Kliimamuutuste mõju kase ja kuuse peenjuurtele ning nendega seotud mikroobikooslustele

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKliima soojenedes ja õhuniiskuse tõustes sõltub Põhja-Euroopa metsade seisund ja süsinikusidumine peenjuurte ja nendega seotud mikroobikoosluste kohanemisvõimest. Antud töös uuriti suurendatud õhuniiskuse ja mullasoojenemise mõju arukase (Betula pendula) ja kuuse (Picea abies ja P. sitchensis) peen- ja imijuurte biomassile, imijuurte morfoloogiale ning ektomükoriissete seente ja risosfääribakterite kooslustele. Manipulatsioonikatsete tulemusi võrreldi mõõtmistega geotermaalsel mullatemperatuurigradiendil ja vaatlustega geograafilisel laiuskraadigradiendil. Kõigil kolmel uuritud puuliigil ilmnes stressitingimustes samasuunaline morfoloogiline reaktsioon, mis väljendus pikemate, vähemharunenud imijuurte moodustamises ning omastava pinna suurendamises juuremassiühiku kohta. Põhjapoolse paiknemise ja õhuniiskuse tõusuga kaasnes suurem peen- ja imijuurte biomass; eksperimentaalne mullasoojendamine ja lõunapoolne paiknemine põhjustasid juurte biomassi ja juurte kudede tiheduse vähenemist, mis viitab kiiremale juurte elutsüklile soojemates muldades. Laiuskraadiuuringutes leiti olulisi kolmepoolseid vastastikmõjusid juurte morfoloogia, neid koloniseeriva seenekoosluse ning mulla ja risosfääri bakterikoosluse vahel. Õhuniiskuse kasvades suurenes seenekoosluses oluliselt hüdrofiilse mütseeliga liikide osakaal. Soojemates muldades esines rohkem suure hüüfimassiga kauglevi-mütseelitüüpi moodustavaid seeni. Nii õhuniiskuse tõustes kui mulla soojenedes suurenes seeneperekond Tomentella osakaal, mis on tõenäoliselt seotud kiirema juurte elutsükliga. Laiuskraadigradiendil määras suure osa imijuuretunnuste ja juurtega seotud mikroobikoosluste struktuuri varieeruvusest mulla süsiniku ja lämmastiku suhe. Käesolevast tööst ilmneb, et kased ja kuused reageerivad keskkonnamuutustele aktiivselt juurte morfoloogiat ja biomassi modifitseerides, millega kaasnevad samaaegsed nihked juurtega seotud mikroobikooslustes, ning nimetatud muutused on omavahel tugevalt seotud. Uuringute tulemused lubavad oletada, et vähemalt uuritud liikide puhul on tegemist üldiste kohanemismustritega niiskema ja soojema kliima suhtes.In the face of rising temperatures and humidity, the functioning and carbon storage of northern European forests is largely dependent on the acclimation ability of fine roots and root-associated microbial communities. We investigated the effects of increased air humidity and soil warming on silver birch (Betula pendula) and spruce (Picea abies and P. sitchensis) fine and absorptive root biomass (FRB, aFRB), absorptive root morphology and the communities of ectomycorrhizal (EcM) fungi and rhizosphere bacteria, comparing results from field manipulation experiments to observations from a small-scale geothermal soil temperature gradient and large-scale latitudinal gradients. We witnessed a uniform morphological response of forming longer and less branched absorptive roots with increased specific root length and area in all studied species to obstructions in nutrient uptake or otherwise stressful growing conditions. Air humidification and a northern location resulted in higher FRB and aFRB, while experimental warming and a southern location caused a decrease in FRB and aFRB and root tissue density, which suggests increased root turnover in warmer soils. Strong trilateral relationships between absorptive root morphology, EcM fungal community and soil bacterial community emerged in the studied birch stands. Humidification caused a shift towards a higher proportion of hydrophilic morphotypes; a higher proportion of long-distance exploration type was recorded in warmer soils. Warming and humidification led to a rise in the proportion of Tomentella spp., possibly related to higher root turnover. On the latitudinal gradient, the soil C:N ratio was the main determinant of variation in absorptive root traits and root-associated microbial community structure. This thesis demonstrates how birches and spruces respond to environmental change through active modifications in root morphology and biomass, concurring with shifts in root-associated microbial community, and all these changes proved to be strongly inter-related. The similar root reactions, irrespective of tree species, stand age, location, or experiment type, permit us to conclude that the observed responses reflect general acclimation patterns, at least for the studied species.https://www.ester.ee/record=b534664

