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Soil processes and nutrient bioavailability in the rhizosphere of Bolax gummifera in a subantarctic environment (Martial Mountains, Ushuaia-Argentina)

Abstract:

The aim of this study was to explore the effects of plants on the underlying substrate and the possible environmental implications of such effects in an extreme environment. For this purpose, we sampled the rhizosphere soil of Bolax gummifera, which is one of the most characteristic vascular plants in the Martial Mountains (Tierra del Fuego, Argentina) where plant cover is typically sparse. Superficial (0-5cm, Rh5) and subsuperficial (5-15cm, Rh15) samples of B. gummifera rhizosphere and bulk soil were collected from a small homogeneous area, and the following parameters were analyzed: particle size, pH, total organic carbon (TOC), total nitrogen (TN), total Fe (TFe), Fe and Al associated with organic matter (soluble in sodium pyrophosphate, C<inf>pyro</inf>), amorphous Fe oxyhydroxides (extracted with ammonium oxalate, Fe<inf>oxa</inf>), crystalline Fe oxyhydroxides (extracted with sodium dithionite, Fe<inf>dit</inf>), bioavailable plant nutrients (soluble in Mehlich 3 extractant) and clay mineralogy. Several differences were found between rhizosphere soil (RS) and bulk soil. The TOC was 8 times higher and the TN and C<inf>pyro</inf> were 4 times higher in the rhizosphere than in the bulk soil. Mineralogical results suggest a slightly higher degree of chemical weathering (mainly affecting biotite and amphibole minerals) in the RS than in bulk soil, consistent with significantly higher nutrient bioavailability in RS (Ca, Mg, K, Co, and Fe). On the other hand, the higher concentrations of C and metals extracted with sodium pyrophosphate suggest the formation of more metal-organic complexes in the rhizosphere than in the bulk soil. This metal fraction is considered as readily mobilizable and available and can be leached from the soil to continental and coastal waters. This effect will be enhanced in cold climates by expansion of plant cover due to the increased temperature expected under climate change.