Carbon Stocks and Fluxes in Rangelands of the Río de la Plata Basin

Abstract

Grasslands are one of the most modified biomes on Earth. Land use changes had a large impact on C stocks of grasslands. Understanding the impact of land use/land cover changes on C stocks and fluxes is critical to evaluate the potential of rangeland ecosystem as C sinks. In this chapter we analyze C stocks and fluxes across the environmental gradients of one of the most extensive temperate rangeland areas: the Río de la Plata Grasslands (RPG) in South America. The analysis summarized information provided by field studies, remote sensing estimates and modelling exercises. Average estimates of Aboveground Net Primary Production (ANPP) ranged from 240 up to 316 gC.m-2.year-1. Estimates of belowground NPP (BNPP) were more variable than ANPP and ranged from 264 up to 568 g C .m-2 .year-1. Total Carbon ranged from 5,004 up to 15,008 gC. m-2. Plant biomass contribution to Total Carbon averaged 13% and varied from 9.5 to 27% among sites. The largest plant C stock corresponded to belowground biomass. Aboveground green biomass represented less than 7% of the plant C. Soil organic C (SOC) was concentrated in the slow and passive compartments of the organic matter. Active soil pool represented only 6.7% of the SOC. The understanding of C dynamics and stocks in the RPG grasslands is still partial and incomplete. Field estimates of ANPP and BNPP are scarce and they are not based on a common measurement protocol. Remotely sensed techniques have the potential to generate a coherent and spatially explicit database on ANPP. However more work is needed to improve estimates of the spatial and temporal variability of radiation use efficiency (RUE). The absence of a flux tower network restricts the ability to track seasonal changes in C uptake and to understand fine scale controls of C dynamics.