Soil respiration response to decade-long warming modulated by soil moisture in a boreal forest.
July 18, 2024
 

     "The effects of long-term climate warming on soil respiration and its drivers remain unclear in forests, which store approximately 40% of global soil carbon. Here we conducted a climate change experiment for 13 years in forest plots planted with tree juveniles at two southern boreal forest sites. Treatments included simultaneous above- and below-ground warming (ambient, +1.7 °C and +3.3 °C) under different rainfall scenarios (100% and 60% of summer rainfall) and contrasting overstory canopy openness (open and closed). Soil respiration increased by 7% and 17% under +1.7 °C and +3.3 °C warming, respectively, averaged across all sites, treatments and years. These increases in respiration were higher than impacts per degree warming of the only two prior long-term, but soil-only, forest warming experiments. Moreover, warming effects on soil respiration varied significantly over time. Under almost all conditions, moist soil exhibited a greater increase in respiration in response to warming than dry soil. Our results suggest that a realistic range of anticipated conditions, including both above- and below-ground temperature and moisture, should be accounted for when predicting warming effects on soil respiration." 

Liang, G., Stefanski, A., Eddy, W. C., Bermudez, R., Montgomery, R. A., Hobbie, S. E., Rich, R. L., & Reich, P. B.

​

Integrated Effects of Site Hydrology and Vegetation on Exchange Fluxes and Nutrient Cycling at a Coastal Terrestrial-Aquatic Interface.
April 16, 2024
 

     "The complex interactions among soil, vegetation, and site hydrologic conditions driven by precipitation and tidal cycles control the biogeochemical transformations and bi‐directional exchange of carbon and nutrients across the terrestrial–aquatic interfaces (TAIs) in coastal regions. This study uses a highly mechanistic model, Advanced Terrestrial Simulator (ATS)‐PFLOTRAN, to explore how these interactions affect exchanges of materials and carbon and nitrogen cycling. We used a transect in the Chesapeake Bay region that spans zones of open water, coastal wetland, transition, and upland forest. We designed several simulation scenarios to parse the effects of the individual controlling factors and the sensitivity of carbon cycling to reaction rate parameters derived from laboratory experiments. Our simulations reveal an active zone for carbon cycling under the transition zones between the wetland and the upland. Evapotranspiration is found to enhance the exchange fluxes between the surface and subsurface domains, resulting in a higher dissolved oxygen concentration in the TAIs. The transport of organic carbon derived from plant leaves and roots provide an additional source of organic carbon needed for the aerobic respiration and denitrification processes in the TAIs. The variability in reaction rate parameters associated with microbial activities is also found to play a dominant role in controlling the heterogeneity and dynamics of the simulated redox conditions. This modeling‐focused exploratory study enabled us to better understand the complex interactions among soil, water and microbes that govern the hydro‐biogeochemical processes at the TAIs, which is an important step toward representing coastal ecosystems in larger‐scale Earth system models" 

Li, B., Li, Z., Zheng, J., Jiang, P., Holmquist, J., Regier, P. J., Hammond, G. E., Ward, N. D., Myers-Pigg, A., Rich, R., Huang, W., O’Meara, T. A., Pennington, S. C., Megonigal, P., Bailey, V. L., & Chen, X.

​

Effects of Warming and Elevated CO2 on Stomatal Conductance and Chlorophyll Fluorescence of C3 and C4 Coastal Wetland Species.
March 19, 2024
 

     "Coastal wetland communities provide valuable ecosystem services such as erosion prevention, soil accretion, and essential habitat for coastal wildlife, but are some of the most vulnerable to the threats of climate change. This work investigates the combined effects of two climate stressors, elevated temperature (ambient, + 1.7 °C, + 3.4 °C, and 5.1 °C) and elevated CO2 (eCO2), on leaf physiological traits of dominant salt marsh plant species. The research took place at the Salt Marsh Accretion Response to Temperature eXperiment (SMARTX) at the Smithsonian Environmental Research Center, which includes two plant communities: a C3 sedge community and a C4 grass community. Here we present data collected over five years on rates of stomatal conductance (gs), quantum efficiency of PSII photochemistry (Fv/Fm), and rates of electron transport (ETRmax). We found that both warming and eCO2 caused declines in all traits, but the warming effects were greater for the C3 sedge. This species showed a strong negative stomatal response to warming in 2017 and 2018 (28% and 17% reduction, respectively in + 5.1 °C). However, in later years the negative response to warming was dampened to < 7%, indicating that S. americanus was able to partially acclimate to the warming over time. In 2022, we found that sedges growing in the combined + 5.1 °C eCO2 plots exhibited more significant declines in gs, Fv/Fm, and ETRmax than in either treatment individually. These results are important for predicting future trends in growth of wetland species, which serve as a large carbon sink that may help mitigate the effects of climate change." 

