciduous shrub, Lycium andersonii, under Free Air CO2 Enrichment (FACE) in the field in an intact Mojave Desert ecosystem to test for the differential effects of CO2 enrichment on short-shoots and actively growing long-shoots during canopy development. Net photosynthesis (Anet) was similar in elevated compared to ambient CO2, but stomatal conductance (gs) reduced by 27% in both shoot types. Lycium andersonii growing in elevated CO2 had larger leaves on short-shoots, and more leaves per shoot length on long-shoots. Enhanced leaf growth did not counter lower gs, and midday plant water potential was similar between treatments. In both short- and long-shoots, down-regulation of photosynthetic electron transport rate (Jmax) occurred under elevated CO2. However, the balance between mesophyll efficiency (estimated by the maximum carboxylation rate of rubisco, Vcmax), and electron transport capacity (Vcmax/Jmax) remained constant in short-shoots, but increased in elevated CO2 grown long-shoots. These results suggest that elevated CO2 lowered investment to photosynthetic electron transport capacity and whole-plant water use, even when leaf growth was stimulated. Such dynamics are likely to enhance the ability of this drought-deciduous species to better cope with the highly variable inter- and intra-annual climate regimes characteristic of North American deserts.
KEY WORDS: Elevated CO2, FACE, Mojave Desert