Sirvi Autor "Espenberg, Mikk" järgi

Nüüd näidatakse 1 - 20 37

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15N tracers and microbial analyses reveal in situ N2O sources in contrasting water regimes of a drained peatland forest
(2024) Masta, Mohit; Espenberg, Mikk; Kuusemets, Laura; Pärn, Jaan; Thayamkottu, Sandeep; Sepp, Holar; Kirsimäe, Kalle; Sgouridis, Fotis; Kasak, Kuno; Soosaar, Kaido; Mander, Ülo
Managed peatlands are a significant source of nitrous oxide (N2O), a powerful greenhouse gas and stratospheric ozone depleter. Due to the complexity and diversity of microbial N2O processes, different methods such as tracer, isotopomer, and microbiological technologies are required to understand these processes. The combined application of different methods helps to precisely estimate these processes, which is crucial for the future management of drained peatlands, and to mitigate soil degradation and negative atmospheric impact. In this study, we investigated N2O sources by combining tracer, isotopomer, and microbial analysis in a drained peatland forest under flooded and drained treatments. On average, the nitrification genes showed higher abundances in the drained treatment, and the denitrification genes showed higher abundances in the flooded treatment. This is consistent with the underlying chemistry, as nitrification requires oxygen while denitrification is anaerobic. We observed significant differences in labelled N2O fluxes between the drained and flooded treatments. The emissions of N2O from the flooded treatment were nearly negligible, whereas the N2O evolved from the nitrogen-15 (15N)-labelled ammonium (15NH4+) in the drained treatment peaked at 147 μg 15N m-2 h-1. This initially suggested nitrification as the driving mechanism behind N2O fluxes in drained peatlands, but based on the genetic data, isotopic analysis, and N2O mass enrichment, we conclude that hybrid N2O formation involving ammonia oxidation was the main source of N2O emissions in the drained treatment. Based on the 15N-labelled nitrate (15NO3-) tracer addition and gene copy numbers, the low N2O emissions in the flooded treatment came possibly from complete denitrification producing inert dinitrogen. At atomic level, we observed selective enrichment of mass 45 of N2O molecule under 15NH4+ amendment in the drained treatment and enrichment of both masses 45 and 46 under 15NO3- amendment in the flooded treatment. The selective enrichment of mass 45 in the drained treatment indicated the presence of hybrid N2O formation, which was also supported by the high abundances of archaeal genes.
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Amazonase madaliku palmisoomuldade mikrobioloogiline lämmastikuringe ning selle seos dilämmastikoksiidi voogudega
(Tartu Ülikool, 2022) Hints, Liina; Espenberg, Mikk; Mander, Ülo; Tartu Ülikool. Geograafia osakond; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
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Distinct microbial communities drive methane cycling in below- and above-ground compartments of tropical cloud forests growing on peat
(2025) Kazmi, Fahad Ali; Mander, Ülo; Khanongnuch, Ramita; Öpik, Maarja; Ranniku, Reti; Soosaar, Kaido; Masta, Mohit; Tenhovirta, Salla A. M.; Kasak, Kuno; Ah-Peng, Claudine; Espenberg, Mikk
Cloud forests are unique yet understudied ecosystems regarding CH4 exchange despite their significance in carbon storage. We investigated CH4 fluxes in peat soil and tree stems of two tropical cloud forests on Réunion Island, one featuring Erica reunionensis and the second a mix of E. reunionensis and Alsophila glaucifolia. The study examined microbiomes across below-ground (soil) and above-ground (canopy soil, leaves, and stems) forest compartments. Metagenomics and qPCR analyses targeted key genes in methanogenesis and methanotrophy in soil and above-ground samples, alongside soil physicochemical measurements. CH4 fluxes from peat soil and tree stems were measured using gas chromatography and portable trace gas analyzers. Peat soil in both forests acted as a CH4 sink (− 23.8 ± 4.84 µg C m− 2 h− 1) and CO2 source (55.5 ± 5.51 µg C m− 2 h− 1), with higher CH4 uptake in sites dominated by endemic tree species E. reunionensis. In forest soils, a high abundance of n-DAMO 16 S rRNA gene (3.42 × 107 ± 7 × 106 copies/g dw) was associated with nitrate levels and higher rates of CH4 uptake and CO2 emissions. NC-10 bacteria (0.1–0.3%) were detected in only the Erica forest soil, verrucomicrobial methanotrophs (0.1–3.1%) only in the mixed forest soil, whereas alphaproteobacterial methanotrophs (0.1–3.3%) were present in all soils. Tree stems in both forests were weak sinks of CH4 (-0.94 ± 0.4 µg C m− 2 h− 1). The canopy soil hosted verrucomicrobial methanotrophs (0.1–0.3%). The leaves in both forests exhibited metabolic potential for CH4 production, e.g., exhibiting high mcrA copy numbers (3.5 × 105 ± 2.3 × 105 copies/g dw). However, no CH4-cycling functional genes were detected in the stem core samples. Tropical cloud forest peat soils showed high anaerobic methanotrophy via the n-DAMO process, while aerobic methanotrophs were abundant in canopy soils. Leaves hosted methanotrophs but predominantly methanogens. These results highlight the significant differences between canopy and soil microbiomes in the CH4 cycle, emphasizing the importance of above-ground microbiomes in forest CH4 gas budgets.
