Measurement of the carbon fluxes in the rhizosphere of Lolium perenne

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.