ABSORPTION OF ATMOSPHERIC NO2 BY SPRUCE (PICEA-ABIES) TREES .2. PARAMETERIZATION OF NO2 FLUXES BY CONTROLLED DYNAMIC CHAMBER EXPERIMENTS

The dynamic chamber technique was applied to investigate NO2 influx in to Picea abies (L.) Karsten branches, and its effects on net photosynt hesis and transpiration, as well as its dependency on irradiance, temp erature and relative humidity. The study aimed to quantify effects of climate on atmospheric NO2 fluxes to spruce. Experiments were performe d with 3- to 4-yr-old branches of 8- to 9-yr-old potted trees under co ntrolled environmental conditions. With ambient NO2 concentrations inc reasing from 35 to 50 nl l(-1) a linear increase in the NO2 influx of up to c. 6.8 mu mol m(-2) s(-1) was observed. From this increase a com pensation point of 1.64 nl l(-1) NO2 was calculated by linear regressi on analysis. In the range of the NO2 concentrations studied, net photo synthesis of spruce was not affected. The responsiveness of the stomat a to changes in irradiance and relative humidity was reduced at 45 nl l(-1) NO2 compared with 25 nl l(-1) NO2. With increasing irradiance up to 1000 mu mol m(-2) s(-1) PAR, increasing NO2 flux to spruce branche s was observed, which was attributed to a light-dependent increase in stomatal aperture. Variation of the temperature between 14 and 35 degr ees C did not affect the NO2 flux, in light or in darkness. Higher tem peratures, up to 45 degrees C, resulted in an increase in NO2 influx i n the light; in darkness, changes in NO2 flux were not observed under these conditions. An increase in relative humidity from 5 to 60% in th e light caused an increase in NO2 influx, whereas in darkness NO2 infl ux was not affected by changes in relative humidity. The increase in N O2 flux in response to r.h. observed in the light could not be explain ed by changes in stomatal aperture. A solution of NO2 in ultra-thin wa ter films covering the needle surface might explain this phenomenon.