Considerable Belowground Carbon Transfer via Direct Root Contact compared to Indirect Interaction and Roles of Each Species in Diverse Plant Communities

High plant diversity is known to enhance soil carbon (C) gains, suggesting belowground C exchange between plants as a mechanism. However, knowledge is still limited to determine which factor governs C transfer between direct root contact and indirect interaction such as movements by microbes. Also, how considerably the transfer works in various plant combinations is not clear. The objective of the research was to measure C transfer from focal to neighboring plants by direct root contact and indirect interaction in various combinations of plant species. Three common species in North American prairie: Switchgrass (SG), bush clover (BC), and black-eyed Susan (BES) were grown with five combinations in thin and aligned boxes which were specially designed to give three compartments with two barriers in one box. In between compartments, half boxes had meshed barriers not to allow direct root contact but indirect interactions, and another half had opened one to give both factors. To trace C transfer, focal plant was pulse-labelled by 13CO2 among three plants in each box, and root tips and fine roots were collected and analyzed after four months. Belowground C transfer from focal to neighboring plants was detected almost in all plant combinations when they had open barriers, while negligible amount of C was transferred through meshed barriers. Especially, focal SG preferred to give its C to neighboring SG and BC by direct root contacts. However, when BC was a focal plant, negligible amount of transferred C was observed in neighboring SG and BES, though it occurred from SG to BC. Result reveals, in diverse plant communities of prairie, belowground C exchange occurs considerably through direct root contact, and the transfer tend to be biased by combination of plant species. This research was funded by the Great Lakes Bioenergy Research Center (Award # DE-SC0018409).