Impact of environmental conditions and soil microbiome on greenhouse gas fluxes from soil and tree stems in hemiboreal drained peatland forest
Date
2024-07-09
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Abstract
Antud doktoritöös uuriti mulla ja puutüvede kasvuhoonegaaside (KHG) voogude aastaaegadevahelist dünaamikat hemiboreaalses kõdusoometsas, keskendudes lähemalt varasemalt väheuuritud talveperioodile ja kevadistele külmumis-sulamistsüklitele. Uuritud kõdusoometsa mulla aastakeskmine bilanss näitas CH₄ sidumist ning N₂O ja CO₂ lendumist. Talvisel perioodil, kui veetase oli kõrgem, jäid mulla CH₄ vood nullilähedaseks, suvel toimus mullas CH₄ sidumine. Sesoonsed mõõtmised näitasid, et mulla hüdroloogia mõjutab CH₄ dünaamikat pikaajaliselt, samas kui temperatuur mängib lühiajalist rolli. Mulla N₂O vooge mõjutasid kiired muutused mulla hüdroloogias, eriti külmumis-sulamissündmuste ajal. Mulla pinnasekihi sulatamine suurendas N₂O heitkoguseid, peamiselt läbi mittetäieliku denitrifikatsiooni anaeroobsetes tingimustes. Puutüved olid kõikide mõõdetud gaaside allikad ning kase tüved olid olulisemad KHG allikad kui kuuse tüved. CH₄ ja N₂O tüvevoogude ajalist dünaamikat iseloomustasid lühiajalised emissioonide piigid, mida põhjustasid CH₄ puhul pikemad kõrge veetasemega perioodid ja N₂O puhul kiired muutused mulla hüdroloogias. Nii mulla kui puutüvede sesoonsed CO₂ vood sõltusid kasvuperioodist, järgides temperatuurimuutusi. Tüvedest eralduvad KHG vood pärinevad peamiselt mullast. Puutüvedest eralduv CH₄ võib aastas tühistada ligi kolmandiku mulla CH₄ sidumise efektist. Märjemal perioodil võib see osakaal tõusta 50%-ni, tõstes esile mulla hüdroloogiliste tingimuste tugevat mõju CH₄ bilansile. Tüve N₂O vood reageerisid rohkem lühiajalistele veetaseme muutustele ja nende panus N₂O koguheitesse jäi madalaks. Tüvevood mängisid olulist rolli temperatuuri muutustega seotud CO₂ koguemissioonis. Käesoleva doktoritöö tulemused näitavad, et tüvevoogude väljajätmine metsa KHG-de bilansist võib põhjustada metsa koguheidete üle- või alahindamist.
In this doctoral thesis, seasonal patterns of soil and tree stem greenhouse gas (GHG) fluxes were studied in a hemiboreal drained peatland forest, focusing more closely on the previously understudied winter period and spring freeze-thaw cycles. The study found that the soil was a net annual sink for CH₄ but a source of N₂O and CO₂. Soil CH₄ fluxes remained near-zero during the dormant season but showed significant CH₄ uptake in the drier period. Seasonal measurements highlighted that soil hydrology had a long-term impact on CH₄ dynamics, while temperature played a more short-term role. Rapid changes in soil hydrology influenced soil N₂O fluxes, particularly during freeze-thaw events. Soil thawing increased N₂O emissions, primarily due to incomplete denitrification under prolonged anaerobic conditions. Tree stems emitted all measured gases, with birch stems playing a more significant role than spruce stems. Stem CH₄ and N₂O fluxes exhibited isolated emission peaks, driven by prolonged wetter periods for CH₄ and rapid hydrological changes for N₂O. Stem CO₂ release followed a seasonal trend, influenced by temperature and photosynthesis. Stem-emitted GHGs likely had a primarily belowground origin. Stem CH₄ emissions offset nearly a third of the soil sink annually, rising to almost half during wetter periods, highlighting the strong impact of soil hydrological conditions on CH₄ dynamics. Stem N₂O fluxes responded more to short-term hydrological changes, and their contribution to total N₂O emissions remained low. Stem fluxes significantly contributed to total CO₂ release, relating to the growing season. Neglecting stem fluxes can lead to inaccurate estimations of forest GHG budgets, underscoring the necessity of integrating these measurements for a comprehensive understanding of GHG dynamics in forest ecosystems.
In this doctoral thesis, seasonal patterns of soil and tree stem greenhouse gas (GHG) fluxes were studied in a hemiboreal drained peatland forest, focusing more closely on the previously understudied winter period and spring freeze-thaw cycles. The study found that the soil was a net annual sink for CH₄ but a source of N₂O and CO₂. Soil CH₄ fluxes remained near-zero during the dormant season but showed significant CH₄ uptake in the drier period. Seasonal measurements highlighted that soil hydrology had a long-term impact on CH₄ dynamics, while temperature played a more short-term role. Rapid changes in soil hydrology influenced soil N₂O fluxes, particularly during freeze-thaw events. Soil thawing increased N₂O emissions, primarily due to incomplete denitrification under prolonged anaerobic conditions. Tree stems emitted all measured gases, with birch stems playing a more significant role than spruce stems. Stem CH₄ and N₂O fluxes exhibited isolated emission peaks, driven by prolonged wetter periods for CH₄ and rapid hydrological changes for N₂O. Stem CO₂ release followed a seasonal trend, influenced by temperature and photosynthesis. Stem-emitted GHGs likely had a primarily belowground origin. Stem CH₄ emissions offset nearly a third of the soil sink annually, rising to almost half during wetter periods, highlighting the strong impact of soil hydrological conditions on CH₄ dynamics. Stem N₂O fluxes responded more to short-term hydrological changes, and their contribution to total N₂O emissions remained low. Stem fluxes significantly contributed to total CO₂ release, relating to the growing season. Neglecting stem fluxes can lead to inaccurate estimations of forest GHG budgets, underscoring the necessity of integrating these measurements for a comprehensive understanding of GHG dynamics in forest ecosystems.
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