The Internal Cycling Of Nutrients In Fine Roots Of Fraxinus Mandshurica And Larix Gemeilinii

The internal cycling of nutrients in fine roots of trees plays an important role in energy transformation and material circulation of forest ecosystem. It is important for reducing the loss of nutrients in trees that the nutrients in dead fine roots retranslocate to trees for reutilization. We studied the internal cycling of nutrient in fine roots between two species Fraxinus mandshurica and Larix gemeilinii on Maoershan Forest Research Station (45°25 ' N, 127°34' E) which owned by Norhteat Forest University, China. We collected the fine root samples from May to September in 2005, compared contents difference of N, P, K, Ca and Mg between live fine roots and dead fine roots, and studied the influnce of fertilization.The results show that there is no internal cycling of calcium in dead fine roots of Fraxinus mandshurica and Larix gemeilinii, but the dead fine roots of two species have the internal cycling of N, P, K. The internal cycling of Mg maybe happen in dead fine roots of Fraxinus mandshurica, but no retranslocation in Larix gemeilinii. The internal cycling rate of N, P, K in Fraxinus mandshurica fine roots is 10.47%, 22.58% and 55.77%, and the rate in Larix gemeilinii fine roots is 23.95%, 33.88%, 41.27%, respectively. The internal cycling rate of K is the biggest, and the rate of N is the smallest, and that the rate of P, K in Fraxinus mandshurica fine roots are bigger than Larix gemeilinii, but the rate of N is smaller than Larix gemeilinii. Thrcr is also no internal cycling of Ca in fertilization plots. The internal cycling of other nutrients in fine roots of Fraxinus mandshurica are accelerated by fertilization, except P. The internal cycling rate of P is descended from 22.58% to 19.77%, but rates of N, K are accelerated to 16.89% 66.78%. However, fertilization inhibits the internal cycling of nutrients in fine roots of Larix gemeilinii. There is no internal cycling of N, K in Larix gemeilinii fine roots, and the rate of P is descended from 33.88% to 22.5%. Comparison of nutrients content in live and dead fine roots of different branch orders in Fraxinus mandshurica trees showed that there also is no internal cycling of Ca, but other nutrients is very different of fine roots in diameters. There is the internal cycling of N from the third-order root, and the internal cycling rate is bigger than roots that were <0.5mm in diameter. The internal cycling of P is from the second-order root, and there are the internal cycling of K in the first-order and second-order roots. But the internal cycling rates of Pand K are smaller than roots that were <0.5mm in diameter. There is no internal cycling of Mg in both the first-order and second-order roots, but ther is the internal cycling of Mg in Fraxinus mandshurica roots that were <0.5mm in diameter.Root order may be an important indication of the internal cycling of nutrient in dead fine roots.