Ericoid shrub encroachment shifts aboveground–belowground linkages in three peatlands across Europe and Western Siberia

Abstract

In northern peatlands, reduction of Sphagnum dominance in favour of vascular vegetation is likely to influence biogeochemical processes. Such vegetation changes occur as the water table lowers and temperatures rise. To test which of these factors has a significant influence on peatland vegetation, we conducted a 3‐year manipulative field experiment in Linje mire (northern Poland). We manipulated the peatland water table level (wet, intermediate and dry; on average the depth of the water table was 17.4, 21.2 and 25.3 cm respectively), and we used open‐top chambers (OTCs) to create warmer conditions (on average increase of 1.2°C in OTC plots compared to control plots). Peat drying through water table lowering at this local scale had a larger effect than OTC warming treatment per see on Sphagnum mosses and vascular plants. In particular, ericoid shrubs increased with a lower water table level, while Sphagnum decreased. Microclimatic measurements at the plot scale indicated that both water‐level and temperature, represented by heating degree days (HDDs), can have significant effects on the vegetation. In a large‐scale complementary vegetation gradient survey replicated in three peatlands positioned along a transitional oceanic–continental and temperate–boreal (subarctic) gradient (France–Poland–Western Siberia), an increase in ericoid shrubs was marked by an increase in phenols in peat pore water, resulting from higher phenol concentrations in vascular plant biomass. Our results suggest a shift in functioning from a mineral‐N‐driven to a fungi‐mediated organic‐N nutrient acquisition with shrub encroachment. Both ericoid shrub encroachment and higher mean annual temperature in the three sites triggered greater vascular plant biomass and consequently the dominance of decomposers (especially fungi), which led to a feeding community dominated by nematodes. This contributed to lower enzymatic multifunctionality. Our findings illustrate mechanisms by which plants influence ecosystem responses to climate change, through their effect on microbial trophic interactions.

Why Andromeda is no goddess for the sustainability of bogs

“…Indeed, past work in bogs has shown that modest increases in temperature can disrupt ericoid mycorrhizal colonisation of A. polifolia via interactions with phenolics produced by Sphagnum (Binet et al, 2017). Thus, the ‘below‐ground components’ element of the structural equation model produced by Buttler et al (2023; their figure 8) may be even more complex than can be deduced from their analyses.…”

“…So what are the proximate mechanisms above‐ and below‐ground that underpin shrubification in peatlands, and what is the relative importance of the two key components of climate change—increased temperature and reduced rainfall—in facilitating such shifts? These questions were the focus of a paper published in this issue by Buttler et al (2023). An important feature of the study relates to the experimental design, which combined field manipulations of climate change factors (water table depth and air temperature) with observational measurements along a natural gradient, thus combining the benefits of both approaches.…”

“…As is the case with many elegant field-based studies, additional questions and complexities are raised. One potential piece of the jigsaw that was not the focus of Buttler et al (2023) was a role of ericoid mycorrhizal fungi, specifically how these fungi may influence interactions among plants and soil processes in response to climate manipulations. Ericaceous roots are often highly branched and very fine, sometimes with diameters of only 15 microns, and the cortical cells are heavily colonised by coils of ericoid mycorrhizal fungal hyphae, which grow into the rhizosphere and proliferate along root surfaces.…”

“…Indeed, past work in bogs has shown that modest increases in temperature can disrupt ericoid mycorrhizal colonisation of A. polifolia via interactions with phenolics produced by Sphagnum (Binet et al, 2017). Thus, the 'below-ground components' element of the structural equation model produced by Buttler et al (2023; their figure 8) may be even more complex than can be deduced from their analyses. Despite these possible gaps, Buttler et al ( 2023) is a timely and important reminder of the need for multi-disciplinary approaches to tackle grand challenges such as climate change impacts and underlies the importance of considering multiple factors as drivers of change.…”

“…Despite these possible gaps, Buttler et al (2023) is a timely and important reminder of the need for multi‐disciplinary approaches to tackle grand challenges such as climate change impacts and underlies the importance of considering multiple factors as drivers of change. Nonetheless, our ability to concurrently manipulate several factors of change is poor (Rillig et al, 2019), and it remains to be tested how peatland functioning and shrub expansion responds to additional factors of nitrogen deposition and elevated atmospheric CO 2 concentrations alongside increased temporal variability of climate.…”