Soil carbon stocks and carbon sequestration rates in seminatural grassland in Aso region, Kumamoto, Southern Japan

Abstract

Global soil carbon (C) stocks account for approximately three times that found in the atmosphere. In the Aso mountain region of Southern Japan, seminatural grasslands have been maintained by annual harvests and/or burning for more than 1000 years. Quantification of soil C stocks and C sequestration rates in Aso mountain ecosystem is needed to make well‐informed, land‐use decisions to maximize C sinks while minimizing C emissions. Soil cores were collected from six sites within 200 km2 (767–937 m asl.) from the surface down to the k‐Ah layer established 7300 years ago by a volcanic eruption. The biological sources of the C stored in the Aso mountain ecosystem were investigated by combining C content at a number of sampling depths with age (using 14C dating) and δ13C isotopic fractionation. Quantification of plant phytoliths at several depths was used to make basic reconstructions of past vegetation and was linked with C‐sequestration rates. The mean total C stock of all six sites was 232 Mg C ha−1 (28–417 Mg C ha−1), which equates to a soil C sequestration rate of 32 kg C ha−1 yr−1 over 7300 years. Mean soil C sequestration rates over 34, 50 and 100 years were estimated by an equation regressing soil C sequestration rate against soil C accumulation interval, which was modeled to be 618, 483 and 332 kg C ha−1 yr−1, respectively. Such data allows for a deeper understanding in how much C could be sequestered in Miscanthus grasslands at different time scales. In Aso, tribe Andropogoneae (especially Miscanthus and Schizoachyrium genera) and tribe Paniceae contributed between 64% and 100% of soil C based on δ13C abundance. We conclude that the seminatural, C4‐dominated grassland system serves as an important C sink, and worthy of future conservation.

Carbon dynamics in anImperatagrassland in Northeast India

“…Like carbon in the pasture components, this carbon can be lost to the atmosphere if soils are disturbed. The present data on soil organic carbon stocks (55.94 t C/ha) can be compared with the 50-164 t C/ha reported by Chan and McCoy (2010) in pasture in Australia and the 28.1-417 t C/ha in semi-natural grassland in Southern China (Toma et al 2013).…”

“…However, grasslands cover approximately 32% of the total land area (Adams et al 1990) and play a significant role in balancing the global C budget (Scurlock and Hall 1998). A number of studies have been conducted on the carbon stocks in different grasslands of the world (Fisher et al 2007;Fidelis et al 2013;Toma et al 2013). Long et al (1992) studied grassland sites in Kenya, Mexico and Thailand and found they accumulated 144 g C/m 2 /yr when protected from fires and concluded these grasslands were potentially significant C sinks.…”

Rationally Managed Pastures Stock More Carbon than No-Tillage Fields

“…According to Rasse et al (2005), the rhizodeposition of C is 2.4 times that derived from the aerial part of plants, and thus makes up the greatest share of SOC (Toma et al, 2013). Nevertheless, in the VRG pasture, the belowground biomass was four times greater than the aboveground biomass.…”

Evaluation of greenhouse gas emissions in aMiscanthus sinensisAndersson-dominated semi-natural grassland in Kumamoto, Japan

“…Grassland ecosystems contribute to the mitigation of rising atmospheric carbon dioxide (CO 2 ) levels by sequestering carbon (C) into the soil (Schlesinger 1990;Lee et al 2007;Toma et al 2013). Grassland ecosystems comprise approximately 41% of the terrestrial land area of the Earth, except for areas of permanent ice cover (White et al 2000).…”

“…In semi-natural M. sinensis grasslands such as the Aso mountain grasslands in southern Japan, plant species have been managed to produce grass biomass for use as feedstock and composting materials, and vegetation structure has remained stable over the long term (Miyabuchi and Sugiyama 2006). In addition, Toma et al (2012Toma et al ( , 2013 highlighted that the semi-natural M. sinensis grassland soils sequester significant amounts of atmospheric C. Indeed, soil C sequestration and the use of such grasslands as a source of harvestable biomass appear to be mutually compatible. Consequently, further research is warranted to determine whether Miscanthus grasslands can mitigate global warming.…”