The Flow Country Peatlands of Scotland: Foreword

First paragraph: In the far north of Scotland, a vast and varied expanse of blanket peatland (Figure 1) extends across an area of 4,000 km2 within the historic counties of Caithness and Sutherland, from the foot of the mountains in the west to the coast in the east. It is the largest expanse of blanket mire in Europe (Lindsay et al. 1988) and the largest single terrestrial carbon store in the UK (Chapman et al. 2009). It is known as the Flow Country. The Flow Country has high conservation value, being of particular importance for its suite of breeding birds which includes the Common Scoter (Melanitta nigra), Greenshank (Tringa nebularia), Dunlin (Calidris alpina), Golden Plover (Pluvialis apricaria) and Hen Harrier (Circus cyaneus), and a refuge for many species normally found closer to the Arctic (Lindsay et al. 1988). The nature conservation importance of this area is reflected in the designation of over 1,300 km2 as Natura 2000 sites under the European Habitats and Birds Directives, including the largest terrestrial Special Area of Conservation (SAC) in the UK, and the current consideration of the Flow Country for World Heritage Site status

Soil fauna precipitate the convergence of organic matter quality during decomposition

Plant litter constitutes the dominant resource to soil food webs, which gradually decompose litter and transform it into soil organic matter. A central paradigm of this transformation posits that differences in quality between distinct litter types disappear during decomposition, as litter types converge towards similar physicochemical characteristics. Yet, this paradigm is debated and not based on clear metrics. It is also largely derived from microbial decomposition studies, while the effect of litter-feeding soil animals, by transforming large quantities of litter into faeces, remains poorly documented. We addressed this knowledge gap by quantifying the variability in physicochemical characteristics amongst leaf litter of six tree species of contrasting quality, before and after conversion into faeces by six soil animal species. We found that litter conversion into faeces by diverse soil animals largely reduced the variability in physical and chemical characteristics between contrasting litter types. We also evaluated the consequences of this animal-driven convergence on further microbial-driven convergence during decomposition, by decomposing intact litter and soil animal faeces and comparing the chemical characteristics of decomposed materials. Chemical variability amongst uningested litter and amongst soil animal faeces converged at similar rates. This indicates that animal- and microbial-driven convergence are additive, and that soil animals precipitate organic matter quality convergence during decomposition. We propose here a new framework and an associated metric to study changes in organic matter quality variability during decomposition, which we argue are essential for an improved understanding and modelling of litter decomposition and soil organic matter formation.Output Status: Forthcoming/Available Onlin

Biotic interactions and biogeochemical processes in the soil environment

Soils play a key role in the terrestrial carbon (C) cycle by storing and emitting large quantities of C. The impact of abiotic conditions (mainly soil temperature and moisture) on soil C turnover is well documented, but unravelling the influence of these drivers across temporal and spatial scales remains an important challenge. Biotic factors, such as microbial abundance and diversity, macro-faunal food webs and below-ground plant (i.e. root) biomass and diversity, play an important role in controlling soil C storage and emission, but remain under-investigated. To better understand the soil processes underlying terrestrial C cycling, the interactions between plants (autotrophs) and soil organisms (heterotrophs) need to be addressed more explicitly and integrated with short- and long-term effects of abiotic drivers. This special issue presents recent advances in field, laboratory, and modelling studies on soil C dynamics, with a particular emphasis on those aiming to resolve abiotic and biotic influences. The manuscripts highlight three areas of investigation that we suggest are central to current and future progress in ecosystem C dynamic research: (1) novel interpretations of abiotic controls on soil CO2 efflux, (2) legacy effects of abiotic drivers of soil C dynamics, and (3) the interaction between plant C dynamics and soil biological processes

