Allocation of carbon to shoots,roots, soil and rhizosphere respiration by barrel medic (Medicago truncatula) before and after defoliation |
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Authors: | Crawford Michael C Grace Peter R Oades J Malcolm |
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Institution: | (1) CRC for Soil and Land Management, Glen Osmond, SA, 5064, Australia;(2) Department of Soil Science, University of Adelaide, Glen Osmond, SA, 5064, Australia;(3) Present address: Department of Natural Resources and Environment, Agriculture Victoria, RMB 1145, Rutherglen, Vic, 3685, Australia;(4) CRC for Soil and Land Management, Glen Osmond, SA, 5064, Australia;(5) Present address: Department of Soil Science, University of Adelaide, Glen Osmond, SA, 5064, Australia |
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Abstract: | The allocation of carbon to shoots, roots, soil and rhizosphere respiration in barrel medic (Medicago truncatulaGaertn.) before and after defoliation was determined by growing plants in pots in a labelled atmosphere in a growth cabinet.
Plants were grown in a 14CO2-labelled atmosphere for 30 days, defoliated and then grown in a 13CO2-labelled atmosphere for 19 days. Allocation of 14C-labelled C to shoots, roots, soil and rhizosphere respiration was determined before defoliation and the allocation of 14C and 13C was determined for the period after defoliation. Before defoliation, 38.4% of assimilated C was allocated below ground,
whereas after defoliation it was 19.9%. Over the entire length of the experiment, the proportion of net assimilated carbon
allocated below ground was 30.3%. Of this, 46% was found in the roots, 22% in the soil and 32% was recovered as rhizosphere
respiration. There was no net translocation of assimilate from roots to new shoot tissue after defoliation, indicating that
all new shoot growth arose from above-ground stores and newly assimilated carbon. The rate of rhizosphere respiration decreased
immediately after defoliation, but after 8 days, was at comparable levels to those before defoliation. It was not until 14
days after defoliation that the amount of respiration from newly assimilated C (13C) exceeded that of C assimilated before defoliation (14C).
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | carbon 13C 14C defoliation partitioning pasture legumes roots |
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