Fine root dynamics and below- and above-ground carbon inputs into soil in boreal forests

• Main Author: Ding, Yiyang
• Other Authors: Vesterdal, Lars, University of Helsinki, Faculty of Agriculture and Forestry, Department of Forest Sciences, Doctoral Programme in Sustainable Use of Renewable Natural Resources, Helsingin yliopisto, maatalous-metsätieteellinen tiedekunta, Uusiutuvien luonnonvarojen kestävän käytön tohtoriohjelma, Helsingfors universitet, agrikultur-forstvetenskapliga fakulteten, Doktorandprogrammet i hållbart utnyttjande av förnybara naturresurser, Helmisaari, Heljä-Sisko
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2021
• Subjects: forest soil science; The Needle; Northern Finland
• Online Access: http://hdl.handle.net/10138/335111

Below-ground carbon (C) allocation studies in boreal forests are scarce and have high levels of uncertainty in ecological and modelling studies. The uncertainty of fine root turnover and the heterogeneity of fine root distribution are the main barriers to quantifying the below-ground C allocation. Unravelling the below-ground C litter inputs of boreal forests, including fine roots and ectomycorrhizal (EcM) mycelia, could provide fundamental information for quantifying biogeochemical cycles. This thesis evaluated the below- and above-ground litter C inputs along a site type gradient of Scots pine (Pinus sylvestris) sites in southern Finland, and a distinct silver birch (Betula pendula) site in northern Finland. Furthermore, the Scots pine pioneer/fibrous root growth phenology was observed and compared with the modelled growth of the above-ground organs (predicted by the dynamic CASSIA model) in southern Finland in 2018, when there was an unusual summer drought. Fine root turnover was observed by minirhizotrons (MR) and the root growth phenology was observed by flat-bed scanners, both of which direct methods are known to provide reliable results in root research. Based on the daily root growth monitoring experiments, we found that the timing of intensive root growth lagged behind the growth of above-ground organs (shoots, secondary xylem, buds, and needles). Interestingly, we found a clear root growth increase while the needle growth decreased, which may have been caused by a shift of non-structural carbohydrates (NSC) from above-ground to below-ground. The low temperature and summer droughts may have constrained the fibrous root growth, but not influenced the pioneer root growth, which indicates that pioneer roots could be more tolerant to severe climate variations. Increasing nutrient availability could clearly increase the above-ground C allocation but not the below-ground allocation. Our study sites CT, VT, MT were named after Cajander’s Finnish site type theory in the order of increasing nutrient ...