Experimental evidence for correlation between leaf shape and temperature in different plant species: suggestions for inferring paleoclimate

Experimental evidence for species-dependent responses in leaf shape to temperature: Implications for paleoclimate inference

by: Melissa L. McKee, Dana L. Royer, Helen M. Poulos

Summarized by: Mckenna Dyjak

What data were used?: Four species of seeds from woody plants were used: Boxelder Maple (Acer negundo L.), Sweetbirch (Betula lenta L.), American Hornbeam (Carpinus caroliniana Walter), and Red Oak (Quercus rubra L.). Three species from transfered saplings were also used: Red Maple (Acer negundo), American Hornbeam (Carpinus caroliniana Walter), and American Hophornbeam (Ostrya virginiana  K.Ko(Mill.)ch). The types of species were chosen because they each exist naturally along the east coast of the United States and have leaf shapes that vary with climate.

Methods:The seeds and saplings were randomly divided into either warm or cold treatments. The warm treatment cabinet had a target average temperature of 25°C (77°F) and the cold treatment cabinet had a target average temperature of 17.1°C (63°F). After three months, five fully expanded leaves were harvested and photographed immediately. The images from the leaves were altered in Photoshop (Adobe Systems) to separate the teeth (zig-zag edges of leaves) from the leaf blade (broad portion of the leaf). The leaf physiognomy (leaf size and shape) was measured using a software called ImageJ. The measured variables were tooth abundance, tooth size, and degree of leaf dissection. The degree of leaf dissection or leaf dissection index (LDI) is calculated by leaf perimeter (distance around leaf) divided by the square root of the leaf area (space inside leaf). The deeper and larger the space between the teeth of the leaf, the greater the LDI.

Results:The leaf responses to the two temperature treatments are mostly consistent with what is observed globally: the leaves from the cool temperature treatment favored having more teeth, larger teeth, and a higher LDI (higher perimeter ratio). However, it was found that the relation between leaf physiognomy (leaf size and shape) and temperature was specific to the type of species. 

Fig.1 Tooth abundance in relation to temperature. The colder temperature (in blue) correlates with an increasing number of teeth in generally all of the plant species tested. The differences can also be observed in the pictures present below the graphs. More leaf teeth (serrated edges along the margins) can be seen under the cold treatment.

Why is this study important?: Paleoclimate (past climate) can be determined by using proxy data which is data that can be preserved things such as pollen, coral, ice cores, and leaves. Leaf physiognomy can be used in climate-models to reconstruct paleotemperature from fossilized leaves. This study supports the idea that leaf size changes correlate with temperature change. However, the responses varied by species and this should be taken into account for climate-models using leaf physiognomy to infer paleoclimate. 

The bigger picture: Studying paleoclimate is important to see how past plants reacted to climate change so we have an idea how plants will respond to modern human-driven climate change.

Citation: McKee ML, Royer DL, Poulos HM (2019) Experimental evidence for species-dependent responses in leaf shape to temperature: Implications for paleoclimate inference. PLoS ONE 14(6): e0218884. https://doi.org/10.1371/journal.pone.0218884

Mckenna Dyjak, Environmental Scientist & Geologist

Hello! My name is Mckenna Dyjak and I am in my last semester of undergrad at the University of South Florida. I am majoring in environmental science and minoring in geology. I have always been very excited by rocks and minerals as well as plants and animals. In high school, I took AP Environmental Science and realized I couldn’t picture myself doing anything other than natural sciences in college. While in college, I joined the Geology Club and realized that I loved geology as well. At that point it was too late in my college career to double major, so I decided to minor in geology instead. Since then, I have been able to go on many exciting field trips and have met amazing people that have helped further my excitement and education in geology. One of my favorite trips was for my Mineralogy, Petrology, and Geochemistry class that went to Mount Rogers in Virginia to observe rock types that would be similar to a core sample we would later study in class. Figure 1 below is a picture of me in Grayson Highlands State Park on that field trip! As you can see, my hiking boots are taped because the soles fell off. Luckily, some of my fellow classmates brought waterproof adhesive tape which saved my life.

Figure 2. University of South Florida Engineering Expo 2020 at EPC booth.

My favorite thing about being a scientist is that everyone has something that they are passionate and knowledgeable about. You can learn so many different things from different people and it is so fun seeing how excited people get about what they are most interested in. It is a great thing to be in a field where constant learning and relearning is the norm. I love to share what I know and learn from others as well. 

 As of now, I am doing an internship with the Environmental Protection Commission of Hillsborough County in the Wetlands Division. At the EPC we are in charge of protecting the resources of Hillsborough County, including the wetlands. An important part of what we do is wetland delineation (determination of precise boundaries of wetlands on the ground through field surveys) which requires a wide knowledge of wetland vegetation and hydric soils (soil which is permanently or seasonally saturated by water resulting in anaerobic conditions)! Once the wetland is delineated, permitting and mitigation (compensation for the functional loss resulting from the permitted wetland impact) can begin. Figure 2 below is a picture of me at the Engineering Expo at the University of South Florida explaining the hydrologic cycle to a younger student at the EPC booth!

Figure 3. Vibracore sampling at Whidden Bay, 2019.

