Field measurements of root respiration and total soil respiration in an alder forest

Variation in root respiration and total soil respiration measured in the fi eld in an alder (Alnus glutinosa) forest is reported here, complementing pr evious studies of below-ground carbon relations. A novel technique, involving minimum disturbance to the roots, was used to measure tree fine-root respiration, while soil respiration was measured in an open system using infrared gas analysis. Calculations by process models of both rhizomicrobial, and bulk soil, respiration were compared with measu rements of total soil respiration. The rhizomicrobial respiration rate was strongly temperature dependent, wit h the variation determined by fine root structural parameters. The data wer e used to calibrate a soil respiration model comprising mineralization and rhizomicrobial respiration submodels. The calculated annual rhizomicrobial respiration (1234 g m(-2)) matched the carbon balance of the alder trees ca lculated in earlier studies; however, the calculated total annual soil CO2 efflux (1754 g m(-2)) was very high compared with other European forest sit es. The modelled total soil respiration fitted well to measured values; a chang ing groundwater table and modified carbon partitioning of the alder trees m ight account for deviations during early summer.