Nutrient use efficiency of current-yr seedlings by using stable isotope (15N)

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1) Nitrogen use efficiency of current-yr seedlings of deciduous broad-leaved tree species In Castanea crenata, percent nitrogen in seeds were not different among seeds from different mother trees of different soil nutrient conditions and not different among seeds of different mass. Seedling mass increment was positively correlated with seed size in nitrogen poor conditions (NPC) but not in nitrogen rich conditions (NRC) , due to that negative relationship between RGR and seed size diminished the effects of seed size on seedling growth in NRC.In which, seedlings from small-seeds showed greater allocation of biomass to the leaves, and greater nitrogen contents in the leaves than the seedlings from large-seeds, resulted in greater RGR in the small-seeded seedlings. Greater leaf nitrogen contents in small-seeded seedlings was due to greater nitrogen absorption from soil (15N) not from seeds (14) .2) Nitrogen and tannin as factors affecting defoliation by herbivores Percentages of defoliation in tree crowns and epicormic branchs were 54% and 81%, respectively, in an oak stands (Quercus mongolica) in the outbreak of the winter moth (Operophtera brumata) . This difference indicated that oaks allocated more defense chemicals, such as tannin, to canopy leaves than to epicormic branch leaves. Canopy leaves had higher nitrogen contents and had higher photosynthetic activity. Such allocation of defense chemicals is thought to have selection advantage particularly in K-strategists, or oak species.