Ciclos de macronutrientes en pastizales serranos de Sierra de la Ventana

摘要: Macronutrient cycling in mountain grasslands of Sierra de la Ventana, Argentina: was assessed grassland sites located on a NE slope at 550, 850 and 1025 m asl, Buenos Aires, Argentina. Previous studies showed ecosystem changes with elevation increase: 1) temperature decreased, 2) evaporation increased, 3) clay base content soils 4) net primary productivity (NPP) did not change significantly, 5) the below-above-ground biomass ratio increased and, 6) NPP allocation to aboveground tissues diminished belowground increased. The objective establish if similar along environmental gradient is attained through nutrient * Laboratorio Investigacion Sistemas Ecologicos y Ambientales (LISEA), Universidad Nacional La Plata, Diagonal 113 N° 469, Piso 2, CC 31, 1900 talares@ceres.agro.unlp.edu.ar 200 CA PEREZ & JL FRANGI Ecologia Austral 17:199-216 Diciembre 2007 CICLOS DE MACRONUTRIENTES EN PASTIZALES 201 pathways resulting use efficiency (NUE) changes. Plant necromass were harvested during one year separated compartments. soil samples analyzed for N, P, K, Ca Mg. Mineral mass calculated as product concentration per dry mass. Nutrient fluxes NUE calculated. Aboveground live had highest concentration, excepted. With increase we noted that: i) K Mg green grasses ii) mineral proportion stocked roots incremented, iii) requirements decreased range (kg ha-1 y-1) 120 107 9 6 84 44 41 34 12 Mg; iv) Nitrogen, P resorption its absolute percent contribution requirements. Except absorption main pathway contributing OM return input due mainly root senescence (55 92% total return, depending site), except whose via litter fall. At leaf level, there differences among sites; ranges 70-80 % 57-68% 42-48% N. Nitrogen proficiency high complete. Foliar N:P (=11 18) suggested P-limitation intermediate upper sites. Gray’s relative turnover rate indicated P-conservative behavior suggesting limiting also lower site. Nutrients circulated slower than biomass. exception higher elevation. Apparently, N any A comparison both extremes more favourable environment invested ANPP, macronutrient requirements; this rates (except K), less-dependent external –absorptionsupply conservative circulation P; less nutrientuse efficient (higher matter production absorbed unit), residence time roots. We concluded that different environments combined two strategic components involved acquisition use: Carbon fractions allocated aboveand biomass, total-, mineralmass, supply pathways, rates, NUE. Changes are specific may be evidence availability limitation regard demand. [