Nutrient cycling in Patagonian ecosystems

The knowledge on nutrient cycling in Patagonian ecosystems of Argentina is scarce. However, studies not directly focused on nutrient cycling provide relevant information about the mechanisms of nutrient conservation in the climatically different ecosystems of the region. Here, we identified indicators of litter decomposition and soil N mineralization rates of some representative species of the dominant plant functional groups along the wide precipitation gradient of Patagonia. Senescent leaves and litter of forest trees have higher C concentration and C/N ratio and lower N concentration than steppe shrubs. Within the tree life form, evergreen species have higher C/N ratio than deciduous species. Differences in N concentration between green and senescent leaves suggest a higher N use efficiency in forest trees than in steppe shrubs. Within the steppe, grasses have higher nutrient use efficiency than shrubs due to their higher C and much lower N, P and K content in senescent leaves and litter. Thus, we hypothesize the occurrence of (i) a gradient from nutrient- conserving ecosystems in wetter sites (Andean-Patagonian forest) to relatively nutrient-rich (low nutrient use efficient) ecosystems in drier sites (Patagonian steppe), and (ii) differences in nutrient conservation mechanisms among different functional groups: in the Andean-Patagonian forests N conservation and N use efficiency is greater in evergreens than in deciduous woody species and in conifers than in broad-leaf species, whereas in the Patagonian steppe, grasses have higher nutrient resorption than shrubs. Likely as a consequence of these differences in litter quality, potential N mineralization is greater in deciduous than in evergreen Patagonian forests. Within the steppe, N inineralization seems to depend on grass and shrub cover, which in turn is regulated by disturbance, largely grazing. Since nutrient conservation in vegetation, specially N, is associated to the rates of litter decomposition and soil N mineralization, the confirmation of these patterns would allow to predict ecosystem resilience and resistance to nutrient losses, and contribute to understand and predict the response of the different Patagonian species or functional groups to interannual climatic variability and natural or anthropogenic disturbances. There is a special need for further research on P cycling, nutrient allocation in vegetation, and field measurements of litter decomposition and N mineralization.