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Summer Research Project 2018

• Title: Group Project: Quantifying the impact of experimentally-induced stress on the physiology and silica uptake rates of temperate forest ecosystems
• Group Project Leader: Tim Rademacher
• Mentors: David Basler; Robinson W. Fulweiler; Tim Rademacher
• Collaborators: David Basler; Robinson W. Fulweiler; Tim Rademacher
• Project Description:

  Temperate forests cover 6% of the global terrestrial surface area, yet they contribute 13% to the net global uptake of carbon by vegetation. The cycling of carbon in temperate forests is therefore of major importance. Projections of future uptake of carbon are consistently increasing, mainly due to CO2 fertilisation effects. Whether the simulated increases are realistic remains actively debated with evidence from experimental studies showing clear limitations on the capacity to sequester carbon. To better understand the carbon sequestration capacity of temperate forest stands, we use experimental treatments to modulate the carbon cycling and investigate physiological and xylogenetic consequences.
  
  Silica (Si) is considered a ‘quasi’-essential nutrient for trees and other terrestrial vegetation. Almost all terrestrial vegetation contains some Si, in fact, Si-accumulating organisms account for 55% of terrestrial net primary production. Si provides structural support as well as defenses against abiotic (e.g., drought, metal toxicity) and biotic (e.g., grazing, bacterial attack) stressors. Understanding how trees take up Si under stress will inform us about the role of Si in tree physiology. However, understanding tree Si uptake also informs us about the availability of Si in downstream ecosystems. In turn, this information is important for understanding phytoplankton growth and food web interactions.
  
  This group project aims at quantifying the responses of physiological functions of trees and soils to various experimental treatments (i.e. girdling, compression, chilling and sugar addition). This feeds into a larger effort to improve our understanding and simulations of the current and future carbon sequestration capacity of temperate forests. Additionally, the project will investigate the effect of stress on tree silica uptake rates.
  
  The project entails three linked sub-projects. Each student is expected to take primary responsibility for one sub-project (approximately 60% of their time) and collaborate on achieving their goals as a group (circa 30% of their time). Each subproject has a primary mentor with the other mentors chipping in. Beyond the sub-projects the students are expected to spend about 10% of their time on assisting the umbrella studies. The students will have at least one group meeting chaired by a mentor per week. Additionally, each student will also meet their respective sub-project mentor on a weekly basis.
  
  1. Limiting photosynthate transport in trees:
  The project is part of a larger experiment that limits photosynthate transport in the phloem by girdling, compression girdling and chilling. The student will work on temporal and between-treatment variations of physiological functions. Working closely with the researcher leading this study the student will learn, perform and analyse measurements of tree physiology (i.e. stem respiration, leaf water potential, photosynthesis). In addition, the student is encouraged to improve and automate measurements and collect additional data series such as diurnal measurements series, which can be used for the correction of long-term measurement series. The primary mentor for this sub-project is Tim Rademacher.
  
  
  2. Effects of limited photosynthate transport on soil respiration:
  Soil respiration is the main path by which carbon fixed by land plants returns to the atmosphere. The goal of this sub-project is to find out how the inhibited sugar transport to the roots affects the release of carbon dioxide from soils. As soil respiration is the sum of the respiration of plant roots, the rhizosphere microbes and soil fauna, we will design and apply additional control treatments to try to disentangle these signals. The primary mentor for this sub-project is David Basler.
  
  3. Si content of stressed trees:
  This project is part of a larger on-going project at at HF focused on quantifying Si concentrations of trees. The goal of this sub-project is to measure Si concentrations in stressed and non-stressed trees over the growing season. We anticipate that trees that are more stressed will contain more Si, however, if water transport mechanisms are disrupted then they may contain less. We will measure Si in the above and below ground biomass as well in the sap. Ultimately our goal is to better understand how Si uptake by trees impacts downstream Si availabilty. The primary mentor for this sub-project is Wally Fulweiler.
  
  Requirements:
  In your application, please indicate which subproject (1, 2, or 3) you are most interested in working on.
  
  Applicants for these sub-projects should have good quantitative and computer skills, ideally with some knowledge of the computing language R. You should be enthusiastic about spending much of your time outside conducting measurements in the forest, which can involve carrying heavy instruments, bugs, poison ivy, ticks, and the typical extremes of New England summer weather. A background in plant biology or engineering are useful, but not required. Equally, a driving license would be useful, but is not required.
  
  Additionally, applicants for sub-project (3) should be interested in the connections between watersheds and downstream receiving waters (e.g., rivers, lakes, estuaries).

• Readings:

• Research Category: Watershed Ecology, Soil Carbon and Nitrogen Dynamics, Physiological Ecology, Population Dynamics, and Species Interactions, Large Experiments and Permanent Plot Studies, Forest-Atmosphere Exchange