Abstract. In this paper we calculated soil carbon stocks in Brazil studying 17 paired sites where soil stocks were determined in native vegetation, pastures and crop-livestock systems (CPS), and in other regional samplings encompassing more than 100 pasture soils, from 6.58 to 31.53 • S, involving three major Brazilian biomes: Cerrado, Atlantic Forest, and the Pampa. The average native vegetation soil carbon stocks at 10, 30 and 60 cm soil depth were equal to approximately 29, 64, and 92 Mg ha −1 , respectively. In the paired sites, carbon losses of 7.5 Mg ha −1 and 11.6 Mg ha −1 in CPS systems were observed at 10 cm and 30 cm soil depths, respectively. In pasture soils, carbon losses were similar and equal to 7.5 Mg ha −1 and 11.0 Mg ha −1 at 10 cm and 30 cm soil depths, respectively. Differences at 60 cm soil depth were not significantly different between land uses. The average soil δ 13 C under native vegetation at 10 and 30 cm depth were equal to −25.4 ‰ and −24.0 ‰, increasing to −19.6 ‰ and −17.7 ‰ in CPS, and to −18.9 ‰, and −18.3 ‰ in pasture soils, respectively; indicating an increasing contribution of C 4 carbon in these agrosystems. In the regional survey of pasture soils, the soil carbon stock at 30 cm was equal to approximately 51 Mg ha −1 , with an average δ 13 C value of −19.6 ‰. Key controllers of soil carbon stock in pasture sites were sand content and mean annual temperature. Collectively, both could explain approximately half of the variance of soil carbon stocks. When pasture soil carbon stocks were compared with the average soil carbon stocks of native vegetation estimated for Brazilian biomes and soil types by Bernoux et al. (2002) there was a carbon gain of 6.7 Mg ha −1 , which is equivalent to a carbon gain of 15 % compared to the carbon soil stock of the native vegetation. The findings of this study are consistent with differences found between regional comparisons like our pasture sites and plot-level paired study sites in estimating soil carbon stocks changes due to land use changes.

We estimated carbon and nitrogen stocks in aboveground biomass (AGB) and belowground biomass (BGB) along an elevation range in forest sites located on the steep slopes of the Serra do Mar on the north coast of the State of São Paulo, southeast Brazil. In elevations of 100 m (lowland), 400 m (submontane), and 1000 m (montane) four 1-ha plots were established, and above- (live and dead) and belowground (live and dead) biomass were determined. Carbon and nitrogen concentrations in each compartment were determined and used to convert biomass into carbon and nitrogen stocks. The carbon aboveground stock (CAGB) varied along the elevation range from approximately 110 to 150 Mg·ha−1, and nitrogen aboveground stock (NAGB), varied from approximately 1.0 to 1.9 Mg·ha−1. The carbon belowground stock (CBGB) and the nitrogen belowground stock (NBGB) were significantly higher than the AGB and varied along the elevation range from approximately 200–300 Mg·ha−1, and from 14 to 20 Mg·ha−1, respectively. Finally, the total carbon stock (CTOTAL) varied from approximately 320 to 460 Mg·ha−1, and the nitrogen total stock (NTOTAL) from approximately 15 to 22 Mg·ha−1. Most of the carbon and nitrogen stocks were found belowground and not aboveground as normally found in lowland tropical forests. The above- and belowground stocks, and consequently, the total stocks of carbon and nitrogen increased significantly with elevation. As the soil and air temperature also decreased significantly with elevation, we found a significantly inverse relationship between carbon and nitrogen stocks and temperature. Using this inverse relationship, we made a first approach estimate that an increase of 1°C in soil temperature would decrease the carbon and nitrogen stocks in approximately 17 Mg·ha−1 and 1 Mg·ha−1 of carbon and nitrogen, respectively.

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Foram avaliadas semelhanças florísticas entre duas fisionomias de Floresta Atlântica na região costeira do Brasil, denominadas Floresta de Restinga e Floresta das Terras Baixas. A hipótese era que, devido à diferença nos processos geomorfológicos, essas duas florestas difeririam em variáveis físico-químicas dos solos, composição florística, biomassa aérea e produção de serapilheira. O trabalho foi conduzido em uma área de 1 ha (100 × 100 m) em cada tipo de floresta, no município de Ubatuba, São Paulo. Foram registrados e medidos todos os indivíduos arbóreos com DAP > 4,8 cm e coletadas amostras de solo e serapilheira. As análises de agrupamento e de ordenação indicaram que os solos e principalmente a flora distribuem-se como grupos bem definidos, concordando com a hipótese de distinção entre as duas florestas. A diversidade de espécies foi maior (p < 0.0001) na Floresta de Terras Baixas (H' = 4,00 nats.indivíduo-1) do que na Restinga (H' = 3,38 nats.indivíduo-1). No entanto, a produção de serapilheira e a biomassa não diferiram (p > 0,05) entre as duas florestas. Esse aparente paradoxo poderia ser explicado supondo-se que, uma vez que espécies diferentes consigam se estabelecer na Restinga ou nas Terras Baixas e encontrem um espectro favorável de condições e recursos, elas tenderiam a persistir e se desenvolver naquele local; nesse caso, embora as condições edáficas difiram entre as duas áreas, cada espécie responderia de modo particular a essas variações, de modo que as florestas poderiam atingir valores semelhantes de biomassa e produção de serapilheira. É provável que o filtro ambiental condicionado pelos solos esteja sendo importante para a forte separação florística entre essas duas florestas.

Abstract. Soils of tropical forests are important to the global budgets of greenhouse gases. The Brazilian Atlantic Forest is the second largest tropical moist forest area of South America, after the vast Amazonian domain. This study aimed to investigate the emissions of nitrous oxide (N 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes along an altitudinal transect and the relation between these fluxes and other climatic, edaphic and biological variables (temperature, fine roots, litterfall, and soil moisture). Annual means of N 2 O flux were 3.9 (± 0.4), 1.0 (± 0.1), and 0.9 (± 0.2) ng N cm −2 h −1 at altitudes 100, 400, and 1000 m, respectively. On an annual basis, soils consumed CH 4 at all altitudes with annual means of −1.0 (± 0.2), −1.8 (± 0.3), and −1.6 (± 0.1) mg m −2 d −1 at 100 m, 400 m and 1000 m, respectively. Estimated mean annual fluxes of CO 2 were 3.5, 3.6, and 3.4 µmol m −2 s −1 at altitudes 100, 400 and 1000 m, respectively. N 2 O fluxes were significantly influenced by soil moisture and temperature. Soil-atmosphere exchange of CH 4 responded to changes in soil moisture. Carbon dioxide emissions were strongly influenced by soil temperature. While the temperature gradient observed at our sites is only an imperfect proxy for climatic warming, our results suggest that an increase in air and soil temperatures may result in increases in decomposition rates and gross inorganic nitrogen fluxes that could support consequent increases in soil N 2 O and CO 2 emissions and soil CH 4 consumption.