Soils and rainfall drive landscape‐scale changes in the diversity and functional composition of tree communities in premontane tropical forest

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.

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“…2) and the high b-diversity across the gradient (Table 2), which is, in turn, due to high turnover of species with narrow elevation ranges (Jankowski et al 2013). Patterns in plant species composition and richness on tropical mountains are thought to be driven mainly by the effects of geographically narrow temperature ranges on niche separation (by directly affecting metabolism and indirectly affecting resource availability), further constrained by land area, lithology, fertility, and disturbance history (Janzen 1967, Colwell et al 2008, Prada et al 2017. Although the high landslide activity and soil erosion in the humid Eastern Andean Cordillera (Clark et al 2013) may be factors in constraining overall diversity at higher elevations in this region, our study identifies a central underlying role for temperature.…”

Section: Discussionmentioning

confidence: 99%

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

Nottingham¹,

Fierer²,

Turner³

et al. 2019

Bulletin Ecologic Soc America

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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.

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“…This area has a high mean annual precipitation (>6 m), a weak dry season with January–April precipitation above 300 mm rain per month (rainfall data 2007–2014, Prada et al. ), and a mean annual temperature of ~20°C (Andersen et al. ).…”

Section: Methodsmentioning

confidence: 99%

“…The Honda watershed soil is derived from rhyolitic tuff with relatively low plant available soil nutrients (Andersen et al 2010). This area has a high mean annual precipitation (>6 m), a weak dry season with January-April precipitation above 300 mm rain per month (rainfall data 2007-2014, Prada et al 2017), and a mean annual temperature of ~20°C (Andersen et al 2010). The soils at the site are classified as fine, kaolinitic, isothermic, Andic Haplohumults (i.e., Ultisols).…”

Section: Site and Species Selectionmentioning

confidence: 99%

Plasticity in nitrogen uptake among plant species with contrasting nutrient acquisition strategies in a tropical forest

Andersen

¹

,

Mayor

²

,

Turner

³

2017

Ecology

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Nitrogen (N) availability influences the productivity and distribution of plants in tropical montane forests. Strategies to acquire soil N, such as direct uptake of organic compounds or associations with root symbionts to enhance N acquisition in exchange for carbon (C), may facilitate plant species coexistence and ecosystem N retention. Alternatively, rapid microbial turnover of soil N forms in tropical soils might promote flexible plant N-uptake strategies and mediate species coexistence. We tested whether sympatric plant species with different root symbiont associations, and therefore potentially different nutrient acquisition strategies, partition chemical forms of N or show plasticity in N uptake in a tropical pre-montane forest in Panama. We traced the movement of three N forms into soil pools, microbes, and seedlings of eleven species differing in root traits. Seedlings were grown in a split-plot field transplant experiment, with plots receiving equimolar mixtures of ammonium, nitrate, and glycine, with one form isotopically labeled in each block. After 48 h, more N was recovered in microbes than in plants, while all pools (extractable organic and inorganic N, microbial biomass, and leaves) contained greater amounts of N from nitrate than from ammonium or glycine. Furthermore, C from dual-labeled glycine was not recovered in the leaves of any seedling, suggesting the studied species do not directly take up organic N or transform organic N prior to translocation to leaves. Nitrogen uptake differed by root symbiont group only for nitrate, with greater N recovery in plants with arbuscular mycorrhizal (AM) associations or proteoid roots compared to orchids. Some root trait groups differed in N recovery among N forms, with greater nitrate uptake than ammonium or glycine by AM-associated and N -fixing plants. However, only five of eleven species showed differences in uptake among N forms. These results indicate flexibility in uptake of N forms in tropical plants across root trait groups, with only a few species displaying weak preferences for a specific N form.

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Soils and rainfall drive landscape‐scale changes in the diversity and functional composition of tree communities in premontane tropical forest

Cited by 41 publications

References 61 publications

Microbes follow Humboldt: temperature drives plant and soil microbial diversity patterns from the Amazon to the Andes

Microbes follow Humboldt: temperature drives plant and soil microbial diversity patterns from the Amazon to the Andes

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

Plasticity in nitrogen uptake among plant species with contrasting nutrient acquisition strategies in a tropical forest

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