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

Abstract

A model for rhizodeposition and root respiration was developed and parameterised based on 14C 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 14CO2 efflux from the soil and 14C 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 14C dynamics in the different pools. The model and the measured 14C dynamics in all pools corresponded well (r 2=0.977). The model describes well 14CO2 efflux from the soil and 14C dynamics in shoots, roots and soil, but predicts unsatisfactorily the 14C content in micro-organisms and DOC. The model also allows for division of the total 14CO2 efflux from the soil in 14CO2 derived from root respiration and 14CO2 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 14CO2 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 14CO2 efflux from the soil mainly during the first day after labelling. The changes in the exudation rate influenced the 14CO2 efflux later than first 24 h after labelling.