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Distinct microbial communities drive methane cycling in below- and above-ground compartments of tropical cloud forests growing on peat
(2025) Kazmi, Fahad Ali; Mander, Ülo; Khanongnuch, Ramita; Öpik, Maarja; Ranniku, Reti; Soosaar, Kaido; Masta, Mohit; Tenhovirta, Salla A. M.; Kasak, Kuno; Ah-Peng, Claudine; Espenberg, Mikk
Cloud forests are unique yet understudied ecosystems regarding CH4 exchange despite their significance in carbon storage. We investigated CH4 fluxes in peat soil and tree stems of two tropical cloud forests on Réunion Island, one featuring Erica reunionensis and the second a mix of E. reunionensis and Alsophila glaucifolia. The study examined microbiomes across below-ground (soil) and above-ground (canopy soil, leaves, and stems) forest compartments. Metagenomics and qPCR analyses targeted key genes in methanogenesis and methanotrophy in soil and above-ground samples, alongside soil physicochemical measurements. CH4 fluxes from peat soil and tree stems were measured using gas chromatography and portable trace gas analyzers. Peat soil in both forests acted as a CH4 sink (− 23.8 ± 4.84 µg C m− 2 h− 1) and CO2 source (55.5 ± 5.51 µg C m− 2 h− 1), with higher CH4 uptake in sites dominated by endemic tree species E. reunionensis. In forest soils, a high abundance of n-DAMO 16 S rRNA gene (3.42 × 107 ± 7 × 106 copies/g dw) was associated with nitrate levels and higher rates of CH4 uptake and CO2 emissions. NC-10 bacteria (0.1–0.3%) were detected in only the Erica forest soil, verrucomicrobial methanotrophs (0.1–3.1%) only in the mixed forest soil, whereas alphaproteobacterial methanotrophs (0.1–3.3%) were present in all soils. Tree stems in both forests were weak sinks of CH4 (-0.94 ± 0.4 µg C m− 2 h− 1). The canopy soil hosted verrucomicrobial methanotrophs (0.1–0.3%). The leaves in both forests exhibited metabolic potential for CH4 production, e.g., exhibiting high mcrA copy numbers (3.5 × 105 ± 2.3 × 105 copies/g dw). However, no CH4-cycling functional genes were detected in the stem core samples. Tropical cloud forest peat soils showed high anaerobic methanotrophy via the n-DAMO process, while aerobic methanotrophs were abundant in canopy soils. Leaves hosted methanotrophs but predominantly methanogens. These results highlight the significant differences between canopy and soil microbiomes in the CH4 cycle, emphasizing the importance of above-ground microbiomes in forest CH4 gas budgets.