Sendall, K. M., Muñoz, C. M. M., Ritter, A. D., Rich, R. L., Noyce, G. L., & Megonigal, J. P.NAMES HERE

​

Time to anoxia: Observations and predictions of oxygen drawdown following coastal flood events.
March 8, 2024
 

     "The coastal terrestrial-aquatic interface (TAI) is a highly dynamic system characterized by strong physical, chemical, and biological gradients. In particular, shifting soil redox conditions and consumption of terminal electron acceptors, due in part to dynamic hydrologic conditions, is a strong driver of carbon availability and transformations across TAIs. However, while redox dynamics are well described, our ability to quantitatively forecast rates of oxic to anoxic shifts in soils with different characteristics and inundation regimes is limited. We integrated field measurements, laboratory incubations, and model simulations to improve mechanistic understanding of oxygen consumption dynamics in coastal soils. Continuous in situ monitoring unexpectedly revealed that flooding caused temporary spikes in subsurface dissolved oxygen followed by rapid consumption in the wetlands. To further investigate these mechanisms in a controlled setting, we performed laboratory incubations using surface and subsurface soils from a TAI gradient (defined here as upland forest to transitional forest to wetland) in Western Lake Erie to measure oxygen consumption rates in TAI soils during flood events. In our experiments, wetland soils reached anoxia the fastest, in ∼ 9 h on average, whereas upland soils turned anoxic in ∼ 18 h. Subsurface upland soils did not turn anoxic even after two weeks of saturation in the lab, and their oxygen consumption patterns suggested carbon and/or nutrient limitation. These results are consistent with in-situ groundwater redox and oxygen measurements in the field, where wetland soils exhibited the highest rates of oxygen consumption along the TAI. Model simulations of oxygen consumption suggested that oxygen consumption had stronger abiotic controls in wetland soils but stronger biotic controls in upland soils, providing a useful framework for future incubation experiments. Microbial activity is a strong driver of oxygen consumption in TAI soils, although it is constrained by the availability of dissolved carbon in subsurface soils." 

Patel, K. F., Rod, K. A., Zheng, J., Regier, P., Machado-Silva, F., Bond-Lamberty, B., Chen, X., Day, D. J., Doro, K. O., Kaufman, M. H., Kovach, M., McDowell, N., McKever, S. A., Megonigal, J. P., Norris, C. G., O’Meara, T., Peixoto, R. B., Rich, R., Thornton, P., … Bailey, V. L.

​

Developing a redox network for coastal saltmarsh systems in the PFLOTRAN reaction model.
March 8, 2024
 

     "Coastal ecosystems have been largely ignored in Earth system models but are important zones for carbon and nutrient processing. Interactions between water, microbes, soil, sediments, and vegetation are important for mechanistic representation of coastal processes and ecosystem function. To investigate the role of these feedbacks, we used a reactive transport model (PFLOTRAN) that has the capability to be connected to the Energy Exascale Earth System Model (E3SM). PFLOTRAN was used to incorporate redox reactions and track chemical species important for coastal ecosystems as well as define simple representations of vegetation dynamics. Our goal was to incorporate oxygen flux, salinity, pH, sulfur cycling, and methane production along with plant-mediated transport of gases and tidal flux. Using porewater profile and incubation data for model calibration and evaluation, we were able to create depth-resolved biogeochemical soil profiles for saltmarsh habitat and use this updated representation to simulate direct and indirect effects of elevated CO2 and temperature on subsurface biogeochemical cycling. We found that simply changing the partial pressure of CO2 or increasing temperature in the model did not fully reproduce observed changes in the porewater profile, but the inclusion of plant or microbial responses to CO2 and temperature manipulations was more accurate in representing porewater concentrations. This indicates the importance of characterizing tightly coupled vegetation-subsurface processes for developing predictive understanding and the need for measurement of plant-soil interactions on the same time scale to understand how hotspots or moments are generated." 

