Morphological and physiological responses of three California oak species to shade

Used three experimental shade treatments: full sunlight (I_full), 50% of full sunlight (I_50%) and 10% of full sunlight (I_10%). Interspecific differences in biomass allocation shade-induced changes in leaf morphology, whole-seedling photosynthetic capacities, and taproot elongation rates may explain, in part, shade tolerance of Quercus agrifolia and shade intolerance of Q. lobata seedlings reported in the literature. However, morphological and physiological responses of Q. douglasii, which recruits in shade, were similar to those of Q. lobata and do not adequately explain the high recruitment of Q. douglasii seedlings in shade. At I_10%, root weights of Q. lobata and Q. douglasii seedlings decreased by 46% and 60%, respectively, and showed similar decreases in total seedling biomass and root:shoot ratios. Shade did not affect whole-seedling biomass, root weight, or root:shoot ratio of Q. agrifolia seedlings. Total seedling leaf area of Q. lobata and Q. douglasii did not increase in shade, whereas at I_10% Q. agrifolia seedlings doubled in leaf area. Specific leaf area and leaf area ratio of Q. agrifolia seedlings also increased substantially more than the other two species. -from Author