Though we work across scales (from individual root branches, to the globe!), the uniting theme behind our research is always nutrients. How do plants get them? What economic trade-offs determine plant nutritional strategy? How does this plant behavior influence the cycling of nutrients through their ecosystems? And how will nutrients drive– and constrain– plant and soil responses to global change? Much of our research takes place in tropical forests, among the most biologically diverse and productive ecosystems on earth. One of the great outstanding questions in these systems is how remarkably large variability in tree functional and chemical traits influences biogeochemical cycling of carbon, nitrogen and phosphorus, and how these interactions might shape the future of these remarkable biomes and their interactions with global climate.
 
We approach these questions using a combination of theory, field sampling, greenhouse experiments, and tools from ecosystem ecology, biogeochemistry, and plant ecophysiology. We are especially interested in interfacing with modelers striving to represent these processes in statistical and earth system models. A few of our lab themes include...

Identifying patterns and drivers (functional, environmental, and phylogenetic) of nutritional strategies in tropical trees

• Dallstream et al. A framework for fine‐root trait syndromes: syndrome coexistence may support phosphorus partitioning in tropical forests
• Marcellus et al. Evolutionary history and root trait coordination predict nutrient strategy in tropical legume trees ​
• Dallstream et al. Strong scale-dependent relationships between fine-root function and soil conditions uncovered with spatially-coupled sampling. ​
• Soper et al. Nitrogen fixation and foliar nitrogen do not predict phosphorus acquisition in tropical trees
• BNF-EXUDE project (Gautreau): How does N fixation integrate with exudation-driven nutritional strategies?

Improving estimation and scaling of symbiotic nitrogen fixation

• Soper et al. A roadmap for sampling and scaling biological nitrogen fixation in terrestrial ecosystems
• Soper et al. Measuring nitrogen fixation by the acetylene reduction assay (ARA): is 3 the magic ratio?
• Reis et al. Global terrestrial nitrogen fixation and its modification by agriculture.

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Measuring and modeling nitrogen cycling in tropical forests

• Nelson (AGU): Identifying blind spots in our understanding of the tropical nitrogen cycle
• NOVA N2O project (Nelson): Effects of drought and warming on tropical forest denitrification
• Soper et al. Remotely sensed canopy nitrogen correlates with N2O emissions in a lowland tropical rainforest 
• Soper et al. Modest  gaseous N losses support conservative N cycling in a lowland tropical rainforest watershed
• Soper et al.  Leaf cutter ants engineer large N2O hot spots in tropical forests

​Drivers of intraspecific variation in plant stoichiometry

• AusStoich project (Sanabria): drivers of stoichiometry in the Australian flora
• Dynarksi et al. Patterns and controls of foliar nutrient stoichiometry and flexibility across United States forests​​​

 We love to collaborate! Soper Lab members can be found working with:
 

• Tropiroot (the Tropical Root Trait Initiative) is a collaboration synthesizing pan-tropical root trait data to understand root functional ecology, represent roots in models, and forecast responses to global change.
• The USGS Powell Center Nitrogen Fixation working group synthesizes global patterns and controls on nitrogen fixation.
• INCyTE (Investigating Nutrient Cycling in Tropical Ecosystems) NSF Research Coordination Network  brings modelers and experimentalists together to think about how to better represent nutrient feedbacks to the global carbon cycle in earth system models.​​

Previous research: ​Woody encroachment

“Tree cover is one of the defining variables of landscapes, their ecological functioning, and their  impact on climate"
                                                                                                                                 Hirota et al (2011) Science

The encroachment of trees and shrubs into natural and managed savannas and grasslands has been occurring on a substantial scale for the past 50-300 years across the globe. This significant shift in the plant community and its functional traits has implications for agricultural productivity, land use, biogeochemical cycling, habitat availability and many other processes. 

Many encroaching species are nitrogen-fixing legumes. By converting potentially large quantities of atmospheric nitrogen into a bioavailable form these species can significantly affect biogeochemical cycling in the systems they invade.

My research on encroachment of Prosopis glandulosa into the subtropical, semi-arid grasslands of south Texas explored three broad themes: 

1. Developing natural abundance stable isotope sampling methods to identify temporal variation in nitrogen fixation in leguminous trees
2. Using soil chronosequences to identify decadal-scale patterns of nitrogen fixation during woody encroachment
3. Quantifying changes in nitrogen trace gas emissions and denitrification during encroachment, and how these are modulated by climate (Also here)