| I explored the imprint of plants on the vertical distribution of soil materials focusing on soil components of crucial significance for ecosystem functioning: Organic carbon, lithospheric nutrients, and salts. My approaches involved global analyses of existing soil data and field experiments. I used data for >2700 soil profiles, combined with vegetation and climate information to test the hypothesis that vegetation type, through patterns of allocation, dominates the vertical distribution of soil organic carbon (SOC). I demonstrated that for a given climate, SOC was always deepest in shrublands, intermediate in grasslands, and shallowest in forests. Data suggested that shoot/root allocation combined with vertical root distributions affect the distribution of SOC with depth.; I hypothesized that the vertical distributions of lithospheric nutrients are dominated by plant cycling relative to leaching, weathering dissolution, and atmospheric deposition (nutrient uplift hypothesis). Based on >10000 profiles, I observed a consistent ranking in the vertical distributions of several nutrients across a broad range of ecosystems (from shallowest, P>K>Ca>Mg>Na=Cl=SO 4). Nutrients strongly cycled by plants were shallower than non-essential/non-limiting elements. Essential nutrients tended to have shallower distributions where they were less abundant.; Global results supported the nutrient uplift hypothesis, which I further tested using afforestation of the native, originally tree-less grasslands of the Pampas (Argentina). Based on paired stands of grassland (low Ca cycling) and Eucalyptus plantations (high Ca cycling) I observed a substantial vertical redistribution of Ca from mid to shallow soil depths after afforestation. Soil exchangeable acidity increased at rates matching acid rain inputs in industrialized regions, although no aboveground acidic inputs were detected from deposition, canopy, litter, and organic soil. Results supported the nutrient uplift hypothesis and suggested that cation redistribution by trees was the dominant mechanism of soil acidification.; In the same study systems I evaluated the dynamics of salts as affected by vegetation types and their water use patterns. Based on stand- and landscape-level observation, I concluded that deeper roots allowing groundwater use to trees triggered an intrusion of salty groundwater in the uplands grassland of the Pampas. This caused a Na accumulation process in the soil, in which physical transport dominated over biological cycling. |
