Jennifer Holm, research scientist at Berkeley Lab’s Climate and Ecosystem Science Division, is a collaborator with the NGEE-Tropics project and serves as the project liaison to E3SM’s Functionally Assembled Terrestrial Ecosystem Simulator (FATES). She was recently a guest feature on Aliyah Kovner’s A Day in the Half-Life podcast. Her appearance on the podcast was dedicated to explaining and demystifying the concept of climate models. For years, models have been employed by climate scientists to anticipate Earth’s long term weather patterns and conditions. Despite the long history of the technology and the importance of its function, many people are still uninformed of the details and significance of climate modeling. Luckily, scientists like Holm have been taking great strides to introduce the public to the ins and outs of these vital processes. While featured on the podcast, Holm detailed the goals of climate science and computing, the kinds of projections you can expect from the modeling processes, the impact the prediction technology has had, the history of climate modeling and the different eras the subject has undergone, and more. At the end, Holm states that the future of climate research will be dependent on the “human element” and the interactions between humans and the environment. We offer a big thank you to Holm for taking steps to bridge the information gap and reaching out to educate audiences. Listen to the full podcast here to learn more about what Jennifer has to say about climate change.

Headshot of Jennifer Holm

Berkeley Lab’s Earth and Environmental Sciences Area (EESA)’s Staff Scientist Robinson Negron-Juarez is going to receive an honorary degree from the National University of the Peruvian Amazon in July. Negron-Juarez has been a part of EESA since 2013, and has been making significant contributions to the Next Generation Ecosystem Experiments – Tropics project. He also created the Wildfire Research Element at EESA.  His research aims to understand the interactions between terrestrial ecosystems and climate conditions. Due to his work on understanding windthrow variability in the Central Amazons, his research on the vulnerability of forests due to severe storm conditions, and his use of Landsat imagery to detect treefall gaps, he has been recognized by the National University of the Peruvian Amazon for his research efforts. When Negron-Juarez isn’t continuing his contributions to the NGEE-Tropics project through his research on deep convection and extreme rainfall events on forestry dynamics, he’s supporting and encouraging indigenous scientists. We applaud his dedication to uplifting his fellow scientists, asking questions few think to ask, and his tireless efforts to discover the truth. Read more about Robinson’s research and this award from the National University of the Peruvian Amazon here.

Image courtesy of EESA’s News and Events site https://eesa.lbl.gov/robinson-negron-juarez-to-receive-honorary-degree/

Soil moisture thresholds of sap velocity.

The Science
Transpiration is the process of water moves through a plant from soil to atmosphere. In humid tropical rainforest region, soil water is recharged during the wet season to support dry season transpiration. Therefore, transpiration is often considered to be light- but not water limited in humid tropical rainforests. However, it’s not clear whether the tropical rainforests with abundant water will become water limited under extreme climate conditions. We used field data to examine dynamics of transpiration, soil water, and meteorological variables during the record-breaking 2015-16 El Niño drought in Central Amazon. We found a shift from light- to water-limitation of sap velocity, and identified a soil moisture threshold of water limitation in Central Amazon.

The Impact
This study suggests a progressively critical role of soil moisture under a drier future. This could happen in Central Amazon and other places that we previously thought have plenty of water. The soil moisture threshold provides a crucial benchmark to test and improve model simulations of future land-atmosphere feedbacks in Amazon under climate change, which are currently inadequate.

Summary
We measured sap velocity, soil water content, and meteorological variables in an old-growth upland forest in the Central Amazon throughout the 2015-16 drought. We found a rapid decline in sap velocity and in its temporal variability during the drought, accompanied by a marked decline in soil moisture and an increase in temperature and vapor pressure deficit. To understand water or light limitation, we examined the covariation of sap velocity with soil water content and net radiation using partial correlation analysis. We found sap velocity was largely limited by net radiation during normal dry seasons, but it shifted to be limited by soil water during drought. Next to identify the timing when this shift occurred, we used a moving window approach to conduct partial correlation analysis at every 10-day and examined how the coefficient changed during the whole period. We found the water stress started to occur in late August to early September in 2015. The soil moisture control continued throughout September, then became intermittent and disappeared after several rainfall events. During the strong water control period, the light control disappeared. We further identified the threshold of soil moisture at 0.33 m 3 /m 3 (around -150 kPa in soil matric potential).

