Shrub expansion modulates belowground impacts of changing snow conditions in alpine grasslands.

Arthur A D Broadbent,Antonios Michas,William J Pritchard,Michael Schloter,Helen K Grant,Irene Cordero,Tim Goodall,Michael Bahn,Richard D Bardgett,Lindsay K Newbold,Andrew Guinta,Helen S K Snell,Robert I Griffiths,Rüdiger Kaufmann,David X Soto,Thomas Crowther

doi:10.1111/ele.13903

Abstract

Climate change is disproportionately impacting mountain ecosystems, leading to large reductions in winter snow cover, earlier spring snowmelt and widespread shrub expansion into alpine grasslands. Yet, the combined effects of shrub expansion and changing snow conditions on abiotic and biotic soil properties remains poorly understood. We used complementary field experiments to show that reduced snow cover and earlier snowmelt have effects on soil microbial communities and functioning that persist into summer. However, ericaceous shrub expansion modulates a number of these impacts and has stronger belowground effects than changing snow conditions. Ericaceous shrub expansion did not alter snow depth or snowmelt timing but did increase the abundance of ericoid mycorrhizal fungi and oligotrophic bacteria, which was linked to decreased soil respiration and nitrogen availability. Our findings suggest that changing winter snow conditions have cross-seasonal impacts on soil properties, but shifts in vegetation can modulate belowground effects of future alpine climate change.

Highlights

Aboveground–belowground linkages shape responses to climate change at the ecosystem scale, but they are still poorly understood (Bardgett et al, 2013; Hagedorn et al, 2019)
We found no significant differences in total fungal or bacterial Phospholipid fatty acid (PLFA) marker abundances in relation to snowmelt timing or shrub expansion (Table S1), the Gram positive: Gram negative (GP:GN) bacterial ratio was greater in the shrub-invaded plots compared to both the shrub removal and the grass-control treatments (Figure 1e)
Stronger effects of snowmelt timing have been found on microbial community composition when the extreme ends of snowmelt timing gradients are tested (Zinger et al, 2009)

Summary

INTRODUCTION

Aboveground–belowground linkages shape responses to climate change at the ecosystem scale, but they are still poorly understood (Bardgett et al, 2013; Hagedorn et al, 2019). We disentangle the belowground effects on microbial communities, microbial- mediated functions, and important plant nutrient pools of two widespread climate change impacts in alpine ecosystems: ericaceous shrub expansion and changing snow conditions. (Bragazza et al, 2015; Vowles & Björk, 2019), which are low-growing and associate with ericoid mycorrhizal fungi (ErM) These ericaceous shrubs are associated with different belowground effects than deciduous shrubs, including increased soil C:N ratios and decreased soil nutrient contents (Grau et al, 2019). We hypothesised that expansion of ericaceous shrubs has no influence on snow depth or snowmelt timing due to their short stature, but does cause an increase in ErM abundance and shifts microbial communities towards oligotrophic taxa, which is associated with altered soil functioning and lower soil N availability. We hypothesised that combined effects of shrub expansion and changing snow conditions are additive, rather than synergistic or antagonistic, as recently reported for multiple co-occurring global change impacts (Broadbent et al, 2020; Song et al, 2019)

MATERIALS AND METHODS

Findings

DISCUSSION