Regional variation in soil carbon and δ13C in forests and pastures of northeastern Costa Rica

Abstract

Recent studies suggest that the direction and magnitude of changes in soil organic carbon (soil C) pools following forest-to-pasture conversion in the tropics are dependent upon initial soil conditions and local factors (e.g. pre-conversion soil C content, soil texture, vegetation productivity, and management practices). The goal of this study was to understand how landscape-scale variation in soil-forming factors influenced the response of soil C pools to forest clearing and pasture establishment in northeastern Costa Rica. We measured soil C and its stable isotopic composition in 24 paired pasture and reference forest sites distributed over large gradients of edaphic characteristics and slope throughout a 1400 km 2 region. We used the large difference in stable C isotopic signatures of C3 vegetation (rain forest) versus C4 vegetation (pasture grasses) as a tracer of soil C dynamics. Soil C pools to 30 cm depth ranged from 26% lower to 23% higher in pastures compared to paired forests. The presence of non-crystalline clays and percent slope explained between 27 and 37% of the variation in the direction and magnitude of the changes in soil C storage following pasture establishment. Stable carbon isotopes (d 13 C) in the top soil (0-10 cm) showed a rapid incorporation of pasture-derived C following pasture establishment, but the vegetation in these pastures never became pure C4 communities. The amount of forest-derived soil C in pasture topsoils (0-10 cm) was negatively correlated to both pasture age and the concentrations of non-crystalline iron oxides. Together these results imply that site factors such as soil mineralogy are an important control over soil C storage and turnover in this region.

Stabilization of recent soil carbon in the humid tropics following land use changes: evidence from aggregate fractionation and stable isotope analyses

“…If possible, turnover times were calculated after equation 1 and 2. Data from this study (black symbols) and from : Veldkamp 1994;Townsend et al 1995;Osher et al 2003;Rhoades et al 2000;Powers and Veldkamp 2005 (volcanic ash soils); Desjardins et al 1994Desjardins et al , 2004Feigl et al 1995;Koutika et al 1997;Powers and Veldkamp 2005;Schwendenmann and Pendall 2006 (open symbols). Note, high turnover times in young pastures are probably due to considerable C 3 (herbs and bushes) input Appendix A Values are given as mean and SD (n = 4) nd, not determined Table A2 Total dry matter yield, soil C storage (g kg -1 soil ), soil C concentration (g kg -1 sandfree aggregates), C/N, and d …”

“…A study in Brazil also reported a more rapid increase of pasture-derived carbon in a coarse textured soil than in a clay soil (Desjardins et al 2004). However, other field studies do not support this observation (Desjardins et al 1994(Desjardins et al , 2004Feigl et al 1995;Koutika et al 1997;Powers and Veldkamp 2005;Schwendenman and Pendall 2006). Texture effects are often masked by other effects like clay mineralogy, land use history, or management (Saggar et al 1996;de Koning et al 2003;Powers and Veldkamp 2005).…”

“…However, other field studies do not support this observation (Desjardins et al 1994(Desjardins et al , 2004Feigl et al 1995;Koutika et al 1997;Powers and Veldkamp 2005;Schwendenman and Pendall 2006). Texture effects are often masked by other effects like clay mineralogy, land use history, or management (Saggar et al 1996;de Koning et al 2003;Powers and Veldkamp 2005). In the volcanic soils, we found no evidence that the amount of noncrystalline compounds contribute to stabilization of recently incorporated soil C. In contrast, the mean 14 C age of total soil C was related to non-crystalline compounds in soils of volcanic parent material (Torn et al 1997) and to the chelation of Al and Fe by organic ligands in temperate Inceptisols, Mollisols and Alfisols (Masiello et al 2004).…”

“…Conversion of tropical forests and pastures to cropland typically decreases soil organic carbon (soil C) stocks by 40-60% (van Noordwijk et al 1997;Guo and Gifford 2002) with coarse textured soils being more susceptible to soil C losses than soils with finer textures (Zinn et al 2005). In contrast, conversion of forests to pastures can result in both gains and losses of soil C, depending on soil properties, climate, and pasture management (Detwiller 1986;Lugo and Brown 1993;Powers and Veldkamp 2005). Forest regrowth on former pastures was found to be associated either with increases or decreases in soil carbon stocks depending on land use history and soil properties (de Koning et al 2003).…”

Windthrows increase soil carbon stocks in a central Amazon forest

“…When including other soil types, our disturbed forest had SCS values (61.4 Mg ha −1 ) higher than most reported SCS values, with the exception of SCS values reported for a region in Mato Grosso (65.3 Mg ha −1 ) and another in Rondônia (62 Mg ha −1 ; Maia et al, 2009). The SCS can be influenced by soil type, texture, and mineral composition (Powers and Veldkamp, 2005;López-Ulloa et al, 2005;Neumann-Cosel et al, 2011). Indeed, the different SCS rates from different soil types are related to important factors such as geology, climate, and soil formation (Adams et al, 1990;Batjes, 1996).…”