青藏高原区域不同功能群植物氮磷生态化学计量学特征

生态化学计量学为揭示植物养分利用状况及植物对环境的适应策略提供了重要手段,研究不同功能群植物在区域尺度生态化学计量学特征中所产生的贡献,有助于揭示区域尺度植物元素特征的形成机制。已有研究多是从不同功能群植物元素生态化学计量学特征的比较上进行分析,未能对每种功能群植物元素含量随地理因子和气候因子的变化规律展开探讨。基于生态化学计量学理论,对青藏高原区域不同功能群植物(豆科、禾本科、莎草科、杂类草)叶片水平N、P元素含量随纬度、海拔、年降水量、年均温度的变化规律展开研究,探讨不同植物功能群在区域尺度植物生态化学计量学特征中所产生的贡献,尝试从植物功能群角度揭示青藏高原高寒区域N、P元素含量特征的形成机制。结果显示,1)不同功能群植物叶片元素含量差异显著,豆科植物N、P元素含量最高,禾本科植物N、P含量最低,N/P比值在不同功能群间差异不显著;2)随纬度变化,莎草科植物P元素及杂类草N元素含量变化显著;随海拔变化,豆科、禾本科植物及杂类草叶片N元素含量变化较为显著;随年降水量和年均温度的变化,杂类草和莎草科植物叶片N、P含量变化显著;3)莎草科植物N、P含量对纬度和降水的响应趋势与区域内所有植物叶片N、P含量对纬度和降水的响应趋势一致,豆科、禾本科及杂类草植物叶片元素含量对海拔和温度的响应趋势与区域内所有植物叶片元素平均含量对海拔和温度的响应趋势一致。研究表明,不同功能群植物元素特征对环境因子的响应不同,植物功能群组成对区域尺度植物生态化学计量学特征有重要作用,但在较大的植物结构层次上(如植物群落、生态系统、区域或全球尺度等),不同功能群植物之间的相互组合会抵消或掩盖掉某一类群的特性,从而对区域尺度植物元素特征的变化规律产生影响。

Characteristics of N and P stoichiometry of plants in different functional groups in the Qinghai-Tibet Plateau regions

Ecological stoichiometry provides an important method for the determination of plant nutrient utilization and plant environmental adaptation strategies. Nitrogen (N) and phosphorus (P) stoichiometries play critical roles in the functions and structures of ecosystems by affecting important ecological processes. Studying the contributions of different functional groups to ecological stoichiometry could help to reveal the formation mechanisms of plant elements on a regional scale. Currently, most studies focus on comparison of ecological stoichiometry characteristics among different functional groups, but fail to discuss the variation in element contents among different plant functional groups with regard to geographic and climatic factors. The Qinghai-Tibet Plateau alpine region has a much higher elevation and lower temperature than the other regions in the same latitude. Thus, this region could provide ideal research conditions for investigating the relationship between plant element characteristics and variations in geographic and climatic factors. Using ecological stoichiometry theory, we analyzed the patterns of N and P contents among different functional groups (legumes, grasses, sedges and forbs) and how these varied with geographical factors (latitude and altitude) and climatic factors (mean annual precipitation and mean annual temperature) in the Qinghai-Tibet Plateau alpine region. We used these data to explore the formation mechanisms of plant N and P features in this region. The results showed that: 1) N and P contents were significantly higher in legumes and much lower in grasses, and that no obvious differences in N/P were found between the four groups. 2) As the latitude increased, the P contents of sedge folia decreased, while the N contents of forb folia increased. The P contents of all sample pool folia were found to decrease. As the altitude increased, the N contents of legume, grass, and forb folia decreased significantly, and the N contents of all plant folia also decreased. As the mean annual precipitation (MAP) increased, the N contents of sedge and forb folia, as well as that of all plant folia increased. As the mean annual temperature (MAT) increased, the N contents of sedge folia decreased, while their P contents increased. All plant folia element contents were found to have no correlation with MAT. 3) Folia N and P contents varied with latitude and MAP in sedges, and with altitude and MAT in legumes, grasses and forbs. These results are consistent with the patterns observed on a regional scale. These results indicate that the characteristics of element contents in different plant functional groups vary with geographic factors and climatic factors, and that plant species composition plays an important role in the regional-scale ecological stoichiometry. These results also show that the combination of different functional group plants can offset or cover up the characteristics of some groups, thereby affecting ecological stoichiometry on a regional scale.