Abstract:

Decomposition and its influencing factor as well as N dynamics of fine woody root (<2 mm diameter) and grass root in four vegetation forms of birch (Betula luminifera)-grass (Hemarthria compressa) compound(HN)，birch (Betula luminifera) plantation (H), grass (Hemarthria compressa) (NC)，cedar (Cryptomeria fortunei) plantation(LS) which were all founded in the process of converting farmland to forest or grass. This study was conducted in Hongya，China with the intact-core technique. The decomposition rate pattern showed a good fit for the Olsoris single-exponential model and the decomposition constant(k) for the four vegetation models were 1.06,0.93,1.32,0.86 a^-1 respectively，with an annual loss in dry weight of 65.49%,60.55%,73.32%,57.51%. C/N of roots was negative significantly correlated with the root decomposition rate for all models during the one year experiment. C concentration of birch was also negative significantly correlated with fine root decomposition rate (P≤0.01). After 90 days lignin concentration relative to initial lignin content of birch and cedar fine roots was negatively correlated with fine root decomposition rate (P≤0.05). As for birch-grass compound model its lignin concentration of mixed roots showed a poorly correlation with fine roots decomposition rate (P=0.087). The rate of N release was strongly influenced by the initial N concentration of the roots. After one year fine root of HN with the highest initial N concentration released the most N and LS with the lowest initial N concentration released the least N.

Key words: models of converting farmland to forest, fine root, grass root, decomposition, N dynamics