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Dynamics of soil microbial nitrogen cycle during a year-long study in a drained peatland forest
(Tartu Ülikool, 2022) Ferch, Zane Walden; Espenberg, Mikk; Mander, Ülo; Tartu Ülikool. Geograafia osakond; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
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Erinevate taimeliikide mõju mikrobioloogilisele metaani- ja lämmastikuringele ning CH4 ja N2O emissioonidele riimveest mõjutatud rannikul
(Tartu Ülikool, 2020) Pille, Kristin; Espenberg, Mikk; Mander, Ülo; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Rannikualad on mitmekesised ökosüsteemid, mis kujunevad mitmete tegurite koosmõjul. Oma mitmekesisuse ning varieeruvusega pakuvad nad mitmeid elutähtsaid ökosüsteemi teenuseid. Tänapäeva üha intensiivistuv inimtegevus ning kliimamuutustega kaasnevad häiringud on suurendanud mõjusid rannikualadele. Erinevad taimed mõjutavad rannikumulla mikroobikooslusi, mõjutades sealseid mikrobioloogilisi metaani- ja lämmastikuringet. Mikrobioloogiliste aineringe häiringute tagajärjel võib aga keskkonda emiteerida kahjulikke kasvuhoonegaase, nagu metaani CH4 ning dilämmastikoksiidi N2O. Käesoleva magistritöö eesmärgiks oli uurida erinevaid riimveelisi rannikualasid Lääne-Eestis ja Ida-Hiinas ning seal kasvavate taimeliikide mõju mikrobioloogilisele metaani- ja lämmastikuringele. Erinevate metaani- ja lämmastikuringe protsesside toimumise potentsiaali määrati protsessile spetsiifiliste markergeenidega. Metaaniringes osalevaid mikroorganisme tuvastati järgmiseid geene kvantifitseerides: metaani tootvaid metanogeenid (mcrA) ning metaani tarbijaid metanotroofid (pmoA). Lämmastikuringes uuriti järgnevaid protsesse: lämmastiku fikseerimine (nifH), nitrifikatsioon (bakterite ja arhede amoA), denitrifikatsioon (nirS, nirK, nosZI, nosZII), dissimilatoorne nitraadi redutseerimine ammooniumiks (nrfA), anaeroobne ammooniumi oksüdatsioon (ANAMMOX spetsiifiline 16S rRNA geen) ning täielik ammooniumi oksüdeerimine (COMAMMOX spetsiifiline 16S rRNA geen). Lisaks uuriti lämmastiku- ja süsinikuringet ühendavat nitritist sõltuvat anaeroobset metaani oksüdeerimist (n-damo spetsiifiline 16S rRNA geen). Neist nelja protsessi vaheetappides – nitrifikatsioon (k.a COMAMMOX), denitrifikatsioon, DNRA ja nitrifitseerijate denitrifikatsioon, käigus võib eralduda keskkonda kahjulikku kasvuhoonegaasi N2O-d. Keskkonnategurite mõju rannikukoosluste mikroorganismidele hinnati metaani ja naerugaasi emissioonide kontsentratsioone mõõtes kambermeetodil ning nende olulisi seoseid geeni- ning keskkonnaparameetrite vahel erinevate statistiliste meetoditega (Spearmani korrelatsioonikoefitsent, ANOVA). Antud magistritöö tulemustest järeldus, et taimed mängivad olulist rolli kasvukeskkonna kujundamises ning seeläbi kahjulike kasvuhoonegaaside heitkoguste emiteerimises. Erinevad keskkonnatingimused määrasid uurimisalade koosluse struktuuri. Keskkonnatingimused soodustasid COMAMMOX-i protsessi läbiviivate mikroorganismide aktiivsust Spartina ja Scirpuse ning kare-kaislaga katsealal, kus mikroorganismide kohastumuste eelistuste kohta rannikusetetes teatakse vähe. ANAMMOX-i suurim 43 geneetiline potentsiaal Hiina katsealadel näitas, et üleliigne lämmastik redutseeriti nii, et minimaalselt eraldus kahjulikku dilämmastikoksiidi. Hiina uurimisala keskkonnatingimused soodustasid nitrifikatsiooni toimumist, seevastu Eestis emiteerus kahjulik N2O-d peamiselt mittetäieliku denitrifikatsiooni tulemina. Uurimisalad erinesid üksteisest peamiselt üldsüsiniku protsentuaalsuse ja anaeroobsete tingimuste poolest, mis pakkus soodsat elukeskkonda just nirK geeni omavatele mikroorganismidele. Suurimad emissioonide kontsentratsioone näidati vanema Spartina alterniflora´ga kaetud alal, kus metaani eraldus