Harvard Forest >

Summer Research Project 2024

• Title: Tracking Carbon from Soils to Sky
• Group Project Leader: Jackie Matthes
• Mentors: Raydaliz Cancel; Jonathan Gewirtzman; Marissa Hanley; Naomi Hegwood; Ashley Keiser; Hannah Naughton
• Collaborators:
• Project Description:

  Overarching Intellectual Theme:
  
  Forest and wetland ecosystems play a critical role in the global carbon cycle that influences the net amount of carbon dioxide and methane in the atmosphere. Trees take up carbon dioxide from the atmosphere through photosynthesis and store complex carbon within their biomass, and they release carbon dioxide through cellular respiration. The metabolism of soil microbes is fueled by the decomposition of biomass and other plant substrates that produce carbon dioxide. Under low oxygen conditions, for example in flooded soils and inside tree trunks, a specialized group of soil microbes can produce methane as the end product of their metabolism instead of carbon dioxide. These complex connections cycle carbon among soils, plants, and the atmosphere within ecosystems at timescales from seconds to centuries.
  
  Understanding how forest and wetland carbon cycling responds to disturbances like invasive insects and extreme climate events (e.g., heatwaves, drought and deluge events) is a major priority for better predicting future impacts on the carbon cycle. At Harvard Forest, we are measuring ecosystem carbon cycling with fast networked sensors and field measurements, and we run experiments in the field and lab to better understand carbon storage and flux..
  
  This overarching project has four subprojects that investigate key uncertainties in forest and wetland carbon cycling. Students across all subprojects will work collaboratively to develop conceptual understanding of project themes. Subproject 1 (2 students) will investigate the processes and weather conditions that influence methane uptake and methane release within upland (typically well-drained and unflooded) and wetland soils at Harvard Forest. Subproject 2 (2 students) will investigate the role of trees in emitting CH4 to the atmosphere, and the effects of wood-dwelling microbes and decay. Subproject 3 (1-2 students) will investigate the nutrient availability and gas fluxes from soils decades after a simulated hurricane event resulting in new forest structure and aboveground carbon inputs to soil to test for long-term inputs of this type of disturbance on soil nutrient budgets and greenhouse gas contributions. Subproject 4 (1-2 students) will measure the movement of carbon from plant biomass into soil pools within an area of hemlock forest that is experiencing tree stress and mortality caused by the invasive hemlock woolly adelgid insect. Students on this subproject will conduct field and lab measurements to measure the microbial processing of carbon as it moves from plants (live root exudates and dead biomass) at points across the landscape.
  
  In more detail, these subprojects will investigate:
  1) Methane dynamics in upland and wetland soils (2 students)
  Emissions and uptake of methane (CH4) between ecosystems and the atmosphere is the largest source of uncertainty in the global atmospheric CH4 budget. Increasing atmospheric CH4 concentrations (Nisbet et al., 2019) is of concern because CH4 is 34 times more effective at trapping heat in the atmosphere compared to an equivalent mass of carbon dioxide over a 100-year timeframe and accounts for 42% of warming since the pre-industrial period (IPCC, 2021).
  Areas with relatively small CH4 uptake and emission rates, like the forest and wetland ecosystems at Harvard Forest, have been largely understudied but could contribute significantly to regional and global budgets. Microbes near the surface of upland (non-flooded) forest soils typically consume atmospheric CH4, but soils can release CH4 to the atmosphere during periods of flooding. Students in this project will measure net CH4 fluxes from soils across an upland to wetland gradient, to understand landscape variability and various ecosystem contributions to forest-level methane exchange with the atmosphere. Students will also probe the zones and mechanisms of production of CH4 throughout the soil profile, by sampling methane buildup in soil pore spaces at different depths, methane dissolved in soil water, and changing biogeochemical conditions (e.g. soil moisture and redox). A typical week on this project will involve 3 full days of fieldwork and 2 days of computer work.
  
  2) Methane production and emission by living trees (1-2 students)
  Historically, most research on forest methane cycling has focused on soils, which are inhabited by microbes that produce methane (methanogens) and microbes that consume methane (methanotrophs). However, trees have recently been recognized to also emit CH4 to the atmosphere, though the reasons are less clear (Covey and Megonigal, 2018; Barbat et. al, 2018). Trees may serve as ‘chimneys’, venting methane from the soil, or as ‘straws’, sucking up soil methane through transpiration. Additionally, they may also harbor their own methanogens, living inside of tree wood. We have recently begun to discover that trees have diverse microbiomes, similar to soils or human guts, and that these microbiomes may include methanogens. However, whether methanogens are associated with a healthy microbiome, or with tree disease and decay, is not yet understood.
  This project will attempt to determine both the amount of methane being released from trees at Harvard Forest, and the internal condition of those trees, to see whether rot and decay are related to tree methane emission. Students on the project will directly measure methane emission from tree stems in upland and wetland areas, and will take 3D scans of trees (using a tool called “sonic tomography”) to map the trees’ internal structure and condition. The project will involve a mixture of field and lab/computer work. A typical week will involve 3-4 full days in the field or lab and 1-2 days of computer work.
  
