Carbon dioxide uptake by plants CO 2 is –About 0.038% in atmosphere –What about inside leaves? –But remember CO 2 uptake is in exchange for H 2 O loss. What about differences in water across the leaf surface?
Crassulacean Acid Metabolism (CAM) Third photosynthetic strategy (CAM): first found in plants in the family Crassulaceae and was therefore called Crassulacean Acid Metabolism. Plants in other families also use this mode of carbon fixation (lots of succulents and epiphytes).
Question Why did C 4 evolve in grasses? – Dogma: A response to rising temperatures and lowering CO 2 – To test this, for 1230 grass spp, 1.1 million specimens GBIF: georeference points Climate: CRU (Climate Resource Unit) DNA sequences: With PHLAWD, built a phylogeny – Chloroplast regions: atpB (59 taxa), matK (266 taxa), ndhF (437 taxa), rbcL (251 taxa), rpl16 (176 taxa), and trnL-trnF (810 taxa) – Nuclear regions: phyB (93 taxa) and the internal transcribed spacer (ITS; 753 taxa)
Question Why did C 4 evolve in grasses? – Forget dogma: Grasses were historically warm adapted C 4 evolution was in response to a drop in precipitation So, the shift was probably from tropical rainforests understories to open tropical savannahs and grasslands!!! The question then becomes, when, why, and how did C 3 grasses evolve cold tolerance?