中文摘要：

植物的光合作用是评估全球变化背景下碳循环的重要环节。目前,氮沉降增加日益明显,作为植物生长关键因子的可利用氮将对植物的光合生理生态过程产生影响。以长白山阔叶红松林主要树种红松和紫椴的幼苗为例,通过模拟氮沉降增加（氮添加量分别为0、23、46和69 kg N hm^-2a^-1）的方法,利用Li-6400光合测定系统分别测算了两个树种的最大净光合速率（A_（max））、气孔导度（G_（smax））和水分利用效率（WUE）的值,并测算了叶氮含量、叶绿素含量、比叶面积、光合氮利用效率（PNUE）的值。通过分析A_（max）随不同施氮量的变化规律,同时结合其他叶片特征参数的变化,进一步探讨植物光合随氮添加的变化原因。研究结果显示：两个树种的A_（max）值在0—46 kg N hm^-2a^-1的氮添加范围内随施氮量的增加而增大,继续增加施氮量至69 kg Nhm^-2a^-1则出现下降。叶绿素含量、G_（smax）、PNUE和比叶面积在不同的氮添加水平下的变化规律与A_（max）的一致,且均与A_（max）呈显著正相关关系。叶氮含量与A_（max）的值仅在0—46 kg N hm^-2a^-1氮添加范围内呈显著正相关。A_（max）与WUE的相关关系不显著。相同氮添加水平下,氮添加对阔叶树种紫椴各生理生态参数（A_（max）、G_（smax）、叶氮含量、比叶面积、PNUE和WUE）的促进程度高于对针叶树种红松各生理生态参数的促进程度。研究结果可为评估氮沉降增加背景下我国东北地区的碳循环提供依据。

英文摘要：

Photosynthesis is an important factor when evaluating the carbon cycle under global climate change scenario.Available nitrogen is a key nutritional factor for plant growth, which affects plant photosynthesis in case of high nitrogen deposition. The ecophysiology parameters of two dominant species （Pinus koraiensis and Tilia amurensis） were studied in a broadleaved-Korean pine mixed forest on Changbai Mountain through nitrogen deposition experiments. The nitrogen input levels were 0, 23, 46, and 69 kg N hm^-2a^-1, respectively. The maximum net photosynthetic rate （Amax）, stomatal conductance （Gsmax）, and water use efficiency （WUE, μmol/mmol ） were measured using a Li-（M00 portable photosynthesis system under different nitrogen input levels. Additionally, leaf nitrogen content, leaf chlorophyll content, specific leaf area, and photosynthetic nitrogen use efficiency （PNUE, μmol mo1^-1 s^-1） were also measured. In this paper, the variation in Amax with increasing nitrogen input was analyzed, and the reason was explored combined with variations in other leaf traits parameters （ G leaf chlorophyll content, leaf nitrogen content, PNUE, WUE, and specific leaf area） under the same treatments. The results showed that nitrogen addition （ 0--46 kg N hm^-2a^-1） resulted in a significant increase in Amax, and when the added nitrogen was further increased to 69 kg N hm^-2a^-1, the Amax decreased. The variations of Gsmax, leaf chlorophyll content, PNUE, and specific leaf area was similar to that of Amax under different nitrogen input levels. Significantly positive relationships were noted between Amax and leaf traits such as G leaf chlorophyll content, PNUE, and specific leaf area under the different nitrogen input levels. A positive relationship was noted between A max and leaf nitrogen content only for nitrogen addition of 0--46 kg N hm^-2a^-1. No significant correlation was noted between Amax and WUE. The increase of eco-physiological factors of Tilia amurensis （Amax=, Gmax, leaf nitrogen con