CONICET | Buscador de Institutos y Recursos Humanos

Afforestation has been proposed as a mechanism to increase terrestrial C storage. However, effects of this change in vegetation on soil weathering and belowground carbon dynamics have not been studied systematically across pedogenic gradients. Here, we present results of leachable element extractions on young (< 100 yr) tephra-derived soils from a Patagonian rainfall gradient consisting of five sites varying from 250 to 2200 mm MAP. Across this gradient, stands of Pinus ponderosa planted in monocultures 40 years ago are adjacent to the natural vegetation, which varies from shrubland steppe to broadleaf forest. Soils were collected from natural vegetation and the adjacent planted pine sites to depth of auger refusal and were extracted with 0.5 M HCl for 24h to target the exchangeable, adsorbed, and amorphous phases of metals. Semi-regular tephra deposits along the gradient resulted in few differences in elemental concentrations in the extractions by vegetation. However, 40 years of pine afforestation has resulted in lower concentrations of extractable K (p < 0.1) and Ca (p < 0.01) within the top 0 ? 30 cm in the planted pine soils. Other elements, while not affected by vegetation type, did respond to the rainfall gradient. Al, Si, P, and Mn all increased in the surface soils with rainfall (p < 0.01), indicating the development of short-range-order (SRO) volcanic mineral phases that retain nutrients such as P and Mn. Furthermore, addition of Al and Si in the linear model to describe soil C across the gradient increased explained variance by 15% over rainfall alone, indicating the importance of these SRO aluminosilicate minerals to soil C retention. Our results reflect changes in tephra derived soils during the early stages of weathering and the potential impacts of afforestation on soil development.