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Parasites (Plants: Non-Weeds) -- Summary
Parasitic plants obtain energy, water and nutrients from their host plants and cause widespread reductions in harvestable yields around the globe. Hence, it is important to understand how rising atmospheric CO2 levels may impact the growth of parasitic plants and the relationships that exist between them and their host plants. In this summary, we review the findings of two papers that have investigated this important subject on non-weed parasitic plants.

Matthies and Egli (1999) grew Rhinanthus alectorolophus (a widely distributed parasitic plant of Central Europe) for a period of two months on the grass Lolium perenne and the legume Medicago sativa in pots placed within open-top chambers maintained at atmospheric CO2 concentrations of 375 and 590 ppm, half of which pots were fertilized to produce an optimal soil nutrient regime and half of which were unfertilized. At low nutrient supply, they found that atmospheric CO2 enrichment decreased mean parasite biomass by an average of 16%, while at high nutrient supply it increased parasite biomass by an average of 123%. Nevertheless, the extra 215 ppm of CO2 increased host plant biomass in both situations: by 29% under high soil nutrition and by 18% under low soil nutrition.

Hwangbo et al. (2003) grew Kentucky Bluegrass (Poa pratensis L.) with and without infection by the C3 chlorophyllous parasitic angiosperm Rhinanthus minor L. (a facultative hemiparasite found in natural and semi-natural grasslands throughout Europe) for eight weeks in open-top chambers maintained at ambient and elevated (650 ppm) CO2 concentrations. At the end of the study, the parasite's biomass (when growing on its host) was 47% greater in the CO2-enriched chambers, while its host exhibited only a 10% CO2-induced increase in biomass in the parasite's absence but a nearly doubled 19% increase when infected by it.

These two observations suggest that the rising CO2 content of the air can have wide and variable effects on parasitic plants, ranging from negative to positive growth responses, depending upon soil nutrition and host plant specificity.

References
Hwangbo, J.-K., Seel, W.E. and Woodin, S.J. 2003. Short-term exposure to elevated atmospheric CO2 benefits the growth of a facultative annual root hemiparasite, Rhinanthus minor (L.), more than that of its host, Poa pratensis (L.). Journal of Experimental Botany 54: 1951-1955.

Matthies, D. and Egli, P. 1999. Response of a root hemiparasite to elevated CO2 depends on host type and soil nutrients. Oecologia 120: 156-161.

Last updated 20 January 2012