Soil Carbon Pools in California’s Annual Grassland Ecosystems

Abstract

Rangeland ecosystems cover approximately one-third of the land area in the United States and half of the land area of California. This large land area, coupled with the propensity of grasses to allocate a considerable proportion of their photosynthate belowground, leads to high soil carbon (C) sequestration potential. Annual grasslands typical of the Mediterranean climates of the western United States differ in their life history strategies from the well-studied perennial grasslands of other regions and thus may also differ in their soil C pools and fluxes. In this study we use the literature to explore patterns in soil C storage in annual grass-dominated rangelands in California. We show that soil C is highly predictable with depth. Cumulative soil C content increased to 2-3-m depth in rangelands with a woody component and to at least 1-m depth in open rangelands. Soil C within a given depth varied widely, with C content in the top 1-m depth spanning almost 200 Mg C ? ha 21 across sites. Soil C pools were not correlated with temperature or precipitation at a regional scale. The presence of woody plants increased C by an average of 40 Mg ? ha 21 in the top meter of soil. Grazed annual grasslands had similar soil C content as ungrazed grassland at all depths examined, although few details on grazing management were available. Soil C pools were weakly positively correlated with clay content and peaked at intermediated levels of aboveground net primary production. Our results suggest that annual grasslands have similar soil C storage capacity as temperate perennial grasslands and offer an important resource for mitigation of greenhouse gas emissions and climate change.

Integrated climate and land use change scenarios for California rangeland ecosystem services: wildlife habitat, soil carbon, and water supply

“…In California annual grasslands, soil C pools in the top meter average 140 Mg C ha -1 though the range in these pools span almost 200 Mg C ha -1 across sites, with higher values where woody vegetation is present (Silver et al 2010). Conversion of rangelands to cropland or urban lands can release large quantities of carbon (Lal 2002;Potthoff et al 2005;Chen et al 2013).…”

Organic Carbon Stocks, Dynamics and Restoration in Relation to Soils of Agroecosystems in Ethiopia: A Review

“…Addition of organic input from cow dung may contribute to slight increment of organic matter in the grazing lands compared with cultivated lands (Mekuria et al, 2009;Haile et al, 2014;Mekuria et al, 2014), but overgrazing may cause degradation of soil organic matter compared with agroforestry systems (Haile et al, 2014). Many findings have shown that grasslands can fix organic carbon in the soil reaching up to 100 Mg C ha -1 ) (Silver et al, 2010). For instance, conversion of free grazing lands to area exclosures have shown potential of increasing carbon stocks in the area (Mekuria et al, 2009), and if continued, this strategy may contribute to achieve equilibrium state in carbon sequestration.…”

Carbon management in dryland agricultural systems. A review

“…Despite the inherently low SOC sequestration rates that have been reported in grasslands when compared with other land uses, their global impact can be significant given the surface covered by this land use (Follett and Schuman 2005). The potential C storage in grasslands varies according to climatic conditions and management (Silver et al 2010). For instance, the last authors reported soil C contents of 200 Mg C ha −1 in the first 100-cm soil depth in annual grass-dominated rangelands in California.…”