Contact: Lin Meng, Lawrence Berkeley National Laboratory, Postdoc researcher, linmeng@lbl.gov

Funding
This work is supported by the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics), as part of DOE’s Terrestrial Ecosystem Science Program – Contract No. DE-AC02-05CH11231. We would like to thank the Large Scale Biosphere-Atmosphere Program (LBA), coordinated by the National Institute for Amazon Researches (INPA), for the use and availability of data, for logistical support and infrastructure during field activities.

Publications
Meng, Lin, et al. “Soil moisture thresholds explain a shift from light-limited to water-limited sap velocity in the Central Amazon during the 2015-16 El Niño drought.” Environmental Research Letters (2022), 17: 064023. https://doi.org/10.1088/1748-9326/ac6f6d

Large uncertainty exists in predictions of future transpiration due to complex interactions between plant physiology and the water and energy budgets.

The Science
Plant transpiration is the largest hydrologic flux of water globally, after precipitation, and therefore plays a large role in driving surface water availability. Transpiration responds to rising atmospheric CO₂ at stomatal to whole-plant to regional-scales, with feedbacks between scales. This study reviewed the biophysical mechanisms by which rising CO₂ impacts global scale plant transpiration. The authors then identify a path forward by which both empirical and modeling focused science approaches work together towards more mechanistic, evaluated prediction of transpiration under future conditions.

The Impact
Recent observations of rising plant transpiration at the global scale are consistent with increasing leaf area due to CO₂ fertilization, but at odds with the well-known stomatal closure response. This increasing water demand results from a complex set of interacting factors and mechanisms, many of which are non-linear. This paper ultimately provides a testable framework of hypotheses regarding how transpiration responds globally to rising atmospheric CO₂. The paper further serves as a call to arms for global empiricists and modelers to unify their efforts to better understanding and predicting transpiration under future conditions.

Summary
Here we review the myriad ways by which rising CO₂ can directly and indirectly influence plant transpiration at the global scale. Many compensating mechanisms and feedbacks make the prediction of transpiration challenging with rising CO₂. Global changes in plant transpiration in response to rising CO₂ will manifest through droughts, vapor pressure deficit, plant physiological processes including shifting leaf area and phenology, and through forest loss (disturbance). We place these mechanisms into a testable framework of hypotheses that outlines a path forward for both empiricists and modelers. The impacts of changing transpiration at large scales are significant for water provision and utilization demands.

Contacts: Sergio Vicente-Serrano, Instituto Pirenaico de Ecología, svicen@ipe.csic.es
Brian Benscoter, U.S. Department of Energy, Biological and Environmental Research (SC-33), Environmental System Science, brian.benscoter@science.doe.gov

Funding
This work was supported by the Spanish Ministry of Science and FEDER; CROSSDRO project financed by the AXIS – sectorial climate impacts and pathways for sustainable transformation, JPI-Climate co-funded call of the European commission; NGM and LRL were supported by the Department of Energy’s Next Generation Ecosystem Experiment-Tropics. DGM acknowledges support from the European Research Council. AK acknowledges support from the European Union Horizon 2020 program.

Publication
Vicente-Serrano S, Miralles D, McDowell N, Brodribb T Domínguez-Castro F, Leung R, Koppa A. The uncertain role of rising atmospheric CO₂ on global plant transpiration. Earth Science Reviews, p. 104055. https://doi.org/10.1016/j.earscirev.2022.104055

Soil phosphorus (P) negatively moderated the pantropical litterfall resistance to cyclones: A 100mg P/kg increase in soil P corresponds to a ~35% decrease in resistance.

