Sipe, Timothy , Kuzma, Nicholas .
Photosynthesis by hay-scented fern (Dennstaedtia punctilobula L.) and its potential impact on nearground enriched carbon dioxide concentrations in a temperate deciduous forest.
SOIL respiration generates a zone of naturally-enriched CO2 (NEC) near the ground that may enhance photosynthesis. Numerous factors regulate NEC concentrations, including the herbaceous stratum. Herbs reduce bulk air movement, allowing NEC concentrations to rise. They also photosynthesize and may deplete the CO2. The balance between these effects is highly dynamic and unexplored. We measured herbaceous stratum structure, gas-exchange, irradiance patterns, and soil respiration during midsummer in a central MA deciduous forest to determine the potential impact of carbon assimilation by herbs on NEC concentrations. The herbaceous stratum in our site is dominated by hay-scented fern (Dennstaedtia punctilobula L.), a common understory species in this region. Photosynthetic light response curves were measured at all combinations of three air temperatures (20,25,30 oC) and six ambient CO2 levels (375-500 ppm). Fern densities and leaf area indices were measured by clipping 1-m radius circular plots. Soil respiration was measured on several occasions in clipped and control plots. Response curves were combined with fern leaf area indices and measurements of vertical gradients of photosynthetic photon flux to estimate total assimilation by the fern stratum. Overall, hay-scented fern showed remarkable acclimation to the shade, with low dark respiration rates, very low light compensation points, and modest maximum assimilation rates. Fern leaf area indices ranged from 1.8 to 2.4 in locations with continuous fern cover. The fern stratum assimilates on average approximately half the CO2 flux from soil respiration on clear days, with maximum values that can exceed the highest soil fluxes. Consequently, hay-scented fern may compete for the CO2 and prevent other species from realizing the NEC benefit.
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1 - Franklin & Marshall College, Department of Biology, P.O. Box 3003, Lancaster, Pennsylvania, 17604-3003, USA
Presentation Type: Poster:Posters for Sections
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM