| Abstract: | Aims Ecosystem light use efficiency (LUE) reflects the ability of CO2 uptake and light utilization via photosynthesis, which is a key parameter in ecosystem models to evaluate ecosystem productivity. The objectives of this study were to: (1) compare the differences of LUE derived from different methods; (2) elucidate the seasonal dynamics of LUE and its regulatory factors; and (3) evaluate the maximum LUE (LUEmax) and its variability based on eddy-covariance (EC) flux.Methods Using the flux data from an EC tower during 2003-2005 at a broad-leaved Korean pine (Pinus koraiensis) mixed forest, Changbai Mountain, two types of LUE indicators were generated from: 1) the apparent quantum yield (ε) estimated with rectangular hyperbolic curve, and 2) the ecological light use efficiency (LUEeco) calculated as the ratio between gross ecosystem productivity (GEP) and photosynthetically-active radiation (Q).Important findings The seasonal variation of ε and LUEeco appeared a unimodal pattern within a year, with the variations significantly dominated by soil surface temperature and Normalized Difference Vegetation Index (NDVI). A positive correlation between GEP and LUE was found for both ε and LUEeco, with the effect of Q on LUE relatively weak. The increase in diffusion radiation appeared favorable for enhanced LUE. Generally, there was a significant positive relationship between ε and LUEeco, while ε was higher than LUEeco, especially during the mid-season. The annual maximum value of ε and LUEeco was (0.087 ± 0.003) and (0.040 ± 0.002) μmol CO2·μmol photon-1 over the three years, respectively. The interannual variability of LUEmax for ε and LUEeco was 4.17% and 4.25%, respectively, with a maximum difference of >8%, likely resulted from considerable uncertainty in model simulations. Our results indicated that the inversion and optimization of maximum LUE should be taken seriously in the application of LUE models. |
