No abstract

Simple light use efficiency ( e e e e ) models of net primary production (NPP) have recently been given great attention (NPP = e e e e ¥ ¥ ¥ ¥ absorbed photosynthetically active radiation). The underlying relationships have, however, not been much studied on a time step less than a month. In this study daily NPP was estimated as the sum of net ecosystem exchange (NEE) and heterotrophic respiration ( R h ) of a mixed pine and spruce forest in Sweden. NEE was measured by eddy correlation technique and R h was estimated from measurements of forest floor respiration ( R f ) and the root share of R f . The total yearly NPP was on average 810 g C m , indicating that between-years variation in NPP is not directly dependent on total Q i . The light was most efficiently used at an average daytime temperature of around 15 ∞ ∞ ∞ ∞ C. At daytime vapour pressure deficit above 1400 Pa e e e e was reduced by approximately 50%.