Soil fertility relates to fungal‐mediated decomposition and organic matter turnover in a temperate mountain forest

Abstract

Fungi are known to exert a significant influence over soil organic matter (SOM) turnover, however understanding of the effects of fungal community structure on SOM dynamics and its consequences for ecosystem fertility is fragmentary.Here we studied soil fungal guilds and SOM decomposition processes along a fertility gradient in a temperate mountain beech forest. High-throughput sequencing was used to investigate fungal communities. Carbon and nitrogen stocks, enzymatic activity and microbial respiration were measured.While ectomycorrhizal fungal abundance was not related to fertility, saprotrophic ascomycetes showed higher relative abundances under more fertile conditions. The activity of oxidising enzymes and respiration rates in mineral soil were related positively to fertility and saprotrophic fungi. In addition, organic layer carbon and nitrogen stocks were lower on the more fertile plots, although tree biomass and litter input were higher. Together, the results indicated a faster SOM turnover at the fertile end of the gradient.We suggest that there is a positive feedback mechanism between SOM turnover and fertility that is mediated by soil fungi to a significant extent. By underlining the importance of fungi for soil fertility and plant growth, these findings furthermore emphasise the dependency of carbon cycling on fungal communities below ground.

Fine root dynamics and below- and above-ground carbon inputs into soil in boreal forests

“…The nutrient-rich site in boreal Scots pine forests was reported to have a high amount of above-ground litter production (Starr et al 2005), which induced a thick organic layer. A faster turnover rate of SOM in a nutrient-rich site was reported to be closely related to soil fungal decomposition (Mayer et al 2021), confirming our assumption. Moreover, a defoliation experiment conducted in northern Finland reported that the defoliation increased the C limitation in colonized EcM mycelia by decreasing the EcM production and percentage of thick-mantled mycorrhizae of Betula pubescens seedlings (Markkola et al 2004).…”

Decay by ectomycorrhizal fungi couples soil organic matter to nitrogen availability

“…Thus, we propose that the abundance of ECM with peroxidases restricts SOM accumulation across gradients of soil inorganic N availability, but that the direction of this relationship depends on the location along a broader continuum of N availability and photosynthate allocation that connects boreal and temperate ecosystems (Figure 6). Exceptions to this pattern could occur where narrower ranges of soil N availability in fertile temperate forests cause less variation in ECM abundance (Mayer et al, 2021) or where dramatic transitions in boreal and subarctic ecosystem types reverse the relationships between environmental stress, host allocation to ECM with greater decay potential, and N availability (Clemmensen et al, 2021).…”

“…In contrast, SOM stocks decline with increasing N availability in fertile boreal forests because of an increase in ligninolytic saprotrophic fungi (Kyaschenko et al, 2017), which also decay lignified compounds in plant litter and SOM using peroxidases (Floudas et al, 2012). In a high-fertility temperate forest, SOM declined with increasing N availability due to greater decay by non-ligninolytic saprotrophic Ascomycete fungi (Mayer et al, 2021). However, relationships between soil inorganic N availability, fungal composition, and SOM remain poorly understood in temperate forests spanning low to intermediate fertility.…”

Correlation of Leaf and Root Traits of Two Angiosperm Tree Species in Northeast China under Contrasting Light and Nitrogen Availabilities

“…[55,56]. Even more, the potential effects of N fertilization on the decomposition processes, e.g., via modified soil microbial communities/activities [57] and/or root exudation patterns [58], and thus, the availability of other nutrients to plants could not be quantified during this experiment-hampering the development of a comprehensive mechanistic understanding.…”