võrreldes Eesti alaga märkimisväärselt ligi neli korda rohkem. Eestis täheldati suuremaid metaanikoguseid lagedalt alalt, kus dilämmastikoksiidi emiteerus rohkem hariliku pillirooga (Phragmites australis) katsealalt. Metaani tarbivate mikroorganismide aktiivsus oli seotud metaani suuremate emissioonidega. Dilämmastikoksiidi korral täheldati oluline seos taimeliigi vanuse ning biomassiga, kus nooremad taimed leevendasid kasvuhoonegaasi emiteerumist atmosfääri. Seevastu taimede puhkeperioodil tuvastati tihe konkurents protsesside läbiviimiseks vajalike substraatide vahel mikroorganismidega, mille tõttu vähenesid kasvuhoonegaasi kogused. Lämmastiku- ja süsinikuringet ühendava n-damo suurimat geneetilist potentsiaal leiti pillirooga ja lagedalt mudaselt alalt, kus eelnimetatud protsess leevendas metaanikoguste paiskamist atmosfääri. Parema kaitse tagamiseks on oluline mõista rannikualades toimuvaid protsesse ning nende seoseid erinevate keskkonnaparameetritega. Taimede potentsiaali vahendada emissioonide vooge ning risosfääris toimuv suhe väärib tähelepanu, sest see võib muuta meie arusaama, kuidas taimed reageerivad lämmastikuühendite kasvule, soolsusele, merevee tõusu või muudele kliimamuutusest intensiivistuvatele teguritele. Uued teadmised ning varasemate teadmiste kinnitused aitavad mõista, kuidas toimub keerukas ranniku ökosüsteem mikroorganismide vaatevinklist ning kuidas seda on võimalik mõjutada taimedega.
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Global peatland greenhouse gas dynamics: state of the art, processes, and perspectives
(New Phytologist, 2025) Mander, Ülo; Öpik, Maarja; Espenberg, Mikk
Natural peatlands regulate greenhouse gas (GHG) fluxes through a permanently high groundwater table, causing carbon dioxide (CO2) assimilation but methane (CH4) emissions due to anaerobic conditions. By contrast, drained and disturbed peatlands are hotspots for CO2 and nitrous oxide (N2O) emissions, while CH4 release is low but high from drainage ditches. Generally, in low-latitude (tropical and subtropical) peatlands, emissions of all GHGs are higher than in high-latitude (temperate, boreal, and Arctic) peatlands. Their inherent dependence on the water regime makes peatlands highly vulnerable to both direct and indirect anthropogenic impacts, including climate change-induced drying, which is creating anthro-natural ecosystems. This paper presents state-of-the-art knowledge on peatland GHG fluxes and their key regulating processes, highlighting approaches to study spatio-temporal dynamics, integrated methods, direct and indirect human impacts, and peatlands' perspectives.
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Global peatland greenhouse gas dynamics: state of the art, processes, and perspectives
(2025) Mander, Ülo; Espenberg, Mikk; Öpik, Maarja
Natural peatlands regulate greenhouse gas (GHG) fluxes through a permanently high groundwater table, causing carbon dioxide (CO2) assimilation but methane (CH4) emissions due to anaerobic conditions. By contrast, drained and disturbed peatlands are hotspots for CO2 and nitrous oxide (N2O) emissions, while CH4 release is low but high from drainage ditches. Generally, in low-latitude (tropical and subtropical) peatlands, emissions of all GHGs are higher than in high-latitude (temperate, boreal, and Arctic) peatlands. Their inherent dependence on the water regime makes peatlands highly vulnerable to both direct and indirect anthropogenic impacts, including climate change-induced drying, which is creating anthro-natural ecosystems. This paper presents state-of-the-art knowledge on peatland GHG fluxes and their key regulating processes, highlighting approaches to study spatio-temporal dynamics, integrated methods, direct and indirect human impacts, and peatlands' perspectives.
