Rhizodeposition by 14co 2-pulse-labelled spring barley grown in small field plots on sandy loam

Abstract

I examined the below-ground transfer of C in spring barley ( Hordeum vulgare L. cv. Alexis) grown in the field in soil cores contained in stainless steel cylinders, and compared results obtained by 14C pulse-labelling and root washing. At four growth stages, shoots of three cylinders were labelled with 14CO 2 for 8–10 h, and the distribution of 14C determined 6 days after labelling (day 6). At maturity (127 days after sowing), the yield of grain, straw and macro-roots (isolated by root washing) was 273.2, 261.7 and 45 g C m −2 respectively. Throughout the growing season, 67–73% of the macro-root C and 45–78% of the 14C retained below-ground (day 6) was in the 0–15 cm of soil layer. Generally, the proportion of below-ground 14C recovered in the 0–15 cm layer decreased throughout the growing season. At early elongation, 36.7% of 14C recovered was translocated below-ground with 7.6, 20.7 and 8.3% being recovered in macro-roots, macro-root free soil and as rhizosphere respiration (root and microbial), respectively, the corresponding values at late grain filling being only 0.7, 1.1 and 3.0%. The half life of 14C deposited in the soil (macro-root free soil) was estimated to 6–42 days depending on the intensity of root growth. The total below-ground transfer of C during the growth of spring barley was estimated to 165.2 g C m −2 (1652 kg C ha −2). Rhizosphere respiration and macro-root C isolated by root washing at maturity accounted for 23.3 and 27.2%, respectively. The amount of C translocated below-ground corresponds to one-third of the above-ground C harvested at maturity.