Ectomycorrhizal fungal mycelial dynamics and its role in forest soil carbon cycling

Most boreal tree species rely on root-associated ectomycorrhizal fungi for nutrient acquisition, in exchange the trees allocate part of their photosynthetically fixed carbon (C) to these fungi. This has a feedback on soil C dynamics as mycorrhizal fungi are important in regulating soil C cycling and storage. However, mycorrhizal fungi are often not included in C dynamics models, as mechanistic understanding of their contribution to mycorrhiza-mediated processes are largely lacking. The aim of the work described in this thesis was to address this knowledge gap by studying the contribution of mycorrhizal fungi in regulating soil C fluxes. This was done by quantifying C fluxes associated with the extraradical mycelium (ERM) of mycorrhizal fungi, and examining how the ERM contributes to variations in soil C cycling along a nemoboreal chronosequence of managed Pinus sylvestris forests. Production and turnover of ERM was quantified by determining ERM biomass in sequentially harvested ingrowth mesh bags and by mathematical modelling. Respiration of ERM was measured as CO2 efflux from mesh bags, and carbon use efficiency (CUE) was calculated from ERM production and respiration rates. We assessed soil fungal communities along the chronosequence and investigated correlations between taxonomic composition and enzyme activities. The ERM standing biomass increased despite decreased production along the chronosequence. This contradiction was explained by a drastic decline in biomass turnover, from seven times to one time per year. The CUE decreased with forest age, but increased tenfold from summer (0.019) to autumn (0.200). This seasonal increase in CUE was associated with a decline in gross photosynthetic production, suggesting that variation in photosynthetic C supply regulates seasonal variations in CUE. Relative abundance of ectomycorrhizal taxa increased with forest age, and was dominated by Atheliaceae species in young forests, and by Cortinarius and Russula species in mature forests. Enzyme activities were related to community composition, and seem to be important for maintaining forest productivity, by facilitating organic nutrient mobilisation. This thesis is a first step in parameterizing mycorrhizal mycelial C fluxes to enable explicit inclusion of ERM parameters in forest ecosystem C models

Climate change mitigation potential of biochar from forestry residues under boreal condition

Forest harvest residue is a low-competitive biomass feedstock that is usually left to decay on site after forestry operations. Its removal and pyrolytic conversion to biochar is seen as an opportunity to reduce terrestrial CO2 emissions and mitigate climate change. The mitigation effect of biochar is, however, ultimately dependent on the availability of the biomass feedstock, thus CO2 removal of biochar needs to be assessed in relation to the capacity to supply biochar systems with biomass feedstocks over prolonged time scales, relevant for climate mitigation. In the present study we used an assembly of empirical models to forecast the effects of harvest residue removal on soil C storage and the technical capacity of biochar to mitigate national-scale emissions over the century, using Norway as a case study for boreal conditions. We estimate the mitigation potential to vary between 0.41 and 0.78 Tg CO2 equivalents yr−1, of which 79% could be attributed to increased soil C stock, and 21% to the coproduction of bioenergy. These values correspond to 9–17% of the emissions of the Norwegian agricultural sector and to 0.8–1.5% of the total national emission. This illustrates that deployment of biochar from forest harvest residues in countries with a large forestry sector, relative to economy and population size, is likely to have a relatively small contribution to national emission reduction targets but may have a large effect on agricultural emission and commitments. Strategies for biochar deployment need to consider that biochar's mitigation effect is limited by the feedstock supply which needs to be critically assessed.acceptedVersio

Oppdatering av kunnskapsgrunnlag for klimatiltak i skog: Gjennomgang av 11 utvalgte tiltak i bestandsskogbruket

