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Slowed Biogeochemical Cycling in Sub-arctic Birch Forest Linked to Reduced Mycorrhizal Growth and Community Change after a Defoliation Event
Authors:Thomas C Parker  Jesse Sadowsky  Haley Dunleavy  Jens-Arne Subke  Serita D Frey  Philip A Wookey
Institution:1.Biological and Environmental Sciences, School of Natural Sciences,University of Stirling,Stirling,UK;2.Department of Animal and Plant Sciences,University of Sheffield,Sheffield,UK;3.Department of Natural Resources and the Environment,University of New Hampshire,Durham,USA;4.Environmental Sciences, School of Life Sciences,Heriot-Watt University,Edinburgh,UK;5.The Ecosystems Center,Marine Biological Laboratory,Woods Hole,USA
Abstract:Sub-arctic birch forests (Betula pubescens Ehrh. ssp. czerepanovii) periodically suffer large-scale defoliation events caused by the caterpillars of the geometrid moths Epirrita autumnata and Operophtera brumata. Despite their obvious influence on ecosystem primary productivity, little is known about how the associated reduction in belowground C allocation affects soil processes. We quantified the soil response following a natural defoliation event in sub-arctic Sweden by measuring soil respiration, nitrogen availability and ectomycorrhizal fungi (EMF) hyphal production and root tip community composition. There was a reduction in soil respiration and an accumulation of soil inorganic N in defoliated plots, symptomatic of a slowdown of soil processes. This coincided with a reduction of EMF hyphal production and a shift in the EMF community to lower autotrophic C-demanding lineages (for example, /russula-lactarius). We show that microbial and nutrient cycling processes shift to a slower, less C-demanding state in response to canopy defoliation. We speculate that, amongst other factors, a reduction in the potential of EMF biomass to immobilise excess mineral nitrogen resulted in its build-up in the soil. These defoliation events are becoming more geographically widespread with climate warming, and could result in a fundamental shift in sub-arctic ecosystem processes and properties. EMF fungi may be important in mediating the response of soil cycles to defoliation and their role merits further investigation.
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