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 dynamics were affected by the cultivars used, and root length followed similar trends as root mass but decreased much faster than root mass between heading and ripening stages. A field experiment was made on a Typic Cryoboroll in 1990 with two barley cultivars to study the above- and below-ground transformation of photosynthetically fixed C in barley-soil systems. The barley cultivars (Abee and Samson) were grown on three replicate plots using a factorial split-plot design. Microplots were destructively sampled 15 days after pulse-labelling. The total C-14 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 Abee at the stem extension and heading stages but there were no differences at the tillering and ripening stages. Root C-14 was correlated with 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.