Kasvuhoonegaaside CO2, CH4 ja N2O vood päiderooga rekultiveeritud ja turbasamblaga taastatud jääkturbasoodest

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Looduslikud sood on vaatamata nende küllaltki väikesele katvusele olulised süsiniku (C) sidujad. Soid on kasutatud väga mitmesugustel eesmärkidel, sealhulgas kütte- ja aiandusturba kaevandamiseks. Turbakaevandamise lõppedes jäävad soodest järele õhema või tüsedama jääkturbakihiga alad ehk jääkturbasood, mis on kuivendamise tulemusel kiirenenud turba lagunemise ja taimkatte ning seeläbi ka CO2 sidumise puudumise tõttu olulised kasvuhoonegaaside (KHGde) allikad. Seega on oluline jääkturbasood taastada viisil, mis nende KHGde emissiooni vähendaks. Erinevate korrastamisviiside aastaseid C ja KHGde bilansse kajastavaid uuringuid on seni aga kirjanduses jätkuvalt vähe. Käesoleva doktoritöö peamiseks eesmärgiks oli uurida päiderooga rekultiveerimise (väetatud ja väetamata uurimisalad) ja turbasamblaga taastamise (kõrge ja madala veetasemega uurimisalad) mõju jääkturbasoode KHGde (CO2, CH4 ja N2O) voogudele. Töö tulemused näitasid, et päiderooga taimestatud uurimisalade KHGde emissioonid olid mahajäetud turbatootmisalaga võrreldes madalamad. Lisaks oli näha, et väetamine vähendas päideroo kasvualade summaarset kasvuhooneefekti tekitavat mõju, kuna selle positiivne efekt biomassi produktsioonile ja seeläbi ka CO2 sidumise intensiivsusele ületas samaaegse N2O emissiooni suurenemise mitmekordselt. Aastased kogubilansid näitasid aga, et olenevalt sademete hulgast võivad päiderooga taimestatud turbatootmisalad olla kokkuvõttes nii C ja KHGde allikad kui ka sidujad ning seega on päiderooga taimestamise tulemuslikkus tugevalt mõjutatud klimaatilistest tingimustest. Veetaseme tõstmine ning turbasambla fragmentide külvamine vähendas KHGde emissiooni mahajäetud turbatootmisalaga võrreldes ligikaudu kaks korda. Selle peamiseks põhjuseks oli oluliselt kahanenud heterotroofne hingamine, mis näitab, et veetaseme tõstmine on väga efektiivne meetod kuivendatud soodes toimuva aeroobse turba lagunemise vähendamiseks. Aastased kogubilansid näitasid aga, et taimestikupoolne CO2 sidumine ei suutnud kolm aastat peale taastamist veel KHGde emissiooni tasakaalustada ning seetõttu olid alad jätkuvalt C ja KHGde allikad. Lisaks, veetaseme erinevuse mõju C ja KHGde bilansile oli taastatud alade omavahelisel võrdlemisel väike. Kokkuvõtvalt näitasid doktoritöö tulemused, et nii päiderooga rekultiveerimine kui ka turbasamblaga taastamine võivad olla efektiivsed meetodid jääkturbasoode kasvuhooneefekti tekitava mõju vähendamiseks.Natural peatlands are an important global carbon (C) sink. Within the past century, however, many peatlands have been drained and exploited for various purposes, including peat extraction for fuel and horticultural use. After cessation of peat extraction activities, vast areas of degraded peat soils remain acting as persistent net sources of C and greenhouse gases (GHGs) due to enhanced peat decomposition and absence of plant CO2 uptake. Thus, there is a need for after-use strategies that mitigate the GHG emission from these areas; currently, however, knowledge about the impact of different after-use options and associated management practices on annual C and GHG balances of abandoned peat extraction areas is limited. The goal of this dissertation was to investigate the impact of i) fertilized and nonfertilized reed canary grass (RCG; Phalaris arundinacea) cultivation and ii) peatland restoration with high and low water table levels (WTLs) on the GHG exchanges (incl. CO2, CH4 and N2O) in abandoned peat extraction areas. The results showed that RCG cultivation reduced the net GHG emissions compared to bare peat soil. Moreover, fertilization increased the climate benefit potential of RCG cultivation since the additional nitrogen supply resulted in enhanced biomass production and associated CO2 uptake which largely exceeded the concurrent increase in N2O emissions. However, the annual C and GHG sink-source strength of the RCG cultivations varied between a sink in a wet and a source in a dry year highlighting its sensitivity to climatic conditions. Restoration of the peat extraction area reduced the net GHG emissions by half relative to bare peat soil. This was mainly due to a large reduction in heterotrophic respiration which advocates raising the WTL as an effective method to reduce the aerobic peat decomposition. On an annual scale, however, both restored treatments acted as net C and GHG sources indicating that CO2 uptake by the re-established vegetation was not yet able to compensate for the GHG emissions. Furthermore, the effect of contrasting WTLs on the C and GHG balances of the restored treatments was limited. Overall, this dissertation concludes that both RCG cultivation as well as peatland restoration may serve as effective methods to mitigate the negative climate impact of abandoned peat extractions areas

