THE RELATION BETWEEN LASER-INDUCED CHLOROPHYLL FLUORESCENCE AND PHOTOSYNTHESIS

The remote sensing literature on laser-induced chlorophyll fluorescenc e has indicated a relation between chlorophyll fluorescence and photos ynthesis but, so far, has not presented a quantitative interpretation of the measurements. The present article presents the development of a model to quantify the gross photosynthesis on the basis of remote mea surements of chlorophyll fluorescence and radiance with the Laser Envi ronmental Active Fluorosensor (LEAF-NL). Combined measurements of the laser-induced chlorophyll fluorescence and CO2 exchange have been carr ied out during several days. Drought and ozone stress were imposed in two separate experiments. The laser-induced fluorescence measurements show a remarkable behavior. After sunrise the fluorescence yield rises first, but at high radiation and high temperature the fluorescence yi eld may decline below the nighttime fluorescence. This extremely stron g quenching of fluorescence is attributed to photosystem deactivation. On the basis of the available laser-induced fluorescence data, a phot osystem energy partitioning model is developed and finally used to pre dict photosynthetic electron transport. The results of this new model are compared with those of the current theory, the results from the ne w model show a fairly good correspondence with the CO2 assimilation da ta. It is believed that the present results are a significant step for ward to the development of practical applications. (C) Elsevier Scienc e Inc., 1998.