Crop Fertilization in a CO2enriched world: is it good to be C3 David M. Rosenthal CCAFS Science Workshop, Cancun, Dec 1 and 2, 2010
Outline• Plant responses to elevated CO2 and other agents of climate change at SoyFACE• Why is photosynthesis of crop plants in the field stimulated less by CO2 than predicted by theory?• Some approaches to optimize (adapt) photosynthesis to global change
Recent evidence indicates atmospheric [CO2] isincreasing more rapidly than the most aggressive IPCC AR4 projection .
How does elevated CO2 stimulate photosynthesis that is the basis for the projected increases in yield?
[CO2] (µmol mol-1) 750 96% of minute averages within ±10%550 Fumigation350 On 0:00 6.00 12:00 18:00 0.00 Time (h)
Increased photosynthesis in C3 crops grown at elevated CO2 increases yield Long, Ainsworth, Leakey, Nosberger, Ort (2006) Science 312, 1918-21
Meta analysis of C3 crops grown at elevated CO2 in FACE experiments Crop Yield Biomass SLA LAI Plant Height Leaf # Starch Sugar Narea Rubisco Jmax Vcmax ci/ca gs A Asat -40 -20 0 20 40 60 80 100 120 Percent Change in Elevated [CO2] Ainsworth and Long (2005) New Phyt. 165:351=-372
No CO2 stimulation in Cassava Greehouse Experiment Gleadow et al. (2009) Plant Biol 11:79-82
Cassava harvested after only 3.5 months ! Elevated Ambient
Ambient CO2 Elevated CO2 Rosenthal et al. unpublished
Rubisco is down regulated at elevated CO2 in cassava
Cassava leaf Carbon/Nitrogen ratio declines at elevated CO2 Rosenthal et al. unpublished
Growth at elevated [CO2] does not increase leaf or tuber cyanide content at SoyFACE Miller, Gleadow unpublished
“[CO2] Fertilization” of C3 cropphotosynthesis falls short of theory Long, Ainsworth, Leakey, Nosberger, Ort (2006) Science 312, 1918-21
Why is photosynthesis of crop plants in the field stimulated less by CO2 than predicted by theory?
400 Current value320240160 Years below 280 ppm, 395 000 (96%)80 Years below 240 ppm, 280 000 (67%) Years below 200 ppm, 83 500 (20%) 0 400 320 240 160 80 0 Time before present, 103 years Various sources ; Luthi et al (2008) NATURE 453: 379-382
Rising tropospheric ozone 0.5 – 2.5 % per yearOzone – Parts Per Billion of Air 80 60 40 2000 2020 2040 2060 2080 2100 (UN-IPCC 2001)
Relationship between Soybean Yield & Ozone Fishman et al.2010 Atmospheric Environment
Summary• Growth at elevated [CO2] stimulated cassava photosynthesis.• Rubisco was down regulated in cassava at elevated [CO2], consistent lower leaf N (no change in cyanide content).• Fresh and dry tuber biomass significantly increased with [CO2], as did harvest index.• Cassava responded similarly to other C3 plants treated with elevated [CO2].• CO2 stimulation of photosynthesis is less than predicted by theory. - lack of adaptation to rapid increase in [CO2] - inhibition due to increasing levels of tropospheric O3 - increased rates of respiration in CO2-grown plants - temperatures above optimum for photosynthesis.
CassavaFACE collaborators: Becky Slattery (UIUC) Kat Grennan (UIUC) Bec Miller (Monash U) Ros Gleadow (Monash U) Claude Fauquet (ILTAB)SBPase overexpression collaborators Christine Raines (U Exeter) Anna Locke (UIUC) Stephen Long (UIUC) SoyFACE 2010