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  1. Vol. 9 No. 6, p. 756-759
     
    Received: May 5, 1969
    Published: Nov, 1969


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doi:10.2135/cropsci1969.0011183X000900060025x

Carbon Uptake and Distribution Before and After Defoliation of Alfalfa1

  1. R. B. Pearce,
  2. Guy Fissel and
  3. G. E. Carlson2

Abstract

Abstract

The deposition and redistribution of 14C was followed during the growth of individual alfalfa plants. 14CO2 was administered at 5 weekly intervals (plants were sampled 2 days after each addition of 14CO2). The plants were then defoliated, and the redistribution of 14C was followed during the subsequent growth.

During the 1st week of 14CO2 uptake, only 17% of the 14C in the ]plant was translocated to crown and roots. By the 5th week, 36% of the 14C in the plant was in crown and roots. It was not until the 3rd week that 14C started to accumulate (exponentially) in the “starch” fraction. This coincided with the time that large roots (> 1 mm in diameter) started to increase in dry weight.

After defoliation, 14C changes in the plant best fit a sigmoid curve. The greatest changes occurring between 3 and 15 days after defoliation. During the 28 days of regrowth, 45% of the 14C was lost (respiration, leaching, and sloughing) from the plant, 19% had moved into top growth and large roots had lost 70% of their original 14C content.

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