O’Meara, T. A., Yuan, F., Sulman, B., Noyce, G., Rich, R., Thornton, P., & Megonigal, J. P.

​

Design and Assessment of a Novel Approach for Ecosystem Warming Experiments in High-Energy Tidal Wetlands
October 30th, 2023
Roy Rich published a paper on the MERIT experiment in JGR: Biogeoscience! Nice work Roy! 

     "The Marsh Ecosystem Response to Increased Temperatures (MERIT) experiment was established in 2018 on the North Sea coast of Germany. Experimental plots are evenly distributed over three elevational marsh zones (pioneer, low marsh, and high marsh) and include three temperature treatments (ambient, +1.5°C, +3.0°C). MERIT's novel design combines active warming (horizontal surface warming cables and vertical soil warming pins) with passive, partially covered domes. The combination of passive aboveground warming with feedback-controlled active surface and belowground heating provides a setup for understanding warming effects on tidal ecosystems without altering the natural impacts of wind, radiation, and tidal inundations at high-energy coastlines. Our design creates opportunities to expand future warming experiments to remote locations and technically challenging environments." 

Roy L. Rich, Peter Mueller, Miriam Fuß, Salomé Gonçalves, Eva Ostertag, Svenja Reents, Hao Tang, Allegra Tashjian, Simon Thomsen, Lars Kutzbach, Kai Jensen, Stefanie Nolte

​

A hydrogeophysical framework to assess infiltration during a simulated ecosystem-scale flooding experiment.
September 8, 2023
 

     "This study presents a framework to quantify changes in soil saturation in response to flooding caused by extreme hydrologic perturbation on coastal ecosystems at the interfaces and transition between terrestrial and aquatic systems. Subsurface heterogeneity limits the use of in situ measurements to quantify subsurface flow during flooding due to the spatial discontinuity in the measured data. While geophysical methods, including time-lapse electrical resistivity imaging (ERI), are increasingly used to monitor soil hydrological processes, their abilities to parameterize flow models have been underutilized. This study combines background ERI, ground penetrating radar (GPR), time-lapse ERI, soil characterization, and a numerical flow model developed using an Advanced Terrestrial Simulator (ATS) code to quantify the infiltration pathway and describe the hydrological dynamics during a simulated flooding experiment. We assessed the use of two conceptual models developed using [1] ERI and GPR data that described the stratigraphic distribution, and time-lapse ERI that mapped permeability contrast, and [2] information from a national soil database for capturing changes in saturation. Combining the ERI and GPR results with soil core data revealed the stratigraphic heterogeneity at the site with a silty clay layer from 1 to 2 m between an overlying loamy topsoil and an underlying saturated silty sand. This silty clay layer could restrict deep infiltration. The time-lapse ERI showed up to a 35% decrease in resistivity, which correlated with soil moisture data (R2 value > 0.53) and revealed preferential infiltration zones used to inform the flow model. Numerical simulation results from both the geophysics- and soil database-informed models quantified changes in soil saturation with calculated soil moistures that agreed with field data. The geophysics-informed model captured more of the system’s variability, reflective of shallow subsurface heterogeneities. The framework presented will serve as a precursor for a robust ecohydrological model that can describe the impacts of extreme events induced by climate change on coastal ecosystems." 

Adebayo, M. B., Bailey, V. L., Chen, X., Hopple, A. M., Jiang, P., Li, B., Li, Z., Martin-Hayden, J. M., Megonigal, J. P., Regier, P. J., Rich, R., Stegen, J. C., Smith, R. W., Ward, N. D., Woodard, S. C., & Doro, K. O.

​

Oxygen priming induced by elevated CO2 reduced carbon accumulation and methane emission in coastal wetlands
January 5, 2023
Genevieve published a paper in Nature Geoscience on the SMARTX elevated CO2 and warming experiment!

