CARBON DISTRIBUTION IN GRASS (FESTUCA-PRATENSIS L) DURING REGROWTH AFTER CUTTING - UTILIZATION OF STORED AND NEWLY ASSIMILATED CARBON

Distribution of net assimilated C in meadow fescue (Fectuca pratensis L.) was followed before and after cutting of the shoots. Plants were continuously labelled in a growth chamber with C-14-labelled CO2 in the atmosphere from seedling to cutting and with C-13-labelled CO2 in the atmosphere during regrowth after the cutting. Labelled C, both C-14 and C-13, was determined at the end of the two growth periods in shoots, crowns, roots, soil and rhizosphere respiration. Distribution of net assimilated C followed almost the same pattern at the end of the two growth periods, i.e. at the end of the C-14- and the C-13-labelling periods. Shoots retained 71-73% of net assimilated C while 9% was detected in the roots and 11-14% was released from the roots. determined as labelled C in soil and as rhizosphere respiration. At the end of the 2nd growth period, after cutting and regrowth, 21% of the residual plant C-14 at cutting (C-14 in crowns and roots) was found in the new shoot biomass. A minor part of the residual plant C-14, 12%, was lost from the plants. The decreases in C-14 in crowns and roots during the regrowth period suggest that C-14 in both crowns and roots was translocated to new shoot tissue. Approximately half of the total root C at the end of the regrowth period after cutting was C-13-labelled C and thus represents new root growth. Root death after cutting could not be determined in this experiment, since the decline in root C-14 during the regrowth period may also be assigned to root respiration, root exudation and translocation to the shoots.