红池坝草地常见物种叶片性状沿海拔梯度的响应特征

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 δ13C 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 δ13C is associated with the p(CO2)i/p(CO2)a(intercellular/ambient partial pressure) ratios of CO2 that are also highly correlated with photosynthesis.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 δ13C has been carried out by Krner 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 of particular 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 black cloth sized 1 m2,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 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 δ13C) were analyzed both for all data pooled(n=56) and specific species.The results showed that in all data pooled,LMA,Narea and foliar δ13C had positive correlations with altitude;the pattern of Nmass was not significantly;LMA and Narea showed significantly positive relationships with foliar δ13C;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.