Abstract: The study on the physiological bases of the shadetolerance of Dactylis glomerata, Lolium perenne, and Hemarthria compressa inter cultivated in Eucalyptus grandis forests with different canopy densities showed that with increasing canopy density, the light saturation point (LSP), light compensation point (LCP), chlorophyll a/b (Chla/Chlb), and the contents of proline (Pro), soluble sugar (SS) and soluble protein (SP) of the three herbages decreased gradually, but the apparent quantum yield (AQY), chlorophyll content (Chl), malondialdehyde(MDA) content, and superoxide dismutase (SOD) activity were in adverse. The daily average net photosynthesis rates (P_n) of H. compressa decreased gradually, while that of D. glomerata and L. perenne increased first and decreased then. When the canopy density was below 0.54 for D. glomerata and below 0.27 for L. perenne, the P_n of the two herbages was higher than CK. There existed significant correlations (P<0.05) between 11 physiological indices of the three herbages and canopy density, and the shadetolerance of the three herbages was in the order of D. glomerata＞L. perenne＞H. compressa, based on the ordination with average subjection function method.

Key words: aroma substance, arbuscular mycorrhizal fungi, aroma metabolism, gland hair, tobacco