Leaf Traits And Relationships Variation In Two Quercus Species Along An Altitudinal Gradient In Qinling Mountain

Local-scale study on leaf traits and their relationships in a single species along environmental gradient is essential for determining the pattern of scaling up eco-physiological processes from the leaf to the ecosystem level. Altitudinal gradients provide an unique and sometimes the best opportunities to study plant responses and adaptation under the global climate change since the climate and vegetation can transform dramatically in short distances along an altitudinal gradient. Here, we quantify thirty-nine leaf traits included eleven morphological traits, fifteen chemical composition and twelve physiological ecological characteristics change in two individual species, Quercus aliena var. acuteserrata (Qa, deciduous) and Quercus spinosa (Qs, evergreen), along an altitudinal gradient in Qinling Mountain, to explore how leaf traits change along the altitudinal gradient within a single species level on the local-scale number, and then the different patterns of two close relatives species which with different life form and leaf phenology responses to environmental were compared. The main results are showed as follow:(1) The leaf shape and size was relatively constant in Qa along the altitudinal, only the dry weight was higher and the leaf shape index was smaller in low altitude than that in medium altitude gradient. There were clear downward trends in the leaf area, perimeter, leaf length and width along the altitude gradient especially the value in the high and medium altitude was significantly less than that in low-altitude suggesting that the size of the Qs leaves more visible change with altitude.(2) Leaf carbon (C), nitrogen (N), phosphorus (P) content in Qa is higher than that in Qs. The N:P ratio changed obviously along altitude in Qa, but the value of the N:P ratio in two species were both greater than17, which points that the growth of two species were both restricted by the P in the Qinling. Non-structural carbohydrate content decreased with increasing altitude in Qa, yet which escalated at high and medium altitude for Qs implying there were different carbon resource allocation and use strategies in two kinds of plant. (3) Althought there were different trends of specific leaf area and leaf dry matter content change along the altitudinal gradient in two species, the same negative relationship between Leaf dry matter content and specific leaf area was also found suggest leaf traits covariant, at least in our study, is subsistent.(4) The relationships between plant functional traits were complex and possess different patterns in two species. There were many significant correlations between leaf morphological traits and chemical composition characteristics too, but the correlations mainly concentrated in four chemical composition characteristics like starch, P, N:P ratio and ash in Qs; while converged in four morphological traits such as leaf dry weight, dry matter content specific leaf area and the L:W ratio.(5) There were different patterns of photosynthetic physiological response to the altitudinal gradient in two species. Leaf photosynthetic rate at high altitude was significantly smaller in Qa, while it significantly larger at high altitude in Qs. Showed that there were different modes of response to the same environmental gradient in different species, the species with different leaf traits adapted their living environment in different strategies.In summary, there were different patterns and adaptation strategies of the morphology traits, chemical composition and photosynthetic physiological and ecological characteristics change with the altitudinal gradient between two species. Which reflecting the leaf traits contain different patterns of response to environmental gradients between the deciduous species and evergreen species. The Qa in high altitude were suffered by the low temperature stress led to break the carbon balance and growth restriction which supports the "Source-limitation" hypothesis; but Qs in high altitude which possess adequate supply of carbon was allocation to against stress support the "Sink or growth-limitation" hypothesis.