Bacterial production determined by [³H]thymidine incorporation in field rhizospheres as evaluated by comparison to rhizodeposition

TY - JOUR

T1 - Bacterial production determined by [3H]thymidine incorporation in field rhizospheres as evaluated by comparison to rhizodeposition

AU - Christensen, Henrik

AU - Rønn, Regin

AU - Ekelund, Flemming

AU - Christensen, Søren

PY - 1995

Y1 - 1995

N2 - In a sandy loam soil cropped to barley bacterial production in the rhizosphere was compared to the results of a parallel investigation on rhizodeposition. Bacterial production was stimulated in the rhizosphere as revealed by an increased biomass of bacteria (643–883 µg C g-1 soil) and protozoa (7.2–15 × 104 cells g-1 soil) as well as elevated thymidine incorporation (9.7–12 pmol g-1 soil) in rhizosphere soil compared to bulk soil. Rhizodeposition, as determined by several pulse labellings with 14CO2, was estimated to be 412 µg C g-1 dry wt soil in the 0–15 cm layer. Bacterial production, as determined by incorporation of 3H-labelled thymidine converted to bacterial C, revealed a plant-induced formation of 1348 µg bacterial C g-1 soil in the 0–15 cm layer. This is probably the first estimate for bacterial production based on thymidine incorporation which has been compared to an estimate of C availability in a terrestrial ecosystem. The discrepancy between the rhizodeposition data and the estimate of bacterial production suggests that conversion factors between [3H]thymidine incorporation and bacterial production obtained in laboratory incubations are not generally applicable to the field situation. It is proposed that estimates of bacterial production should be based on measurements of actual conversion factors to improve the accuracy of the method.

AB - In a sandy loam soil cropped to barley bacterial production in the rhizosphere was compared to the results of a parallel investigation on rhizodeposition. Bacterial production was stimulated in the rhizosphere as revealed by an increased biomass of bacteria (643–883 µg C g-1 soil) and protozoa (7.2–15 × 104 cells g-1 soil) as well as elevated thymidine incorporation (9.7–12 pmol g-1 soil) in rhizosphere soil compared to bulk soil. Rhizodeposition, as determined by several pulse labellings with 14CO2, was estimated to be 412 µg C g-1 dry wt soil in the 0–15 cm layer. Bacterial production, as determined by incorporation of 3H-labelled thymidine converted to bacterial C, revealed a plant-induced formation of 1348 µg bacterial C g-1 soil in the 0–15 cm layer. This is probably the first estimate for bacterial production based on thymidine incorporation which has been compared to an estimate of C availability in a terrestrial ecosystem. The discrepancy between the rhizodeposition data and the estimate of bacterial production suggests that conversion factors between [3H]thymidine incorporation and bacterial production obtained in laboratory incubations are not generally applicable to the field situation. It is proposed that estimates of bacterial production should be based on measurements of actual conversion factors to improve the accuracy of the method.

U2 - 10.1016/0038-0717(94)00133-L

DO - 10.1016/0038-0717(94)00133-L

M3 - Journal article

SN - 0038-0717

VL - 27

SP - 93

EP - 99

JO - Soil Biology & Biochemistry

JF - Soil Biology & Biochemistry

IS - 1

ER -