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The Deleterious Effects of a Major Root Parasite of Rice Are Greatly Reduced by Atmospheric CO2 Enrichment
Watling, J.R. and Press, M.C.  2000.  Infection with the parasitic angiosperm Striga hermonthica influences the response of the C3 cereal Oryza sativa to elevated CO2. Global Change Biology 6: 919-930.

According to the authors, the root hemiparasitic angiosperm Striga hermonthica (Del) Benth "infects mainly tropical grasses with the C4 photosynthetic pathway, including a number of important crop species such as maize, sorghum, sugar cane and millets."  However, it also infects rice, a C3 crop, particularly throughout much of Africa, where it is currently one of the region's most economically important parasitic weeds.

What was done
Upland rice (Oryza sativa L. cv. 'Namroo' from Keyna) was grown in pots in controlled environment chambers maintained at 350 and 700 ppm CO2 in either the presence or absence of the root parasite for a period of eighty days after sowing, during which a number of biochemical and physiological measurements were made on the plants, and after which the various parts of the plants were harvested and weighed.

What was learned
The doubling of the air's CO2 concentration in this experiment reduced the negative impact of the root parasite on photosynthesis and growth of rice.  In ambient air, the presence of the parasite reduced the biomass of rice to only 35% of what it was in the absence of the parasite; whereas in air enriched with CO2, the biomass of infected plants was reduced to but 73% of what it was in the absence of the parasite.

What it means
In the words of the authors, "these results demonstrate that elevated CO2 concentrations can alleviate the impact of infection with Striga on the growth of C3 hosts such as rice and also that infection can delay the onset of photosynthetic down-regulation in rice grown at elevated CO2."  Hence, as the air's CO2 concentration continues to rise, we can expect to see African agriculturalists reap ever greater harvests of rice, as the deleterious effects of this important crop parasite grow ever smaller, compliments of humanity's ever increasing CO2 emissions.