How does the C grass Eragrostis pilosa respond to elevated carbon dioxide and infection with the parasitic angiosperm Striga hermonthica?

Eragrostis pilosa (Linn.) P Beauv., a C grass native to east Africa, was grown at both ambient (350 μmol mol and elevated (700 μmol mol ) CO in either the presence or absence of the obligate, root hemi-parasite Striga hermonthica (Del.) Benth. Biomass of infected grasses was only 50% that of uninfected grasses at both CO concentrations, with stems and reproductive tissues of infected plants being most severely affected. By contrast, CO concentration had no effect on growth of E. pilosa, although rates of photosynthesis were enhanced by 30-40% at elevated CO . Infection with S. hermonthica did not affect either rates of photosynthesis or leaf areas of E. pilosa, but did bring about an increase in root∶shoot ratio, leaf nitrogen and phosphorus concentration and a decline in leaf starch concentration at both ambient and elevated CO . Striga hermonthica had higher rates of photosynthesis and shoot concentrations of soluble sugars at elevated CO , but there was no difference in biomass relative to ambient grown plants. Both infection and growth at elevated CO resulted in an increase in the Δ C value of leaf tissue of E. pilosa, with the CO effect being greater. The proportion of host-derived carbon in parasite tissue, as determined from δ C values, was 27% and 39% in ambient and elevated CO grown plants, respectively. In conclusion, infection with S. hermonthica limited growth of E. pilosa, and this limitation was not removed or alleviated by growing the association at elevated CO .