Convergence, divergence or chaos? Consequences of tree trunk decay for pedogenesis and the soil microbiome in a temperate natural forest

• Published in: Geoderma 2020-10, Vol.376, p.114499, Article 114499
• Main Authors: Šamonil, P., Daněk, P., Baldrian, P., Tláskal, V., Tejnecký, V., Drábek, O.
• Format: Article
• Language: English
• Subjects: Biochemical effects of trees; Old-growth forest dynamics; Podzolization; Soil evolution; Soil microorganisms; Tree-soil interactions
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2020.114499

•Entic Podzols under trunks had more nutrients, higher CEC and pH compared to control.•Convergence of soil properties below trunks prevailed over divergence and chaos.•Lying trunks affected soil characteristics at a maximum about 25 yrs after the fall.•Convergence in mineral soils typically terminated circa 53 yrs after trunk fall.•The effects of decomposing trunks was modelled to depths of over 60 cm.•There is some threshold between trunks and soils limiting changes in the microbiome. The biochemical effects of trees may significantly influence local pedogenesis as well as pedocomplexity, biodiversity and forest dynamics on both stand and landscape scales. One such effect is the decay of tree trunks, which is driven by organisms, and especially by the microbiome. Decomposition modifies soil formation, which due to the existence of many feedbacks affects the composition of the decomposer community. We aimed to uncover general trends in the evolution of Entic Podzols as well as individual trajectories of soil properties below decaying beech trunks in an old-growth mountain forest. In particular, we used mathematical models to distinguish soil convergence, divergence and chaotic behaviour to enhance a general theory of pedogenesis. We further aimed to calculate the depth and time of convergence if this scenario is prevailing in the study plot. Pedogenetic pathways were assessed regarding the changing composition of fungal and bacterial communities in soils to obtain a complex picture of the decaying trunk-soil microbiome system. We sampled the decaying wood layer under 24 lying beech trunks and corresponding organic horizons on adjacent control microsites occupied by decaying beech leaves. At the same time we sampled underlying mineral soil horizons at both microsites (wood vs. leaves), all on Entic Podzols and granite (in total 192 soil samples). Individual trunk fall events were dated using precise dendrochronology, with the resulting chronosequence covering trunks lying for 8–52 years. We analysed decomposition processes (with a wide spectra of organic acids and ions analysed), soil chemistry (28 additional soil properties assessed), and the microbiome composition in both decaying organic matter and soils (relative abundances of the 200 most common bacterial and fungal OTUs analysed). During the first stage of trunk decay, underlying Entic Podzols responded with a significant increase of nutrients, pH, and CEC, and the maximal divergence compared to contr