Model for rhizodeposition and CO2 efflux from planted soil and its validation by 14C pulse labelling of ryegrass

A model for rhizodeposition and root respiration was developed and parameterised based on C-14 pulse labelling of Lolium perenne. The plants were grown in a two-compartment chamber on a loamy Haplic Luvisol under controlled laboratory conditions. The dynamics of (CO2)-C-14 efflux from the soil and C-14 content in shoots, roots, micro-organisms, dissolved organic carbon (DOC) and soil were measured during the first 11 days after labelling. Modelled parameters were estimated by fitting on measured C-14 dynamics in the different pools, The model and the measured C-14 dynamics in all pools corresponded well (r(2)=0.977). The model describes well (CO2)-C-14 efflux from the soil and C-14 dynamics in shoots, roots and soil, but predicts unsatisfactorily the C-14 content in microorganisms and DOC. The model also allows for division of the total (CO2)-C-14 efflux from the soil in (CO2)-C-14 derived from root respiration and (CO2)-C-14 derived from rhizomicrobial respiration by use of exudates and root residues. Root respiration and rhizomicrobial respiration amounted for 7.6% and 6.0% of total assimilated C, respectively, which accounts for 56% and 44% of root-derived (CO2)-C-14 efflux from the soil planted with 43-day-old Lolium perenne. respectively. The sensitivity analysis has shown that root respiration rate affected the curve of (CO2)-C-14 efflux from the soil mainly during the first clay after labelling. The changes in the exudation rate influenced the (CO2)-C-14 efflux later than first 24 h after labelling.