Abstract: Fine root biomass plays an important role in the carbon cycling of forest ecosystem, and fine root morphology (e.g., diameter, length, and specific length) is one of the main factors affecting fine root absorbing function. However, fine root biomass and morphology are generally controlled by soil resource availability. In 2003 and 2004, by using in-growth core approach, different order fine root samples were collected from the 17 year-old Fraxinus mandshurica and Larix gmelinii plantations at the Maoershan Experiment Station of Northeast Forestry University, and the effects of nitrogen (N) fertilization on the fine root biomass, morphology, and N content of the two tree species were studied. The results showed that N fertilization had significant (P<0.05) negative effects on the biomass of the 1st-3rd order roots of F. mandshurica and L. gmelinii, the diameter of the 2nd-4th order roots of F. mandshurica and the 3rd order roots of L. gmelinii, and the specific root length of the 1st-4th order roots of F. mandshurica and the 1st order roots of L.gmelinii, but had no significant effects on root length. N fertilization only increased the N content of the 1st-2nd order roots of F. mandshurica significantly (P<0.05). It was suggested that the fine root biomass, morphology, and N content of test tree species were correlated with soil resource availability, but the responses of the two species to N fertilization were differed.

Key words: Bt corn, Straw decomposition, Soil enzyme, Soil fertility