By Jacquelyn Veatch
When samples of seeds are collected in the field and brought back to the lab, there is a lot of work to do to get them ready for cultivation and experiments. As a new undergraduate research assistant in the Gedan Lab, many of my hours at the lab bench are spent cleaning seeds and looking for seed viability.
No, “cleaning seeds” does not mean little seed baths with soap and a rubber ducky. The tall grasses that are taken from the marshes and end up at the lab bench in front of me have hundreds of seeds that need to be separated from their stems, leaves and other supporting structures. I do this by grinding the plants gently with the graded rubber shown on the red tray below to release the seeds. Next, I transfer the seeds and debris to the metal mesh plates to separate this mixture by size, collecting the seeds in brown paper bags.
This technique differs for each species of grass. For example, the Aster subulatus stick together, so once they are on the metal mesh plate, I use the cardboard box shown at left to push excess stems and leaves through the mesh, leaving the fluffy white seeds on the top.
After the seeds are cleaned, I weigh the entire sample and a sub-sample of 100 carefully separated seeds. This gives us an idea of how many clean seeds are in the sample and is a lot more efficient than counting all of the seeds, I would graduate before I would finish! The sample of 100 clean seeds is then taken to the microscope to check for seed viability. Using tweezers and a scalpel, I cut open each seed and record what I find. Below are a few examples of seeds I have been working on this past semester.
Three Echinochloa crus-galli seeds are shown in the leftmost image with the burr-like awn. The bottom Echinochloa crus-galli has not yet been cut open, the top left is empty, and the top right has a seed, meaning it is likely viable. The Aster subulatus seeds are too small to cut open; these seeds are wind dispersed. They love to float along the ventilation drafts in our lab while I am trying to count and weigh them (sending me leaping across the lab after them!). The rightmost image shows three Panicum virgatum seeds. At the bottom of this image is a Panicum virgatum before it has been cut open. The upper right seed appears to be viable. Looking closely at the upper left seed, a black structure inside the floret can be seen. This has not developed into a seed, so I would score this as unviable.
Recording my findings of the 100 seed samples, we have a pretty good understanding about how many seeds in the total sample will germinate, given the right conditions. Next steps for these seeds: to the greenhouse and the incubation chamber this spring!
Un aplauso por postdoc Eduardo Fernández Pascual, for winning the prestigious Marie Curie COFUND – Clarín fellowship. He will return to the University of Oviedo in Asturias, Spain at the end of this year. We have loved having Eduardo in the Gedan Lab! We look forward to seeing the next chapter of his plant community ecology research, and for the chance to visit Eduardo in his home state.
We are proud to be included in a GW Today article about the diverse research going on in GW's Harlan Greenhouse, which will be dedicated in honor of GW alum and botany major, Dr. Harlan, B.S. ’35, next week. Research by John Lill, Amy Zanne, Arnaud Martin, and the Gedan Lab was featured in the article. The Harlan greenhouse is located on the top floor of the SEH. It is flourishing under the care of greenhouse manager Rachel Klein and is open to students on Fridays from 12-3pm.
We're lucky to have a great volunteer in the lab this summer, rising GW senior Lily Segalman, who spent the last semester sailing the Pacific Seas. Hear her stories about sea sickness and microplastics in a GW Today story about her trip. After trading her lifejacket for marsh boots, Lily will keep working with the Gedan Lab in the field and lab this fall.
By Maxwell Sall
As a new undergraduate research assistant in Professor Gedan’s lab as of the 2017 Spring semester, I have been spending my time not in the field, but in GW’s well-lit, shiny Science and Engineering Hall, working on various projects to transform samples collected during the last field season into qualitative and quantitative data.
Recently, my main focus has been on determining the relative viability of seeds collected last fall. While germinating planted seeds can take 3-4 weeks to determine the viability of grass species, we have been using Tetrazolium (TZ) testing, which can accurately predict the seed viability in a three-day procedure. First, a sample of each species is wrapped in damp paper towels, and soaked in a refrigerator overnight. Hydration initiates cellular respiration in the seeds, which will allow us to measure their viability. The next day, we cut the seeds in half, and then soak them overnight in a 1% tetrazolium chloride solution. If the seeds are viable, dehydrogenase enzyme activity will reduce the colorless tetrazolium solution to formazan red, leaving the seeds brightly stained.
