Stable carbon composition of vegetation and soils across an altitudinal range in the coastal Atlantic Forest of Brazil

There was no consistent change in the delta (13) C values of leaves, trunks, litter, or soil with altitude in the Atlantic Forest of Brazil. Several studies have found a direct relationship between the stable carbon isotopic composition (delta C-13) of plants and soils, and altitude, generally thought to be caused by greater carboxylation coupled with morphological changes in leaves at higher altitude. However, most of these studies were conducted in temperate areas of the globe with only a few in tropical areas. To fill this information gap, our main objective was to investigate the stable carbon isotopic composition of leaves, trunks, litter samples, and soil across an elevational range in the coastal Atlantic Forest of the Southeast region of Brazil. Our main hypothesis based on previous work is that the delta C-13 values in plants and soil, and soil turnover times will increase with elevation. Samples were taken from Restinga (0-50 m), Lowland (100-150 m), Submontane (300-500 m), and Montane (1000-1100 m) forests. The overall foliar delta C-13 was -32.2 +/- A 1.7 aEuro degrees, increasing by almost 4 aEuro degrees in trunks (-28.4 +/- A 1.5 aEuro degrees), almost 2 aEuro degrees in litter (-30.3 +/- A 1.0 aEuro degrees), and 4.5 aEuro degrees in soil organic matter (-27.7 +/- A 0.9 aEuro degrees). There was no clear trend towards higher delta C-13 values at higher elevation, neither for vegetation components nor soils. There was also no clear trend for soil carbon turnover times (beta), estimated by the regression between the logarithm carbon concentration and delta C-13 values. The only significant differences observed across the elevational range in vegetation tissues were lower foliar delta C-13 and higher soil delta C-13 in the Lowland forest stand, and higher trunk delta C-13 in the Submontane forest stand compared with other forest types.