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Human-Impacted Natural Ecosystems Drive Climate Warming
(2025) Mander, Ülo; Pärn, Jaan; Espenberg, Mikk; Peñuelas, Josep
Current greenhouse gas budgets do not account for most indirect anthropogenic impacts. In this perspective, we call for attention to greenhouse gas fluxes from human-impacted natural ecosystems and their mitigation measures. The article highlights the increasing greenhouse gas (GHG) emissions from natural ecosystems, including CO2, CH4, and N2O. These emissions are becoming significant drivers of global warming, surpassing those from fossil fuel combustion. We introduce the concept of "anthro-natural emissions" on the example of peatlands, referring to emissions from natural ecosystems indirectly impacted by human activities. The concept helps bridge the gap between natural and anthropogenic impacts, providing a more comprehensive understanding of GHG emissions. Anthro-natural emissions are expected to rise as climate warming progresses, contributing to the overall GHG balance. Peatlands, which store approximately 30% of the world's soil carbon, are under increasing pressure from climate warming and human activities. The article emphasizes the importance of addressing both natural and human-impacted ecosystems to mitigate climate change effectively. Increasingly frequent droughts are identified as a major threat to global terrestrial ecosystems, particularly wetlands. The drying of wetlands challenges their capacity to act as carbon sinks and alters their roles in climate regulation. The insights provided are essential for developing effective adaptation strategies relying on soil carbon sequestration as a long-term solution against climate warming. According to our study, the proportion of natural, anthro-natural, and directly disturbed peatlands is approximately 40-20-40, and the ratio is increasing towards anthro-natural peatlands. We highlight a change of paradigm for assessing the importance of different GHG sources. Further, it highlights the need for conservation and restoration of peatlands and renaturalization of forest ecosystems.
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Human-Impacted Natural Ecosystems Drive Climate Warming
(2025) Mander, Ülo; Pärn, Jaan; Espenberg, Mikk; Peñuelas, Josep
Current greenhouse gas budgets do not account for most indirect anthropogenic impacts. In this perspective, we call for attention to greenhouse gas fluxes from human-impacted natural ecosystems and their mitigation measures. The article highlights the increasing greenhouse gas (GHG) emissions from natural ecosystems, including CO2, CH4, and N2O. These emissions are becoming significant drivers of global warming, surpassing those from fossil fuel combustion. We introduce the concept of “anthro-natural emissions” on the example of peatlands, referring to emissions from natural ecosystems indirectly impacted by human activities. The concept helps bridge the gap between natural and anthropogenic impacts, providing a more comprehensive understanding of GHG emissions. Anthro-natural emissions are expected to rise as climate warming progresses, contributing to the overall GHG balance. Peatlands, which store approximately 30% of the world's soil carbon, are under increasing pressure from climate warming and human activities. The article emphasizes the importance of addressing both natural and human-impacted ecosystems to mitigate climate change effectively. Increasingly frequent droughts are identified as a major threat to global terrestrial ecosystems, particularly wetlands. The drying of wetlands challenges their capacity to act as carbon sinks and alters their roles in climate regulation. The insights provided are essential for developing effective adaptation strategies relying on soil carbon sequestration as a long-term solution against climate warming. According to our study, the proportion of natural, anthro-natural, and directly disturbed peatlands is approximately 40–20–40, and the ratio is increasing towards anthro-natural peatlands. We highlight a change of paradigm for assessing the importance of different GHG sources. Further, it highlights the need for conservation and restoration of peatlands and renaturalization of forest ecosystems.
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Impact of management on peatland microbiome and greenhouse gas emissions
(2017-10-10) Espenberg, Mikk; Truu, Marika, juhendaja; Truu, Jaak, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Turbaalad leiavad rakendust põllumajanduses, metsanduses, energiatootmises, reoveekäitluses ja ka teistes valdkondades. Kui võtta arvesse üha suurenevat inimmõjutuste ja kliimamuutuste survet neile aladele, siis on turbaalade süsiniku- ja lämmastikuringe väga olulised nii keskkondlikust, ökoloogilisest kui ka majanduslikust vaatevinklist. Käesoleva doktoritöö eesmärk oli uurida erinevate majandusmeetmete mõju turbaalade mikrobioomile ja kasvuhoonegaaside emissioonile. Põhjapoolkera parasvöötme turbaalade kuivendamisel väheneb CH4 emissioon, kuid selle mõju on CH4 emissioonile väiksem rabades võrreldes madalsoodega. Kuivendamine avaldab suurt mõju ka troopilise turbaala gaasiemissioonidele ja selle mikroobikooslusele. Kuigi CH4 ja potentsiaalse N2 emissioonid kahanesid troopilise turbaala kuivendamisel, siis N2O voog atmosfääri suurenes. Troopilise turbaala kuivendamine muutis lisaks bakterite ja arhede arvukusele ning liigilisele koosseisule oluliselt ka erinevaid lämmastikuringe protsesse läbiviivate mikroorganismide arvukusi. Kuivendamise tulemusena vähenes denitrifikatsiooni ja N2 fikseerimise potentsiaal troopilise turbaala pinnases. Põhjapoolkera parasvöötme häiritud turbaalade taassoostamine suurendab CH4 emissiooni. Mahajäetud turbakaevandusalade taimestamine päiderooga bioenergia tootmise eesmärgil vähendas CH4 emissiooni, kuigi metanogeenide arvukus turba erinevates kihtides jäi ligikaudu samale tasemele või siis isegi suurenes katseperioodi jooksul. Lisaks sellele on turbaalasid sooderikastes piirkondades võimalik kasutada reovee puhastamiseks, et kaitsta veekogude ökosüsteeme reoainete eest. Turbaalapuhastites on oluline roll ka taimedel, mis võivad olla läbi erinevate mehhanismide efektiivseteks reoainete eemaldajateks veest.