På oppdrag fra Miljødirektoratet og Landbruksdirektoratet har vi gått gjennom kunnskapsstatus på 11 ulike tiltak utvalgt av direktoratene. Alle tiltakene ligger innenfor det tradisjonelle bestandsskogbruket. Tiltakene er vurdert ut fra hvordan de kan øke skogens netto CO2-opptak (karbonlagring), men for noen tiltak også betydning for andre klimagasser og for biogeofysiske effekter som albedo. Utvalget er ikke uttømmende, og også andre tiltak gjennom omløpet vil ha effekt på skogens CO2-opptak. Potensielle substitusjonseffekter gjennom tilgang på mer tømmer eller tømmer med høyere kvalitet er ikke inkludert. Klimatilpasning har vært med i vurderingen av alle tiltak. Det er korte omtaler av tiltakenes effekter på naturmangfold.Oppdatering av kunnskapsgrunnlag for klimatiltak i skog: Gjennomgang av 11 utvalgte tiltak i bestandsskogbruketpublishedVersio

Framskrivninger for arealbrukssektoren (LULUCF) under FNs klimakonvensjon: Sensitivitets- og usikkerhetsanalyser

Arealbrukssektoren (engelsk: Land Use, Land-Use Change and Forestry, LULUCF) omfatter arealbruk og arealbruksendringer, med tilhørende utslipp og opptak av CO2, CH4 (metan) og N2O (lystgass), og er en del av det nasjonale klimagassregnskapet under FNs klimakonvensjon. I oktober 2022 ble det publisert oppdaterte, nasjonale framskrivninger for sektoren (Mohr mfl. 2022), basert på data og metodikk fra Norges siste rapportering til FNs klimakonvensjon (Miljødirektoratet mfl. 2022). Som en oppfølging av det arbeidet presenteres her et utvalg sensitivitets- og usikkerhetsanalyser som illustrerer følsomheten og usikkerheten i framskrivningene for noen parametre. Dette er klima (RCP4.5 versus 8.5 og et gjennomsnitt av disse to), to utvalgte typer arealbruksendring (avskoging, og overgang fra myr og skog på organisk jord til annen arealbruk), samt inndata brukt i Yasso07.Framskrivninger for arealbrukssektoren (LULUCF) under FNs klimakonvensjon: Sensitivitets- og usikkerhetsanalyserpublishedVersio

Ectomycorrhizal necromass turnover is one-third of biomass turnover in hemiboreal Pinus sylvestris forests

Societal Impact Statement Efficient mitigation of climate change requires predictive models of forest ecosystems as sinks for atmospheric carbon. Mycorrhizal fungi are drivers of soil carbon storage in boreal forests, yet they are typically excluded from ecosystem models, because of a lack of information about their growth and turnover. Closing this knowledge gap could help us better predict future responses to climate change and guide policy decisions for sustainable management of forest ecosystems. This study provides new estimates of the production and turnover of mycorrhizal mycelial biomass and necromass. This information can facilitate the integration of mycorrhizal fungi into new predictive models of boreal forest soils. Summary center dot In boreal forests, turnover of biomass and necromass of ectomycorrhizal extraradical mycelia (ERM) are important for mediating long-term carbon storage. However, ectomycorrhizal fungi are usually not considered in ecosystem models, because data for parameterization of ERM dynamics is lacking. center dot Here, we estimated the production and turnover of ERM biomass and necromass across a hemiboreal Pinus sylvestris chronosequence aged 12 to 100 years. Biomass and necromass were quantified in sequentially harvested in-growth bags, and incubated in the soil for 1-24 month, and Bayesian calibration of mathematical models was applied to arrive at parametric estimates of ERM production and turnover rates of biomass and necromass. center dot Steady states were predicted to be nearly reached after 160 and 390 growing season days, respectively, for biomass and necromass. The related turnover rates varied with 95% credible intervals of 1.7-6.5 and 0.3-2.5 times yr-1, with mode values of 2.9 and 0.9 times yr-1, corresponding to mean residence times of 62 and 205 growing season days. center dot Our results highlight that turnover of necromass is one-third of biomass. This together with the variability in the estimates can be used to parameterize ecosystem models, to explicitly include ERM dynamics and its impact on mycorrhizal-derived soil carbon accumulation in boreal forests

