Growth and nutrition of a mycorrhiza defective tomato mutant and its mycorrhizal wild-type progenitor differ under elevated and ambient atmospheric CO₂ concentrations

Tim Cavagnaro, Shannon Sokolow, Louise Jackson

Both the intra- and extra-radical phases of AM growth are altered by elevated CO₂, probably indirectly as a result elevated CO₂ effects on plants.  While some studies show an increase in intraradical colonization of roots (percent colonization) by AMF with elevated CO₂, other do not. In those studies where effects were seen they generally disappeared when the confounding effect of increased root biomass was factored out. At a finer scale of resolution, elevated CO₂ can lead to an increase in the abundance of arbuscules in roots, although not always. Both the ephemeral nature of arbuscules and size asymmetry between mycorrhizal and non-mycorrhizal plants, need to be considered here. Although more limited in number, field studies of the effect of elevated CO₂ on AMF have either shown no effect or an increase in AM fungal abundance; again these observed increases could also have been as a result of vegetational change. Field studies are particularly important as interactions between the complex assemblages of AMF that typically occur in the field are taken into account. Extraradical growth of AMF can increase with elevated CO₂; although this does not necessarily lead to an increase in AMF P uptake. Again plant size asymmetry and the rapid turnover of hyphae of AMF in soil (5-6 days) are important.

Currently we are working on the data analyses of a laboratory based experiment in which we grew the mycorrhiza defective tomato mutant (rmc) and its mycorhrizal wild-type progenitor (76R MYC+) under ambient and elevated CO₂ conditions to determine whether:

1. 
   
   Mycorrhizal colonization of tomato is altered by elevated CO₂ and


2. 
   
   If there are any effects of elevated CO₂ on plant growth and macro- and micro-nutrient concentrations.