Brazil is a megadiverse country, including two hotspots of biodiversity: the Atlantic Forest and the Cerrado, besides the Amazon region, the vast contiguous tropical forest on Earth, and the Northeast Caatinga, the only arid vegetation type of the country. In these biomes there are several major threatens including land-use and global climatic changes. It is key to understand the biogeochemical functioning of such diverse vegetation to predict future responses in face of these changes. For the first time, there is enough data to investigate broad biogeographic patterns of foliar carbon (C), nitrogen (N), C:N ratio, and associated N stable isotope (δ15N) from a total of 6275 trees collected in 54 sites from the major vegetation types of the country, Preference was given to mature, fully expanded, healthy sunlit leaves from branches located in the middle of the canopy. As Brazil is mainly a tropical country, only two sampling sites had mean annual temperature (MAT) < 20°C, most of the sites had MAT varying from 20 to 27°C. On the other hand, mean annual precipitation (MAP) varied from 400 to 2500 mm.
Results/Conclusions
Grouping data by vegetation types, revealed biogeographic patterns in elements concentrations as well as on N stable isotope ratios. It seems that such patterns are ultimately coordinated by MAP, but not by MAT. An inverse correlation was found between leaf N and MAP. This correlation is not generalized on a global scale, but seems a common trend in the tropics. Two other studies found the same trend, followed by a direct correlation between leaf life longevity, higher content of structural carbon, and MAP, suggesting that in wetter areas plants invest more in structural carbon to avoid large losses to herbivores, following the “leaf economics spectrum”. This hypothesis is supported by the fact that foliar C:N ratio was directly correlated with MAP in our sites. High precipitation may also decrease N availability in wetter places, decreasing foliar N, but also leading to lower foliar δ15N by decreasing the δ15N of soil available N. This second hypothesis is supported by the fact that an inverse correlation between foliar δ15N and MAP, and a direct correlation between foliar N and δ15N were found in this study. Land use changes, mainly deforestation, coupled with climate changes, may alter precipitation patterns over the country, potentially leading to profound changes in the physiological and biogeochemical traits of Brazilian plants.