Microbes Follow Humboldt: Temperature Drives Plant and Soil Microbial Diversity Patterns from the Amazon to the Andes

Abstract

More than 200 years ago, Alexander von Humboldt reported that tropical plant species richness decreased with increasing elevation and decreasing temperature. Surprisingly, coordinated patterns in plant, bacterial, and fungal diversity on tropical mountains have not yet been observed, despite the central role of soil microorganisms in terrestrial biogeochemistry and ecology. We studied an Andean transect traversing 3.5 km in elevation to test whether the species diversity and composition of tropical forest plants, soil bacteria, and fungi follow similar biogeographical patterns with shared environmental drivers. We found coordinated changes with elevation in all three groups: species richness declined as elevation increased, and the compositional dissimilarity among communities increased with increased separation in elevation, although changes in plant diversity were larger than in bacteria and fungi. Temperature was the dominant driver of these diversity gradients, with weak influences of edaphic properties, including soil pH. The gradients in microbial diversity were strongly correlated with the activities of enzymes involved in organic matter cycling, and were accompanied by a transition in microbial traits towards slower-growing, oligotrophic taxa at higher elevations. We provide the first evidence of coordinated temperature-driven patterns in the diversity and distribution of three major biotic groups in tropical ecosystems: soil bacteria, fungi, and plants. These findings suggest that interrelated and fundamental patterns of plant and microbial communities with shared environmental drivers occur across landscape scales. These patterns are revealed where soil pH is relatively constant, and have implications for tropical forest communities under future climate change.

Host-associated microbiomes are predicted by immune system complexity and climate

“…Thus, increasing climatic variability appears to promote coexistence and diversity of external microbiomes, perhaps through ecological succession or dormancy mechanisms [5]. Nottingham et al [69] found that both plant diversity and soil microbiome diversity follow temperature (and elevation) gradients at a regional scale with more species under warmer conditions. At a global scale, the external plant microbiome richness was also negatively correlated with elevation (Pearson's correlation, N = 85, r = − 0.324, P = 0.002), but mean annual temperature was not significantly correlated with these plant microbiomes (r = − 0.174, P = 0.111).…”

Spatial and temporal turnover of soil microbial communities is not linked to function in a primary tropical forest

“…Bacteria are less sensitive to vegetation than soil fungi, especially in tropical forests (Barbaran et al 2015). Instead, shifts in bacterial community composition track environmental variation in soil nutrients as observed here and in Camenzind et al (2018), as well as moisture (Kivlin and Hawkes 2016b), temperature (Nottingham et al 2018), and pH (Alfaro et al 2017). Our study suggests that fungal responses to the environment are not linear: fungi were mostly sensitive to small changes in resource availability and moisture and large changes in pH, but these plateaued at intermediate levels of environmental dissimilarity.…”

Investigation of an Elevational Gradient Reveals Strong Differences Between Bacterial and Eukaryotic Communities Coinhabiting Nepenthes Phytotelmata

“…Of these microbial elevational gradient studies, only a handful have compared diversity patterns of syntopic microbes and macrobes coinhabiting the same microhabitats. The results of these studies have also been inconsistent, with some finding that microbes and macrobes follow concordant patterns of richness (generally decreasing richness with increasing elevation) [6,22], and others finding that microbes and macrobes exhibit differing patterns [21,25,40]. Other, more general analyses have found that bacteria and micro-eukaryotes respond differently to environmental factors within the same habitats, with eukaryotes having stronger dispersal limitation [41][42][43][44][45].…”

“…Microbes have not been as extensively studied in the context of elevational gradients, but the past decade has seen an increasing number of studies examining elevational patterns of bacteria in soil [6,[8][9][10][11][12][20][21][22] and to a lesser extent, aquatic habitats [23][24][25][26]. Similar studies have also been conducted for fungi [27][28][29][30][31][32][33][34][35] and protists [18,[36][37][38][39].…”