|其他摘要||The leaf economics spectrum (LES) is a combination of chemical, structural and physiological traits. It reflects the trade-off strategy how plants obtain resources from environment and has currently become one of the key issues in global ecology. Although it has been widely used and extended to various fields, there is no a unified explanation about its formation mechanism and driving force. Mean annual precipitation mainly ranges from 133 to 5300mm, which almost involves main vegetation types. However, some large geographic regions are poorly represented in global, especially in China etc. So it is very important to examine whether a leaf economic spectrum exists and discuss its driving force in the regional scale. Four desert plants in three representative areas including Apocynum venetum, Eleagnus angustifolia, Alhagi sparsifolia and Kareliniacaspia which lived in the arid land of Xinjiang were chosen as research materials. Six typical leaf traits such as leaf carbon assimilation rate (A), leaf dark respiration rate (Rd), leaf nitrogen concentration (N), leaf phosphorus concentration (P), leaf mass per area (LMA), leaf photosynthetic nitrogen use efficiency (PNUE) were measured. The aim of this study was to settle the position of four desert plants in the global leaf economic spectrum, to examine that a leaf economic spectrum existed within four desert plants and to explore how climate factors and leaf venation traits modulated it.
Our main results were identified as follows:
(1) All traits variation ranges of the four desert plants in the arid land were basically the position of low pay-off strategies in LES. The relationships among these traits were similar to the global results, and the relationships of traits on mass explained the trade-off strategies of desert plants better. The convergence of total leaf traits variation occurred among these species. The principal components axis totally explained 80% of the leaf trait variances, PCA1 and PCA2 explained 59.12% and 20.43% of the leaf trait variances, respectively. The results provided further evidence that the leaf economic spectrum might exist in desert plants. In addition, Alhagi sparsifolia and Karelinicaspia would be more inclined to have thicker leaves, slow photosynthetic rate than Apocynum venetum and Eleagnus angustifolia for their survival.
(2) A leaf economic spectrum existed within four desert plants. There was difference of leaf traits on mass and on area in the same species from different geographic distribution sites. For their variation extent, however, the variation degree of Apocynum venetum and Eleagnus angustifolia was much smaller than that of Alhagi sparsifolia and Kareliniacaspia.
(3) The leaf economic spectrum of four desert plants in the arid land was largely influenced by climate. In hotter, drier areas, leaf mass per area (LMA) and leaf nitrogen concentration on area (Na) were higher, while leaf carbon assimilation rate on mass (Am), leaf dark respiration on mass (Rdm) and photosynthetic nitrogen use efficiency (PNUE) were lower. The negative relationship between leaf mass per area (LMA) and leaf carbon assimilation rate on mass (Am), the positive relationship between leaf nitrogen concentration on mass (Nm) and leaf carbon assimilation rate on mass (Am) and the negative relationship between leaf mass per area (LMA) and leaf phosphorus concentration on mass (Pm) became weaker and weaker, while other relationships showed different responses. With the increasing of traits number, the modulation of leaf traits in this frame by climate became less. Only 78.9% of total trait variation could be explained. Climate was a main driving force which leaded to the convergence variation on leaf economic traits in the arid land.
(4) The venation theory could well explain the variation of leaf traits from the physiological level in desert plants. There was difference of leaf venation traits among these desert plants from different geographic distribution sites. All these trends showed that Mosuowan population was highest, Cele population was next and Turpan population was lowest. It indicated that these trends largely linked to climate. It was shown that vein density (VD), leaf loopiness of veins (ξ) and leaf distance between veins (d) would all decrease at drier sites.All species between vein density (VD) and leaf area (LA), leaf mass per area (LMA) were negatively correlated with each other, and were weak positively correlated with leaf carbon assimilation (Am).|