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766794 
Journal Article 
Comparative responses of model C3 and C4 plants to drought in low and elevated CO2 
Ward, JK; Tissue, DT; Thomas, RB; And, ; Strain, BR 
1999 
Yes 
Global Change Biology
ISSN: 1354-1013
EISSN: 1365-2486 
5 
8 
857-867 
WOS:000085051700003 
Interactive effects of CO2 and water availability have been
predicted to alter the competitive relationships between C3 and C4 species over geological and
contemporary time scales. We tested the effects of drought and CO2 partial pressures (pCO(2))
ranging from values of the Pleistocene to those predicted for the future on the physiology and
growth of model C3 and C4 species. We grew co-occurring Abutilon theophrasti (C3) and Amaranthus
retroflexus (C4) in monoculture at 18 (Pleistocene), 27 (preindustrial), 35 (current), and 70
(future) Pa CO2 under conditions of high light and nutrient availability. After 27 days of
growth, water was withheld from randomly chosen plants of each species until visible wilting
occurred. Under well-watered conditions, low pCO(2) that occurred during the Pleistocene was
highly limiting to C3 photosynthesis and growth, and C3 plants showed increased photosynthesis
and growth with increasing pCO(2) between the Pleistocene and future CO2 values. Well-watered C4
plants exhibited increased photosynthesis in response to increasing pCO(2), but total mass and
leaf area were unaffected by pCO(2). In response to drought, C3 plants dropped a large amount of
leaf area and maintained relatively high leaf water potential in remaining leaves, whereas C4
plants retained greater leaf area, but at a lower leaf water potential. Furthermore, drought-
treated C3 plants grown at 18 Pa CO2 retained relatively greater leaf area than C3 plants grown
at higher pCO(2) and exhibited a delay in the reduction of stomatal conductance that may have
occurred in response to severe carbon limitations. The C4 plants grown at 70 Pa CO2 showed lower
relative reductions in net photosynthesis by the end of the drought compared to plants at lower
pCO(2), indicating that CO2 enrichment may alleviate drought effects in C4 plants. At the
Pleistocene pCO(2), C3 and C4 plants showed similar relative recovery from drought for leaf area
and biomass production, whereas C4 plants showed higher recovery than C3 plants at current and
elevated pCO(2). Based on these model systems, we conclude that C3 species may not have been at a
disadvantage relative to C4 species in response to low CO2 and severe drought during the
Pleistocene. Furthermore, C4 species may have an advantage over C3 species in response to
increasing atmospheric CO2 and more frequent and severe droughts. 
Abutilon theophrasti; Amaranthus retroflexus; C3 species; C4 species; carbon dioxide; climate change; drought; Pleistocene