ABOVEGROUND AND BELOWGROUND TRANSFORMATION OF PHOTOSYNTHETICALLY FIXED CARBON BY 2 BARLEY (HORDEUM-VULGARE L) CULTIVARS IN A TYPIC CRYOBOROLL

Work with barley cultivars had shown that barley root and shoot mass d ynamics were affected by the cultivars used, and root length followed similar trends as root mass but decreased much faster than root mass b etween heading and ripening stages. A field experiment was made on a T ypic Cryoboroll in 1990 with two barley cultivars to study the above- and below-ground transformation of photosynthetically fixed C in barle y-soil systems. The barley cultivars (Abee and Samson) were grown on t hree replicate plots using a factorial split-plot design. Microplots w ere destructively sampled 15 days after pulse-labelling. The total C-1 4 activity in shoots and roots of Samson was significantly higher than that of Abee over the growing season. The ratio of shoot C-14:root C- 14 increased faster for Abee than for Samson over the growing season. In contrast, the C-14 remaining in soil, and in microbial biomass and water-soluble organic-C was significantly higher for Samson than for A bee at the stem extension and heading stages but there were no differe nces at the tillering and ripening stages. Root C-14 was correlated wi th soil C-14. Most of C-14 respired by soil microorganisms during a 10 -day incubation came from water-soluble organic-C-14, which indicated that water-soluble organic-C is very available to soil microorganisms. A greater proportion of photosynthetically fixed C was stabilized in soil under Samson than under Abee. The below-ground allocation of C is controlled by the cultivar and may be one of the strategies to reduce global CO2 in the atmosphere.