Drivers of C cycling and sequestration on plant-soil system in a grazed mountain grassland of Sierras Grandes of Córdoba, Argentina.

JOSÉ MANUEL MERILES; AGUSTÍN SARQUIS; SOFÍA PESTONI; NATALIA PÉREZ HARGUINDEGUY

Harpenden

Simposio; 6th International Symposium on Soil Organic Matter 2017; 2017

Rothamsted Research

IntroductionStudies of decomposition and stabilization of soil organic matter (SOM) have been historically separated. Recently there have been several efforts on integrating those aspects of SOM dynamics but we are still far froma common ground for work on it.ObjectivesWe aim at contributing in this sense by studying some of the mechanisms by which changes in vegetation affect C pools and C fluxes on plant-soil systems.MethodsWe measured litter and root dry mass and C:N ratio on two vegetation physiognomies (thick tussocks and grazing lawns) at 5, 15 and 30 cm soil depth. At 5 cm depth we also determined fluorescein diacetate activity ofmicrobial communities. Within the following months we will determine microbial community structure (PLFA analysis) and SOC content in particulate OM and mineral associated OM.ResultsWe found over 200 times more C in aboveground litter in tussock patches than in grazing lawns, while C in roots was almost 5 times higher in grazing lawns compared to tussock. Thin roots were between half of total (in grazing lawns 0-5 cm depth) and 50 times (in tussock 15-30 cm depth) more abundant than thick roots. C:N ratios were around 40 and 50 for thin and thick roots, respectively. Microbial activity was similar in the twophysiognomies.ConclusionContrasting C inputs to soil like those found here, has been found in other grazed grasslands without nutrient and water deficit. This pattern makes difficult to predict their impact on SOC. If roots are the main source ofSOC, as many studies have shown, SOC should be higher in lawns. However, even if only a fraction of aboveground litter is incorporated to SOC it may counteract the pattern of root C and we may find no differences between SOC from the physiognomies. In addition, the higher proportion of fine roots (a more labile input) in tussocks compared to lawns may also enhance the impact of that source of C on SOC. We hopeour future results will help to shed light on this.