杉木人工林凋落物量动态对氮沉降增加的响应

 通过野外模拟试验，研究了杉木人工林凋落物量对氮沉降增加的响应。试验设计为4种处理（N0, N1, N2, N3），增加氮量分别为0、60 、120 和240 kg·hm^-2·a^-1。通过3 a监测发现，2005年各处理的年凋落量分别是2 427.50、2 238.10、2 286.66和2 599.50 kg·hm^-2，2006年凋落量分别是1 008.83、1 164.10、1 147.30和976.47 kg·hm^-2，2007年凋落量分别是1 557.85、1 445.60、1 595.85和1 555.85 kg·hm^-2。从3 a的试验时间来看，凋落物总量表现为先下降后上升，高氮处理（N3）前期提高凋落物量的作用比较明显，但随后逐渐表现为抑制作用；中氮处理（N2）逐渐表现为增加凋落物量的作用，低氮处理（N1）作用不明显。不同水平的氮沉降处理对凋落物各组分存在不同影响， N2处理对增加叶凋落物量有一定的促进作用，但N1和N3处理表现为抑制作用；氮沉降处理均表现出降低枝和皮凋落量的作用，但对落果和碎屑物有显著的增加作用。

Responses of Litterfall Production in Chinese Fir Plantation to Increased Nitrogen Deposition

A field simulated experiment was conducted in a Chinese fir plantation to study the effects of nitrogen deposition on the literfall production. Treatments were designed as N0 (0 kg·hm^-2·a^-1), N1 (60 kg·hm^-2·a^-1), N2 (120 kg·hm^-2·a^-1) and N3 (240 kg·hm^-2·a^-1). According to three years’ collection, the annual litterfall production for the four treatments was estimated, respectively, at 2 427.50, 2 238.10, 2 286.66 and 2 599.50 kg·hm^-2in the year 2005, 1 008.83, 1 164.10, 1 147.30 and 976.47 kg·hm-2 in 2006, 1 557.85, 1 445.60, 1 595.85 and 1 555.85 kg·hm^-2 in 2007, suggesting that litterfall production firstly showed a decline then an increase. Compared with N0, N3 treatment increased the litterfall production significantly in 2005, but showed some inhibitive effects in the following years. N2 treatment promoted litterfall production after the first year, but N1 had no consistent effects.. The various components of litterfall revealed different response to nitrogen deposition, with the annual flux for leaf fall responding positively to N2 treatments but negatively to N1 and N3. The treatments decreased the litterfall amount for braches and barks but increased the fractions of fruits and miscellancous materials.