Smithsonian Institution Office of Fellowships and Internships

Help, a Tapir is Trying to Eat My Leaves! A Month of Plant Ecophysiology in Yasuní

Figure 5. Omaca, the sample eating Tapir (tried, but did not succeed). Jokes aside, a remarkable animal to be around while doing science! Photo credit: Benjamin Blonder.

It’s hard being a plant leaf - being eaten is a major risk. In tropical forests, ~10-15% (>70% in some species) of leaf area can be lost via herbivory (Cardenas et al., 2014; Coley & Barone, 1996). Plants may counteract herbivory via resistance, where chemical or mechanical defenses are used to deter herbivores, or resilience, where the effect of unavoidable damage is mitigated (Kursar & Coley, 1996). Each strategy predicts that certain leaf traits should be correlated with herbivory, but few consistent empirical relationships have been found (e.g., with leaf thickness, shear resistance, leaf age). Thus broad-scale predictions of herbivory response and impacts on forest productivity are challenging. Venation network traits may predict herbivory response, which vary widely across species. Networks with more looping (reticulate veins) have redundant flow pathways, which could increase damage resistance and/or improve resilience by limiting damage spread. However, linkages of looping with herbivory have not been explored.

Thus, we (Dr. Luiza Aparecido and Dr. Benjamin Blonder, Arizona State University-ASU*) packed our botanical plant presses (five of them!) and our portable photosynthesis machine (LI6800, Li-Cor Inc., Lincoln, NE) and headed to the Ecuadorian Amazon to investigate whether vein looping does indeed mitigate the effects on leaf gas exchange of a damaged vein network, in this case a simulated herbivory attack. Data collection was made possible due to a 2018 CTFS-ForestGEO research award and via collaboration with Yasuní principal investigator and Pontificia Universidad Católica del Ecuador (PUCE) professor, Dr. Renato Valencia, and PUCE collaborator Dr. Rafael Cárdenas.

The journey to Estación Científica Yasuní was not an easy feat. International travelling aside, the route from Quito included a 10-h bus ride, 1.5-h truck ride, 10-min canoe trip across the Rio Napo (Figure 1), and 2-h van ride to the station. However, all is worth it after arrival, secluded with tropical nature, other fellow field ecologists, and members of the local Huaorani Indigenous communities.

PI Benjamin Blonder and PUCE undergraduate student Emily Guevara Heredia crossing the Napo River in Ecuador towards Yasuni Scientific Station. Photo credit: Luiza Aparecido.

Our goal was to collect branch samples of a wide range of tree species (32 total) within the Smithsonian/ForestGEO 50-ha plot within Yasuní National Park (Ecuador). Samples were retrieved during the daytime for gas exchange measurements. Branches were placed in buckets filled with water (to maintain sample viability), and also treated to simulate an herbivory attack, by cutting major and minor veins (Figure 2). After gas exchange measurements were taken from treated and untreated leaves (Figure 3), they were scanned and dried out in an oven to be subsequently stored for future lab analyses at Arizona State University. Sample collection and leaf pressing were meticulously done by undergraduate senior Emily Guevara Heredia (PUCE), and field botanist Pablo Alviar (Yasuni) (Figure 4).

Figure 2. Undergraduate student Emily Guevara Heredia applies vein damage treatment to leaves. Photo credit: Benjamin Blonder.
Figure 3. Postdoctoral researcher Luiza Aparecido adjusts leaves before measuring gas exchange rates using a portable photosynthesis system (LI6800). Photo credit: Benjamin Blonder.
Figure 4. Field botanist Pablo Alviar prepares to cut a target branch while undergraduate student Emily Guevara Heredia waits for the felled sample. Photo credit: Luiza Aparecido.

Even though we were able to collect samples for all 32 species, not all samples were viable for gas exchange. The first limitation was time. Taking measurements of various branches from various species replicates was highly intensive. Some species did not acclimate or stabilize its metabolism while in a bucket of water, so there were numerous branch samples and time lost. In the end, we were able to collect high quality gas exchange data from 20 species. Other challenges encountered in the field included: species that were hard to find (once again, time running out); dodging storms and floods; branches that were too old or too herbivorized for measurements; insects affecting the machine mechanics; branches with such hard wood that the pruner did not work; thousands of leaves to scan and keep track; and many other tropical creature encounters.

