Plant and soil carbon stocks in grassland patches maintained by extensive grazing in the highlands of central Argentina

Abstract

Grasslands are valued by their capacity to store carbon (C) as well as by their livestock production. However, focussing grassland management on one of these characteristics might negatively affect the other. Here, we describe for the first time the amount of C stored in the plant and soil compartments of extensively grazed highland grasslands of central Argentina. We quantified C stocks of standing plant, litter, and roots biomass, and soil (0–100 cm depth) in three coexisting grassland types associated with different livestock use: lawns and open and closed tussock grasslands (from higher to lower grazing use) and analysed how those stocks vary across grassland types. Our main results showed that these mountain grasslands represent an important regional C reservoir, with total C stocks (plant plus soil) ranging from 110 to 472 Mg C ha−1, with more than 95% of C being stored in soils. Differences in soil C stocks up to 30 cm depth were not associated with grassland types. However, in grazing lawns (higher livestock use), belowground plant C increased, whereas aboveground plant C was reduced. Overall, resulting in a 14% lower C stored in the plant-soil system up to 30 cm depth than in tussock grasslands. Our study shows that highland grasslands of central Argentina maintain huge soil C reservoirs. However, livestock use could reduce surface C stocks by affecting the plant biomass compartments, which could have a long-term effect on soil C stocks. These findings have direct implications for mountain grasslands management and conservation in the context of climate change mitigation.