| Fine root, as the research focus and highlight at home and abroad, is the key factor of the underground ecological processes of forest, and influences the productions of forest ecosystem. Root growth shows some certain plasticity, and root morphology can change under different environment and affect absorption and utilization of nutrients and water. By studying effects of nutrient on fine root morphology patermeters, we can understand the relation between fine root morphology characters of different orders and nutrient supply and illuminate the effects of fertilization on fine root production, turnover and lifespan. Therefore, it is important to estimate effects of nutrients on fine root morphology for understanding the psychological and ecological functions of fine roots, instructing forestry manufacture and increasing forest ecosystem production.This study investigated the influence of nitrogen (N), phosphorus (P) and nitrogen and phosphorus (N+P) on indexes of fine root morphology of different orders through fertilization on a Japanese larch (Larix kaempferi) plantation of 16 years old. The purposes are to systematically analyze the effects of fertilization on fine root morphology indexes such as biomass, diameter, length, specific root length, surface area, specific surface area, volume and tissue density of Japanese larch, and to study variation rules of nutrients of fine root (eg. C, N, P, TNC, C/N, C/P and N/P). The results are summarized as follows:(1) Fine root biomass of Japanese larch mainly concentrated in the surface soil layer, about 65% - 73%. Different nutrient had different impacts on fine root biomass. N fertilization significantly decreased the total fine root biomass and the biomass of each root order, but P and N+P treatment increased the total fine root biomass. Correlation analysis proved that content of total soil N and available soil N closely related with fine root biomass, while P fertilization showed slight correlations with fine root biomass.(2) The mean value of diameter and length of first root order presented minimum, were 0.29- 0.32 mm and 4.5-6.2 mm, respectively, the mean value of diameter and length of fifth root order achieved maximum, were 1.04 -1.33 mm and 70.5-104.4 mm, respectively. The mean value of root diameter and root length markedly increased with root order. Fertilization mainly affected mean diameter and mean length of the first and second root orders in surface soil layer, however no significant effects on roots of high-ranking orders and each order of roots survived in sub-surface soil layer. N fertilization remarkably decreased the mean root diameter of first and second root order lived in surface soil layer while N and N+P treatment notably decreased the mean root length of first order.(3) Root length density (RLD) of different orders of Larix kaempferi living in surface soillayer was much greater than that of living in sub-surface soil layer, but the specific root length (SRL) had no significant difference between soil layers. SRL and RLD of first order were maximum, 49.11-60.39 m-g"1 for SRL of surface soil layer and 6041.20-7753.24 m-m"3 and 1896.05-3136.88 m-m'3 for RLD of surface soil layer and sub-surface soil layer, respectively. SRL and RLD of the fifth root order were minimum, 2.90-4.95 m-g"1 for specific root length and 190.75-373.42 m-m"3 and 125.00-138-29 m.m"3 for surface soil layer and sub-surface soil layer respectively. RLD and SRL decreased with the increase of root order. Total root length of first root order was greatest and 50-57% of total length of five orders. The total root length of first, second and third orders in different sample plot account for 88-94% of total root length of five orders. Fertilization had no significant effect on SRL, RLD, accumulative length and total length of fine root of different orders, except that N fertilization obviously increased the specific root length of the first order survived in surface layer.(4) Root number of Japanese larch in surface layer was 1.5-3.9 times greater than that of sub-surface soil layer. Fertilization decreased the number ratio of the same order root lived surface and sub-surface soil layer. The root number of first order in surface soil layer was maximum(11.73xl05-13.35xl05 unit-m"2), the root number of fifth order was minimum(1937-7229 unit-m"2), the root number markedly reduced with the root order increasing, and the numbers of first and second orders roots amount to over 95% of the root number of five orders. No significant difference was found about fine root number and its distribution rules of different orders when fertilization was performed.(5) Fine root surface area and volume of each order of Japanese larch survived in surface soil layer were markedly greater than those of in the sub-surface soil layer. The surface area and volume of first order were greatest, about 5.67-7.45 m2-m"2 and 1.86-2.29 m2-m"2 for surface area and about 414.50-574.69 m3-m"3 and 143.67-221.83 m3-m"3 for volume for surface soil layer and sub-surface soil layer respectively. The surface area of the fifth order root was least, about 0.65-1.27 m2-m"2 and 0.47-0.58 m2-m"2 for surface soil layer and sub- soil layer, respectively, and so was the fine root volume which were 179.85-352.50 m3-m"3 for surface soil layer and 137.66-184.60 m3-m"3 for sub-surface soil layer. Surface area and volume of fine root remarkably decreased with the increase of root order. Fertilization had no obvious impacts on fine root surface area and volume of each root order, but the specific surface area of fine root increased with N addition. P and N+P had no significant influence on specific surface area of fine root of all root orders.(6) Fine root tissue density of each order in surface and sub-surface soil layers had no significant difference. Tissue density of the first and second orders was much lower (0.224-0.28 g-cm"3), but it was relatively much higher for the fine root of the third, fourth and fifth root orders (0.25-0.35 g-cm"3). Fine root tissue density increased with the increase of root order.(7) Nutrients content (N and P) of fine root for different orders of Japanese larch in surface soil layer were greater than that of in sub-surface soil layer. N and P content were both lessened with the increase of root order. C/N and C/P ratio of different orders had no differences, the C/N and C/P ratio of the first order was the lowest(26:1-28:1;365:1-390:1) and the C/N and C/P ratio of the fifth order obtained the highest value(53:1-60:1;850:1-948:1). C/N and C/P ratio markedly increased with root order increasing.(8) Total C of Fine root of Japanese larch in surface soil layer was slightly higher that in sub-surface soil layer, there were no significant difference among fine root total C of different root orders, and the content of total C was about 470-490 mg-g"1. Fertilization had no significant impact on fine root total C of each root order. The total non-structural carbohydrate (TNC) of first order fine root was lowest (126.31±19.19 mg-g"1) while the fifth order fine root (208.77±24.46 mg-g"1) was highest. TNC increased with the increase of root order. TNC of fine root for lower three orders in N+P plots was higher significantly than that in N, P and control plots, but there was no significant difference for TNC of fine root for all orders among N, P plots and control plots, except for fourth-order in subsurface soil layer.In conclusion, effect of fertilization on total biomass of fine roots was not significant. For fine root morphology characters, effect of fertilization was significant only for lower order (first order and second order), but no significant for higher order (third order and fourth order). The significance occurred also for effect of fertilization on nutrient content of lower order roots, especially for effects of P and N+P on P content, N/P-. C/P and TNC content of lower order roots.
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