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Importance of N2O in greenhouse gas budgets of tropical peatlands
(Frontiers in Environmental Science, 2025) Pärn, Jaan; Espenberg, Mikk; Soosaar, Kaido; Kasak, Kuno; Thayamkottu, Sandeep; Schindler, Thomas; Ranniku, Reti; Sohar, Kristina; Mander, Ülo; Melling, Lulie; Malaverri, Lizardo Fachín
Tropical peatland ecosystems significantly influence Earth’s climate through their greenhouse gas exchange. Permanently wet peatlands take up carbon dioxide in plants and accumulate organic carbon in soil but release methane. Man-made drainage of peat releases carbon dioxide and nitrous oxide. Exchange of the greenhouse gases in relationship with tropical conditions are poorly understood. This is a global-scale field study of fluxes of three greenhouse gases – carbon dioxide, methane and nitrous oxide – and their environmental drivers across the full moisture range of tropical peatlands. We show that net emission of carbon dioxide dominates greenhouse gas budgets in drained tropical peatlands while nitrous oxide emission is the second most important contributor. Tropical peat swamp forests in their natural wet states are large greenhouse gas sinks and should be a global conservation and restoration priority.
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Importance of N2O in greenhouse gas budgets of tropical peatlands
(2025) Pärn, Jaan; Espenberg, Mikk; Soosaar, Kaido; Kasak, Kuno; Thayamkottu, Sandeep; Schindler, Thomas; Ranniku, Reti; Sohar, Kristina; Malaverri, Lizardo Fachín; Melling, Lulie; Mander, Ülo
Tropical peatland ecosystems significantly influence Earth’s climate through their greenhouse gas exchange. Permanently wet peatlands take up carbon dioxide in plants and accumulate organic carbon in soil but release methane. Man-made drainage of peat releases carbon dioxide and nitrous oxide. Exchange of the greenhouse gases in relationship with tropical conditions are poorly understood. This is a global-scale field study of fluxes of three greenhouse gases – carbon dioxide, methane and nitrous oxide – and their environmental drivers across the full moisture range of tropical peatlands. We show that net emission of carbon dioxide dominates greenhouse gas budgets in drained tropical peatlands while nitrous oxide emission is the second most important contributor. Tropical peat swamp forests in their natural wet states are large greenhouse gas sinks and should be a global conservation and restoration priority.
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Interactions of fertilisation and crop productivity in soil nitrogen cycle microbiome and gas emissions
(2025) Kuusemets, Laura; Mander, Ülo; Escuer-Gatius, Jordi; Astover, Alar; Kauer, Karin; Soosaar, Kaido; Espenberg, Mikk
Fertilised soils are a significant source of nitrous oxide (N2O), a highly active greenhouse gas and a stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N2O emissions into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N2O and N2 emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N2O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with an increased mineral N fertilisation rate. Crop type also has a significant impact on soil N2O emissions. Higher N2O emissions were attained with the application of manure in comparison to mineral fertilisation. Manure amendment also increased the number of N cycle genes that are significant in the variations of N2O. The study indicates that N2O emissions were mainly related to nitrification in the soil. Quantification of nitrogen cycle functional genes also showed the potential role of denitrification, comammox (complete ammonia oxidation) and dissimilatory nitrate reduction to ammonium (DNRA) processes as a source of N2O. Our study did not find soil moisture to be significantly linked to N2O emissions. The results of the study provide evidence that, for wheat, a fertilisation rate of 80 kg N ha−1 is closest to the optimal rate for balancing biomass yield and N2O emissions and achieving a high NUE. Sorghum showed good potential for cultivation in temperate climates, as it showed a similar biomass yield compared to the other crop types and fertilisation rates but maintained low N2O emissions and N losses in a mineral N fertilisation rate of 80 kg N ha−1.
