C Kenny, P J Murray, N Ostle, B Davies

        Measurement of carbon fluxes in plants in the field under ambient conditions has always been problematical. The present study combines two approaches to allow plants to be labelled with 13C in situ and to allow collection of root exudates. The approach taken allows quantification of carbon assimilation and exudation by the plants and enables us to determine the pattern of root exudation over time.
        Briefly, the stable isotope delivery (SID) system consists of a gas delivery and handling system housed in a mobile laboratory linked to a series of chambers which are inserted over the sward. A pulse of 13CO2 is injected into the air passing through the chambers. In the present study, at an upland grassland site, a number of microlysimeters containing Agrostis capillaris plants growing in sand were placed under the chambers. This enabled us to collect root exudates every 6h for 4 days.
        Preliminary results indicate that the plants were heavily labelled with the isotope and identified a diurnal pattern of C exudation from the plants.