| Popis: |
Boreal forests play an important role in the global carbon cycling, as their soils represent a substantial terrestrial sink for atmospheric CO2 globally. In this biome, fungi are pivotal components as drivers of decomposition and nutrient cycling. Rapid development of molecular techniques increases our knowledge of fungal species distribution in different environments. However, scaling from small-scale community composition to ecosystem level processes is challenging. High throughput sequencing, enzyme assays and stable isotope analyses were used to investigate how fungal diversity and community composition responded to ecosystem fertility and forest harvesting. Radiocarbon dating and a carbon sequestration model were combined to estimate long-term carbon dynamics in soil profiles. Using data collected within a large-scale national sampling program, drivers of organic matter accumulation across the entire latitudinal range of the Swedish boreal forest were explored. Multivariate statistics and structural equation modelling were used to yield correlative relationships between environmental parameters, fungal communities and soil carbon dynamics. The re-establishing ectomycorrhizal community during stand development after clear-cutting was dominated by Atheliaceae in younger stands and by Cortinarius and Russula in older stands. The latter genera correlated positively with nutrient-mobilising enzymes, indicating aggravated nutrient limitation. A risk that shorter rotation periods could lead to the loss of symbiosis-driven recycling of organic nutrient pools and constrain long-term forest productivity was identified. Fungal-driven oxidation constrained belowground organic matter accumulation and promoted ecosystem fertility in an old-growth forest. Oxidative decomposition was regulated by fertility-related shifts between fungal guilds with contrasting decomposing capacities. Long-term humus build-up was driven by differences in root decomposition rates, whereas leaf litter decomposition was found to be of minor regulatory importance. Within soil profiles, carbon and nitrogen dynamics were significantly related to ecosystem fertility, root decomposition and fungal community composition. Belowground fungal communities were important components in mediating effects of climate, soil fertility and forest management on accumulation of soil organic matter in Swedish boreal region. Overall, the results collected across different scales and ecosystem types underlined soil fungi as the principal drivers of carbon and nitrogen dynamics in boreal forest ecosystems. The thesis highlights a major potential to increase the predictive power of forest ecosystem models by including soil fungi as integrated components. |
