Influence of soil texture on carbon dynamics and storage potential in tropical forest soils of Amazonia

Abstract

[1] Stable and radiocarbon isotopes were used to investigate the role of soil clay content in the storage and dynamics of soil carbon in tropical forest soils. Organic matter in clay-rich Oxisols and Ultisols contains at least two distinct components: (1) material with light d 13 C signatures and turnover times of decades or less; and (2) clay-associated, 13 C-enriched, carbon with turnover times of decades at the surface to millennia at depths >20 cm. Soil texture, in this case clay content, exerts a major control on the amount of slowly cycling carbon and therefore influences the storage and dynamics of carbon in tropical forest soils. Soils in primary tropical forest have been proposed as a potentially large sink for anthropogenic carbon. Comparison of carbon stocks in Oxisols sampled near Manaus, Brazil, shows no measurable change in organic carbon stocks over the past 20 years. Simple models estimating the response of soil carbon pools to a sustained 0.5% yr À1 increase in productivity result in C storage rates of 0.09 to 0.13 MgC ha À1 yr À1 in soil organic matter, with additional potential storage of 0.18 to 0.27 MgC ha À1 yr À1 in surface litter and roots. Most storage occurs in organic matter pools with turnover times less than a decade. Export of carbon in dissolved form from upland terra firme Oxisols likely accounts for <0.2 MgC ha À1 yr À1 , but more work is required to assess the export potential for periodically inundated Spodosols.

Warming-induced northwestward migration of the East Asian monsoon rain belt from the Last Glacial Maximum to the mid-Holocene

“…2) and they exhibit a good correlation with the grain size and magnetic susceptibility records. Given that the L 1-1 loess unit has a low organic matter content (<0.5%) (31), the effects of percolation of soluble organic substances (32) and soil texture (33,34) on the observed glacial-interglacial δ 13 C pattern ( Fig. 2) need to be carefully evaluated before definitively linking the δ 13 C records to C 3 /C 4 vegetation change.…”

Past and present land use influences on tropical riparian zones: an isotopic assessment with implications for riparian forest width determination

“…Our results, in turn, show that after approximately 13 to 60 years under C 4 plants, a proportion of 25 -30% C 3 derived carbon still can be found in the riparian areas of watersheds 1 and 2. Differences between the present study and the one by Vitorello et al (1989) might be related to soil characteristics such as texture (Roscoe et al 2001) or other factors affecting soil carbon turnover rate (Powers & Schlesinger 2002;Telles et al 2003) such as soil moisture that might be typically higher in riparian soils compared to upland soils (Luizã o et al 2004). Moreover, the long-term persistence of C 3 signals in the riparian areas of watersheds 1 an 2 might be attributed to highly recalcitrant organic matter or organic matter that is tightly bound to clay soil particles (Roscoe et al 2001, Powers & Schlesinger 2002, Telles et al 2003, Alcâ ntara et al 2004, Marin-Spiotta et al 2009).…”

Windthrows increase soil carbon stocks in a central Amazon forest

“…At the studied region, the relief is undulating with altitude ranging from 40 to 180 m a.s.l. Soils on upland plateaus and the upper portions of slopes have high clay content (Oxisols), while soils on slope bottoms and valleys have high sand content (Spodosols; Telles et al, 2003) and are subject to sporadic inundations (Junk et al, 2011). The yellow Oxisols are found primarily on plateaus and slopes.…”

“…The yellow Oxisols are found primarily on plateaus and slopes. In general, the soils are well drained and have low fertility, low pH, low cation exchange capacity, high aluminum concentration, and low organic carbon (Ferraz et al, 1998;Telles et al, 2003).…”