Efecto del pastoreo sobre la productividad primaria neta subterránea de un pastizal templado

Grazing directly affects above-ground fraction of vegetation and indirectly the below-ground part. There is a poor knowledge of the effect of grazing on below-ground net primary productivity (BNPP) in grasslands. Our aim was to quantify the effect of grazing on BNPP up to 25 cm depth in a south-central Uruguayan grassland, in four sampling periods, distributed uniformly throughout a year. At the beginning of each period, five cylindrical holes of 5 cm diameter x 25 cm depth, in three exclosures sites aged between 4 and 17 years, and at their adjacent grazed areas, were performed. Ingrowth cores filled with free roots soil were placed in the hole, extracted after three months and divided in 3 depths (0-5, 5-10 and 10-25 cm). For 25 cm profile, the annual BNPP was 41% higher in grazed areas (505 g.m-2.year-1) than in exclosures areas (357 g.m-2.year-1). The annual BNPP decreased with soil depth similarly at grazed and exclosures areas. Half of the annual BNPP of whole profile was concentrated in the two shallowest layers (0-5 and 5-10 cm). BNPP for the profile of 25 cm presented interaction grazing x sampling periods marginally significant, indicating different trajectories of BNPP. This study is one of the few in the Río de la Plata grasslands that assesses the effect of grazing on BNPP and the first using ingrowth cores. Quantifying the effect of grazing on BNPP allows understanding the dynamics of C sequestration in the soil, an ecosystem service particularly valued in grasslands.