Dynamics of the rhizosphere effect in soils

In a greenhouse experiment with continuous labeling of oat plants in a 13CO2 atmosphere, the ratios between different carbon and nitrogen pools in the rhizosphere and nonrhizosphere soil, i.e., the values of the rhizosphere factor R f , were determined. The mean values of the rhizosphere factor varied from 0.9 (the water-soluble nitrogen pool) to 4.6 (the pool of 13C-labeled dissolved organic carbon). We split the carbon and nitrogen pools into three groups depending on the mean R f value. Group I with high R f values (>2) included the most labile labeled organic carbon pools and the active component of the soil microbial biomass. Group II with the rhizosphere factor values 1 < R f < 2 included the more conservative pools of the total dissolved organic carbon and the microbial biomass in the soil. The only representative of group III (R f < 1) was the water-soluble nitrogen pool. The dynamics of the rhizosphere factor had a maximum during the period of the rapid root growth rate (the tillering, booting, and earing stages) for most members of group I; a maximum during the period of the intensive root turnover (the milk ripeness and wax stages) was detected for the pools-representatives of group II. The dynamics of the rhizosphere factor for the soluble nitrogen had no prominent trends.