关键词: 西藏, 薄毛海绵杜鹃, 林线, 种群分布

Abstract: The experiments of decomposition of fine roots were carried out in pine forest(PF), pine-broadleaved mixed forest(PBF)and evergreen broadleaved forest(EBF)in the Dinghushan biosphere reserve. Regression analyses showed that the power function of X/X₀=e^-kt with Adj.r²(0.989- 0.993)very well fitted with the data of dry mass loss against time(year). The theoretical values of annual decomposition rate of roots with diameter≤2mm derived from the equations were 43.44%, 43.97%, 46.91% for PF,PBF and EBF respectively and also fitted very well with the measured values(43.15%, 43.90%, 45.68%). Decay coefficients(K)were 0.570 for PF, 0.579 for PBF and 0.633 for EBF. The decomposition rate of roots with diameter of 2-4mm is lower(38.54%)than that of roots with diameter≤2mm.No significant difference of the decomposition rates was found between the decomposing roots buried in mesh bags of 0.25mm and 1.00mm. At the 170th day, about 95% soluble carbohydrate was leached out. At the 300th day, The released rate ranged 20.2%-57.3% for N, 52.3%-82.5% for P, 68.6%-83.4% for K, 75.9%-79.1% for Mn and 41.7%-79.1% for Zn. The negative values(-14.8% to -70.2% for Ca, 5.2% to -59.6% for Mg)implied that a tendency of accumulation for element Ca and Mg occured during decomposition proceses.

Key words: Tibet, Rhododendron aganniphum var. schizopeplum, timberline, population distribution.