Abstract
Bare soils in the area of retreating glaciers are ideal environments to study the role of microorganisms in the early soil formation and in processes of mineral weathering. The aim of our study was to investigate whether the source of carbohydrate would influence the patterns of organic acids exuded by fungal species. Three pioneering fungus species, isolated from fine granitic sediments in front of the Damma glacier from the central Swiss Alps, have previously been found to have the capability to exude organic acids and dissolve granite powder. In batch experiments, various carbohydrates, including glucose, cellulose, pectin, pollen, and cell remnants of cyanobacteria, fungi, and algae, were applied as carbohydrate sources and the patterns of exuded organic acids recorded. The results showed that two fungi, the zygomycete fungus Mucor hiemalis and the ascomycete fungus Penicillium chrysogenum, released a significantly higher amount of organic acids in dependence on specific carbohydrate sources. Pollen and algae as carbohydrate sources triggered significantly the exudation of malate in M. hiemalis, and pollen and cellulose that of oxalate in P. chrysogenum. We conclude that the occurrence of complex carbohydrate sources in nutrient-deficient deglaciated soils may positively influence the exudation of organic acids of fungi. In particular, pollen and remnants of other microorganisms can trigger the exudation of organic acids of fungi in order to promote the weathering of minerals and to make nutrients available that would otherwise be trapped in that cryospheric environment.
Highlights
Soils of glacier forefields are inhabited by a large variety of microorganisms, such as bacteria, cyanobacteria, archaea, green algae, and fungi (Bardgett et al 2007, Frey et al 2013, Zumsteg et al 2012)
Nitrogen was measured in glucose, cellulose, and pectin only in small amounts (
It is estimated that the accumulation rate of soil organic C at glacier forefields is between 1 and 36 g m−2 yr−2 (Dumig et al 2011), and it is likely that the soil organic C is a mixture of ancient recalcitrant C, of recent organic C which was deposited, and of recent C from cell wall remnants of auto- and heterotrophic microorganisms (Bardgett et al 2007, Miltner et al 2012)
Summary
Soils of glacier forefields are inhabited by a large variety of microorganisms, such as bacteria, cyanobacteria, archaea, green algae, and fungi (Bardgett et al 2007, Frey et al 2013, Zumsteg et al 2012). Have been shown to exude organic acids, that play an important role in weathering the parent rock material of the glacier forefield (Brunner et al 2011, Frey et al 2010, Lapanje et al 2012) The microorganisms secrete these acids in order to make available the nutrients that would otherwise be trapped in the environment (Gadd 1999, Rosling et al 2007, Rosling 2009). These acids have the chemical capacity to dissolve granite and increase the concentration of macro- and micronutrients in solution, 1748-9326/14/025002+09$33.00 c 2014 IOP Publishing Ltd Printed in the UK
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