Leaf area index is the principal scaling parameter for both gross photosynthesis and ecosystem respiration of Northern deciduous and coniferous forests

Abstract

Data on net CO2 exchange from eight forests in Denmark, Sweden, Finland and Iceland were used to analyse which factors were controlling photosynthesis and respiration. The forests consisted of different species ranging in climatic condition from temperate to subarctic. Only well mixed conditions were analysed (u* > 0.3 m s−1). The parameters of a light response function showed strong seasonal variations with similar behaviour for all stands except for a beech forest where the development of a vigorous ground vegetation in spring affected the photosynthesis parameters differently as compared to the other forests. The beech forest also showed the highest respiration rates in the earlier part of the growing season in contrast to the other forests that showed maximum values in late part of July. The mean half‐monthly nighttime respiration rates were well explained by an equation with one fitting parameter, the respiration rate at 10 °C, with an r2= 0.864 for all stands together. The difference between the stands concerning both photosynthesis and respiration parameters were largely explained by the differences in LAI. After normalizing for LAI, the only remaining correlation was between respiration and stand age. These results are promising for application of remote sensing for estimation of respiration as well as gross primary productivity from forests.

Identification of a general light use efficiency model for gross primary production

“…APAR is chosen instead of S 0 as used in the Jarvis et al (2004) study for better comparability with other studies and because of the overwhelming evidences for the significance of the leaf area index or FPAR as scaling-factor for soil-vegetation-atmosphere-transfer processes (Watson, 1958;Monteith, 1977;Tucker and Sellers, 1986;Goetz and Prince, 1999;Gower et al, 1999;Lindroth et al, 2008), an explanatory power and intrinsic scaling factor which cannot be compensated by other environmental variables used in the light use efficiency model approach. The model performance varies between the water availability surrogates at the study sites, but none of them delivers the best results in every case.…”

Assessing seasonality of biochemical CO<sub>2</sub> exchange model parameters from micrometeorological flux observations at boreal coniferous forest

“…Since their mutual relationship is considered to be relatively constant -1.68 to 2.0 at 25 • C (Medlyn et al, 2002b;Leuning, 2002), even though the magnitudes of the parameters may vary considerably, this was considered important. Also, in the Eq.…”

“…According to the literature, the biochemical model parameters are considered to have a relatively constant ratio to each other, the relation J max /V c(max) usually being around 1.68 to 2.0 (Medlyn et al, 2002b;Leuning 2002) at 25 • C. Since the Roberntz and Stockfors (1998) temperature dependencies of J max and V c(max) are dissimilar this ratio is dependent on temperature: at 20 • C their ratio has been estimated to be 2.68 (Leuning, 1997). In our measurements the relationship between the two biochemical parameters was not as represented in the literature: J max had larger values at higher temperatures.…”

Quantifying the effect of forest age in annual net forest carbon balance

“…On the other hand, Rh and ER decline due to a reduction in litterfall and substrate availability through decomposition. The resulting imbalance between GPP and ER persists until vegetation and soil C pools increase up to the point when ER comes into equilibrium with GPP (Schwarz et al 2004, Lindroth et al 2008, Luyssaert et al 2008, Tang et al 2014.…”