Carbon partitioning and below-ground translocation by Lolium perenne

Carbon (C) balance, rhizodeposition and root respiration during development of Lolium perenne were studied on a loamy Gleyic Cambisol by (CO2)-C-14 pu lse labeling of shoots in a two-compartment chamber under controlled labora tory conditions. The losses from shoot respiration were about 36% of the total assimilated C . The highest respiration intensity was measured in the first night after t he labeling, and diminishes exponentially over time. Total CO2 efflux from the soil (root respiration, microbial respiration of exudates and dead roots) in the first eight days after the C-14 pulse label ing increased with plant development from 2.7 to 11% of the total C-14 assi milated by plants. A model approach used for the partitioning of rhizospher e respiration showed that measured root respiration was between 1.4 and 3.5 % of assimilated 14C, while microbial respiration of easily available rhiz odeposits and dead root residues was between 0.9 and 6.8% of assimilated C. Both respiration processes increased during plant development. However, on ly the increase in root respiration was significant. The average contributi on of root respiration to total (CO2)-C-14 efflux from the soil was approxi mately 46%. Total (CO2)-C-14 efflux from the soil was separated into plant-derived and soil-derived CO2 using C-14 labeling. Additional decomposition of soil orga nic matter (positive priming effects) in rhizosphere was calculated by subt racting the CO2 efflux from bare soil from soil-derived CO? efflux from soi l with plants. Priming effects due to plant rhizodeposition reach 60 kg of C ha(-1) d(-1). C-14 incorporated in soil micro-organisms (extraction-fumig ation) amounts to 0.8-3.2% of assimilated C. The total below-ground transfe r of organic C by Lolium perenne was about 2800 kg of C ha(-1). The C input into the soil consists of about 50% of easily available organic substances . (C) 2001 Elsevier Science Ltd. All rights reserved.