Alpine Plant Traits, Soil Processes, and Climate Gradients

Aboveground plant communities are tightly linked to belowground systems, including soil microbes, mycorrhizal fungi, and the processes they drive: soil respiration (the release of CO2 from soils), nitrogen mineralization (conversion of organic nitrogen into plant-available forms), and extracellular enzyme activity (microbial enzymes that break down organic matter). Together these belowground processes regulate carbon and nutrient cycling, controlling whether a meadow is a net source or sink of carbon. A recurring theme in RMBL-area research is dominant species removal: experimentally pulling out the most abundant plant (such as the bunchgrass Festuca thurberi) to test whether ecosystem function hinges on a few key species or is buffered by the wider community. Researchers increasingly combine these removals with experimental warming, often using open-top chambers, to disentangle the direct effects of climate from indirect effects mediated by changes in plant composition.

Foundational work

Early synthesis papers established the conceptual scaffolding for this neighborhood. Sundqvist and colleagues showed that elevational gradients are powerful but complicated tools for understanding global change, because temperature, precipitation, and soil properties all shift together (Sundqvist et al., 2013). Global syntheses then quantified how plant traits track climate, finding that mean annual temperature explains more variation in plant traits than precipitation does (Moles et al., 2014), and that warming can drive substantial losses of soil carbon, especially where soil carbon stocks are large (Crowther et al., 2016).

At RMBL specifically, foundational measurements documented that leaf mass per area and root mass per length both decrease with elevation across many species, suggesting consistent trait shifts with the cold, short seasons of higher meadows. Early water-addition experiments revealed that belowground processes respond to changes in moisture on shorter timescales than aboveground plant growth does, foreshadowing the importance of separating short-term microbial responses from longer-term plant community change. Globally, Mayor and colleagues showed that elevation drives convergent shifts in nutrient stoichiometry across treeline ecosystems, linking plant nutrient content to changes in soil organic matter and microbial properties (Mayor et al., 2017).

Key findings

A central insight from RMBL is that intraspecific variation, differences in traits within a single species, can be as important as differences between species. Read and colleagues showed that within-species trait variation along the West Elk Mountains gradient was higher than global averages and actually swamped interspecific variation, making trait-based models of community composition perform worse than a simple null model (Read et al., 2017). For root traits, almost all variation occurred within rather than between species. This means that a single species growing at different elevations can effectively become a different functional entity.

Dominant species removal and nitrogen addition experiments have repeatedly shown that montane communities are surprisingly resilient. Four years after removing the dominant Festuca thurberi, communities converged back toward the original dominant's traits, while inorganic nitrogen addition boosted aboveground biomass by about 60% without changing species diversity (Read et al., 2017). Fungal partnerships also proved robust: arbuscular mycorrhizal and dark septate endophyte colonization of co-dominant Helianthella quinquenervis did not change after years of nitrogen addition or dominant removal, although proximity to neighboring plants strongly shaped colonization patterns (Henning et al., 2019). Plant removals also had only marginal effects on nitrogen mineralization rates, though they significantly reduced the variability of those rates across the elevation gradient (Rewcastle et al., 2022).

Integrating biodiversity with ecosystem function, Prager and colleagues found that taxonomic, functional, and phylogenetic diversity were each positively linked to peak growing season carbon uptake, but in a combined model only phylogenetic diversity remained a direct driver, with climate acting indirectly through biodiversity (Prager et al., 2021). Belowground patterns, meanwhile, defy simple rules: a global meta-analysis found no consistent relationship between soil microbial diversity and either temperature or soil pH, with linear, humped, trough-shaped, and flat patterns all equally likely across studies (Hendershot et al., 2017).

Current frontier

Research since 2020 has shifted from documenting patterns to explicitly testing how warming and species loss interact, and how those interactions vary across elevations. The Warming and Removal in Mountains (WaRM) network, anchored at RMBL, combines passive warming with dominant species removal at high- and low-elevation sites and uses distributed experiments to overcome the limitations of single-site studies (Prager et al., 2022). Results from this framework show that effects are highly context dependent: warming roughly doubled soil respiration at low elevation but had no detectable effect at high elevation (Sharon, 2020), and warming combined with dominant removal produced interactive effects on microbial biomass and enzyme activity that neither treatment produced alone (Spinella et al., 2024). Plant community responses were similarly site-specific, with warming reducing biomass at low elevation but only removal affecting biomass at high elevation (Calhoun, 2020).