When we ran our first replicate of seeds through the TZ test, we learned specific features of each species’ seed morphology which helped us more effectively dissect and stain the second replicate of seeds. Panicum virgatum seeds, for example, are surrounded by a sheath that obscured the seed from absorbing the Tetrazolium solution. In our second replicate, we removed the seeds from the sheath, and observed an almost 20% vitality rate within our sample.
All of these species were extremely small, and their dissection required some seriously precise hand-eye coordination. The white endosperm of Sorghum halepense, for example does not stain, so when we first tested the seeds using a latitudinal cut, it seemed that none of the seeds were viable. Using a longitudinal cut on the second replicate to view the seeds’ embryo, we found that roughly 70% of the seeds were stained.
The percent viability of the species we tested varied greatly. Some species, such as Iva frutescens, showed 100% viability. Several species, including Baccharis hamilifolia showed a viability rate of approximately 10%. In our small sample, not a single Spartina cynosuroides seed showed signs of staining. We are currently studying the germination of these species, whose seeds we planted in the greenhouse at the end of January. Our results from the TZ testing will inform the relative germination rate that each species shows.
As it gets warmer outside and my midterms pass, I can’t help but look forward to going out into beautiful tidal wetlands this summer, to see how all of this data is collected, and how it plays a larger role in addressing the big research questions that Professor Gedan’s lab is tackling.
By Emily Kottler
Our lab studies the tidal marshes of the Chesapeake Bay. While we on the research end pursue an in depth understanding of long-term changes resulting from sea level rise, land managers are working on the front lines to preserve these treasured habitats. Wetlands are a refuge for a diversity of native wildlife, serving as nursery grounds for commercial fish and nesting sites for rare birds. These vibrant and productive natural systems are under threat due to accelerated sea level rise, which can drown the foundation species of grasses that root firmly into the sediment and build the marsh. These grasses prevent erosion and provide a much-needed buffer for waves and coastal storms.
The rising threat of sea level rise necessitates forward-thinking management strategies that move beyond the protection of current wetland area and work to prepare for the new marsh distributions. One such method is thin layer deposition, a technique that is being utilized at the Blackwater National Wildlife Refuge on an ambitious scale: the first project of its size in the Chesapeake Bay.
Thin layer deposition is the practice of distributing a layer of dredged sediment on the marsh to raise its elevation. In time, tidal grasses grow through the added sediment (sometimes supplemented with restoration plantings), and a new marsh flat is established at a higher elevation. This type of restoration is more than just a short-term solution: it allows the dominant grasses to thrive, and they in turn will continue to build up the marsh’s elevation.
Similar projects have recently been enacted at wildlife refuges on the Gulf Coast and in New England, so it’s very exciting to see this kind of broad-scale wetland restoration happening in our proverbial backyard. At Blackwater the U.S. Fish & Wildlife Service, The Conservation Fund and the Audobon Society have come together to fund this project, and it was implemented using current sea level rise projections and research into marsh grass growth conducted by the U.S. Geological Survey. Researchers, engineers and land managers from different agencies have come together to make this conservation effort possible.
Thin layer deposition is not without risk. The force of the hoses used to deposit the sediment knocks over existing vegetation, and it will only recover if the sediment layer of a proper thickness (i.e. thin enough for the vegetation to grow through, but thick enough to sufficiently raise the vegetation above the sea water). Blackwater managers and restoration ecologists have done their best to mitigate this risk through pilot studies in smaller areas of the marsh, determining the right amount of sediment to add, where it will land with the application technique, and how it will settle and affect marsh plants.
We conduct field research at Blackwater NWR, and are looking forward to future endeavors there. If researchers and land managers work together to understand the problems posed by sea-level rise and put into place management strategies grounded in solid research, together we can preserve these unique and beneficial habitats.