  3) Long-term soil nutrient and gas cycling after hurricane disturbance (2 students)
  Storm damage uproots trees and indirectly damages those not uprooted, creating differences in forest topography, carbon inputs, nutrient demand, and light and moisture availability. While the forest ecology of storm disturbance and regrowth is well-documented, soil biogeochemical impacts are less understood. We propose to follow up on a soil biogeochemical analysis performed two years post-pulldown to assess whether a storm-impacted temperate hardwood forest results in significantly different soil N, C, and greenhouse gas cycling decades after disturbance relative to a neighboring undisturbed plot.
  Based on the results of Bowden et al. (1993), we know that pulldown minimally affected soil nutrient cycling initially with no changes in CO2 or CH4 fluxes between the control and pulldown plots and a slight decrease in net N2O production. Since 1993, the downed wood has largely decomposed, with many trunks predominantly incorporated into the soil litter and mineral profile. Saplings of pre-existing trees (mostly red oak, red maple, and birch) have grown in, but the overall community composition has not changed significantly and biomass growth in the control plot has been similar to that in the pulldown plot.
  Based on these forest developments over the last three decades, we predict that:
  1: Hurricane blowdown will result in increased CO2 production in dry sites and decreased CO2 production in moist sites compared to the control plot, with opposite trends in CH4 patterns, based on higher carbon availability.
  2: Hurricane blowdown will result in overall higher N availability but more active mineralization, denitrification and N2O production that ultimately remove litter N inputs to soil more rapidly than the control plot.
  Students will take regular gas samples (twice monthly and before and after storm events) in the hurricane and control plots using PVC collars installed in November 2023. Sampling will use a Li-Cor gas analyzer for in situ CO2 analysis with sub-samples taken for CH4 and N2O analysis at UMass using a gas chromatograph equipped with electron capture (N2O) and flame ionization (CO2, CH4) detectors. Nutrient pools and redox indicators will be measured monthly in the litter and top 5 cm of mineral soil. These measurements will include exchangeable ammonium and nitrate, pH, soil redox potential, soil moisture, and reactive Fe speciation. Methods will include field incubations, continuous field data logging, and laboratory chemical analysis of soil nutrients and metals. Students will spend ~1-2 days/week in the field, 1-2 days/week in the lab, and remaining time working on data analysis and science communication (background understanding and presentation development).
  
  4) Hemlock decline and plant-soil feedbacks (1-2 students)
  Eastern hemlock is a foundation tree species that plays a unique role in structuring ecosystem processes. At Harvard Forest, the eastern hemlock species has been in decline since about 2013 due to stress and mortality from the invasive insect hemlock woolly adelgid. The impact of the hemlock woolly adelgid represents a major forest disturbance, which is likely to become more common with climate change. The hemlock woolly adelgid causes a slow decline in hemlock health, and eventual death, but its impact on hemlock health varies across space. An unexplored driver is the role of plant-soil feedbacks, or the carbon and nutrient exchanges between plant roots and soil microbes. A major goal of this subproject is measure root exudation across hemlock populations of various ages and health to examine differences in plant-soil feedbacks. In addition, these plant-soil feedbacks have connections to soil carbon cycling and storage, which the student(s) in this project will also explore through measurements of soil pools and fluxes. The project will involve a mixture of field and lab/computer work. A typical week will involve 3-4 full days in the field or lab and 1-2 days of computer work.
  
  General requirements for all projects:
  
  1. Participate in field data collection, including ~8 hours per field day with biting insects and hot, humid, sometimes rainy, conditions. Field data collection days will often require early morning departures (meeting to leave at ~8 am) and packing a lunch to eat in the field (there will not be time to return to the dining hall for lunch most days).
  
  2. Hike with scientific gear (20-30 lb. pack) in forested off-trail terrain.
  
  3. Willingness to work in a collaborative team of students and mentors. Practice clear communication with other students and mentors. Be willing to ask questions about everything from procedures and logistics to the theoretical background of our research. Make and help to identify mistakes, which are expected, respected, inspected, and corrected, and be willing to learn together as a project team.
  
  4. Willingness to be flexible with day-to-day tasks that range from field research to computer analysis of data, and pitching in to help students and mentors across subprojects.

• Readings:

  Readings
  Nisbet et al., Science 2014, DOI: 10.1126/science.124782
  Delwiche et. al ESSD 2021, doi:10.5194/essd-13-3607-2021
  Orwig and Foster, The Journal of the Torrey Botanical Society 1998, 125(1): 60-73.
  Ellison et al. Frontiers in Ecology and the Environment 2005, doi: 10.1890/1540-9295(2005)003[0479:LOFSCF]2.0.CO;2
  Covey and Megonigal New Phyt. 2018
  Barba et. al. New Phyt 2018
  Van der Putten et al. J. of Ecol. 2013, https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12054
  Kristensen et al. J. of Ecol 2019, https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.13319
  Bowden et al. Biogeochemistry 1993, https://link.springer.com/article/10.1007/BF00000871

• Research Category: Watershed Ecology, Soil Carbon and Nitrogen Dynamics, Physiological Ecology, Population Dynamics, and Species Interactions, Large Experiments and Permanent Plot Studies, Invasive Plants, Pests & Pathogens, Forest-Atmosphere Exchange, Conservation and Management