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Browsing by Subject "C13 syrjäytyminen"

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  • Salko, Sini-Selina (2020)
    Soil respiration is a process in which soil organic carbon is released in the atmosphere as carbon dioxide. In boreal forests, soil carbon storage is particularly high relative to the carbon storage of aboveground biomass. Due to the large size of the forest areas of the biome, boreal forests’ soil organic carbon storage is globally is significant. The cool climate drives the formation of soil carbon storage in boreal regions. With climate change, the growing conditions can become drier and warmer than they have been in the past, which can accelerate the carbon release from soil to the atmosphere, thereby further warming the climate. Soil respiration is divided into two distinct processes: heterotrophic respiration where carbon dioxide is released from decomposi-tion of dead organic matter, and autotrophic cellular respiration of plant roots and root associated fungi. Increase in heterotrophic respiration in relation to litter formation rate implies a decrease in the carbon stock of the soil, whereas increase in autotrophic respiration implies an acceleration in the activity of the photosynthesizing biomass and, at the same time, an increase in the amount of carbon stored in the root system. The effect of drought on the activity of both components has been studied extensive-ly, and it appears that autotrophic terrestrial respiration responds to drought more slowly and less strongly in the boreal forest ecosystem. Atmospheric carbon dioxide contains two stable carbon isotopes, carbon-12 and carbon-13, of which C3 plants prefer lighter carbon-12 in photosynthesis. The relationship between these carbon isotopes is expressed with δ13C-value, and the discrimina-tion of carbon-13 in photosynthesis reflected in the cellular respiration of the autotrophic organisms. As a result, the δ13C-value of autotrophic respiration has been found to be lower than the δ13C value of heterotrophic respiration, as carbon-13 is discriminated less in the heterotrophic respiration. However, it has been found that during a drought period there is less discrimination of car-bon-13 in plants’ carbon assimilation, as the photosynthesizing plant may not be as selective for the carbon as when it is not exposed to drought. Thus, there is a difference in the δ13C-value of the soil respiration components, but it becomes smaller as the components experience drought. The purpose of this study was to determine whether the respiration rate of the components vary in different ways as they experi-ence drought by examining whether autotrophic respiration decreases more slowly than heterotrophic. In addition, it was sought to determine whether the components could be distinguished by their δ13C-value, so the study examined the development of the components’ δ13C-valu during drought. The measurements were done in two different experiment sites. The first one was an artificial drought experiment with pine saplings (Pinus sylvestris) in a greenhouse, where carbon dioxide flux and its δ13C-flux was measured from pine roots and their soil by incubation method. Second one was in a Pirkanmaa pine forest where carbon dioxide flux and its δ13C-flux were measured with incubation method and chamber measuring method. After the sampling, the development of the phenomenon was examined together with moisture- and temperature conditions at the time of the measure-ment. In this study, soil respiration’s autotrophic component changed more slowly in relation to drought than the heterotrophic compo-nent. In addition, in the pine forest, the δ13C-value of autotrophic respiration was below the heterotrophic δ13C-value, as the theory suggests. However, there was no clear development in relation to drought with the components’ δ13C-value. In the green-house experiment, no clearly distinguishable development was observed between the development of the components, and the δ13C-value of soil respiration was rather similar between the components. In both experiment sites, there appeared to be sources of error as environmental conditions improved unexpectedly in both the greenhouse and in the forest. Furthermore, it can be stated that the less destructive chamber measuring protocol seems to produce more reliable data.