Mineralisation and leaching of C from 13C labelled plant litter along an initial soil chronosequence of a glacier forefield

Abstract

Soils are accumulating C during their initial development but little is known on the evolution of soil C fluxes and their components. In this study, we investigated soil CO2 effluxes and leaching of dissolved organic carbon (DOC) during initial stages of soil formation along the granitic Damma glacier forefield in the Swiss Alps. We added isotopic labelled litter (Leucanthemopsis alpina, δ13C = +88‰) to soil columns in three successional stages (10 yr, 70 yr, 120 yr) and traced the ‘new’ litter-derived C in soil CO2 effluxes, DOC leaching, and in phospholipid fatty acids (PLFA), biomarkers for soil microbial communities. The results showed increasing total soil C fluxes with progressing soil development due to increasing C stocks in plants and soils. Throughout three summer months, 15–63% of the added litter C were lost via mineralisation and leaching. Along the initial soil chronosequence, litter-derived CO2 C effluxes did not change systematically with soil age. The distribution of δ13C signatures in PLFAs was very similar at all site ages, suggesting that decomposer communities did almost not change with succession. Instead, moisture conditions of surface soils varying at the local scale seemed to primarily control litter mineralisation with the driest topsoils and lowest mineralisation at the oldest site. Only a small fraction of the added litter, less than 1% was leached as DOC at 10 cm depth. This indicates a strong removal of litter-derived DOC with passage through the mineral soils. The highest litter-derived DOC leaching occurred in the initial soils with the smallest contents of secondary Fe and Al oxides as potential sorbents for DOC. Litter addition had a negligible priming effect on soil respiration and DOC leaching in all three successional stages.