Carbon and nitrogen dynamics in early stages of forest litter decomposition as affected by nitrogen addition

施氮条件下森林凋落物分解早期的碳和氮动态

The effects of nitrogen （N） availability and tree species on the dynamics of carbon and nitrogen at early stage of decomposition of forest litter were studied in a 13-week laboratory incubation experiment. Fresh litter samples including needle litter （Pinus koraiensis） and two types of broadleaf litters （Quercus mongolica and Tilia amurensis） were collected from a broadleaf-korean pine mixed forest in the northern slope of Changbai Mountain （China）. Different doses of N （equal to 0, 30 and 50 kg.ha^-1yr^-1, respectively, as NH4NO3） were added to litter during the experiment period. The litter decomposition rate expressed as mass loss and respiration rate increased significantly with increasing N availability. The mass loss and cumulative CO2-C emission were higher in leaf litter compared to that in needle litter. The dis- solved organic Carbon （DOC） concentrations in litter leachate varied widely between the species, but were not greatly affected by N treatments. Regardless of the N addition rate, both N treatments and species had no significant effect on dissolved organic N （DON） concentrations in litter leachate. About 52-78% of added N was retained in the litter. The percentage of N retention was positively correlated （R^2=0.9 1, p〈0.05） with the litter mass loss. This suggested that a forest floor with easily decomposed litter might have higher potential N sink strength than that with more slowly decomposed litter.

通过13周实验室培养试验，研究了施氮和树种对森林凋落物早期分解过程中碳和氮动态的影响，新鲜凋落物样品包括针叶（红松）和两种阔叶（蒙古栎和紫椴），采自长白山北坡阔叶红松林。试验共包括3个施氮梯度（0、30和50kg·ha^-1．a^-1 NH4NO3）。以质量减少和呼吸速率表征的凋落物分解速率随可溶性氮的增加而显著增加，阔叶凋落物质量减少和累积CO2—C释放量比针叶凋落物高，不同物种之间凋落物沥出物中溶解性有机碳（DOC）浓度变化较大，但施氮处理对DOC的影响不大。除了施氮率，施氮处理和物种对凋落物沥出物中溶解性有机氮（DON）浓度都没有显著影响。有52—78％的外加氮滞留在凋落物中，氮滞留率与凋落物质量减少呈正相关（R^2=0．91，P〈0．05），这表明易分解凋落物覆盖的森林地面比分解较慢的凋落物覆盖的森林地面有更高的N汇潜力。图3表1参40。