ROOT TO SHOOT RATIO OF CROPS AS INFLUENCED BY CO2

Crops of tomorrow are likely to grow under higher levels of atmospheri c CO2. Fundamental crop growth processes will be affected and chief am ong these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO2 conc entration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO2 concentration will a ffect roots and shoots of crop plants proportionally. Since elevated C O2 can induce changes in plant structure and function, there may be di fferences in allocation between root and shoot, at least under some co nditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability, Herein we review root to shoot allocation as af fected by increased concentrations of atmospheric CO2 and provide reco mmendations for further research. Review of the available literature s hows substantial variation in R:S response for crop plants. In many ca ses (59.5%) R:S increased, in a very few (3.0%) remained unchanged, an d in others (37.5%) decreased. The explanation for these differences p robably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO2 enrichment will ad d substantially to the global change response data base.