Decomposition of C-13-labelled wheat root systems following growth at different CO2 concentrations

We tested whether the amounts of carbon (C) mineralized from decomposing wh eat (Triticum aestivum L. cv. Tonic) roots were related to the quantity (i. e. root dry weight per plant) or the chemical composition of material which had been grown at ambient or elevated CO2 concentrations (350 or 700 mu mo l CO2 mol(-1)). Plants were grown in C-13-depleted CO2 to distinguish root- derived C from soil-derived C. Over periods of up to ca, 400 d, root C, soi l C and nitrogen (N) mineralization were measured from: (i) root systems le ft in situ in soil; (ii) soil after removal of visible roots; and (iii) equ al amounts of roots added to fresh soil. Root systems in situ showed transi ently faster C mineralization rates after growth at elevated [CO2] compared with ambient [CO2]. Ultimately, there were no [CO2]-related differences in the amounts of C or N mineralized from root system in situ. Specific rates of C loss from extracted roots were not significantly different for roots from the two [CO2] treatments. The potential accuracy of the C-13 method wa s demonstrated and C-13/C-12 fractionation during root decomposition was ne gligible. We conclude that when wheat is grown under elevated [CO2], subseq uent root decomposition will not necessarily be affected. Ift does, it is l ikely to do so via an effect of [CO2] on the amounts of root material produ ced per unit of soil rather than on the chemical quality of that material. (C) 2000 Elsevier Science Ltd. All rights reserved.