[Effects of nitrogen fertilization on fine root lifespan of Fraxinus mandshurica and Larix gmelinii].

Root observation tubes (minirhizotrons) were used to study the effects of nitrogen addition on the fine root growth of Fraxinus mandshurica and Larix gmelinii, with the correlations between the fine root lifespan and nitrogen availability analyzed. After the nitrogen addition, the fine root number of F. mandshurica and L. gmelinii had a decreasing trend, but the fine root diameter became larger and the branching ratio decreased. The survival rate of F. mandshurica fine roots increased, and the median root lifespan prolonged 105 days, compared with the control. No significant responses to the nitrogen addition were observed in the survival rate of L. gmelinii fine roots. The first-order fine roots with smaller diameter, the roots in surface soil (0-15 cm), and the fine roots newly born in spring and summer were vulnerable to extend their lifespan by nitrogen addition, suggesting that the fine roots with higher physiological activity were easily to be affected by nitrogen fertilization.

[Effects of fertilization on fine root diameter, root length and specific root length in Larix kaempferi plantation].

With 16 years old Larix kaempfersoil plantation in the mountainous area of eastern Liaoning Province as test object, this paper studied the effects of fertilization on the fine root diameter, root length, and specific root length (SRL) of the first to fifth order roots. The results showed that with ascending root orders, the mean fine root diameter and root length increased, while the SRL decreased significantly. Among the five order roots, the first order roots were the thinnest in diameter, the shortest in length, and the highest in SRL, but the fifth order roots were in reverse. The variance coefficients for the fine root diameter, root length, and SRL increased from the first to the fifth order roots. Except for the first order roots, soil depth had no significant influence on the fine root diameter, root length and SRL. Fertilization affected the fine root diameter, root length, and SRL of the first and the second order roots significantly, hut had little effects on other order roots. N fertilization decreased the mean diameter of the first and the second order roots significantly, and N or N + P fertilization decreased the mean length of the first order roots in surface soil (0-10 cm) significantly. The SRL of the first order roots in surface soil increased significantly under N fertilization.

[Effects of fertilization on fine root biomass of Larix kaempferi plantation].

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).