Litter chemical quality and bacterial community structure influenced decomposition in acidic forest soil

Organic matter sequestration is influenced by both biotic and abiotic factors, which determine the rate of decomposition and result into distinguish soil forming processes and different humus types. Previous observations indicated that podzol soils and mor humus form typically develop under spruce forest, while under beech forest the higher mineralization rate leads to moder humus and the development of dystric cambisol. This study was designed to observe the forming of the different microbial communities participating in diverse decomposition processes reflecting the soil types developed under naturally occurring beech and artificially planted spruce forests. A litterbag experiment was performed with beech and spruce litter placed respectively to beech and spruce forests. In the beech forest, the observed litter decomposition rate reached the exponential faze after 15 months, while in the spruce forest a steeper decrease was noted only 29 months after the litter burial. Thus, the study focused on the period between 15 and 29 months to observe the exponential stages of recalcitrant organic matter transformation. In this period, the chemical composition of two litters was distinguished by higher contents of Mn and Ca in beech and higher content of Fe, S, N and P in spruce. On top of that, the beech litter released higher amount of dissolved organic carbon and its associated bacterial community was enriched with r-selected taxa that correlated positively with organic acids and cations. In contrast, the more acidic spruce litter was dominated by K-selected acidophilic community and its turnover rate was slower, resulting in increased carbon sequestration. The higher pH and humus quality of beech cambisol also correlates with its observed higher resilience to disturbances by acidification, pests or climate change in mountainous environments.