The stable carbon and nitrogen isotopic composition of vegetation in tropical forests of the Amazon Basin, Brazil.

摘要

Here we present the within-site, seasonal, and interannual variations of the carbon ( delta 13C) and nitrogen ( delta 15N) isotope ratios of leaves, wood, bark and litter from four sites in the Amazon region, Brazil. Samples were collected in Manaus (3 degrees 06'07"S; 60 degrees 01'30"W), Ji-Parana (10 degrees 53'07"S; 61 degrees 57'06"W), and Santarem (2 degrees 26'35"S; 54 degrees 42'30"W) with mean annual precipitation of 2207, 2040 and 1909 mm respectively. The overall average for all leaf samples was -32.3+or-2.5 per mil for delta 13C and +5.8+or-1.6 per mil for delta 15N (n=756). The leaf delta values at these sites were often but not always statistically distinct from each other. The delta 13C values varied from -37.8 per mil to -25.9 per mil. Pronounced differences in delta 13C values occurred with height associated with differences in forest structure. The delta 13C of leaf dry matter showed seasonal variations associated with the length of the dry season, despite the fact that total annual precipitation was similar among the studied sites. Leaf delta 15N values ranged from +0.9 per mil to a maximum value of +10.9 per mil, and the Santarem sites showed more enriched values than Manaus and Ji-Parana sites. No seasonal variation was detected in the delta 15N of leaves, but significant differences were observed among sites and with changes in canopy height. The isotope ratio data are consistent with our current understanding of the roles of light, water availability, and recycling of soil-respired CO2 influences on delta 13C and consistent with our understanding that an open nitrogen cycle can lead to high delta 15N values despite a significant number of legumes in the vegetation..