Foliar Bio-Physical and Spectral Properties Associated with Light Environment in a Mature Poplar Stand

This study evaluates the ability of reflectance (R) and chlorophyll fluorescence (ChlF) parameters to express the differences in foliar properties associated with varying light environment. In the summer of 2007 a tall crane was used to acquire foliar reflectance measurements and collect samples from sunlit and shaded tree crowns, from the upper and lower canopy of a mature tulip poplar (Lirodendron Tulipifera L.) forest. Leaf-level photosynthesis, R, ChlF spectra and kinetics and bio-physical parameters were measured on excised samples. The differences in the light environment greatly affected the spectral and biophysical data, especially the photosynthetic parameters (Amax, LUE, photochemical quenching, Qp, Qn, Qp/Qn). For sunlit foliage, ChlF kinetics (Fo, Fm, Fs, and Fv/Fm) were significantly lower than shaded foliage. Our analysis indicated that some of the tested spectral bio-indicators (e.g. PRI1, RE2, G035, Dmax) were strongly associated with LUE and differed significantly depending on the light environment. ChlF as compared to R indices followed more closely the trends in LUE, which emphasizes the application of ChlF for the timely detection of changes in vegetation physiology and carbon dynamics.