Carbon flows in the rhizosphere of ryegrass (Lolium perenne)

This study addresses the issue of carbon (C) fluxes through below ground pools within the rhizosphere of Lolium perenne using the 14C pulse labeling. Lolium perenne was grown in plexiglas chambers on topsoil of a Haplic Luvisol under controled laboratory conditions. 14C-CO2 efflux from soil, as well as 14C content in shoots, roots, soil, dissolved organic C (DOC), and microbial biomass were monitored for 11 days after the pulsing. Lolium allocates about 48 % of the total assimilated 14C below the soil surface, and roots were the primary sink for this C. Maximum 14C content in the roots was observed 12 hours after the labeling and it amounts to 42 % of the assimilated C. Only half of the 14C amount was found in the roots at the end of the monitoring period. The remainder was lost through root respiration, root decomposition, and rhizodeposition. Six hours after the 14C pulse labeling soil accounted for 11 %, DOC for 1.1 %, and microbial biomass for 4.9 % of assimilated C. 14C in CO2 efflux from soil was detected as early as 30 minutes after labeling. The maximum 14C-CO2 emission rate (0.34 % of assimilated 14C h—1) from the soil occurred between four and twelve hours after labeling. From the 5th day onwards, only insignificant changes in carbon partitioning occurred. The partitioning of assimilated C was completed after 5 days after assimilation. Based on the 14C partitioning pattern, we calculated the amount of assimilated C during 47 days of growth at 256 g C m—2. Of this amount 122 g C m—2 were allocated to below ground, shoots retained 64 g C m—2, and 70 g C m—2 were lost from the shoots due to respiration. Roots were the main sink for below ground C and they accounted for 74 g C m—2, while 28 g C m—2 were respired and 19 g C m—2 were found as residual 14C in soil and microorganisms.