Acclimation of Fine Root Systems to Soil Warming: Comparison of an Experimental Setup and a Natural Soil Temperature Gradient

Global warming is predicted to impact high-latitude and high-altitude forests severely, jeopardizing their overall functioning and carbon storage, both of which depend on the warming response of tree fine root systems. This paper investigates the effect of soil warming on the biomass, morphology and colonizing ectomycorrhizal community of spruce fine and absorptive fine roots. We compare the responses of spruce roots growing at a man-made long-term soil warming (+ 4°C) experiment to results obtained from a geothermal soil temperature gradient (+ 1 to + 14°C) extending to the forest die-off edge, to shed light on the generalizability of the warming response and reveal any thresholds in acclimation ability. Trees in warmer soils formed longer and less-branched absorptive roots with higher specific root length and area, and lower root tissue density in both spruce stands, irrespective of warming method and location. Soil warming at the experimental warming site also supported the occurrence of a more varied EcM community and an increase in the abundance of Tomentella spp., indicating a shift in nutrient foraging. Fine and absorptive fine root biomass decreased toward warmer soil, with a sharp reduction occurring between + 4 and + 6°C from the ambient and leading to the collapse of the fine root system at the geothermal gradient. At the experimental warming site, the applied + 4°C warming had no effect on fine and absorptive fine root biomass. The similar fine root responses at the two warming sites suggest that the observations possibly reflect general acclimation patterns in spruce forests to global warming.We thank Krista Lõhmus for valuable discussions, Kessy Abarenkov for guidance with uploading the EcM fungal sequences, and Aale Puri, Aulis Puri, Laura Soon and Marta Arula for assistance in the laboratory. We acknowledge the EU through the European Regional Development Fund (Center of Excellence ENVIRON and EcolChange), the Estonian Ministry of Education, Research projects IUT2-16, IUT34-9 and Lydia and Felix Krabi Scholarship Fund for financial support. We are very grateful to ExpeER for financing the field work of Kaarin Parts and analyses of EcM fungal community samples at the Achenkirch experimental area. This work contributes to the Icelandic ForHot-Forest Project (IRF Fund, No. 163272-051), the CAR-ES Nordic Network, the ClimMani (ES1308) and the Biolink COST Actions (FP1305).Peer Reviewe

Adaptive root foraging strategies along a boreal–temperate forest gradient

The tree root–mycorhizosphere plays a key role in resource uptake, but also in the adaptation of forests to changing environments. The adaptive foraging mechanisms of ectomycorrhizal (EcM) and fine roots of Picea abies, Pinus sylvestris and Betula pendula were evaluated along a gradient from temperate to subarctic boreal forest (38 sites between latitudes 48°N and 69°N) in Europe. Variables describing tree resource uptake structures and processes (absorptive fine root biomass and morphology, nitrogen (N) concentration in absorptive roots, extramatrical mycelium (EMM) biomass, community structure of root-associated EcM fungi, soil and rhizosphere bacteria) were used to analyse relationships between root system functional traits and climate, soil and stand characteristics. Absorptive fine root biomass per stand basal area increased significantly from temperate to boreal forests, coinciding with longer and thinner root tips with higher tissue density, smaller EMM biomass per root length and a shift in soil microbial community structure. The soil carbon (C) : N ratio was found to explain most of the variability in absorptive fine root and EMM biomass, root tissue density, N concentration and rhizosphere bacterial community structure. We suggest a concept of absorptive fine root foraging strategies involving both qualitative and quantitative changes in the root–mycorrhiza–bacteria continuum along climate and soil C : N gradients.Peer reviewe

Global diversity and geography of soil fungi

Fungi play major roles in ecosystem processes, but the determinants of fungal diversity and biogeographic patterns remain poorly understood. Using DNA metabarcoding data from hundreds of globally distributed soil samples, we demonstrate that fungal richness is decoupled from plant diversity. The plant-to-fungus richness ratio declines exponentially toward the poles. Climatic factors, followed by edaphic and spatial variables, constitute the best predictors of fungal richness and community composition at the global scale. Fungi show similar latitudinal diversity gradients to other organisms, with several notable exceptions. These findings advance our understanding of global fungal diversity patterns and permit integration of fungi into a general macroecological framework