Mycorrhizal fungal mycelium - carbon use efficiency

Data on respiration, carbon use efficiency, mycelial biomass, mycelial production, gross primary production and sporocarp production. Biomass estimates are based on amounts of ergosterol (a fungal-specific biomass marker), quantified using liquid chromatography. Growth estimates are derived from biomass estimates and mathematical models. Estimates of carbon use efficiency are based on growth and respiration estimates. Gross primary production estimates are based on eddy covariance flux measurements

Data from: Carbon use efficiency of mycorrhizal fungal mycelium increases during the growing season but decreases with forest age across a Pinus sylvestris chronosequence

1. In boreal forest soils, mycelium of mycorrhizal fungi is pivotal for regulating soil carbon (C) cycling and storage. The carbon use efficiency (CUE), a key parameter in C cycling models, can inform on the partitioning of C between microbial biomass, and potential soil storage, and respiration. Here we test the dependency of mycorrhizal mycelial CUE on stand age and seasonality in managed boreal forest stands. 2. Based on mycelial production and respiration estimates, derived from sequentially incubated ingrowth mesh bags, we estimated CUE on an ecosystem-scale during a seasonal cycle and across a chronosequence of eight, 12- to 158-years-old, managed Pinus sylvestris forest stands characterised by decreasing pH and nitrogen (N) availability with increasing age. Mycelial respiration was related to total soil respiration, and by using eddy covariance flux measurements, primary production (GPP) was estimated in the 12- and 100-years-old forests, and related to mycelial respiration and CUE. 3. As hypothesized, mycelial CUE decreased significantly with increasing forest age by c. 65%, supposedly related to a shift in mycorrhizal community composition and a metabolic adjustment to reduce their own biomass N demand with declining soil N availability. Furthermore, mycelial CUE increased by a factor of five over the growing season; from 0.03 in May to 0.15 in November, and we propose that the seasonal change in CUE is regulated by a decrease in photosynthate production and temperature. The respiratory contribution of mycorrhizal mycelium ranged from 14 to 26% of total soil respiration, and was on average 17% across all sites and occasions. 4. Synthesis: Carbon is retained more efficiently in mycorrhizal mycelium late in the growing season, when fungi have access to a more balanced C and nutrient supplies. Earlier in the growing season, at maximum host plant photosynthesis, when belowground C availability is high in relation to N, the fungi respire excess C resulting in lower mycelial CUE. Additionally, C is retained less efficiently in mycorrhizal fungal biomass in older forest stands characterized by more nutrient depleted soils than younger forest stands

Variations in biomass of fungal guilds are primarily driven by factors related to soil conditions in Mediterranean Pinus pinaster forests

Soil fungi are vital for regulating ecosystem carbon balance and productivity, by driving processes related to soil carbon and nutrient cycling. The rate and capacity of fungi-mediated processes are linked to fungal biomass dynamics and identifying the drivers of fungal biomass is important for predicting ecosystem responses to environmental changes. Here, ergosterol-based fungal biomass estimates and ITS2-based fungal community composition profiles were used to assess biomass of fungal guilds. Effects of forest management (thinning), environmental factors (soil chemical properties, microclimate, weather and forest stand composition) and season were related to the fungal biomass dynamics to identify the guild-specific drivers of biomass. Biomass of most fungal guilds increased with nutrient availability (nitrogen and potassium in particular) and decreased with forest thinning, and variation in total biomass was mainly driven by variation in mycorrhizal biomass. Most fungal guilds reached a minimum in biomass during summer except for mycorrhizal and root-associated ascomycetes, which instead reached a minimum during winter. Mycorrhizal fungi and root-associated ascomycetes displayed similar spatiotemporal variability in biomass. Yeasts and moulds were the only fungi displaying strong linkages with microclimate, whereas pathogenic and moss-associated fungi largely diverged in their responses to the environmental factors. The results of our study highlight that environmental factors related to the availability of soil nutrients may have an overall stronger effect on variation in biomass of fungal guilds in Mediterranean Pinus pinaster forests than direct influences of microclimate, weather and forest management