Sirvi Autor "Kuusemets, Laura" järgi

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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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8. klassi õpilaste arvamused abakuse kasutamisest matemaatikatundides
(Tartu Ülikool, 2018) Kuusemets, Laura; Pihlap, Sirje, juhendaja; Tartu Ülikool. Sotsiaalteaduste valdkond; Tartu Ülikool. Haridusteaduste instituut
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Abakuse õppematerjalide loomine ja tunni läbiviimist toetavad materjalid õpetajatele ning õpilaste ja õpetajate tagasiside loodud õppematerjalidele
(Tartu Ülikool, 2020) Kuusemets, Laura; Pihlap, Sirje, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond; Tartu Ülikool. Matemaatika ja statistika instituut
Abakus ehk arvelaud on traditsiooniline arvutamise vahend, mille järjepideva harjutamise tulemusena on võimalik arendada peastarvutamise oskust, samuti arendab see ajufunktsioone, näiteks töömälu, tähelepanu ning püsivus. Aasias on abakus koolides laialt levinud, Eestis aga puuduvad kaasaegsed õppematerjalid. Käesoleva töö eesmärgiks oli luua kaasaegsed eestikeelsed Jaapani abakuse õppematerjalid ning selgitada välja ekspertide ehk õpetajate ning õpilaste hinnangud loodud õppematerjalidele. Õppematerjalide täiendamise eesmärgiga koguti õpetajatelt ning õpilastelt ettepanekuid materjalide arendamiseks. Tegevusuuringu raames valmis õppematerjalide veebileht abakusope.weebly.com. Loodud õppematerjale hindas viis õpetajat ning õpilast, kelle hinnangud olid positiivsed. Õppematerjalide arendamiseks tehtud ettepanekud olid seotud tehnilise teostusega (nt heli kvaliteedi parandamine) ning õppematerjali sisuga (nt näidete ning illustratsioonide lisamine). Ettepanekutele toetudes on käesolevas magistritöös toodud välja edasised tegevussuunad koostatud materjali arendamiseks ning rakendamiseks.
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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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Nitrifikatsiooni ja denitrifikatsiooni protsesside määramine reaalaja PCR-i ja isotoopanalüüsi meetoditega kuivendatud ja üleujutatud kõdusoometsades
(Tartu Ülikool, 2021) Kuusemets, Laura; Espenberg, Mikk, juhendaja; Mander, Ülo, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Dilämmastikoksiid ehk naerugaas (N2O) on ohtlik kasvuhoonegaas, mille kõige olulisemad voogude allikad mullast on nitrifikatsiooni ja denitrifikatsiooni protsess. Käesoleva bakalaureusetöö eesmärk oli uurida kõdusoometsades kuivenduse ja üleujutuse mõju erinevatele lämmastikuringe protsessidele ja N2O emissioonile kasutades molekulaarseid ja isotoopanalüüsi meetodeid. Käesolevas töös läbiviidud kuivendamise ja üleujutamise eksperiment toimus jänesekapsa-kõdusoo kasvukohatüüpi kõdusoometsas Eestis. Reaal-aja polümeraasi ahelreaktsiooni (qPCR) kasutati mullaproovidest bakterite ja arhede 16S rRNA, nitrifikatsiooni (bakterite ja arhede amoA) ja denitrifikatsiooni (nirK, nirS, nosZ I ja nosZII) geenikoopiate arvukuse määramiseks. Lisaks mõõdeti mulla ja gaasi isotoopset koosseisu ning N2O emissiooni. Töö tulemused näitasid, et erinev hüdroloogiline režiim mõjutab nitrifikatsiooni ja denitrifikatsiooni protsesse. Kuivendatud aladel määrab N2O vooge nitrifikatsiooni protsess ja üleujutatud aladel denitrifikatsiooni protsess. Suurimad N2O emissioonide kontsentratsioonid tulenesid kuivendatud aladelt nitrifitseerijate denitrifikatsioonil ammoniaaki oksüdeerivate bakterite vahendusel.