Abstract: To test the preference of Phyllostachys edulis and Quercus glaucaseedlings for nitrate-N (NO₃^--N) and ammonium-N (NH₄⁺-N), we grew their seedlings in hydroponic culture with five different NH₄⁺-N∶NO₃^--N ratios (100∶0, 75∶25, 50∶50, 25∶75, 0∶100), and measured SPAD values of the leave, root morphology, and root nitrate reductase activity (NRA). The results showed that both nitrogen forms and ratios significantly affected growth characteristics of P. edulis and Q. glauca seedlings. SPAD values, root length, root surface area and NRA of P. edulis seedlings were higher in the 75∶25 treatment than in the other treatments (P<0.05). Root length and root surface area of Q. glauca seedlings were higher in the 25∶75 treatment than in the other treatments (P<0.05). The SPAD values of Q. glauca leaves were higher in the 0∶100 treatment with nitrate as the sole nitrogen source than in the other treatments (P<0.01). The NRA in roots of Q. glauca correlated positively with nitrate concentration in nutrient solution, but not forP. edulis seedlings. Our findings indicate that P. edulisprefers ammonium at seedling stage, while Q. glaucaprefers nitrate.

Key words: Pinusmassoniana plantation, forest gap, litter decomposition, microbial biomass.