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Interactions of fertilisation and crop productivity in soil nitrogen cycle microbiome and gas emissions
(2025) Kuusemets, Laura; Mander, Ülo; Escuer-Gatius, Jordi; Astover, Alar; Kauer, Karin; Soosaar, Kaido; Espenberg, Mikk
Fertilised soils are a significant source of nitrous oxide (N2O), a highly active greenhouse gas and a stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N2O emissions into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N2O and N2 emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N2O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with an increased mineral N fertilisation rate. Crop type also has a significant impact on soil N2O emissions. Higher N2O emissions were attained with the application of manure in comparison to mineral fertilisation. Manure amendment also increased the number of N cycle genes that are significant in the variations of N2O. The study indicates that N2O emissions were mainly related to nitrification in the soil. Quantification of nitrogen cycle functional genes also showed the potential role of denitrification, comammox (complete ammonia oxidation) and dissimilatory nitrate reduction to ammonium (DNRA) processes as a source of N2O. Our study did not find soil moisture to be significantly linked to N2O emissions. The results of the study provide evidence that, for wheat, a fertilisation rate of 80 kg N ha−1 is closest to the optimal rate for balancing biomass yield and N2O emissions and achieving a high NUE. Sorghum showed good potential for cultivation in temperate climates, as it showed a similar biomass yield compared to the other crop types and fertilisation rates but maintained low N2O emissions and N losses in a mineral N fertilisation rate of 80 kg N ha−1.
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Lämmastikreostuse eemaldamise geneetiline potentsiaal vabaveelistes tehismärgalades
(Tartu Ülikool, 2022) Kuusk, Kadri; Espenberg, Mikk; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Põllumajanduses on viimastel aastakümnetel kasutatud üha rohkem lämmastikväetisi, et hoogustada toiduainete tootmist kasvavale maailma elanikkonnale. Reaktiivse lämmastiku kasutamise märkimisväärne suurenemine on põhjustanud tugevat lämmastikureostust ning hakanud mõjutama inimeste ja ökosüsteemide heaolu. Tehismärgalade kasutamine lämmastikreostuse eemaldamiseks on kuluefektiivne viis, kuidas eemaldada üleliigsest väetiste kasutamisest tingitud hajusreostust ning leevendada keskkonnaprobleeme. Käesolevas töös uuriti lämmastikreostuse eemaldamise geneetilist potentsiaali kolme vabaveelise märgala vahel (EST, FRA ja USA). Tulemustest selgus, et denitrifikatsioonil on geneetiliselt suurem potentsiaal toimuda Vända (EST) ja Ohio (USA) tehismärgalas ning Rampilloni (FRA) tehismärgalas on suurem potentsiaal nitrifikatsioonil. Lisaks on Vända märgalal geenikoopiate põhjal suurem potentsiaal edukamaks ANAMMOX-i, COMAMMOX-i ja DNRA protsessi toimimiseks ning N2 fikseerimiseks võrreldes Rampilloni märgalaga.
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Lühiajalise üleujutuse mõju mulla mikrobioloogilisele lämmastikuringele kaldaäärses lepikus
(Tartu Ülikool, 2021) Reiss, Kristel; Espenberg, Mikk; Mander, Ülo; Tartu Ülikool. Geograafia osakond; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
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Meltwater of freeze-thaw cycles drives N2O-governing microbial communities in a drained peatland forest soil
(2025) Kazmi, Fahad Ali; Espenberg, Mikk; Pärn, Jaan; Masta, Mohit; Ranniku, Reti; Mander, Ülo; Thayamkottu, Sandeep
Soil freeze-thaw cycles affect N2O fluxes in high- and mid-latitude regions, but understanding microbial processes behind N2O will help clarify the long-term impact of freeze-thaw on climate change. The aim of this study was to investigate the impacts of freeze-thaw cycles on microbial abundances and N2O emissions in a hemi-boreal drained peatland forest. The soil freeze-thaw experiment involved artificial heating to thaw the topsoil after freezing. Results showed that thawing of the 5 cm topsoil increased soil water content (SWC) and N2O emissions. Microbial analysis demonstrated that the abundance of soil prokaryotes increased with thawing. N2O emissions were negatively correlated with NH4+-N while ammonia-oxidizing archaea and bacteria, including complete ammonia oxidizers, increased their abundance. This indicates a potential nitrification pathway. The abundance of nitrite reductase genes (nirK and nirS) showed a positive correlation with N2O fluxes, while nosZ genes did not increase. The results provide an insight into the impact of soil freeze-thaw cycles on N2O fluxes and the underlying microbial processes. The dynamics of SWC during the thawing period were the most direct driver of the increase in N2O emissions. Incomplete denitrification was the dominant process for the N2O emissions during the thaw. More than 80% of produced N2O was denitrified to inert N2, as shown by high potential N2 emissions. The frequency of freeze-thaw events is expected to increase due to climate change; therefore, determining the underlying microbial processes of the N2O emissions under freeze-thaw is of great importance in predicting possible impacts of climate change in forests.