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

The Kulbacksliden Research Infrastructure: a unique setting for northern peatland studies

Boreal peatlands represent a biogeochemically unique and diverse environment in high-latitude landscape. They represent a long-term globally significant sink for carbon dioxide and a source of methane, hence playing an important role in regulating the global climate. There is an increasing interest in deciphering peatland biogeochemical processes to improve our understanding of how anthropogenic and climate change effects regulate the peatland biogeochemistry and greenhouse gas balances. At present, most studies investigating land-atmosphere exchanges of peatland ecosystems are commonly based on single-tower setups, which require the assumption of homogeneous conditions during upscaling to the landscape. However, the spatial organization of peatland complexes might feature large heterogeneity due to its varying underlying topography and vegetation composition. Little is known about how well single site studies represent the spatial variations of biogeochemical processes across entire peatland complexes. The recently established Kulbacksliden Research Infrastructure (KRI) includes five peatland study sites located less than 3 km apart, thus providing a unique opportunity to explore the spatial variation in ecosystem-scale processes across a typical boreal peatland complex. All KRI sites are equipped with eddy covariance flux towers combined with installations for detailed monitoring of biotic and abiotic variables, as well as catchment-scale hydrology and hydrochemistry. Here, we review studies that were conducted in the Kulbacksliden area and provide a description of the site characteristics as well as the instrumentation available at the KRI. We highlight the value of long-term infrastructures with ecosystem-scale and replicated experimental sites to advance our understanding of peatland biogeochemistry, hydrology, ecology, and its feedbacks on the environment and climate system

Refining the role of phenology in regulating gross ecosystem productivity across European peatlands

Abstract The role of plant phenology as regulator for gross ecosystem productivity (GEP) in peatlands is empirically not well constrained. This is because proxies to track vegetation development with daily coverage at the ecosystem scale have only recently become available and the lack of such data has hampered the disentangling of biotic and abiotic effects. This study aimed at unraveling the mechanisms that regulate the seasonal variation in GEP across a network of eight European peatlands. Therefore, we described phenology with canopy greenness derived from digital repeat photography and disentangled the effects of radiation, temperature and phenology on GEP with commonality analysis and structural equation modeling. The resulting relational network could not only delineate direct effects but also accounted for possible effect combinations such as interdependencies (mediation) and interactions (moderation). We found that peatland GEP was controlled by the same mechanisms across all sites: phenology constituted a key predictor for the seasonal variation in GEP and further acted as distinct mediator for temperature and radiation effects on GEP. In particular, the effect of air temperature on GEP was fully mediated through phenology, implying that direct temperature effects representing the thermoregulation of photosynthesis were negligible. The tight coupling between temperature, phenology and GEP applied especially to high latitude and high altitude peatlands and during phenological transition phases. Our study highlights the importance of phenological effects when evaluating the future response of peatland GEP to climate change. Climate change will affect peatland GEP especially through changing temperature patterns during plant-phenologically sensitive phases in high latitude and high altitude regions.Peer reviewe

Statistical upscaling of ecosystem CO2 fluxes across the terrestrial tundra and boreal domain: Regional patterns and uncertainties

