LABORATORY AND FIELD STUDIES OF BIOGENIC VOLATILE ORGANIC-COMPOUND EMISSIONS FROM SITKA SPRUCE (PICEA-SITCHENSIS BONG) IN THE UNITED-KINGDOM

Isoprene and monoterpene emission rates were measured from Sitka spruc e (Picea sitchensis Bong.) with a dynamic flow-through branch enclosur e, both in the laboratory and in the field in the United Kingdom. In t he laboratory, emission rates of isoprene comprised over 94% of the id entified VOC species, and were exponentially related to temperature ov er a period of 1 day. This exponential relationship broke down at simi lar to 33 degrees C. Field measurements were taken on five sampling da ys in 1992 and 1993, in Grizedale Forest, Cumbria. Total emission rate s were in the range 36-3771 ng g(-1) h(-1). Relative emissions were mo re variable than suggested by laboratory measurements, with monoterpen es contributing at least 64% to the total emissions in most cases. The re was a significant variation in the basal emission rate both across the growing season and between different ages of vegetation, the cause s of which are as yet unknown. Total emission rates, in July 1993, wer e estimated to be between 0.01 and 0.27% of assimilated carbon.