红池坝草地常见物种叶片性状沿海拔梯度的响应特征

Response characteristics of leaf traits of common species along an altitudinal gradient in Hongchiba Grassland,Chongqing

叶片性状是决定植物光合能力和羧化能力的关键因素,研究叶片性状在海拔梯度上的变化特征是解释植物对于环境变化的适应策略的重要手段。以分布于红池坝(109°58'E,31°30'N)草地的5个常见物种红三叶(Trifolium pratense)、老鹳草(Geranium wilfordii)、紫菀(Aster tataricus)、火绒草(Leontopodium leontopodioides)和绣线菊(Spiraea prunifolia)为研究对象,分析了所有物种(n=56)和不同物种的叶片比叶重(LMA)、叶氮含量(单位面积氮含量Narea、单位重量氮含量Nmass)以及叶片δ13C含量沿海拔梯度(815—2545m)的变化趋势及叶片性状之间的关系。研究结果表明:所有物种样品(n=56)的比叶重(LMA)、Narea和δ13C含量沿海拔梯度的增加呈显著增加趋势;Nmass沿海拔梯度的变化趋势不明显;δ13C含量与LMA、Narea呈现极显著正相关关系;不同物种的叶片性状沿着海拔梯度的响应特征有所不同,绣线菊(S.prunifolia)和老鹳草(G.wilfordii)的叶片性状沿海拔梯度的分布规律与所有物种(n=56)样品分布规律一致,红三叶(T.pratense)、紫菀(A.tataricus)、火绒草(L.leontopodioides)的各叶片性状沿海拔梯度的分布特征有所不同。

Abstract： Leaf Mass per Area （ LMA）, mass- and area-based nitrogen content （leaf N per unit area, Narea; leaf N per unit mass, Nmass ） and foliar δ^133C are fundamental leaf traits, describe dry mass in leaves and the return on investments of nutrients, and operates largely independently of growth form, plant functional type or biome. As a reflection of the per-area cost of producing new leaves, LMA significantly correlates with leaf N. Leaf N is strongly correlated with photosynthetic capacity, as N is essential for the synthesis of Rubisco, the key enzyme of photosynthesis. Foliar δ^13 is associated with the p（CO2）i/p（CO2）a （intercellular/ambient oartial pressure） ratios of COo that are also highly correlated withphotosynthesis. These correlations provide a useful link between processes on short-term leaf-level scales and on long-term plant-and community-level scales. Understanding the patterns of these fundamental traits is essential for predicting ecosystem functioning in response to environmental change. To date, the most representative research about leaf traits and foliar δ^13C has been carried out by Kfirner et al and Wright et al at the global scale and their findings have been confirmed in other studies. Nevertheless, there remains the opportunity for further studies on the adaptive significance and function of leaf traits in different environments and for different species. And changes of leaf traits along an altitudinal gradient are ofparticular use in the study of the adaptive characters of plants under the influences of environmental changes. In this study, five common species of the grassland, Trifolium pratense, Geranium wilfordii, Aster tataricus, Leontopodium leontopodioides and Spiraea prunifolia, were particularly studied on the altitudinal transect （815--2545 m） in Hongchiba （109°58＇ E, 31°30＇ N）, Chongqing. To measure LMA, mature, fully expanded and healthy leaves were harvested from the middle of plants of each of the five species in plots along the altitudinal gradient （ not all species occurred in all plots）. We avoided aging, discolored, and damaged leaves. The leaves were placed on A4 paper （21 cm×29.7 cm） with a background of a blackcloth sized 1 m^2, and then photographed using a camera on a tripod. The leaves were then dried in an oven at 85 ℃ for 24 hours and weighed to 0.01 g. ENVI software was used to calculate the leaf area/A4 paper area ratio, and together with leaf weight to calculate LMA. Leaf samples were crushed by a mortar and then measured for N and δ^13C on a Finnigan MAT253 isotope ratio mass spectrometer to a precision of ±0.1‰. The patterns of leaf traits （ including leaf mass per area （ LMA）, leaf nitrogen content, and foliar δ^13C） were analyzed both for all data pooled （n = 56） and specific species. The results showe万 that in all data pooled, LMA, Narea, and foliar δ^13C had positive correlations with altitude; the pattern of Nmass not significantly; LMA and N showed significantly positive relationships with foliar δ^13C; the adaptive features of leaf traits among different species were not consistent, leaf traits of S. prunifolia and G. wilfordii showed the same trends as all data pooled along the altitudinal gradient, whereas, T. pretense, A. tataricus and L. leontopodioides showed different patterns with increasing altitude.