氮添加对油松不同径级细根分解及其养分释放的影响

Response of decomposition and nutrient release in different diameter fine roots of Pinus tabuliformis plantation to N addition

采用4个梯度的林地氮处理(N_0、N_3、N_6和N_9依次为0、3、6和9 g N·m-2·a-1),利用分解袋试验,研究了N添加对油松不同径级细根分解及养分释放过程的影响.结果表明:细根分解过程分为快速分解(0~60 d)和慢速分解(60~300 d)两个阶段.0~0.4、0.4~1和1~2mm细根分解的质量百分数在第60天分别为7.6%、10.4%和11.4%,在第300天分别为19.8%、23.5%和30.5%,说明较细的根系分解较慢.N添加显著降低了0~0.4 mm细根的分解速率,但对0.4~1和1~2 mm细根分解速率无显著影响,与对照(N0)相比,N3、N6和N9处理试验期间分解速率分别降低2.1%、4.5%和5.8%.N添加显著增加了0~0.4和0.4~1 mm细根C和N残留率,但对1~2 mm细根C和N残留率无显著影响,且对3个径级细根P残留率无显著影响.与对照相比,N3、N6和N9处理分别增加了0~0.4 mm细根中8.1%、9.4%和4.5%的C残留率和5.3%、16.3%和16.7%的N残留率;同时增加了0.4~1 mm细根中2.5%、2.5%和0.9%的C残留率和0.9%、2.3%和3.9%的N残留率.0~0.4、0.4~1 mm细根C、N、P迁移模式总体表现为直接释放,而1~2 mm细根N为富集-释放模式.氮沉降可能主要通过影响0~0.4mm细根(主要为1和2级细根)的分解过程,从而降低细根的分解速率.

We examined the effects of four nitrogen （N） addition treatments, i.e., N0（0 g N·m^-2 a^-1）, N3（3 g N·m^-2 a^-1）, N6（6 g N·m^-2 a^-1） and N9（9 g N·m^-2 a^-1） on the decomposition and nutrient release processes of fine roots with different diameters in Pinus tabuliformis plantation using litterbag method. The results showed that the decomposition process of fine roots could be divided into rapid （0-60 d） and slow （60-300 d） decomposition stages. The decomposition mass percentages of fine roots with 0-0.4 mm, 0.4-1 mm and 1-2 mm were 7.6%, 10.4% and 11.4% on the 60th day and 19.8%, 23.5% and 30.5% on the 300th day, respectively, indicating that finer root had lower decomposition rates. N addition reduced significantly the decomposition rates of fine roots with 0-0.4 mm diameter, but had no significant influence on those of root with 0.4-1 mm and 1-2 mm diameters. Compared with the control, N3, N6 and N9 treatments reduced the decomposition rates by 2.1%, 4.5% and 5.8%, respectively. N addition increased both the C and N remaining percentages of fine roots with 0-0.4 mm and 0.4-1 mm diameters, but had no significant influence on those with 1-2 mm diameters. Additionally, P remaining percentages of fine roots had no response to the N addition. Compared with the control, N3, N6 and N9 treatments increased the root C remaining percentages by 8.1%, 9.4% and 4.5% in 0-0.4 mm diameter roots, and 2.5%, 2.5% and 0.9% in 0.4-1 mm diameter roots, respectively. Similarly, N3, N6 and N9 treatments also increased the root N remaining percentages by 5.3%, 16.3% and 16.7% in 0-0.4 mm diameter roots and 0.9%, 2.3% and 3.9% in 0.4-1 mm diameter roots, respectively. The transfer models for C, N and P in 0-0.4 mm and 0.4-1 mm diameters were direct releasing, and the transfer models for N showed an enrichingreleasing model. N deposition may decrease the fine root decomposition rates mainly by affecting the decomposition process of fine roots with 0-0.4 mm diameters （mainly the first two order roots）.