The Science
Tropical cyclone regimes are shifting with climate change. In 2020, tropical cyclones affected 36 million people and caused $56 billion in damages globally. Changing tropical cyclone regimes may lead to long-lasting effects on tropical forests under climate change. This pantropical meta-analysis investigated the importance of total soil P in mediating forest litterfall (flux of dead plant material from the canopy to the forest floor) resistance (ability to withstand change) and resilience (capacity to return to pre-cyclone condition) to 22 tropical cyclones. Results showed that soil P negatively moderated the pantropical litterfall resistance to cyclones. As soil P increased by 100 mg P/kg, resistance decreased by 32% to 38%.

The Impact
Our results suggest that soil P will partially determine the pantropical forest litterfall resistance and resilience in the face of intensifying cyclone disturbance. This study is the first to document the pantropical role of phosphorus as a factor mediating tropical forest responses to cyclones. Litterfall mass and nutrient pulses caused by cyclones both respond and contribute to resource heterogeneity that can affect species regeneration, growth, and competitive interactions. Additional research can test how plant functional groups and species across pantropical forest ecosystems differ in their resistance and resilience to cyclones to represent cyclone disturbance responses in predictive modeling.

Summary
While the influence of tropical cyclone frequency and intensity on the structure and function of tropical forests have been widely studied, much less attention has been given to the role of resource availability on the functional stability of tropical forests across the globe in the face of cyclone disturbance. Single-site studies in Australia and Hawaii suggest that litterfall on low-phosphorus (P) soils is more resistant and less resilient to cyclones. We conducted a meta-analysis to investigate the pantropical importance of total soil P in mediating forest litterfall resistance and resilience to 22 tropical cyclones. We evaluated cyclone-induced and post-cyclone litterfall mass (g/m 2 /day), and P and nitrogen (N) fluxes (mg/m 2 /day) and concentrations (mg/g), all indicators of ecosystem function and essential for nutrient cycling.

Across 73 case studies in Australia, Guadeloupe, Hawaii, Mexico, Puerto Rico, and Taiwan, total litterfall mass flux increased from ~2.5 ± 0.3 to 22.5 ± 3 g/m 2 /day due to cyclones, with large variation among studies. Litterfall P and N fluxes post-cyclone represented ~5% and 10% of the average annual fluxes, respectively. Post-cyclone leaf litterfall N and P concentrations were 21.6 ± 1.2% and 58.6 ± 2.3% higher than pre-cyclone means. Mixed-effects models determined that soil P negatively moderated the pantropical litterfall resistance to cyclones, with a 100 mg P/kg increase in soil P corresponding to a 32% to 38% decrease in resistance. Based on 33% of the resistance case studies, total litterfall mass flux reached pre-disturbance levels within one-year post-disturbance. Across pantropical forests observed to date, our results indicate that litterfall resistance and resilience in the face of intensifying cyclones will be partially determined by total soil P. This work will support benchmarking of ELM-FATES predictions against pantropical ground data.

Contact: Barbara Bomfim, Postdoctoral researcher NGEE-Tropics, Lawrence Berkeley National Laboratory, bbomfim@lbl.gov

Funding
This research was supported as part of the Next Generation Ecosystem Experiments-Tropics (NGEE), funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. ORNL is managed by UT-Battelle, LLC, for the DOE. This research utilized data from Luquillo Long-Term Ecological Research (LTER) Program which is currently supported by NSF to the Institute for Tropical Ecosystem Studies, University of Puerto Rico, and to the International Institute of Tropical Forestry USDA Forest Service.

Publication
Bomfim, B., Walker, A.P., McDowell, W.H., Zimmerman, J.K., Feng, Y., Kueppers, L.M., Linking soil phosphorus with forest litterfall resistance and resilience to cyclone disturbance: a pantropical meta‐analysis. Global Change Biology gcb.16223 (2022) https://doi.org/10.1111/gcb.16223