Global imprint of mycorrhizal fungi on whole-plant nutrient economics

Abstract

Mycorrhizal fungi are critical members of the plant microbiome, forming a symbiosis with the roots of most plants on Earth. Most plant species partner with either arbuscular or ectomycorrhizal fungi, and these symbioses are thought to represent plant adaptations to fast and slow soil nutrient cycling rates. This generates a second hypothesis, that arbuscular and ectomycorrhizal plant species traits complement and reinforce these fungal strategies, resulting in nutrient acquisitive vs. conservative plant trait profiles. Here we analyzed 17,764 species level trait observations from 2,940 woody plant species to show that mycorrhizal plants differ systematically in nitrogen and phosphorus economic traits. Differences were clearest in temperate latitudes, where ectomycorrhizal plant species are more nitrogen use- and phosphorus use-conservative than arbuscular mycorrhizal species. This difference is reflected in both aboveground and belowground plant traits and is robust to controlling for evolutionary history, nitrogen fixation ability, deciduousness, latitude, and species climate niche. Furthermore, mycorrhizal effects are large and frequently similar to or greater in magnitude than the influence of plant nitrogen fixation ability or deciduous vs. evergreen leaf habit. Ectomycorrhizal plants are also more nitrogen conservative than arbuscular plants in boreal and tropical ecosystems, although differences in phosphorus use are less apparent outside temperate latitudes. Our findings bolster current theories of ecosystems rooted in mycorrhizal ecology and support the hypothesis that plant mycorrhizal association is linked to the evolution of plant nutrient economic strategies.

Global Root Traits (GRooT) Database

“…In terms of phylogenetic coverage, data in GRooT include the major clades of vascular plants, with, on average, four traits included per species. Thereby, phylogenetic coverage in GRooT opens the possibility to use the data in large-scale phylogenetic studies like analyses of trait conservatism Averill et al, 2019) or assessments of trait relationships and trade-offs across the phylogeny.…”

“…While root traits are likely to capture key dimensions of plant form and function, plant evolutionary history, and responses to environmental variability (Bardgett et al, 2014;Laliberté, 2016;Valverde-Barrantes et al, 2017;Ma et al, 2018;Kong et al, 2019), they remain underrepresented in large-scale comparative studies and global models. Accordingly, root traits remain absent from nearly all existing studies that define the global spectrum of plant form and function (Wright et al, 2004;Chave et al, 2009;Reich, 2014;Díaz et al, 2016) but see Averill et al, (2019).…”

Global mycorrhizal fungal range sizes vary within and among mycorrhizal guilds but are not correlated with dispersal traits

“…183 million years ago (Lutzoni et al., 2018). These mycorrhizal fungal types also differ in function, with AM fungi largely accessing inorganic nutrients in soils while EM fungi can decompose organic forms of N and P, leading to different nutrient use strategies among plant hosts of the two groups (Averill, Bhatnagar, Dietze, Pearse, & Kivlin, 2019). In addition, while host specificity of mycorrhizal fungal associations are still unresolved (Opik & Peay, 2016), general differences are recognized between AM and EM fungi.…”

“…The large functional variation between and within AM and EM fungal guilds has led to many studies of how mycorrhizal fungal guilds might impact ecosystem functions such as carbon storage, nutrient cycling and litter decomposition across space (e.g. Averill et al., 2019;Averill, Turner, & Finzi, 2014;Keller & Phillips, 2019;Sulman et al., 2019). Historically, most biogeographic maps of mycorrhizal associations relied on host plant mycorrhizal types (Barcelo, Bodegom, & Soudzilovskaia, 2019;Bueno et al., 2017;Steidinger et al., 2019).…”

Relationship Between Belowground Carbon Allocation and Nitrogen Uptake in Saplings Varies by Plant Mycorrhizal Type

“…Theory also predicts that the C cost of N uptake is a function of not only soil N availability but also the type of mycorrhizal fungi a plant associates with . Recent work shows plant mycorrhizal association can be considered an integrative plant functional trait, with plants from distinct mycorrhizal groups displaying differences in other plant nutrient traits such as leaf and root N (Averill et al, 2019), leaf and root litter decay rates (Keller and Phillips, 2019;See et al, 2019) and foliar resorption . Moreover, trees associated with ectomycorrhizal (ECM) fungi are believed to allocate more C to their symbionts, which in turn have the capacity to mine N from SOM.…”