Comparison of Carbon Assimilation Capacity by Restored Prairie with Natural Plant Communities.

Soils offer significant carbon storage potential and plants represent a vehicle through which CO₂ can be scrubbed from the atmosphere and stored in soils. Approximately half of assimilated carbon is stored for long periods of time in soils as organic carbon or as woody products. The goal of this research was to empirically measure the gross primary productivity (GPP) or carbon assimilation rate of mixed plant canopies and to compare GPP of restored prairies, comprised mainly of Switchgrass and Big Bluestem, with six diverse plant communities. The surface area of seven plant community types were mapped using GIS and the canopy composition of each community type was determined in replicate locations.  Light use efficiency (LUE) curves, the quantity of CO₂ absorbed as a function of light intensity, were measured for thirteen diverse plant species (or genera groups) that predominate the Pierce Cedar Creek Institute plant community in southwest Michigan using a LI-COR 6400 XTR gas exchange meter. Using hourly solar radiation levels at the incident and successive leaf canopy layers, the quantity of CO₂ assimilated by species and plant community type were calculated for the 2009 growing season. Significant differences existed among species for LUE relationships, with C4 prairie grasses producing the highest GPP at high light levels, followed by prairie forbs and woody invasive shrubs. Significant differences existed for annual GPP of the seven plant communities with restored tall grass prairie and autumn olive-invaded meadow communities producing the highest GPP.  While exhibiting lower GPP than prairie, young successional forests had higher GPP than older forests. These differences account for significant variation in the total capacity for CO₂ assimilation and potential carbon storage by the variety of plant communities and encourage efforts to restore prairie ecosystems and direct selective tree harvest to maximize carbon storage.