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Gas exchange and photosynthetic acclimation over subambient to elevated CO2 in a C3-C4 grassland

Anderson, LJ, H Maherali, HB Johnson, HW Polley, and RB Jackson
Global Change Biology
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Atmospheric CO2 (Ca) has risen dramatically since pre-glacial times and is projected to double in the next century. As part of a four-year study, we examined leaf gas exchange and photosynthetic acclimation in C3 and C4 plants using unique chambers that maintained a continuous Ca gradient from 200 to 550 ╬╝mol mol-1 in a natural grassland. Our goals were to characterize linear, non-linear, and threshold responses to increasing Ca from past to future Ca levels. Photosynthesis (A), stomatal conductance (gs), leaf water-use efficiency (A/gs) and leaf N content were measured in three common species: Bothriochloa ischaemum, a C4 perennial grass, Bromus japonicus, a C3 annual grass, and Solanum dimidiatum, a C3 perennial forb. Assimilation responses to internal CO2 concentrations (A/Ci curves) and photosynthetically active radiation (A/PAR curves) were also assessed, and acclimation parameters estimated from these data. Photosynthesis increased linearly with Ca in all species (P

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