Response of soil organic matter dynamics to conversion from tropical forest to grassland as determined by long-term incubation

Abstract

Understanding soil organic carbon (SOC) responses to land-use changes requires knowledge of the sizes and mean residence times (MRT) of specific identifiable SOC pools over a range of decomposability. We examined pool sizes and kinetics of active and slow pool carbon (C) for tropical forest and grassland ecosystems on Barro Colorado Island, Panama, using long-term incubations (180 days) of soil and stable C isotopes. Chemical fractionation (acid hydrolysis) was applied to assess the magnitude of nonhydrolysable pool C (NHC). Incubation revealed that both grassland and forest soil contained a small proportion of active pool C (<1%), with MRT of~6 days. Forest and grassland soil apparently did not differ considerably with respect to their labile pool substrate quality. The MRT of slow pool C in the upper soil layer (0-10 cm) did not differ between forest and grassland, and was approximately 15 years. In contrast, changes in vegetation cover resulted in significantly shorter MRT of slow pool C under grassland (29 years) as compared to forest (53 years) in the subsoil (30-40 cm). The faster slow pool turnover rate is probably associated with a loss of 30% total C in grassland subsoil compared to the forest. The NHC expressed as a percentage of total C varied between 54% and 64% in the surface soil and decreased with depth to~30%. Grassland NHC had considerably longer MRTs (120 to 320 years) as compared to slow pool C. However, the functional significance of the NHC pool is not clear, indicating that this approach must be applied cautiously. Keywords Active pool carbon. Forest conversion. Grassland. Incubation. Mean residence time. Non-hydrolysable carbon. Slow pool carbon .

Carbono total e δ13C em agregados do solo sob vegetação nativa e pastagem no bioma cerrado

“…A assinatura isotópica aumentou significativamente em profundidade sob essa área, passando de -26 ‰ na camada de 0-5 cm para -23 ‰ na camada de 10-20 cm. Esses resultados estão de acordo com outros estudos realizados em perfis de solos sob vegetação nativa de ciclo C 3 (Volkoff & Cerri, 1987;Schwendenmann & Pendall, 2008) e podem ser atribuídos à discriminação isotópica do C feita pelos microrganismos do solo durante a decomposição da material orgânico (Balesdent & Mariotti, 1996). Na pastagem, os valores tenderam a decrescer com a profundidade, passando de -14,5 ‰ na camada de 0-5 cm para -15,0 ‰ na camada de 10-20 cm, indicando a gradativa substituição da MOS original pela adicionada pela espécie C4 (Figura 3).…”

“…A porção de substituição foi mais elevada que a encontrada por outros autores em estudos realizados no bioma Cerrado (Roscoe et al, 2001) e semelhante à verificada em Latossolos e Neossolos da Amazônia (Choné et al, 1991;Trumbore et al, 1995;Neill et al, 1997) e na América Central (Schwendenmann & Pendall, 2008). Entretanto, os resultados foram consistentes quando considerado que a conversão da vegetação nativa em pastagem leva à substituição de metade ou mais do C derivado da vegetação nativa no período de 8 a 20 anos e de aproximadamente 100 % em 80 anos (Feigl et al, 1995).…”

“…O aumento do TRM em profundidade indica maior estabilidade e menor taxa de renovação do C à medida que se aprofunda no perfil do solo -característica também reportada por Schwendenmann & Pendall (2008). Os resultados obtidos são semelhantes aos apresentados por , que mostraram elevada variabilidade no TRM para solos tropicais, com valores entre 13 e 108 anos.…”

Distribution of Organic Carbon in Pitch Pine Plantation in Kongju, Korea

“…SOC of top soil and 50 cmdepth soil in this pitch pine plantation was 1.46 ± 0.06 and 0.25 ± 0.02 %, respectively. SOC is a complex mixture of carbon compounds derived from plants, animals, and microbes, which vary greatly in their amount and decomposition dynamics (Schwendenmann and Pendall 2008).…”

Tropical forest restoration: Fast resilience of plant biomass contrasts with slow recovery of stable soil C stocks

“…The turnover time of these fractions can range from days (active pool), decades (slow pool), to centuries (recalcitrant pool) due to their specific chemical or physical stabilities. Different land use types vary in the proportions of these soil C pools (Guo & Gifford, ), and both active and slow pools are considered to be sensitive to land use change (Schwendenmann & Pendall, ). Conversion of natural forest to plantations decreased the physically, chemically and biochemically protected slow C pools in surface and deep soils in one study in subtropical forest (Lyu et al., ).…”