Mulla orgaanilist süsinikuvaru mõjutavate süsinikuvoogude varieeruvus ja lagunemise dünaamika hemiboreaalsetes okasmetsades

Väitekirja elektrooniline versioon ei sisalda publikatsiooneMaailma muldades on salvestunud rohkem süsinikku kui atmosfääris ja taimedes kokku, kusjuures metsamullad on ühed suurimad orgaanilise süsiniku reservuaaridest. Seega võivad juba väikesed muutused mullasüsinikuvoogudes oluliselt mõjutada nii regionaalset kui globaalset süsinikuringet ning seeläbi ka kliimat. Käesolevas doktoritöös hinnati Eesti hemiboreaalsete okasmetsade kõige dünaamilisemaid maapealseid ja maa-aluseid mulla süsinikuvoogusid: puude ning alustaimestiku maapealsete osade ning peenjuurte (läbimõõt <2mm) produktsiooni, mullahingamist, hariliku kuuse ning hariliku männi okaste ja peenjuurte ning standardmaterjalide (α-tselluloos, roheline ja rooibos tee) lagunemist ning okka- ja peenjuurte varisest makrotoitainete (lämmastik, fosfor, kaalium) vabanemist kolmeaastase lagunemise käigus. Globaalsel tasandil hinnati tee kui standardmaterjali lagunemist mõjutavaid keskkonnategureid. Samuti analüüsiti Yasso07 mullamudeli simulatsioonitulemuse usaldusväärsust ja vastavust rahvusvaheliste süsinikuraporteerimise tingimustele. Töös leiti, et puude peenjuurte produktsioon ja käive on ühed olulisemad tegurid, mis määravad mulla süsinikuvaru suuruse. Lagunemise dünaamikat mõjutas kõige enam substraadi tüüp ning mulla makrotoitainete sisaldus, kusjuures temperatuuri ning sademete mõju avaldus ainult ebasoodsates (näiteks väga kuivades) tingimustes. Töö käigus mõõdetud ja modelleeritud mulla süsinikuvoogude ja varude hinnangud on oluline sisend Eesti kasvuhoonegaaside inventuuraruande metsandussektori andmete täpsustamisel, toetades seeläbi teaduspõhist kliimapoliitika arengut.Globally, soils store more carbon (C) than combined in the atmosphere and terrestrial biomass, while forest soils contain one of the world’s largest organic carbon stocks. Hence, minor changes in the balance between the forest soil organic carbon (SOC) stocks and associated C fluxes could have a significant effect on the C cycle at regional as well as global level, thereby affecting the climate. The overall aim of this thesis was to estimate the variability of annual soil C fluxes and the dynamics of the associated processes, such as above- and belowground (fine root, <2mm) litter production of trees and understory; soil respiration; decomposition of site-specific Norway spruce and Scots pine fine roots, needle litter and standardised materials (α-cellulose, green and rooibos tea), the release of macronutrients (nitrogen, phosphorus, potassium) from fine root and needle litter in hemiboreal coniferous forests in Estonia over the course of three years; and the factors controlling decomposition of standardised substrates from local to global scale. In addition, the applicability of the Yasso07 soil model in carbon balance accounting was evaluated. One of key findings was that fine root production and turnover could be one of the most important factors that determine the size and the C dynamics of forest SOC pool. Litter decomposition was mainly controlled by the substrate type and soil macronutrients, while the effect of temperature and precipitation was only important under less favourable (e.g xeric) climatic conditions. The estimates of the measured and modelled soil C stocks and fluxes presented in this thesis would considerably improve the accuracy of the forestry sector data in the Estonian greenhouse gas inventory, and hence support implementation of science-based climate change policyhttps://www.ester.ee/record=b524383

Territorial and Consumption-Based Greenhouse Gas Emissions Assessments: Implications for Spatial Planning Policies

The quantification of greenhouse gas (GHG) emissions is increasingly important in spatial planning for regions, cities, and areas. The combination of territorial and consumption-based accounting (CBA) approaches can currently be considered best practice for calculating GHG emissions at sub-national levels, in terms of informing local decision-making about the different climate impacts of spatial planning policies, both within the boundaries of a given region and for the inhabitants of that region. This study introduces four European case studies that were conducted using the two quantification approaches to assess the climate impacts of locally relevant planning policies. The case studies represent different scales of spatial planning, different European planning systems, and different situations in terms of data availability. Territorial results are not suitable for inter-regional comparison, but rather for internal monitoring, while CBA allows for comparison and provides a comprehensive picture of the global carbon footprint of residents, however, with indications that are more difficult to link to spatial planning decisions. Assessing impacts, and in particular interpreting results, requires both methodological understanding and knowledge of the local context. The results of the case studies show that setting climate targets and monitoring the success of climate action through a single net emissions figure can give false indications. The study shows that the two approaches to quantifying GHG emissions provide complementary perspectives on GHG emissions at the sub-national level and thus provide a more thorough understanding of the GHG emission patterns associated with spatial planning policies. The identification of the regional differences in GHG emission sources and mitigation potentials are the main functions of sub-national GHG inventories and the impact assessment for spatial planning. Harmonization of the data collection for sub-national GHG inventories and the transparency of underlying assumptions would greatly support the coherence of climate action and the implications to spatial planning

