Effects of Tree Composition and Soil Depth on Structure and Functionality of Belowground Microbial Communities in Temperate European Forests

Abstract

Depending on their tree species composition, forests recruit different soil microbial communities. Likewise, the vertical nutrient gradient along soil profiles impacts these communities and their activities. In forest soils, bacteria and fungi commonly compete, coexist, and interact, which is challenging for understanding the complex mechanisms behind microbial structuring. Using amplicon sequencing, we analyzed bacterial and fungal diversity in relation to forest composition and soil depth. Moreover, employing random forest models, we identified microbial indicator taxa of forest plots composed of either deciduous or evergreen trees, or their mixtures, as well as of three soil depths. We expected that forest composition and soil depth affect bacterial and fungal diversity and community structure differently. Indeed, relative abundances of microbial communities changed more across soil depths than in relation to forest composition. The microbial Shannon diversity was particularly affected by soil depth and by the proportion of evergreen trees. Our results also reflected that bacterial communities are primarily shaped by soil depth, while fungi were influenced by forest tree species composition. An increasing proportion of evergreen trees did not provoke differences in main bacterial metabolic functions, e.g., carbon fixation, degradation, or photosynthesis. However, significant responses related to specialized bacterial metabolisms were detected. Saprotrophic, arbuscular mycorrhizal, and plant pathogenic fungi were related to the proportion of evergreen trees, particularly in topsoil. Prominent microbial indicator taxa in the deciduous forests were characterized to be r-strategists, whereas K-strategists dominated evergreen plots. Considering simultaneously forest composition and soil depth to unravel differences in microbial communities, metabolic pathways and functional guilds have the potential to enlighten mechanisms that maintain forest soil functionality and provide resistance against disturbances.

Mycorrhizal type and tree diversity affect foliar elemental pools and stoichiometry

“…Furthermore, the plastic tarp, initially installed to prevent the growth of weeds that introduce other mycorrhizal types, may have inhibited some processes in nutrient cycling, such as accumulation of organic matter through litter fall and its direct interaction with soil organisms (Berg & McClaugherty, 2014). Plants usually modulate their belowground microbiome partly through the quality and composition of litter (Pollierer et al ., 2007; Prada‐Salcedo et al ., 2022). Therefore, we may expect that species richness effects could be more pronounced in case of direct litter input.…”

“…New Phytologist (2024) 242: 1614-1629 www.newphytologist.com Ó 2024 The Authors New Phytologist Ó 2024 New Phytologist Foundation through litter fall and its direct interaction with soil organisms (Berg & McClaugherty, 2014). Plants usually modulate their belowground microbiome partly through the quality and composition of litter (Pollierer et al, 2007;Prada-Salcedo et al, 2022). Therefore, we may expect that species richness effects could be more pronounced in case of direct litter input.…”

Mycorrhizal fungi modulate tree diversity effects on nutrient dynamics

“…Furthermore, the plastic tarp, initially installed to prevent the growth of weeds that introduce other mycorrhizal types, may have inhibited some processes in nutrient cycling, such as accumulation of organic matter through litter fall and its direct interaction with soil organisms (Berg & McClaugherty, 2014). For example, plants usually modulate their belowground microbiome partly through the quality and composition of litter (Pollierer et al ., 2007; Prada-Salcedo et al ., 2022). Therefore, we expect that species richness effects would be more pronounced in case of direct litter input.…”

Effects of forest age and seasonal changes on soil microbial community diversity in Chinese fir plantations

“…In the fungal community, there was no signi cant trend in the various indicators, and the results of measurements at different soil depths were similar. One possible reason is that soil depth primarily shaped bacterial communities, while plant species structure in uenced fungi [44]. Former studies showed that the predicted bacterial diversity in the topsoil was higher than in the corresponding subsoil [30].…”