The regional variability in tundra and boreal carbon dioxide (CO2) fluxes can be high, complicating efforts to quantify sink-source patterns across the entire region. Statistical models are increasingly used to predict (i.e., upscale) CO2 fluxes across large spatial domains, but the reliability of different modeling techniques, each with different specifications and assumptions, has not been assessed in detail. Here, we compile eddy covariance and chamber measurements of annual and growing season CO2 fluxes of gross primary productivity (GPP), ecosystem respiration (ER), and net ecosystem exchange (NEE) during 1990-2015 from 148 terrestrial high-latitude (i.e., tundra and boreal) sites to analyze the spatial patterns and drivers of CO2 fluxes and test the accuracy and uncertainty of different statistical models. CO2 fluxes were upscaled at relatively high spatial resolution (1 km(2)) across the high-latitude region using five commonly used statistical models and their ensemble, that is, the median of all five models, using climatic, vegetation, and soil predictors. We found the performance of machine learning and ensemble predictions to outperform traditional regression methods. We also found the predictive performance of NEE-focused models to be low, relative to models predicting GPP and ER. Our data compilation and ensemble predictions showed that CO2 sink strength was larger in the boreal biome (observed and predicted average annual NEE -46 and -29 g C m(-2) yr(-1), respectively) compared to tundra (average annual NEE +10 and -2 g C m(-2) yr(-1)). This pattern was associated with large spatial variability, reflecting local heterogeneity in soil organic carbon stocks, climate, and vegetation productivity. The terrestrial ecosystem CO2 budget, estimated using the annual NEE ensemble prediction, suggests the high-latitude region was on average an annual CO2 sink during 1990-2015, although uncertainty remains high

The ABCflux database : Arctic-boreal CO2 flux observations and ancillary information aggregated to monthly time steps across terrestrial ecosystems

Past efforts to synthesize and quantify the magnitude and change in carbon dioxide (CO2) fluxes in terrestrial ecosystems across the rapidly warming Arctic-boreal zone (ABZ) have provided valuable information but were limited in their geographical and temporal coverage. Furthermore, these efforts have been based on data aggregated over varying time periods, often with only minimal site ancillary data, thus limiting their potential to be used in large-scale carbon budget assessments. To bridge these gaps, we developed a standardized monthly database of Arctic-boreal CO2 fluxes (ABCflux) that aggregates in situ measurements of terrestrial net ecosystem CO2 exchange and its derived partitioned component fluxes: gross primary productivity and ecosystem respiration. The data span from 1989 to 2020 with over 70 supporting variables that describe key site conditions (e.g., vegetation and disturbance type), micrometeorological and environmental measurements (e.g., air and soil temperatures), and flux measurement techniques. Here, we describe these variables, the spatial and temporal distribution of observations, the main strengths and limitations of the database, and the potential research opportunities it enables. In total, ABCflux includes 244 sites and 6309 monthly observations; 136 sites and 2217 monthly observations represent tundra, and 108 sites and 4092 observations represent the boreal biome. The database includes fluxes estimated with chamber (19 % of the monthly observations), snow diffusion (3 %) and eddy covariance (78 %) techniques. The largest number of observations were collected during the climatological summer (June-August; 32 %), and fewer observations were available for autumn (September-October; 25 %), winter (December-February; 18 %), and spring (March-May; 25 %). ABCflux can be used in a wide array of empirical, remote sensing and modeling studies to improve understanding of the regional and temporal variability in CO2 fluxes and to better estimate the terrestrial ABZ CO2 budget. ABCflux is openly and freely available online (Virkkala et al., 2021b, https://doi.org/10.3334/ORNLDAAC/1934).Peer reviewe

COSORE: A community database for continuous soil respiration and other soil‐atmosphere greenhouse gas flux data

Globally, soils store two to three times as much carbon as currently resides in the atmosphere, and it is critical to understand how soil greenhouse gas (GHG) emissions and uptake will respond to ongoing climate change. In particular, the soil‐to‐atmosphere CO2 flux, commonly though imprecisely termed soil respiration (RS), is one of the largest carbon fluxes in the Earth system. An increasing number of high‐frequency RS measurements (typically, from an automated system with hourly sampling) have been made over the last two decades; an increasing number of methane measurements are being made with such systems as well. Such high frequency data are an invaluable resource for understanding GHG fluxes, but lack a central database or repository. Here we describe the lightweight, open‐source COSORE (COntinuous SOil REspiration) database and software, that focuses on automated, continuous and long‐term GHG flux datasets, and is intended to serve as a community resource for earth sciences, climate change syntheses and model evaluation. Contributed datasets are mapped to a single, consistent standard, with metadata on contributors, geographic location, measurement conditions and ancillary data. The design emphasizes the importance of reproducibility, scientific transparency and open access to data. While being oriented towards continuously measured RS, the database design accommodates other soil‐atmosphere measurements (e.g. ecosystem respiration, chamber‐measured net ecosystem exchange, methane fluxes) as well as experimental treatments (heterotrophic only, etc.). We give brief examples of the types of analyses possible using this new community resource and describe its accompanying R software package