Nariation In Leaf Metabolic Ecological Exponent And Leaf Traits Along Environmental Gradients

The metabolic ecology theory was main for the entire plant at present, explore the metabolic ecology mechanism at leaves can improve the understanding of the metabolic ecology theory. Plant leaf traits is the strategy that plant adapt to the environment, which was reflected at the leaf scale. Leaf traits reveal the adaptive strategies of plants to their habitat conditions in the process of evolution and may vary with changes in environment. Consequently, the study to investigate the pattern of variation in plant leaf traits and relation of it to environmental factors in the context of global change has important significance. Previous studies have demonstrated that metabolic exponent varied across aridity gradients. We hypothesized that plant leaf traits (leaf carbon isotope composition, stomatal density, leaf area, leaf mass, etc.) and their relatioships, and metabolic rate varies across environmental gradients, and thus leads to the variation of leaf metabolic ecological exponent.Altitude is an important topographical factors. Changes in elevation comprehensive reflects the gradient temperature, precipitation, and light. We explored the metabolic exponent in response to altitudinal gradient at the leaf level, and through the integration of large-scale data analysis, to reveal leaf mass per area (LMA) variation with large-scale environmental gradients. We also measured specific leaf area, leaf carbon content, leaf nitrogen content, leaf phosphorus content, leaf carbon isotope composition (δ13C) and stomatal density in Mt. Tianmu Reserve, in order to analyze leaf trait variation along the altitudinal gradient. The results obtained are as follows:1. Leaf metabolic exponent varies with environmental gradient. The results indicated that leaf metabolic exponent range from-0.423to-0.344, which is different from plant metabolic exponent (-0.25). These results are consistent with the theoretical prediction. Leaf metabolic exponent in individual leaves range from0.577to0.656, close to the change range of2/3. It is shown that surface-area limits on leaf metabolism rate, is consistent with the morphology that was restricted by leaf photosynthesis and respiration. 2. In a certain temperature range, LMA (1/SLA) decreased with MAT, which is consistent with the theoretical prediction. LMA of China’s flora that have been published (148.29g·m-2) was significantly higher than the global average (127.7g·m-2), a potential cause for such a high LMA may be the low soil P content in China. There were significant differences in LMA among different plant functional types. Trees produced more LMA than shrubs and herbs did. Among woody plants, evergreen woody species had significantly higher LMA than deciduous woody species. Similarly, there was higher LMA in coniferous than in broadleaf species. LMA increases from south to north China, longitudinal gradients also exhibit a decrease from west to east. LMA decreased with MAP, but increased with MAE and AI. MAE and AI were the strongest climatic variable modulating LMA.3. Leaf trait varies with altitude in subtropical monsoon climate region, which may be one of the reasons that drive leaf metabolic exponent changed. The results showed that specific leaf area decreased with increasing altitude, stomatal density increased with increasing altitude. Leaf carbon, nitrogen, phosphorus content along an altitudinal variation was not significant.813C value in Mt. Tianmu is substantially lower than those in desert regions. There is no significant difference in δ13C between vascular plants (-29.9‰) and mosses (-29.1‰), however, trees (-29.0%o) had significantly higher δ13C values than herbs (-30.3‰).δ13C was positively correlated with altitude. The altitudinal trend in δ13C is the consequence of the interaction between temperature, atmospheric pressure and soil water content.4. Leaf traits arc linked to each other. Specific leaf area was positively correlated with leaf nitrogen content, leaf N:P was positively correlated with leaf phosphorus content, leaf nitrogen content was positively correlated with leaf phosphorus content. leaf nitrogen content and leaf phosphorus content, leaf mass and leaf area, leaf water content and leaf area, leaf water content and leaf mass, leaf thickness and leaf area showed high goodness of fit and allometric relationships. There was significant positive relationship between leaf mass and leaf area at each altitude. The slopes showed a great degree of variability among altitudes (0.859-1.299). Furthermore, there was a highly significant positive relationship between the estimated slopes and altitude.The above results showed that environment can drive the variation of leaf traits, relationship between leaf traits, and metabolism, thus affecting leaf metabolic exponent. It confirmed the hypothesis of this study, expanded and improved the metabolic ecology theory, and its application in predicting the level of plant organs. It also contributed to the study of leaf ecology, leaf economic spectrum and carbon cycle.