Soil formation, nutrient supply and ecosystem productivity on basaltic lava vs rhyolitic pumice on Alcedo Volcano, Galapagos

Context. Rock type may exert strong control on pedogenesis and resulting soil characteristics. Little is known on how different volcanic lithologies influence soil formation and nutrient supply and thereby affect ecosystem productivity in volcanic landscapes. Aims. The aim of this study was to investigate lithologic control on the mentioned properties and processes. Methods. We conducted a side-by-side comparison of two contrasting sites in close proximity on Alcedo Volcano, Galapagos, one on basaltic lava and the other on rhyolitic pumice. Key results. The lava site was covered by lush, stratified woodland, whereas the pumice site was covered by grassland with only few plant species. The soil on lava was a Leptosol, whereas on pumice, an Andosol had formed. Both soils had similar pH (6.0-6.5 in H2O), but the soil organic carbon stocks at the lava site were almost twice as high as at the pumice site (I 3.1 +/- 1.6 vs 7.6 +/- 1.3 kg m(-2) to 25 cm depth). The soil at the pumice site had considerably lower levels of Mehlich-3-extractable P, Ca, Mg, Cu, Zn and B. Soil microbes at the pumice site had lower biomass P (and a higher C:P ratio) and excreted more phosphatase. The grass biomass here also showed lower (and deficient) levels of P and other nutrients compared to the lava site. Conclusion and implications. The contrasting lithologies and their bearings on soil formation and nutrient availability diversify the aboveground and belowground ecosystems and favour the development of distinct ecological niches in close proximity.