The newest frontier uses whole-community transplants to simulate climate change directly. Moving intact turfs of plants and soil across a 400-meter elevation gradient, Seltzer (Seltzer, 2025) found that soil bacteria and archaea responded fastest to warming, followed by fungi and then plants, with communities shifting within one to two growing seasons to resemble those at the destination elevation. Trait composition shifted from fast-growth strategies toward conservation and survival strategies under warming. Cooling responses were weaker and slower, hinting at asymmetry in how mountain ecosystems will track climate change.

Open questions

Key uncertainties remain about how aboveground and belowground communities will stay coupled as they respond at different speeds, whether the resilience observed over four to six years of manipulation will hold over decades, and how interactions between warming, drought, nitrogen deposition, and species loss will play out as multiple stressors accumulate. The role of intraspecific trait variation in buffering or amplifying community responses to warming is poorly understood, as is the question of whether dominant species at high elevations will continue to anchor ecosystem function or be replaced by upslope migrants. Better integration of distributed experiments, long-term natural gradients, and emerging tools like hyperspectral imaging will be essential for predicting how the meadows of the Gunnison Basin will look, function, and cycle carbon by mid-century.

References

Calhoun, M. (2020). Investigating alpine plant community responses to simulated warming and dominant species removal at a low and high elevation in the Colorado Rocky Mountains. →

Crowther, T.W., Todd-Brown, K.E.O., Rowe, C.W., Wieder, W.R., Carey, J.C. (2016). Quantifying global soil carbon losses in response to warming. Nature. →

Hendershot, J.N., Read, Q.D., Henning, J.A., Sanders, N.J., Classen, A.T. (2017). Consistently inconsistent drivers of patterns of microbial diversity and abundance at macroecological scales. Ecology. →

Henning, J.A., Read, Q.D., Sanders, N.J., Classen, A.T. (2019). Fungal colonization of plant roots is resistant to nitrogen addition and resilient to dominant species losses. Ecosphere. →

Kattge, J., Bönisch, G., Díaz, S., Lavorel, S., Prentice, I.C., Leadley, P., Wirth, C. (2020). TRY plant trait database - enhanced coverage and open access. Global Change Biology. →

Mayor, J.R., Sanders, N.J., Classen, A.T., Bardgett, R.D., et al. (2017). Elevation alters ecosystem properties across temperate treelines globally. Nature. →

Moles, A.T., Perkins, S.E., Laffan, S.W. (2014). Which is a better predictor of plant traits: temperature or precipitation? Journal of Vegetation Science. →

Prager, C.M., Boelman, N.T., Eitel, J.U.H., Gough, L., Greaves, H.E., et al. (2021). Climate and multiple dimensions of plant diversity regulate ecosystem carbon exchange along an elevational gradient. Ecosphere. →

Prager, C.M., Classen, A.T., Sundqvist, M.K., Barrios-Garcia, M.N., et al. (2022). Integrating natural gradients, experiments, and statistical modeling in a distributed network experiment: An example from the WaRM Network. Ecology and Evolution. →

Read, Q.D., Henning, J.A., Classen, A.T., Sanders, N.J. (2017). Aboveground resilience to species loss but belowground resistance to nitrogen addition in a montane plant community. Journal of Plant Ecology. →

Read, Q.D., Henning, J.A., Sanders, N.J. (2017). Intraspecific variation in traits reduces ability of trait-based models to predict community structure. Journal of Vegetation Science. →

Rewcastle, K.E., Henning, J.A., Read, Q.D., Sanders, N.J., Classen, A.T. (2022). Plant removal across an elevational gradient marginally reduces rates, substantially reduces variation in mineralization. Ecology. →

Seltzer, L. (2025). The impacts of environmental change on plant and microbial communities: A turf transplant experiment in the Colorado Rocky Mountains. →

Sharon, A. (2020). The Impact of Warming and Species Removal on Soil Respiration at Low and High Elevations. →

Spinella, J., Rewcastle, K.E., Henning, J.A., Classen, A.T. (2024). Context dependence of warming induced shifts in montane soil microbial functions. Functional Ecology. →

Sundqvist, M.K., Sanders, N.J., Wardle, D.A. (2013). Community and Ecosystem Responses to Elevational Gradients: Processes, Mechanisms, and Insights for Global Change. Annual Review of Ecology, Evolution, and Systematics. →

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