     "Warming temperatures and elevated CO2 are inextricably linked global change phenomena, but they are rarely manipulated together in field experiments. As a result, ecosystem-level responses to these interacting facets of global change remain poorly understood. Here we report on a four-year field manipulation of warming and elevated CO2 in a coastal wetland. Contrary to our expectations, elevated CO2 combined with warming reduced the rate of carbon accumulation due to increases in plant-mediated oxygen flux that stimulated aerobic decomposition via oxygen priming. Evidence supporting this interpretation includes an increase in soil redox potential and a decrease in the nominal oxidation state of the dissolved organic carbon pool. While warming alone stimulated methane (CH4) emissions, we found that elevated CO2 combined with warming reduced net CH4 flux due to plant–microbe feedbacks. Together, these results demonstrate that ecosystem responses to interacting facets of global change are mediated by plant traits that regulate the redox state of the soil environment. Thus, plant responses are critical for predicting future ecosystem survival and climate feedbacks." 

Genevieve L. Noyce, Alexander J. Smith, Matthew L. Kirwan, Roy L. Rich  & J. Patrick Megonigal

​

Even modest climate change may lead to major transitions in boreal forests
August 10, 2022
Roy published a paper in Nature on the impacts of warming in southern boreal forests!

“The sensitivity of forests to near-term warming and associated precipitation shifts remains uncertain. Herein, using a 5-year open-air experiment in southern boreal forest, we show divergent responses to modest climate alteration among juveniles of nine co-occurring North American tree species.” 

Reich, P.B., Bermudez, R., Montgomery, R.A., Rich, R.L., Rice, K.E., Hobbie, S.E., and Stefanski, A. (2022).

 

Considering coasts: Adapting terrestrial models to characterize coastal wetland ecosystems
June 15, 2021
Genevieve, Roy, and Pat published modified E3SM models to mimic tidal marsh dynamics and SMARTX findings in Ecological Modeling!

“The Energy Exascale Earth System Model (E3SM) simulates fully coupled processes and interactions among water, energy, carbon and nutrient cycles. E3SM connects vegetation and soil dynamics through nutrient uptake, plant production, litterfall and decomposition as a function of abiotic parameters (e.g. temperature and moisture). However, E3SM is designed to characterize terrestrial ecosystems and connects land and open ocean systems using a single streamflow transport term, ignoring the complex dynamics of energy, water, carbon, and nutrients in coastal systems. The goals of our project were to: (1) Parameterize a point version of E3SM to capture coastal wetland habitats and (2) Determine marsh community responses to increased temperature and elevated CO₂.” 

O’Meara, T.A., Thornton, P.E., Ricciuto, D.M.,Noyce, G. L., Rich, R.L., and Megonigal, J. P. (2021).

 

Biogeochemical and plant trait mechanisms drive enhanced methane emissions in response to whole-ecosystem warming
April 19, 2021
Genevieve and Pat published findings from SMARTX in Biogeosciences!

“Climate warming perturbs ecosystem carbon (C) cycling, causing both positive and negative feedbacks on greenhouse gas emissions. In 2016, we began a tidal marsh field experiment in two vegetation communities to investigate the mechanisms by which whole-ecosystem warming alters C gain, via plant-driven sequestration in soils, and C loss, primarily via methane (CH₄) emissions. Here, we report the results from the first 4 years.”

Noyce, G. L. and Megonigal, J. P. (2021).

 

Synergistic effects of four climate change drivers on terrestrial carbon cycling
November 23, 2020
Roy published a paper in Nature Geoscience with TeRaCON collaborators!

"Disentangling impacts of multiple global changes on terrestrial carbon cycling is important, both in its own right and because such impacts can dampen or accelerate increases in atmospheric CO₂ concentration. Here we report on an eight-year grassland experiment, TeRaCON, in Minnesota, United States, that factorially manipulated four drivers: temperature, rainfall, CO₂ and nitrogen deposition.”

Reich, P. B., Hobbie, S. E., Lee, T. D., Rich, R., Pastore, M. A., & Worm, K. (2020). 

 

Nothing to see here, check back soon!