Carbon partitioning patterns of mycorrhizal versus non-mycorrhizal plants: real-time dynamic measurements using 11 CO2.

Gas exchange and carbon allocation patterns were studied in two populations of Panicum coloratum, an Africa C-4 grass. The plants were grown in split-root pots, containing partially sterilized soil, with one side either inoculated (I) or not inoculated (NI) with a vesicular arbuscular (VA) mycorrhizal Fungus, Gigaspora margarita. Net carbon exchange rates (CER) and stomatal conductances were measured with conventional gas exchange apparatus, and carbon assimilation, translocation, and allocation were measured using photosynthetically-fixed 11 CO2 . Mycorrhizal infection on one half of the split-root system caused a 20%, increase in CER. The effect on CER was less in tillers on the opposite side of the plants from the infected half of the roots. The rate at which photosynthates were stored in the leaves was 45% higher. Sink activity (concentration of labelled photosynthates in stem phloem tissue) more than doubled in 1 versus NI plants. CER and stomatal conductances, along with most of the carbon allocation patterns, were nearly identical between the NI (control) high grazing and low grazing ecotypes. However, VA mycorrhizal fungi caused a greater storage of photosynthates in the low grazing ecotype.