INVESTIGATING SHORT-TERM CARBON FLOWS IN THE RHIZOSPHERES OF DIFFERENT PLANT-SPECIES, USING ISOTOPIC TRAPPING

Many difficulties exist in studying rhizosphere carbon flows in situ because of limited methodologies. Current photosynthate allocation to root respiration, rhizosphere microbial respiration and soluble root exudates in the rhizospheres of winter wheat (Triticum aestivum L.), tall fescue (Festuca arundinacea Schreb.) and buffalo gourd (Cucurbita foetidissima HBK) were investigated using an isotopic trapping procedure. Plants were grown in containers with 165 g of sandy clay loam soil for 3 wk before the time of C-14 pulse labeling. Most root exudates were utilized by the microbes in the immediate rhizosphere and released as (CO2)-C-14. Only a small amount of exudates was found in the bulk soil (2.7, 2.5, and 3.7% in the control treatments of wheat, tall fescue, and buffalo gourd respectively). The isotopic trapping mechanism was valid for all three species even though the patterns of total rhizosphere respiration (measured as total (CO2)-C-14 rates during the initial 8 h of tracing for the three plant species were different in peak time and peak height. The isotopic trapping procedure can be used in rhizosphere studies for various plant species in principle. Some modifications to the procedure may be needed for different plant-soil systems.