Measurement of the carbon fluxes in the rhizosphere of Lolium perenne

Abstract

Roots release a wide range of organic compounds called rhizodeposits, which affect some of the soil parameters such as pH, water holding capacity, stability of the soil aggregates or microbial activity. They are also considered to be one of the major sources of the carbon (C) for rhizospheric microorganisms and contribute to CO₂ emission from soil, making up to 60 % of total CO₂ efflux from soil. Additionally, rhizodeposits can alter soil organic matter (SOM) decomposition rates. Because of these strong reasons, therefore, the carbon translocation by plants was investigated. The distribution pattern of tracer (¹⁴C) in the system plant-soil by means of the pulse labelling has been investigated in the pot-scale experiment. Rhizosphere-derived CO₂ accounted for 11 % of total assimilated ¹⁴C. The ¹⁴C activity and total carbon presented in the roots, rhizosphere-derived CO₂, microbial biomass (MB), dissolved organic carbon (DOC) in the soil have been measured. Maximal ¹⁴C activity in DOC and MB occurred at the sixth hour while in the roots it was detected at twelfth hour after labelling. The changes of the ¹⁴C content in investigated pools have been divided into two phases: the first phase lasted for first four days after labelling with fast decrease of ¹⁴C and in the next phase only inconsiderable changes occurred.