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N transformations in nitrate-rich groundwaters: combined isotope and microbial approach
(2025) Deb, Sushmita; Espenberg, Mikk; Well, Reinhard; Bucha, Michał; Jakubiak, Marta; Mander, Ülo; Jędrysek, Mariusz-Orion; Lewicka-Szczebak, Dominika
This study explores nitrogen transformations in groundwater from an agricultural area utilizing organic fertilizer (wastewater from yeast production) by integrating isotope analysis, microbial gene abundance, and the isotope FRactionation And Mixing Evaluation (FRAME) model to trace and quantify nitrogen cycling pathways. Groundwater samples with elevated nitrate concentrations were subjected to controlled laboratory incubations with application of a novel low-level 15N tracing strategy to investigate microbial processes. Isotope analyses of nitrate, nitrite, and nitrous oxide (N2O), coupled with microbial gene quantification via quantitative polymerase chain reaction (qPCR), revealed a shift from archaeal-driven nitrification to bacterial denitrification in post-incubation suboxic conditions, stimulated by glucose addition. FRAME modelling further identified bacterial denitrification as the dominant pathway of N2O production, which was supported by increased nosZI, nirK, and nirS gene abundance and observed isotope effects. Simultaneously with the intensive nitrate reduction, it was observed that the majority of nitrite is likely produced through nitrification processes linked to dissolved organic nitrogen (DON) oxidation. Nitrate reduction had a minor contribution to the total nitrite pool. The results demonstrate the efficacy of integrating multi-compound isotope studies and microbial analyses to unravel nitrogen cycling mechanisms. This approach provides a robust framework for addressing nitrogen pollution in groundwater systems and improving water quality management strategies.
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N transformations in nitrate-rich groundwaters: combined isotope and microbial approach
(2025) Deb, Sushmita; Espenberg, Mikk; Well, Reinhard; Bucha, Michał; Jakubiak, Marta; Mander, Ülo; Jędrysek, Mariusz-Orion; Lewicka-Szczebak, Dominika
This study explores nitrogen transformations in groundwater from an agricultural area utilizing organic fertilizer (wastewater from yeast production) by integrating isotope analysis, microbial gene abundance, and the isotope FRactionation And Mixing Evaluation (FRAME) model to trace and quantify nitrogen cycling pathways. Groundwater samples with elevated nitrate concentrations were subjected to controlled laboratory incubations with application of a novel low-level 15N tracing strategy to investigate microbial processes. Isotope analyses of nitrate, nitrite, and nitrous oxide (N2O), coupled with microbial gene quantification via quantitative polymerase chain reaction (qPCR), revealed a shift from archaeal-driven nitrification to bacterial denitrification in post-incubation suboxic conditions, stimulated by glucose addition. FRAME modelling further identified bacterial denitrification as the dominant pathway of N2O production, which was supported by increased nosZI, nirK, and nirS gene abundance and observed isotope effects. Simultaneously with the intensive nitrate reduction, it was observed that the majority of nitrite is likely produced through nitrification processes linked to dissolved organic nitrogen (DON) oxidation. Nitrate reduction had a minor contribution to the total nitrite pool. The results demonstrate the efficacy of integrating multi-compound isotope studies and microbial analyses to unravel nitrogen cycling mechanisms. This approach provides a robust framework for addressing nitrogen pollution in groundwater systems and improving water quality management strategies.