Synergistic interactions between detritivores disappear under reduced rainfall

Understanding the consequences of altered rainfall patterns on litter decomposition is critical to predicting the feedback effect of climate change on atmospheric CO2 concentrations. While their effect on microbial decomposition received considerable attention, their effect on litter fragmentation by detritivores, the other dominant decomposition pathway, remains largely unexplored. Particularly, it remains unclear how different detritivore species and their interactions respond to changes in rainfall quantity and frequency. To fill this knowledge gap, we determined the contribution to litter decomposition of two detritivore species (millipede and isopod), separately and in combination, under contrasting rainfall quantity and frequency in a temperate forest. Although halving rainfall quantity and frequency decreased top-soil moisture by 7.8 and 13.1%, respectively, neither millipede- nor isopod-driven decomposition were affected by these changes. In contrast, decomposition driven by both detritivore species in combination was 65.5% higher than expected based on monospecific treatments under high rainfall quantity, but unchanged or even lower under low rainfall quantity. This indicates that while detritivore activity is relatively insensitive to changes in rainfall patterns, large synergistic interactions between detritivore species may disappear under future rainfall patterns. Incorporating interspecific interactions between decomposers thus seems critical to evaluate the sensitivity of decomposition to altered rainfall patterns

Slowed biogeochemical cycling in sub-arctic birch forest linked to reduced mycorrhizal growth and community change after a defoliation event

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 slow-down 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 (e.g. /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 immobilize 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

An incubation study of GHG flux responses to a changing water table linked to biochemical parameters across a peatland restoration chronosequence

Large areas of northern peatlands have been drained and afforested with conifers in the 20th century. This has led to changes in the hydrology of the peatlands, the quality and quantity of organic matter inputs and soil microbial communities, which are all likely to impact on greenhouse gas (GHG) fluxes. Considerable areas of these forest plantations are undergoing restoration, and our aim was to assess whether contrasting compositions of peat, in conjunction with hydrological changes in a controlled lab experiment, impact on GHG fluxes. We incubated vegetation free cores (at 8 °C) from a near-natural bog, restoration sites felled in 1998, 2006, 2012 and a current forest plantation at (a) low water tables, (b) high tables or (c) water tables that were changed from low to high. Results show that peat quality and nutrient availability in the pore water have been altered by the forest plantations, which resulted in dissimilar carbon dioxide (CO2) fluxes between the sites under the same temperature and water table conditions. Higher CO2 fluxes were found in the peat cores from the forest plantations than from sites that have undergone restoration and from the near-natural bog. However, there were few differences in methane (CH4) fluxes from the different sites, indicating that on its own (i.e., in the absence of biotic interactions under field conditions) the effects of forestry on CH4 flux are limited

Spatial patterns in soil organic matter dynamics are shaped by mycorrhizosphere interactions in a treeline forest

Aims In the Swedish sub-Arctic, mountain birch (Betula pubescens ssp. czerepanovii) forests mediate rapid soil C cycling relative to adjacent tundra heaths, but little is known about the role of individual trees within forests. Here we investigate the spatial extent over which trees influence soil processes. Methods We measured respiration, soil C stocks, root and mycorrhizal productivity and fungi:bacteria ratios at fine spatial scales along 3 m transects extending radially from mountain birch trees in a sub-Arctic ecotone forest. Root and mycorrhizal productivity was quantified using in-growth techniques and fungi:bacteria ratios were determined by qPCR. Results Neither respiration, nor root and mycorrhizal production, varied along transects. Fungi:bacteria ratios, soil organic C stocks and standing litter declined with increasing distance from trees. Conclusions As 3 m is half the average size of forest gaps, these findings suggest that forest soil environments are efficiently explored by roots and associated mycorrhizal networks of B. pubescens. Individual trees exert influence substantially away from their base, creating more uniform distributions of root, mycorrhizal and bacterial activity than expected. However, overall rates of soil C accumulation do vary with distance from trees, with potential implications for spatio-temporal soil organic matter dynamics and net ecosystem C sequestration

Ecosystems in transition: Interactions and feedbacks with an emphasis on the initial development

First paragraph: In this Special Issue of Biogeosciences on "Ecosystems in transition: Interactions and feedbacks with an emphasis on the initial development", we bring together research on ecosystems undergoing state transitions, including artificially created and naturally formed sites, most of them in an initial stage of development. State transitions of an ecosystem may occur either when a formerly stable system state is disturbed or when a developing system gradually achieves new functions during succession. Thus, state transitions of ecosystems are not necessarily restricted to a deterioration of ecosystems but can also be observed during initial ecosystem evolution.Output Type: Editoria