| In the past 100 years, global climate has changed vastly, particularly the increase of atmospheric CO2 concentration and global warming are becoming increasingly apparent. Although the mechanisms for these changes have been not resolved thoroughly, climate change has widespread and profound effects on many plant's biological processes, which leads the interactions between plant and environment to be more complicated. Due to the long-term limitation of low temperature, plant species growing in alpine ecosystem is thought to be very sensitive to global climate change, especially increasing temperature, and plant species of different developmental stage could be different in the sensitivity to climate change. Meanwhile, owing to a broader geographic range, widespread plant species encounters diverse habitats, and hence populations from contrasting habitat could be also different in response to environmental change. In this study, to better understand and predict the effects of climate change on plant species in the future, by means of stable isotope technique in conjunction with plant morphological and structural properties we investigated the ecophysioligical responses of leaf fitness-related traits in alpine plant species Picea crassifolia, Picea likiangensis var. linzhiensis, Abies georgei var. smithii, Quercus aquifolioides and Larix griffthiana, and in widespread plant species Pinus tabulaeformis, Hippophae neurocarpa (ssp. neurocarpa and ssp. stellatopilosa) and Ostryopsis (Ostryopsis davidiana and Ostryopsis nobilis) along environmental gradients such as precipitation, temperature and altitude, to explore the adaptability of them to environmental changes.Along altitudinal gradients, our results showed that leaf traits in P. crassifolia had significant differences between mature and juvenile trees, while leaf traits in P. likiangensis var. linzhiensis and A. georgei var. smithii had no such differences. Moreover,δ13C and LMA were higher in mature trees than those in juvenile trees, whereas other leaf traits showed inconsistent differences between trees of different ages along altitudinal gradients. Our results also showed that leaf traits in P. crassifolia and A. georgei var. smithii had similar changing patterns in mature and juvenile trees along altitudinal gradients; by contrast, most of leaf traits in P. likiangensis var linzhiensis exhibited markedly differing patterns between mature and juvenile trees:nonlinear vs linear; and leaf traits in L. griffthiana also showed different altitudinal trends between east and west slope of the Sygera Mountains. Further, our data suggested that whether in mature or in juvenile trees, foliarδ13C was closely correlated with other leaf traits in P. crassifolia and P. likiangensis var linzhiensis, while such relationships was lack in A. georgei var. smithii, and foliarδ13C had close relationships with leaf morphological and structural traits, rather than leaf N concentrations in Q. aquifolioides. In addition, foliarδ15N in Q. aquifolioides initially increased and consequently declined with increasing altitude, and was apparently correlated with Nmass,Narea,C:Nand St/N.Across broad environmental scales, we found that leaf fitness traits showed apparent differences among populations of P. tabulaeformis, H. neurocarpa and Ostryopsis, and these differences in leaf traits were contributed to the variations in environmental factors such precipitation, temperature and altitude. As MAP increased, foliarδ13C andδ15N in populations of P. tabulaeformis and H. neurocarpa declined significantly, they decreased markedly only across sites of MAP≤550 mm in populations of Ostryopsis. With increasing MAT, only in Ostryopsis foliarδ13C showed a pronounced declined trend; in contrast, foliarδ15N in populations of P. tabulaeformis, H. neurocarpa and Ostryopsis all had a significant decreasing trend. With increasing altitude, foliarδ13C andδ15N in populations of P. tabulaeformis and Ostryopsis had a markedly upward trend respectively, while foliarδ15N in populations of H. neurocarpa had an apparently downward trend. Along environmental gradients such as precipitation, temperature and altitude, other leaf traits showed inconsistent trends among specie and subspecies. Moreover, we also found that there were close correlations between leaf traits, for example, the positive relationship betweenδ13C andδ15N, and betweenδ13C,δ15N and LMA, Nmass and Narea; but these relationships were affected by species and subspecies. Additionally, compared to ssp. stellatopilosa restricting in a narrow ecological distribution, the values of plasticity index of leaf traits were higher in ssp. neurocarpa with a wide geographical distribution.Overall, we draw the following conclusions:(1) along elevation gradients, there are apparent differences in leaf traits and their changing trends, and their correlations between mature and juvenile trees; and meanwhile such differences are also effected by tree species examined; (2) foliarδ13C and LMA are used as important indicators signaturing tree age and height, whereas other tarits are not due to the effects of tree age and altitude; (3) LMA is primarily responsible for the variations in foliarδ13C with altitude, and leaf N concentrations is the secondary factor, while the effect stomatal parameters on foliarδ13C is not pervasive due to tree age and species specificity; (4) With increasing altitude foliarδ15N shows a initial increasing and then decreasing trend, and is correlated significantly with leaf N concentrations, suggesting N availability has a important role in the shifts of foliarδ15N with altitude, and N cycling is relatively open at around 3300 m; (5) across broad geographic scales, precipitation and temperature have a general and consistent influence on foliarδ13C andδ15N in response to environmental changes, while such a effect is lack for other traits owing species specificity; (6) LMA and leaf N concentrations are two primary factors affecting the response of foliarδ13C to water availability, by contrast, leaf N concentrations and N availability are contributed to affecting the response ofδ15N to water availability; (7) a striking correlation betweenδ13C andδ15N among populations of P. tabulaeformis and Ostryopsis suggests that there are close rinks among carbon, nitrogen and water cycling, and water availability has a strong influence on carbon and nitrogen cycling; (8) for two subspeces of H. neurocarpa, the magnitude of phenotypic plasticity in leaf traits is correlated positively with the level of environmental heterogeneity in their habitats.
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