Models for reporting forest litter and soil C pools in national greenhouse gas inventories: methodological considerations and requirements

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Effects of climate and atmospheric nitrogen deposition on early to mid-term stage litter decomposition across biomes

International audienceLitter decomposition is a key process for carbon and nutrient cycling in terrestrial ecosystems and is mainly controlled by environmental conditions, substrate quantity and quality as well as microbial community abundance and composition. In particular, the effects of climate and atmospheric nitrogen (N) deposition on litter decomposition and its temporal dynamics are of significant importance, since their effects might change over the course of the decomposition process. Within the TeaComposition initiative, we incubated Green and Rooibos teas at 524 sites across nine biomes. We assessed how macroclimate and atmospheric inorganic N deposition under current and predicted scenarios (RCP 2.6, RCP 8.5) might affect litter mass loss measured after 3 and 12 months. Our study shows that the early to mid-term mass loss at the global scale was affected predominantly by litter quality (explaining 73% and 62% of the total variance after 3 and 12 months, respectively) followed by climate and N deposition. The effects of climate were not litter-specific and became increasingly significant as decomposition progressed, with MAP explaining 2% and MAT 4% of the variation after 12 months of incubation. The effect of N deposition was litter-specific, and significant only for 12-month decomposition of Rooibos tea at the global scale. However, in the temperate biome where atmospheric N deposition rates are relatively high, the 12-month mass loss of Green and Rooibos teas decreased significantly with increasing N deposition, explaining 9.5% and 1.1% of the variance, respectively. The expected changes in macroclimate and N deposition at the global scale by the end of this century are estimated to increase the 12-month mass loss of easily decomposable litter by 1.1– 3.5% and of the more stable substrates by 3.8–10.6%, relative to current mass loss. In contrast, expected changes in atmospheric N deposition will decrease the mid-term mass loss of high-quality litter by 1.4–2.2% and that of low-quality litter by 0.9–1.5% in the temperate biome. Our results suggest that projected increases in N deposition may have the capacity to dampen the climate-driven increases in litter decomposition depending on the biome and decomposition stage of substrate

Early stage litter decomposition across biomes

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from −9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.This work was performed within the TeaComposition initiative, carried out by 190 institutions worldwide. We thank Gabrielle Drozdowski for her help with the packaging and shipping of tea, Zora Wessely and Johannes Spiegel for the creative implementation of the acknowledgement card, Josip Dusper for creative implementation of the graphical abstract, Christine Brendle for the GIS editing, and Marianne Debue for her help with the data cleaning. Further acknowledgements go to Adriana Principe, Melanie Köbel, Pedro Pinho, Thomas Parker, Steve Unger, Jon Gewirtzman and Margot McKleeven for the implementation of the study at their respective sites. We are very grateful to UNILEVER for sponsoring the Lipton tea bags and to the COST action ClimMani for scientific discussions, adoption and support to the idea of TeaComposition as a common metric. The initiative was supported by the following grants: ILTER Initiative Grant, ClimMani Short-Term Scientific Missions Grant (COST action ES1308; COST-STSM-ES1308-36004; COST-STM-ES1308-39006; ES1308-231015-068365), INTERACT (EU H2020 Grant No. 730938), and Austrian Environment Agency (UBA). Franz Zehetner acknowledges the support granted by the Prometeo Project of Ecuador's Secretariat of Higher Education, Science, Technology and Innovation (SENESCYT) as well as Charles Darwin Foundation for the Galapagos Islands (2190). Ana I. Sousa, Ana I. Lillebø and Marta Lopes thanks for the financial support to CESAM (UID/AMB/50017), to FCT/MEC through national funds (PIDDAC), and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. The research was also funded by the Portuguese Foundation for Science and Technology, FCT, through SFRH/BPD/107823/2015 (A.I. Sousa), co-funded by POPH/FSE. Thomas Mozdzer thanks US National Science Foundation NSF DEB-1557009. Helena C. Serrano thanks Fundação para a Ciência e Tecnologia (UID/BIA/00329/2013). Milan Barna acknowledges Scientific Grant Agency VEGA (2/0101/18). Anzar A Khuroo acknowledges financial support under HIMADRI project from SAC-ISRO, India

Early stage litter decomposition across biomes

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVINInternational audienceThrough litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging fro