Sirvi Autor "Thayamkottu, Sandeep" järgi

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Dual controls of vapour pressure deficit and soil moisture on photosynthesis in a restored temperate bog
(Science of The Total Environment, 2025) Thayamkottu, Sandeep; Masta, Mohit; Skeeter, June; Pärn, Jaan; Knox, Sara H.; Smallman, T. Luke; Mander, Ülo
Despite only covering ~3 % of the land mass, peatlands store more carbon (C) per unit area than any other ecosystem. This is due to the discrepancy between C fixed by the plants (Gross primary productivity (GPP)) and decomposition. However, this C is vulnerable to frequent, severe droughts and changes in the peatland microclimate. Plants play a vital role in ecosystem C dynamics under drought by mediating water loss to the atmosphere (surface water vapour conductance) and GPP by the presence/absence of stomatal regulation. This is dependent on soil moisture, air temperature, and vapour pressure deficit (VPD). Although there is ample evidence of the role of VPD on stomatal regulation and GPP, the impact of soil moisture is still debated. We addressed this knowledge gap by investigating the role of bulk surface conductance of water vapour in shifts between climatic (Air temperature (Tair), incoming shortwave radiation (SWR) and VPD) and water limitation of GPP in a peat bog in Canada. A causal analysis process was used to investigate how environmental factors influenced GPP. The results suggested that stomatal regulation in response to increased VPD caused the reduction in GPP in 2016 (~2.5 gC m−2 day−1 as opposed to ~3 gC m−2 day−1 in 2018). In contrast, GPP was limited again in 2019 due to the dry surface. This was driven by the relaxed stomatal regulation adopted by the ecosystem following the initial drought to maximise C assimilation. We found the threshold at which surface water decline limited GPP was at about −8 cm water table depth (82.5 % soil moisture). The causal inference corroborated our findings. The temporal variations of water and energy limitation seen in this study could increasingly restrict GPP due to the projected climate warming.
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Ecosystem scale modelling of carbon and nitrogen cycles in peatlands
(Tartu Ülikooli Kirjastus, 2025-06-02) Thayamkottu, Sandeep; Pärn, Jaan, juhendaja; Mander, Ülo, juhendaja; Smallman, Thomas Luke, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Maakera kliima soojeneb ja äärmuslikud kliimasündmused sagenevad. Seda tingivad peamiselt maakasutuse ja maakatte muutused (LULCC) ning nendest tulenevad kasvuhoonegaaside (KHG) heitmed. Sood mängivad olulist rolli globaalses süsiniku ja kasvuhoonegaaside bilansis, salvestades süsinikku muldadesse (kus seda on rohkem kui maismaa taimestikus). Ökosüsteemi, piirkondliku ja globaalse süsiniku ja KHG-bilansside koostamisel on olulised mulla veebilanss, vee liikumine mulla-taime-atmosfääri süsteemis ja ilmategurid, mis mõjutavad taimede kasvu (fotosünteetiliselt aktiivne kiirgus, aururõhu defitsiit (VPD), õhutemperatuur ja sademed). Empiiriline teadmine sellest, kuidas mulla niiskuse muutused mõjutavad mulla kasvuhoonegaaside heitkoguseid, on vajalik, mõistmaks soo-ökosüsteemides toimuvaid protsesse. Käesolev doktoritöö täidab teadmiste lünki süsiniku ja N2O voogudest ning nende põhjustest ökosüsteemi tasandil. Uuring leidis, et kasvuperioodi kambrimeetodil mõõdetud KHG bilansis oli ülekaalus CO2 ja et KHG heitmed on kõrgeimad mõõdukal mullaniiskusel. Edasised uuringud CO2 voogude kohta subarktilises madalsoos ja niiske parasvöötme taastatud rabas käsitlesid CO2 väetamis-efekti ning VPD ja mulla niiskuse muutuste mõju taimekasvule. Tulemused näitavad ka fotosünteesi saaduste jagunemist erinevatesse ökosüsteemi osadesse. Mullaniiskus hakkas taimekasvu piirama, kui veetase langes alla teatud läve. See lävi on maapinnale palju lähemal kui varem arvati. See doktoritöö aitab parandada teadmisi hüdrokliima mõjust kasvuhoonegaasidele, eriti süsiniku voogudele.
