Search

Summary: Mycorrhizal fungi associated with boreal trees and ericaceous shrubs are central actors in organic matter (OM) accumulation through their belowground carbon allocation, their potential capacity to mine organic matter for nitrogen (N) and their ability to suppress saprotrophs. Yet, interactions between co‐occurring ectomycorrhizal fungi (EMF), ericoid mycorrhizal fungi (ERI), and saprotrophs are poorly understood.We used a long‐term (19 yr) plant functional group manipulation experiment with removals of tree roots, ericaceous shrubs and mosses and analysed the responses of different fungal guilds (assessed by metabarcoding) and their interactions in relation to OM quality (assessed by mid‐infrared spectroscopy and nuclear magnetic resonance) and decomposition (litter mesh‐bags) across a 5000‐yr post‐fire boreal forest chronosequence.We found that the removal of ericaceous shrubs and associated ERI changed the composition of EMF communities, with larger effects occurring at earlier stages of the chronosequence. Removal of shrubs was associated with enhanced N availability, litter decomposition and enrichment of the recalcitrant OM fraction.We conclude that increasing abundance of slow‐growing ericaceous shrubs and the associated fungi contributes to increasing nutrient limitation, impaired decomposition and progressive OM accumulation in boreal forests, particularly towards later successional stages. These results are indicative of the contrasting roles of EMF and ERI in regulating belowground OM storage. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition can enhance carbon (C) capture and storage in northern coniferous forests but it may also enhance the demand for phosphorus (P). While it is well established that long‐term N enrichment can decrease decomposition and enhance the accumulation of C in soils, it remains uncertain if a higher demand and acquisition of P influence soil C.We studied microbial phosphorus mobilization and growth within a long‐term N enrichment experiment in a Norway spruce forest, where N deposition was simulated by adding 0, 12.5 or 50 kg N ha−1 year−1 for 21 years (n = 12), by incubating microbial ingrowth cores with needles and humus with low and high P content, and with sand with and without mineral apatite P.Long‐term N enrichment had no effect on microbial P mobilization in needles and humus and did not enhance the positive effect that apatite had on fungal growth. However, it consistently strengthened the retention of C in the soil by decreasing decomposition of needle and humus, both with low and high P content, and by increasing fungal growth in sand‐filled ingrowth cores. Furthermore, we did not find any evidence that higher microbial P mobilization in response to N enrichment affected soil C storage.These results show that long‐term N enrichment in relatively young soils dominated by coniferous trees and ectomycorrhizal fungi can have relatively small impact on microbial P mobilization from organic sources and on the potential to mobilize P from minerals, and subsequently that elevated P demand due to N enrichment is unlikely to lead to a reduction in the soil C accumulation rate. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Anthropogenic nitrogen (N) enrichment in boreal forests has been shown to enhance aboveground net primary production and downregulate soil respiration, but it is not well understood if these effects are driven by reduced belowground C allocation or shifts between biomass production and respiration in fine-roots and ectomycorrhizal fungi (EMF). We utilized an experiment in a Pinus sylvestris (L.) forest simulating anthropogenic N enrichment with additions of low (3, 6, and 12 kg N ha−1 yr−1) and high (50 kg N ha−1 yr−1 × 12 yr) doses of N (n = 6) and measured the production of needles, fine-roots, and EMF mycelium during the 12th and 13th year of the experiment. We created a biomass production efficiency index by relating the biomass production rate to root-associated respiration, including both root and EMF respiration. The high N treatment enhanced the production of both needles and fine-roots, with a relatively larger increase in fine-roots, and strongly increased fine-root biomass production efficiency but had no effect on the fungal biomass in fine-roots or the production of EMF mycelium. The low N treatments had no effect on any of the measured variables. These results show that high levels of N enrichment drive shifts in the use of C allocated below ground, with less C going towards metabolic functions that result in rapid C emissions, and more C going towards the production of new tissues. • High N addition doubled Pinus sylvestris fine-root production. • High N addition reduced autotrophic soil respiration by one third. • Low N additions had no effect on fine-roots or soil respiration. • Neither low or high N addition had any effect on EMF biomass or production. • High levels of N deposition enhance fine-root production efficiency. [ABSTRACT FROM AUTHOR]