Ecological Controls of Rhizosphere Processes and Soil Organic Matter Dynamics at a Sub-arctic Treeline

• Main Author: Parker, Thomas C
• Other Authors: Subke, Jens-Arne, Wookey, Philip A, This work was funded by NERC research Studentship training grant NE/J500434/1 and supported by fungding from from the European Union Seventh Framework Programme FP7/2007-2013 under grant agreement no 262693 INTERACT .
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 2015
• Subjects: Rhizosphere; Global change; Climatology Trees Sweden; Soil and the environment sweden; Arctic; Climate change; Empetrum nigrum; Northern Sweden; Tundra
• Online Access: http://hdl.handle.net/1893/22369; http://dspace.stir.ac.uk/bitstream/1893/22369/1/Parker_2015_Thesis_Final.pdf

Rapid climate change in the Arctic and Sub-Arctic is causing vegetation change across large areas of tundra. Shrubs and trees are undergoing range expansions as part of an over-all trend of ‘greening’ of the tundra. This is of importance because northern peatlands contain around half of total soil carbon (C) and there is a potential for productive vegetation to interact with this C in a number of ways: (1) Ectomycorrhizal fungi (ECM) in symbiosis with trees and shrubs could potentially stimulate decomposition through extracellular enzyme production whilst extracting nitrogen (N) for their hosts; (2) deep snow, trapped by tall vegetation insulates the soil, resulting in higher winter-time microbial activity and has potential to influence growing season microbial activity; (3) the biochemistry of litter and decomposition environment associated with more productive vegetation could result in accelerated mass loss of litter and stimulate decomposition of older soil C. This thesis investigates how productive sub-arctic plant species in Northern Sweden interact with soil C by using ‘space-for-time’ transitions from forests (Betula pubescens), through intermediate shrub vegetation (Betula, Salix), to tundra heath (Empetrum nigrum). This was to test how ECM fungi, winter snow accumulation, defoliation events and litter input influence C cycling. C stocks, respiration rates and ECM growth rates were measured across these ecotones. It was found that birch forests and shrub stands had significantly lower soil C storage and higher respiration rates than adjacent heaths. This is contrary to the predictions of earth system models. Higher ECM growth rates at plots with low C storage and high cycling rates implied that they had an important role in the stimulation of C decomposition. To test whether snow cover in forests over winter had an important effect on C cycling, soils were transplanted between forest and heath (different snow cover), and respiration rates were measured over summer. It was found that deep snow cover over ...