Kathryn was awarded the competitive Delaware Sea Grant-Delaware National Estuarine Research Reserve Healthy Coastal Ecosystems Fellowship for a project entitled Blue carbon distribution across estuarine salinity gradients in the Delaware and Chesapeake Bays. Congratulations, Kathryn! We're all looking forward to this work in summer 2017.
Whenever I’ve told people what I’ve been doing this summer, their response has been something like “You’re doing marine field work? That sounds so cool! That’s so lucky you get to spend your day out on a boat/at the beach.” And then they ask “So what do you actually do out there?” Well, the answer is we do a lot of cool things, but it’s not quite what you’re imagining.
By Kathryn Norman
Our work isn’t quite your typical day at the beach. First off, the ecosystems we’re studying are the marshes between the barrier island and the mainland, so we don’t really spend any time with our toes in the sand. Instead we spend our time suited up in muck boots, boating between tidal creeks, traipsing around the higher edges of the marsh, or wading through water and getting stuck in mud in the lower parts marsh. As part of our study, we’re collecting data on elevation, salinity, vegetation distribution, and taking soil samples. The work is dirty, smelly, and because we’re in the marsh, it can be really hot and buggy if there isn’t a breeze.
It isn’t glamorous. But, the small moments of the job make it worth it, beyond the obvious big-picture goals of developing research questions and collecting data. Seeing the world wake up as the sun rises over the water, a bald eagle taking off from it’s perch in the early morning, watching diamondback terrapins sun themselves on mud banks as we zip past in the boat, or the march of what seems like a million fiddler crabs as they scurry across the marsh beneath our feet. In these special moments I’m beyond lucky to experience this job because it’s beautiful. It’s also pretty fun most of the time, despite the hazards. Our lab group has running comedy routines about becoming the Saltsquatch, the marsh version of Sasquatch and the gamble of jumping off the boat onto marsh of questionable firmness (best case scenario being “terra firma", worst case being “soup”). This past month, we honed our skills in “the wetland Olympics”: the main event was the quadrat throw: points awarded for height, distance, rotations and for “sticking the landing,” or whether or not the quadrat pole stand lands standing straight up in the ground.
Between the heat, the bugs, the joking around, and getting the job done, I enjoy thinking about the complexities of our system; a system that has for centuries has been neglected and overlooked by society as just a breeding ground for mosquitoes and used as a dumping ground for sewage and debris. For centuries these systems have provided a variety of ecosystem services for society, such as nutrient removal, water filtration, protection from storms, and provide vital habitat for many species that are commercially harvest. As a result of rising mean global temperatures, these systems are immediately threatened by sea level rise. While it is currently believed that wetland ecosystems can survive increases in mean sea level by moving inland, the issue is complicated by the fact that development along coastlines, and the current rapid rate of sea level rise, would prevent this natural behavior.
The main research question that I am working on is about barrier island and back-barrier coupling. We want to understand how variation in elevation, vegetation density/distribution, and salinity in the back-barrier impact blue carbon storage in the marsh. We hope the results of these findings might have implications for firstly, how carbon storage can be quantified in a marsh and secondly, how it will be impacted by sea level rise. Yet, perhaps the most exciting part of our work is the immediacy of it all. Never before has there been a greater need to understand of wetlands ecosystems, as it might soon be too late. My work will add to the dialogue of what we know about these ecosystems so that they may be preserved to society’s best efforts.
With the close of our field season comes the beginning of my first semester of classes at GW. After all our hard work, I’m ready to be out of the field for a little bit and I’m eager to start examining the data we collected. I know by May I’ll be itching to get out and gather the missing puzzle pieces in our project, but for now I’m looking forward to the rhythm of being a student again, with classes and assignments.
Until next time,
We are going to New Orleans in December for the Restore America's Estuaries & The Coastal Society Summit. Keryn has organized a session, “Sea level rise, marsh migration, and coastal land conversion” and Kathryn will present a poster on her barrier island work.
GW has a beautiful new research greenhouse located on the 8th floor of the Science and Engineering Hall. Plants and seeds are being collected. Photos coming soon.