Mycorrhizal tree impacts on topsoil biogeochemical properties in tropical forests

Abstract

In tropical regions, the patterns of carbon (C) and nutrient properties among ecosystems dominated by distinct mycorrhizal associations are unknown. We aim to reveal whether the dynamics differ and the ecological drivers and ecosystem functioning implications of such differences. Based on a dataset of 97 tropical forest sites, we related EcM trees abundance (as a proxy for the transition from AM to EcM trees dominance) to different topsoil properties, climatic conditions and microbial abundance proxies through Generalized Additive Models. Higher abundances of EcM trees were correlated with higher topsoil concentrations of total nitrogen and C, extractable phosphorus and potassium, δ13C, mean annual temperature, precipitation, microbial (bacterial and fungal) biomass and the relative abundance of saprotrophic fungi. Synthesis. Our results reveal consistent differences in carbon and nutrient content between arbuscular mycorrhizal (AM‐) and EcM‐dominated vegetation across the tropical biome, pointing to lower soil fertility and lower rates of C and nutrient transformation processes in EcM‐dominated forests. These patterns associate with lower topsoil C accumulation when compared to AM vegetation, which contrasts with patterns reported for temperate forests. We suggest that different mechanisms of soil organic matter accumulation explain the contrasting impacts of EcM dominance on topsoil properties of temperate and tropical biomes. Global vegetation and C models should account for the contrasting impacts of distinct mycorrhizal vegetation in different climatic zones.

Soil microbial community response to ectomycorrhizal dominance in diverse neotropical montane forests

“…We found a strong relationship between EM dominance and bulk soil microbiome composition in diverse neotropical montane forests. The relative abundance of EM-associating tree species in tropical forests is associated with significant shifts in soil properties (Barceló et al 2022 ), yet it remains unclear how these shifts influence soil microbial composition. In support of our hypothesis, we found clear differentiation in soil microbial communities between stand mycorrhizal types across a range of forests differing in parent material and soil chemical properties, with stand mycorrhizal type explaining slightly greater variation in prokaryotic communities than site location.…”

Seasonality regulates the structure and biogeochemical impact of ectomycorrhizal fungal communities across environmentally divergent neotropical dry forests

“…In support of greater nutrient recapture by tropical ECM trees, Lin et al (2018) also found that ECM trees produced more root length per soil volume and had greater rhizosphere effects on N transformations. To determine the ECM plant traits that most influence soil biogeochemistry in tropical dry forests, future studies should compare leaf and root traits of ECM plant species growing outside of mono‐dominant stands with those of nearby AM‐associated plant species (Barceló et al, 2022).…”

Towards understanding the impact of mycorrhizal fungal environments on the functioning of terrestrial ecosystems.

“…To date, the differences between impacts of distinct mycorrhizal fungal guilds on soil processes remain poorly understood and contradicting evidence has been accumulated in regard to virtually each of the aspects of similar or differential impacts of distinct mycorrhizal fungal guilds on soil processes (Table 1). The most striking contradictions and uncertainties are manifested across the following domains: (i) Impacts of individual mycorrhizal fungal guilds on soil carbon differ between the tropics and temperate zones (Barceló et al, 2022;Fernandez & Kennedy, 2016a), which suggests that key aspects of the mechanisms attributed to mycorrhiza might be underpinned by other mechanisms of ecosystem functioning than mycorrhizas, or they are underpinned by complex interactions of mycorrhizal fungal guilds with climatic conditions; (ii) Contribution of different mycorrhizal fungal guilds to carbon transfer and to processes taking place in distinct soil carbon pools (e.g. fresh plant litter, mycorrhizal fungal biomass, and soil organic matter at distinct depth levels) seems to differ (Cheeke et al, 2017;Frey, 2019), while we are still very far from understanding the full complexity of these exact patterns; (iii) Mechanisms underpinning the influences of ECMF and of ERMF on soil processes are likely to differ a lot (Lindahl et al, 2002), while many studies consider these two fungal guilds as a joint pool (e.g.…”