Roots Mediate the Effects of Snowpack Decline on Soil Bacteria, Fungi, and Nitrogen Cycling in a Northern Hardwood Forest

Abstract

Rising winter air temperature will reduce snow depth and duration over the next century in northern hardwood forests. Reductions in snow depth may affect soil bacteria and fungi directly, but also affect soil microbes indirectly through effects of snowpack loss on plant roots. We incubated root exclusion and root ingrowth cores across a winter climate-elevation gradient in a northern hardwood forest for 29 months to identify direct (i.e., winter snow-mediated) and indirect (i.e., root-mediated) effects of winter snowpack decline on soil bacterial and fungal communities, as well as on potential nitrification and net N mineralization rates. Both winter snowpack decline and root exclusion increased bacterial richness and phylogenetic diversity. Variation in bacterial community composition was best explained by differences in winter snow depth or soil frost across elevation. Root ingrowth had a positive effect on the relative abundance of several bacterial taxonomic orders (e.g., Acidobacterales and Actinomycetales). Nominally saprotrophic (e.g., Saccharomycetales and Mucorales) or mycorrhizal (e.g., Helotiales, Russalales, Thelephorales) fungal taxonomic orders were also affected by both root ingrowth and snow depth variation. However, when grouped together, the relative abundance of saprotrophic fungi, arbuscular mycorrhizal fungi, and ectomycorrhizal fungi were not affected by root ingrowth or snow depth, suggesting that traits in addition to trophic mode will mediate fungal community responses to snowpack decline in northern hardwood forests. Potential soil nitrification rates were positively related to ammonia-oxidizing bacteria and archaea abundance (e.g., Nitrospirales, Nitrosomondales, Nitrosphaerales). Rates of N mineralization were positively and negatively correlated with ectomycorrhizal and saprotrophic fungi, respectively, and these relationships were mediated by root exclusion. The results from this study suggest that a declining winter snowpack and its effect on plant roots each have direct effects on the diversity and abundance of soil bacteria and fungal communities that interact to determine rates of soil N cycling in northern hardwood forests.

Surprising relationships between soil pH and microbial biomass and activity in a northern hardwood forest

“…Another study found that winter snowpack decline associated with global warming increased bacterial richness and phylogenetic diversity (2016). However, any effects of changing soil climate conditions may have been mediated by effects on root growth, which is impaired by soil freezing associated with the snowpack decline (Sorensen et al 2019).…”

The subalpine shrub Dasiphora fruticosa alters seasonal and elevational effects on soil microbial diversity and ecosystem functions on the Tibetan Plateau

“…In particular, shrubs have been shown to affect microbial communities in some ecosystems (Collins et al, 2018;Gorzelak et al, 2012) as a result of alleviating understorey microenvironments. Therefore, microbes might be good candidates and several studies have already assessed changes in microbial communities in winter (Fournier et al, 2020;Sorensen et al, 2019).…”

“…In particular, shrubs have been shown to affect microbial communities in some ecosystems (Collins et al, 2018; Gorzelak et al, 2012) as a result of alleviating understorey microenvironments. Therefore, microbes might be good candidates and several studies have already assessed changes in microbial communities in winter (Fournier et al, 2020; Sorensen et al, 2019). For example, Sorensen et al (2019) have shown that tree roots cannot buffer elevation effect on bacterial richness in winter, but may buffer elevation effects on bacterial β ‐diversity.…”

“…Therefore, microbes might be good candidates and several studies have already assessed changes in microbial communities in winter (Fournier et al, 2020; Sorensen et al, 2019). For example, Sorensen et al (2019) have shown that tree roots cannot buffer elevation effect on bacterial richness in winter, but may buffer elevation effects on bacterial β ‐diversity. Yet, whether and how shrubs buffer season and elevation effects on microbial α ‐ and β ‐diversity directly and indirectly via changing biotic and abiotic factors remains to be further investigated in alpine ecosystems.…”

Measurement of Volatile Compounds for Real-Time Analysis of Soil Microbial Metabolic Response to Simulated Snowmelt

“…Accurate characterization of the activity of soil microbiomes is key to understanding how the soil compartment functions and responds to chronic and acute perturbations ( Bardgett and van der Putten, 2014 ; Delgado-Baquerizo et al, 2019 ). Snowpack dynamics for example are strongly influenced by climate driving forces such as atmospheric warming and precipitation patterns, and in turn regulate both plant and microbial activity ( Brooks et al, 1998 ; Lipson et al, 2002 ; Steltzer et al, 2009 ; Wipf, 2010 ; Sorensen et al, 2019 ). Our prior work observed that snowmelt induced a significant shift in soil water potential, dynamic biomass growth and turnover that corresponded to a reassembly of the soil microbiome ( Sorensen et al, 2020 ).…”