氮添加对油松不同径级细根分解及其养分释放的影响

采用4个梯度的林地氮处理(N₀、N₃、N₆和 N₉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1～2 mm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0～0.4 mm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.

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

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 were7.6%, 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).