Investigating mineral weathering and soil carbon storage across a Patagonian climate by vegetation pedogenic matrix

HODGES CAITLIN; VIVANCO LUCIA; ARAUJO PATRICIA INÉS; AUSTIN AMY

Conferencia; Goldschmidt Conference®; 2022

Tephra-derivedsoils retain more organic carbon (C) than soils formed from any other parentmaterial, but past work probing the mineralogical mechanisms behind suchretention have been limited (mainly) to the tropics. Here we present results ofour work evaluating the effects of both precipitation and vegetation type onsoil weathering and organic C storage in young, tephra-derived soils in atemperate climate. We conducted our investigation across five sites in thePatagonian Andes that vary from 250 mm to 2200 mm mean annual precipitation. Ateach of the sites are paired plots of natural vegetation, which changes fromgrasses to closed-canopy forest with increasing precipitation, and stands of Pinus ponderosa planted inmonocultures about 35 years ago. Soils were collected from both vegetationtypes across the gradient to the depth of auger refusal and were extracted with0.5 M HCl for 24h to target the combined exchangeable and adsorbed metals, andsecondary short-range-ordered mineral phases. Our results indicate that pineafforestation 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 therainfall gradient. Al, Si, P, and Mn all increased in the surface soils withrainfall (p < 0.01), indicating the development of short-range-ordervolcanic mineral phases that retain nutrients such as P and Mn. Furthermore,soil C increases in the soils across the gradient, and addition of Al, Si, andCa in the linear model to describe soil organic C explained more of the totalvariance than rainfall and vegetation type alone, indicating the importance ofsecondary minerals and cation bridging to soil C retention. Importantly, thelower concentration of Ca in planted pine soils may signal a permanent decreasein the potential soil C stored in afforested soils due to a lower capacity forcation bridging. Our results reflect changes in tephra-derived soils during theearly stages of weathering in a temperate climate and the potential impacts ofafforestation on soil development and C storage.