Stability of organic carbon in deep soil layers controlled by fresh carbon supply

Abstract

The world's soils store more carbon than is present in biomass and in the atmosphere. Little is known, however, about the factors controlling the stability of soil organic carbon stocks and the response of the soil carbon pool to climate change remains uncertain. We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon, soil incubations and radiocarbon dating. Here we show that the supply of fresh plant-derived carbon to the subsoil (0.6-0.8 m depth) stimulated the microbial mineralization of 2,567 +/- 226-year-old carbon. Our results support the previously suggested idea that in the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained. We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature. Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon.

Soil aggregate fraction-based 14C analysis and its application in the study of soil organic carbon turnover under forests of different ages

“…Its production would significantly increase with increasing stand ages [82][83][84], thus supplying more WSOC to the soil. In addition, the increase in the production of plant litter could accelerate the decomposition of the native organic matter in soil by priming effect [85,86]. Hence, the turnover times of SOC are observed to decrease with the increase of stand age.…”

“…Overall, there is an increase in the proportion of topsoil CO 2 emission from older organic carbon pool (2-63 μm soil aggregate fraction), but a decreasing trend from younger organic carbon pools (>250 μm and 63-250 μm soil aggregate fractions) during the young and middle-age stage after afforestation of grassland. This is because the increase in fresh carbon from plant litter input to soils may have stimulated the microbial activity by priming effect, accelerating mineralization of native old carbon in soils [85]. However, the proportion of topsoil CO 2 emission from older organic carbon pool (2-63 μm soil aggregate fraction) begins to decrease while that from younger organic carbon pools (>250 μm and 63-250 μm soil aggregate fractions) begins to rebound.…”

Drying/rewetting cycles mobilize old C from deep soils from a California annual grassland

“…For example, incubation of deep soils from a California grassland environment (Ewing et al, 2006) demonstrated that the breaking of soil structures can result in respiration of old C, suggesting that physical structures can be important in making C unavailable for decomposition. Fontaine et al (2007) found that adding labile C could stimulate breakdown of deep soil C, and concluded that it was of poor enough quality that microbes could not grow on it without exogenous energy sources. In contrast, Xiang et al (2008) found that in grassland soils from 1 m depth, multiple dry/wet cycles increased microbial total respiration and biomass up to 6-fold.…”

Compartimentos de carbono orgânico em Latossolo cultivado com hortaliças sob diferentes manejos

“…Esse fenômeno de degradação de matéria orgânica estável, quando do aporte de matéria orgânica fresca, já foi relatado em vários estudos (Bell et al, 2003;Fontaine et al, 2007).…”

“…Em contrapartida, alguns trabalhos têm mostrado que o aporte de matéria orgânica fresca pode levar ao aumento das taxas de degradação da matéria orgânica estável do solo (Fontaine et al, 2007), em decorrência do efeito "priming". Esse fenômeno também pode ser potencializado por elevados aportes de N em ambientes ricos em C (Kuzyakov et al, 2000), o que é comum em sistemas de produção de hortaliças.…”