But nothing tops our interactions with a local tapir (named Omaca) who often visited the station, and for more than a few days tried to eat our samples (Figure 5). We had not planned for any ‘real’ herbivory in the study - only simulated damage! Fortunately she was friendly enough, and placated with other branches and fruits from the station grounds. But, overall, measuring gas exchange in such exuberant forest alongside interesting people made the whole trip a wonderful experience.

After 20 days of gas exchange measurements and data collection, we headed back to Quito and later Phoenix, Arizona (USA) to proceed with our leaf venation analyses. This process involves chemically clearing leaves, in which non-lignified tissue is dissolved, leaving only the vein structures of the leaf. Our PUCE bachelors’ thesis student Emily was an essential part of this process, in which she not only brought all the dried leaf samples from Ecuador but also was able to stay with our team in the United States for several months, leading efforts to complete at least one whole-leaf and one microscope slide of the vein architecture sample from each species (Figure 6). Believe me, this was no easy task!

Figure 6. Ecuadorian undergraduate student Emily Guevara Heredia shows pressed leaf samples collected in Ecuador at Arizona State University before fragmenting samples for chemical processing and future microscope mounting. Photo credit: Luiza Aparecido.

Currently, we are working hard on retrieving the leaf venation parameters from these samples (Figure 7), in which looping and vein density are our main parameters to be correlated to gas exchange dynamics after vein damage. Preliminary results from gas exchange measurements indicate a large variability of responses among species. Some species decreased gas exchange rates when both major and minor veins were damaged; while other species decreased one over the other, or increased (interestingly!), or no effect at all from damage. We are hoping that vein parameters and other leaf traits (such as leaf mass per area) will help us explain these highly variable responses. This study will not only excel in the field of leaf ecophysiology, but will most certainly strengthen our understanding on how various defense mechanisms and resource allocation strategies can balance the effect of stressors within highly biodiverse ecosystems.

*Benjamin Blonder’s lab has now moved to the University of California, Berkeley.

Figure 7. Vein architecture of a Inga umbratica leaf sample after undergoing chemical processing. Sample processing and image credit: Emily Heredia (PUCE undergraduate student), Miguel Duarte and Martha Ryan (both ASU undergraduate students).

REFERENCES

Cárdenas RE, Valencia R, Kraft NJB, Argoti A, & Dangles O (2014) Plant traits predict inter- and intraspecific variation in susceptibility to herbivory in a hyperdiverse Neotropical rain forest tree community. Journal of Ecology 102(4):939-952.

Coley PD & Barone J (1996) Herbivory and plant defenses in tropical forests. Annual Review of Ecology and Systematics 27(1):305-335.

Kursar TA & Coley PD (2003) Convergence in defense syndromes of young leaves in tropical rainforests. Biochemical Systematics and Ecology 31(8):929- 949.

Benjamin Blonder

Benjamin Blonder is an ecologist focusing on plant response to climate change, past and present. He received his PhD at the University of Arizona and was a Natural Environment Research Council independent research fellow at the Environmental Change Institute at the University of Oxford (England). Currently, he is an assistant professor at the University of California at Berkeley in the Department of Environmental Science, Policy, and Management and previously was assistant professor at Arizona State University’s School of Life Sciences. Dr. Blonder also maintains a long-term research program at the Rocky Mountain Biological Laboratory. He is also interested in improving science education through experiential approaches. He co-founded the University of Arizona Sky School, a program that provides inquiry-based outdoor science education to K-12 students throughout the southwest.

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Luiza Aparecido

Luiza Aparecido is a Brazilian plant ecologist and forest engineer that has worked in extreme sites, such as the Amazon and Sonoran desert. She earned her PhD at Texas A&M University, and has been a postdoctoral research scholar at Arizona State University since 2018. Her background is strongly based on forest biometry and sampling; phytosociological surveys; plant functional biology; plant ecophysiology; wood anatomy and hydraulics; and environmental biophysics. Dr. Aparecido is focused on investigating how plant communities function in response to disturbances (climatic or physical), and how that can be applied to models and conservation practices.

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