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Greening of a boreal rich fen driven by CO2 fertilisation
(Agricultural and Forest Meteorology, 2024) Thayamkottu, Sandeep; Smallman, T. Luke; Pärn, Jaan; Mander, Ülo; Euskirchen, Eugénie S.; Kane, Evan S.
Boreal peatlands store vast amounts of soil organic carbon (C) owing to the imbalance between productivity and decay rates. In the recent decades, this carbon stock has been exposed to a warming climate. During the past decade alone, the Arctic has warmed by ∼ 0.75°C which is almost twice the rate of the global average. Although, a wide range of studies have assessed peatlands’ C cycling, our understanding of the factors governing source / sink dynamics of peatland C stock under a warming climate remains a critical uncertainty at site, regional, and global scales. Here our focus was on answering two key questions: (1) What drives the interannual variability of carbon dioxide (CO2) fluxes at the Bonanza Creek rich fen in Alaska, and (2) What are the internal carbon allocation patterns during the study years? We addressed these knowledge-gaps using an intermediate complexity terrestrial ecosystem model calibrated by a Bayesian model-data fusion framework at a weekly timestep with publicly available eddy covariance, satellite-based earth observation, and in-situ datasets for 2014 to 2020. We found that the greening trend (a relative increase of leaf area index ∼0.12 m2 m-2 by 2020) in the fen ecosystem is forced by a CO2 fertilisation effect which in combination resulted in increased gross primary production (GPP). Relative to 2014, GPP increased by ∼75 gC m-2 year-1 (by 2020; 95% confidence interval (CI): -41.35 gC m-2 year-1 to 213.55 gC m-2 year-1) while heterotrophic respiration stayed constant. Consistent with the observed greening, our analysis indicates that the ecosystem allocated more C to foliage (∼50%) over the structural (A carbon pool consisting of branches, stems and coarse roots; ∼30%) and fine root C pools (∼20%).
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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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Soil moisture and microbiome explain greenhouse gas exchange in global peatlands
(Scientific Reports, 2025) Pärn, Jaan; Thayamkottu, Sandeep; Öpik, Maarja; Bahram, Mohammad; Tedersoo, Leho; Espenberg, Mikk; Davison, John Alexander; Kasak, Kuno; Maddison, Martin; Niinemets, Ülo; Ostonen, Ivika; Soosaar, Kaido; Sohar, Kristina; Zobel, Martin; Mander, Ülo
Earth's climate is tightly connected to carbon and nitrogen exchange between the atmosphere and ecosystems. Wet peatland ecosystems take up carbon dioxide in plants and accumulate organic carbon in soil but release methane. Man-made drainage releases carbon dioxide and nitrous oxide from peat soils. Carbon and nitrous gas exchange and their relationships with environmental conditions are poorly understood. Here, we show that open peatlands in both their wet and dry extremes are greenhouse gas sinks while peat carbon/nitrogen ratios are high and prokaryotic (bacterial and archaeal) abundances are low. Conversely, peatlands with moderate soil moisture levels emit carbon dioxide and nitrous oxide, while prokaryotic abundances are high. The results challenge the current assumption of a uniform effect of drainage on greenhouse gas emissions and show that the peat microbiome of greenhouse-gas sources differs fundamentally from sinks.
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Soil moisture and temperature in wetland soils derived from remote sensing
(Tartu Ülikool, 2023) Lazovik, Hleb; Pärn, Jaan; Thayamkottu, Sandeep; Tartu Ülikool. Geograafia osakond; Tartu Ülikool. Loodus- ja täppisteaduste valdkond