Total and Labelled CO₂ Emission and ¹⁴C Partitioning as Affected by Streptomycin and Benomyl

Abstract

Application of an antibiotic (streptomycin) and a fungicide (benomyl) in order to separate root respiration and microbial respiration of exudates was tested using two plant species (ryegrass and spring wheat) growing on a Haplic Luvisol. Both xenobiotics were added to the soil with growing plants either separately or in combination. Plants were ¹⁴C-pulse labelled and both labelled and total CO₂ emission from soil were measured. After seven days plants were harvested, dried and total carbon and C content in shoots and roots were determined.

Growing plants increased the total CO₂ emission from soil by about 2.5 times in comparison to unplanted soil. The temporal pattern of ¹⁴CO₂ evolution in control treatments was similar as reported in the literature with maximum emission rates (0.55 % and 0.15 % of assimilated C per hour for wheat and ryegrass, respectively) during the first day after labelling. It was affected by both xenobiotics used but in different ways. With ryegrass streptomycin decreased CO₂ emission rates during the first day after labelling, while it left the second phase of tracer emission unchanged; with spring wheat the ¹⁴CO₂ evolution rates were reduced on the second day. Applied xenobiotics did not change the ¹⁴C content in the shoots, but smaller tracer amounts were found in the roots and in soil-derived CO₂. This was more pronounced for ryegrass than for spring wheat plants.