Soil carbon (C) sequestration in grasslands may mitigate rising levels of atmospheric carbon dioxide (C02) but there is still great uncertainty about the size, distribution and activity of this "sink". Carbon accumulation in grassland ecosystems occurs mainly below ground where soil organic matter (SOM) is located in discrete pools, the characteristics of which have now been described in some detail. Carbon sequestration can be determined directly by measuring changes in C stocks or by simulation modelling. Both methods have many limitations but long-term estimates rely almost exclusively on modelling. Management practices and climate strongly influence C sequestration rates, which, in temperate grasslands across Europe, range from 4.5 g C/m~2/year(a C source) to 40 g C/m~2/year (a C sink). Because of uncertainties in location of sinks and their activity, we currently only have enough information to infer the order of magnitude of soil C sequestration rates in temperate grasslands.
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