Abstract: With 16 years old Larix kaempferi plantation in eastern mountain area of Liaoning Province as test object, this paper studied its total fine root biomass, fine root biomass at different soil depths, and biomass of different root orders under effects of fertilization. The results showed that compared with no fertilization, applying N decreased the total fine root biomass significantly (P<0.05), while the difference between applying P and N+P was not significant. The fine root biomass in top soil (0-10 cm) was significantly (P<0.01) higher than that in subsoil (10-20 cm), and in all treatments, it accounted for 64%-73% of the total. The effects of fertilization on fine root biomass varied with soil depth and root orders. In top soil, N fertilization decreased five orders (except the second order) fine root biomass significantly (P<0.05), while P and P+N fertilization had no significant effects (P>0.05), except the fifth order root in treatment P, and the second order root in treatment P+N (P<0.05). In subsoil, treatments N and P had no effects on five orders fine root biomass (P>0.05), while treatment N+P increased the first order fine root biomass significantly (P<0.05).

Key words: digestive enzyme., antibiotics, combined toxicity, earthworm, heavy metal