Soil and vegetation carbon stocks in Brazilian Western Amazonia: relationships and ecological implications for natural landscapes

Abstract

The relationships between soils attributes, soil carbon stocks and vegetation carbon stocks are poorly know in Amazonia, even at regional scale. In this paper, we used the large and reliable soil database from Western Amazonia obtained from the RADAMBRASIL project and recent estimates of vegetation biomass to investigate some environmental relationships, quantifying C stocks of intact ecosystem in Western Amazonia. The results allowed separating the western Amazonia into 6 sectors, called pedo-zones: Roraima, Rio Negro Basin, Tertiary Plateaux of the Amazon, Javari-Juruá-Purus lowland, Acre Basin and Rondonia uplands. The highest C stock for the whole soil is observed in the Acre and in the Rio Negro sectors. In the former, this is due to the high nutrient status and high clay activity, whereas in the latter, it is attributed to a downward carbon movement attributed to widespread podzolization and arenization, forming spodic horizons. The youthful nature of shallow soils of the Javari-Juruá-Purus lowlands, associated with high Al, results in a high phytomass C/soil C ratio. A similar trend was observed for the shallow soils from the Roraima and Rondonia highlands. A consistent east-west decline in biomass carbon in the Rio Negro Basin sector is associated with increasing rainfall and higher sand amounts. It is related to lesser C protection and greater C loss of sandy soils, subjected to active chemical leaching and widespread podzolization. Also, these soils possess lower cation exchangeable capacity and lower water retention capacity. Zones where deeply weathered Latosols dominate have a overall pattern of high C sequestration, and greater than the shallower soils from the upper Amazon, west of Madeira and Negro rivers. This was attributed to deeper incorporation of carbon in these clayey and highly pedo-bioturbated soils. The results highlight the urgent need for refining soil data at an appropriate scale for C stocks calculations purposes in Amazonia. There is a risk of misinterpreting C stocks in Amazonia when such great pedological variability is not taken into account.

Soil-vegetation relationships and community structure in a "terra-firme"-white-sand vegetation gradient in Viruá National Park, northern Amazon, Brazil

“…These geological units are mostly represented by deep sand beds, which suffered an in situ pedogenesis, as pointed out in studies in the State of Amazonas (Andrade et al 1997, Bravard and Righi 1990. High rainfall rates contribute directly to the processes of podzolization and arenization of the soils which in turn, are associated with high leaching and consequent chemical impoverishment (Schaefer et al 2008). Table I shows the chemical and physical properties of two Spodosols in the study area.…”

Landscape and soil regionalization in southern Brazilian Amazon and contiguous areas: methodology and relevance for ecological studies

“…Therefore, this area involves great soil spatial variability, mainly regarding to soil texture which is highly related to ecological processes. It was not highlighted in previous ecological modeling studies, mainly those related to soil organic matter dynamics (Bernoux et al, 2002;Batjes and �ijk-dynamics (Bernoux et al, 2002;Batjes and �ijk-shoorn, 1999;Batjes, 2005;Cerri et al, 2007;Cochrane and Cochrane, 2006;Holmes et al, 2006;Moraes et al, 1995;Schaefer et al, 2008).…”

Characterization of Organic Matter under Different Pedoenvironments in the Viruá National Park, in Northern Amazon

“…This geological unit largely comprises a deep sandy mantle, formed by in situ pedogenesis of Cenozoic sediments or igneous and metamorphic rocks, as shown in studies of soils from the state of Amazonas (Bravard and Righi, 1990;Mendonça et al, 2013). The high rainfall contributes to soil podzolization and arenization processes (Schaefer et al, 2008).…”