氮-硫沉降对邓恩桉及杉木人工林凋落物C和N残留率的影响

采用二次正交回归旋转设计，以Na2S04为硫源、46％CO（NH2）2为氮源模拟氮一硫沉降，分析了不同氮一硫沉降水平下邓恩桉（Eucalyptus dunnii Maiden）和杉木Cunninghamia lanceolata（Lamb．）Hook．]人工林凋落物中C和N残留率的动态变化，并采用Olson指数模型对c和N分解模型进行拟合。结果表明：在不同氮一硫沉降水平下，在1年内随处理时间延长邓恩桉和杉木凋落物的C和N残留率总体上均呈下降趋势；且N较难释放，总体表现为“释放一富集一释放”的动态过程；但在不同氮一硫沉降水平下及不同处理时间凋落物中C和N残留率均有极显著差异（P〈0．01）。凋落物中C和N分解的Olson指数模型的相关性总体上达到极显著或显著（P〈0．05）水平；邓恩桉和杉木凋落物中C和N的平均分解系数分别为0．877和0．208、0．704和0．600，平均周转期分别为3．148和15．877a，4．090和4．947a，显示凋落物中C释放速率大于N，杉木凋落物的C周转期大于邓恩桉但其N周转期则小于后者。在Na2SO4164kg·hm-1·a-1的水平下，氮沉降对邓恩桉凋落物的C和N释放及杉木凋落物的N释放有促进作用，但对杉木凋落物的C释放有抑制作用；在46％CO（NH：）：150或256kg·hm-2·a-1。的水平下，硫沉降也具有同样的作用。随分解时间的延长，邓恩桉凋落物的C／N值呈波动但总体减小的趋势，而杉木凋落物的C／N值呈波动趋势；但在不同氮一硫沉降水平下凋落物的C／N值均有极显著差异，且邓恩桉凋落物C／N值的变化幅度总体上大于杉木凋落物。

Effect of simulated nitrogen-sulfur deposition on residual rates of C and N in litters of Eucalyptus dunnii and Cunninghamia lanceolata plantations

Taking Na2SO4 as sulfur source and 46% CO（NH2）2 as nitrogen source to simulate nitrogen- sulfur deposition, dynamic change of residual rates of C and N in litters of Eucalyptus dunnii Maiden and Cunninghamia lanceolata （Lamb.） Hook. plantations under different levels of simulated nitrogen-sulfur deposition was studied by the quadratic rotation-orthogonal combination design, and decomposition models of C and N were fitted by the Olson exponential rates of C and N in litters of E. dunnii and C. model. The results show that during one year, residual lanceolata appear generally a decreasing tendency with prolonging of treatment time under different levels of nitrogen-sulfur deposition, and N release is more difficult with the dynamic process ＂ release-enrichment-release＂, but there are extremely significant differences in residual rates of C and N of litters among different levels of nitrogen-sulfur deposition and among different treatment times （P〈0.01）. The correlation of Olson exoonential models of C and Ndecomposition in litters reaches generally extremely significant or significant （P〈0.05） levels. Average decomposition coefficients of C and N in litters of E. dunnii and C. lanceolata are O. 877 and 0. 208, 0. 704 and 0. 600, average turnover periods of them are 3. 148 and 15. 877 a, 4. 090 and 4. 947 a, respectively, indicating that C release rate in litters is higher than that of N, and C turnover period in C. lanceolata litter is longer than that in E. dunnii litter but N turnover period of the former is shorter than that of the latter. Under level of Na2SO4 164 kg · hm-2 · a-1 , nitrogen deposition has a promoting effect on C and N release in E. dunnii litter and on N release in C. lanceolata litter but has a inhibiting effect on C release in C. lanceolata litter, and sulfur deposition has the same effects under level of 46% CO （ NH2 ） 2 150 or 256 kg · hm-2 · a-1 With prolonging of decomposition time, C/N value in E. dunnii litter appears a trend of fluctuation and general decreasing, while that in C. lanceolata litter appears a fluctuation trend. There are extremely significant differences in C/N value in litters under different levels of nitrogen-sulfur deposition, and variation range of C/N value in E. durmii litter is generally bigger than that in C. lanceolata litter.