ESPAS - An advanced phytotron for measuring carbon dynamics in a whole plant-soil system

The use of carbon isotopes as tracers is essential for measuring carbon flows in an intact whole plant-soil system. Here, we describe an Experimental Soil Plant Atmosphere System (ESPAS) to perform pulse-labelling and steady-state labelling experiments with (CO2)-C-13 and (CO2)-C-14. The ESPAS facility is an environmental research tool that is used to measure the carbon fluxes from the atmosphere to the roots and into the soil and the microbial biomass and to study decomposition of plant residues and soil organic matter. The influence of environmental conditions in the atmosphere or in soil on the carbon allocation and turnover in the plant-soil ecosystem can be quantified. The design and the technical description of the phytotrons is presented and evidence is provided that the phytotrons are equivalent. For this purpose, Triticum aestivum plants were cultivated in the phytotrons for 39 days and shoot growth, root growth and water use were compared. No significant differences were observed for plant growth and water use. As an example of the practical application of the equipment, an experiment with elevated atmospheric CO2 is presented. Data are given on the uptake of C-14 under ambient (350 mu L L(-1)) and elevated (700 mu L L(-1)CO(2) in Lolium perenne and Festuca arundinacea and the distribution of C-14 among different plant-soil compartments i.e. shoot, root, root-soil respiration, and soil. We conclude that these phytotrons yield detailed information on gross carbon flows in a whole plant-soil system that can not be obtained without sensitive carbon tracers. Such data are important for proper calibration of simulation models on soil organic matter.