Global mycorrhizal plant distribution linked to terrestrial carbon stocks

Abstract

Vegetation impacts on ecosystem functioning are mediated by mycorrhiza, a plant-fungal association formed by most plant species. Ecosystems dominated by distinct mycorrhizal types differ strongly in their biogeochemistry. Quantitative analyses of mycorrhizal impacts on ecosystem functioning are hindered by the absence of information on mycorrhizal distribution. We present the first global high-resolution maps of vegetation biomass distribution among main types of mycorrhizal associations. Arbuscular, ecto-, ericoid and non-mycorrhizal vegetation store 241±15, 100±17, 7±1.8 and 29 ± 5.5 GT carbon in aboveground biomass, respectively. Soil carbon stocks in both topsoil and subsoil are positively related to the biomass fraction of ectomycorrhizal plants in the community, though the strength of this relationship varies across biomes. We show that human-induced transformations of Earth’s ecosystems have reduced ectomycorrhizal vegetation, with potential knock-on effects on terrestrial carbon stocks. Our work provides a benchmark for spatially explicit global quantitative assessments of mycorrhizal impacts on ecosystem functioning and biogeochemical cycles.One Sentence SummaryFirst maps of the global distribution of mycorrhizal plants reveal global losses of ectomycorrhizal vegetation, and quantitative links between mycorrhizal vegetation patterns and terrestrial carbon stocks.

Mycorrhizal types differ in ecophysiology and alter plant nutrition and soil processes

“…Based on soil C content and dominant vegetation, Averill et al . () estimated that EcM forests store 1.7‐fold C ha −1 more than AM‐dominated forests globally, but much of this could be attributable to EcM dominance in colder habitats (Soudzilovskaia et al ., ) that exhibit slower C and nutrient cycling (Makkonen et al ., ). These results were recently extrapolated to all terrestrial biomes, further suggesting that AM‐dominated forest ecosystems store more carbon in aboveground biomass, whereas EcM‐dominated systems store more carbon in soil (Soudzilovskaia et al ., ).…”

“…() estimated that EcM forests store 1.7‐fold C ha −1 more than AM‐dominated forests globally, but much of this could be attributable to EcM dominance in colder habitats (Soudzilovskaia et al ., ) that exhibit slower C and nutrient cycling (Makkonen et al ., ). These results were recently extrapolated to all terrestrial biomes, further suggesting that AM‐dominated forest ecosystems store more carbon in aboveground biomass, whereas EcM‐dominated systems store more carbon in soil (Soudzilovskaia et al ., ). However, three recent North American temperate forest studies revealed no overall mycorrhizal‐type effect (Zhu et al ., ), opposite trends in deep soil (Craig et al ., ), or an interplay between forest type, mycorrhizal type and soil depth (Jo et al ., ).…”

“…Since then, research teams have tested related hypotheses in field studies, microcosm experiments and meta‐analyses integrating plant ecophysiological, soil and climate data from the mycorrhizal‐type perspective. Global modelling reveals that differences in the key ecosystem processes among mycorrhizal types are important from the perspectives of climate change and biosphere functioning (Averill, Turner & Finzi, ; Terrer et al ., ; Soudzilovskaia et al ., ; Sulman et al ., ).…”

Global distribution patterns of mycoheterotrophy

“…Therefore, the observed dichotomy in the distribution of AM and EM mycoheterotrophic plants does not reflect the global distribution pattern of AM and EM fungi, indicating that the distribution of particular mycorrhizal types does not constrain the global distribution of mycoheterotrophic plants. Evidently, our knowledge on the abundance of plants associated with each mycorrhizal type is limited, the only source available at the moment being the maps from Soudzilovskaia et al (). These maps give a rough estimation of the abundance of plants associated with each mycorrhizal type and at a coarser resolution than our 1‐km 2 grid cells with mycoheterotrophic plants records, highlighting the need to develop more accurate proxies for mycorrhizal abundance at the global scale.…”

“…To investigate these alternative hypotheses, we considered the land‐class categories from the Climate Change Initiative (CCI) Land Cover maps (ESA, ) to infer vegetation type. For the association with autotrophic plants featuring the same mycorrhizal type, we used the global maps of % biomass of autotrophic plants associated with AM and EM fungi (Soudzilovskaia et al, ), as proxy for the abundance of autotrophic plants. The Land Cover maps were obtained with a spatial resolution of 300 m, which we rescaled to the 1‐km 2 grid used in this study.…”