Outside of environmental science, I have a passion for geology or more specifically, sedimentary geology. I have been fortunate enough to have amazing professors in my sedimentary classes and have discovered my love for it! I enjoy going on the field trips for the classes and expanding my knowledge in class during lectures. I am interested in using sedimentary rocks to interpret paleoclimate (climate prevalent at a particular time in the geological past)  and determining how past climate change affected surface environments. One really awesome field trip I got to go on was for my Sedimentary Environments class where we took core samples in Whidden Bay and Peace River. In Figure 3 I am in the water, knee deep in smelly mangrove mud, cutting the top of our core that we will eventually pull out and cap. I plan on attending graduate school in Fall of 2021 in this particular area of study.

The study and reconstruction of paleoclimate is important for our understanding of the natural variation of climate and how it is changing presently. To gather paleoclimate data, climate proxies (materials preserved in the geologic record which can be compared to what we know today) are used. I am interested in using paleosols (a stratum or soil horizon that was formed as a soil in a past geological period) as proxy data for determining paleoclimate. Sediment cores (seen in Figure 4) can also be used to determine past climate. The correlation between present day climate change and what has happened in the geologic past is crucial for our push to mitigate climate change.

Figure 4. Core sample from Figure 3.

I urge aspiring scientists to acquire as much knowledge they can about different areas of science because they are all connected! It doesn’t matter if it is from a book at the library, a video online, or in lecture. You also do not have to attend college to be a scientist; any thirst for knowledge and curiosity of the world already has you there.

Geology of the Mount Rogers Formation and Virginia Creeper Trail

Mckenna here- This post will show you the geology of the Mount Rogers Formation and Virginia Creeper Trail on a recent field trip I took to Virginia!

Day 1

Image 1. Our professor leading us to a geology lookout point on the way to Abingdon to see an outcrop (visible rock formation).

On October 10th of 2019, my Mineralogy, Petrology, and Geochemistry class went on a 4 day field trip to Abingdon, Virginia. Imagine this: it’s October. You love fall but you’ve lived in Florida your whole life, and you finally get to wear all the winter clothes you bought for no apparent reason. Considering these facts, my excitement for the trip was through the roof. After a 14 hour ride in a van with 10 other people and frequent restroom stops (much to the dismay of my professor) we finally arrived in Abingdon, Virginia to the joys of leaves turning colors and a crisp feeling in the air. A van full of (mostly) Florida-born students  seeing fall leaves for what was probably the first time was a van full of amazement and pure excitement. It sounds silly, but it was really wholesome seeing how giddy everyone got just by seeing some colorful trees (me included). We got to our hotel and prepared for the next day spent in the field. 

Day 2

Image 2. Rhyolite at Mt. Rogers with visible high silica flow banding (lava flow)

We woke up early in the morning and were able to enjoy a delightful breakfast made by the hotel to kick start our day. I packed my lunch and snacks and put on layers of clothes to be ready for any weather. I put on my new wool socks from the outlet store and old hiking boots that seemed structurally sound at the time (important to note for later). On our way to Mount Rogers in Damascus, Virginia we happened to take a road conveniently coined “The Twist”. As a long term participant in unwillingly becoming motion sick in situations such as going down one of the curviest roads in Virginia, I wasn’t thrilled. Luckily, I knew mountain roads could be bad so I packed some Dramamine which I made sure I took every time we got in the van from then on. 

Once we got to Mount Rogers my friend and I immediately had to use the bathroom which in this case, was wherever you felt like the trees concealed you enough. They don’t really mention this too much for field trips/field camps but bring toilet paper!! It will make your life a lot easier. After this venture, we were soon on the hunt for rhyolite. Rhyolite is a type of rock that my professor has talked a lot about and I had heard from other students that it is mostly what you will be seeing on the Virginia trip. It is a type of igneous rock that has a very high silica content so it is considered felsic (which is usually light colored). Rhyolite is made up of the minerals quartz, and plagioclase with smaller amounts of hornblende and biotite

The upper part of the Mount Rogers Formation consists mostly of rhyolite which we have, thanks to the continental rifting that occurred around 750 mya. The volcanoes that were once present here erupted and the igneous rock formed from the lava flow. 

Figure 1. Formation of rift valley in Mt. Rogers (From Radford)

We used our rock hammers that you can see in Image 2 to break off bits of Rhyolite and observe them under our handheld lenses. Through these lenses, we could (almost) easily identify the minerals present in our rock samples. 

Stop after stop, we observed more rhyolite. It became quite easy to answer our professor’s questions as to what type of rock we were looking at; the answer was usually “Whitetop Rhyolite”. There were, however, different types of rocks as we descended down the side of the mountain: buzzard rock and cranberry gneiss.

Image 3. Buzzard rock
Image 4. Cranberry gneiss

 

 

 

 

 

 

 

 

After we were finished at our first destination, we drove off to Grayson Highlands State Park. Here we observed more outcrops of rhyolite with a new fun bonus: tiny horses. Apparently, these tiny horses were let loose here in the late 20th century to control the growth of brush in the park. Now, there are around 150 of them that live in the park and are considered wild. While the park discourages petting the horse, you are able to get a cool selfie with them!

Image 5. Selfie with tiny horse in Grayson Highlands State Park

At the state park , there were lots and lots of giant rocks to climb on which everyone seemed to enjoy doing. So, while climbing the rocks, we were also observing and identifying them so it was a great combination. I was taking the liberty to climb almost every rock I saw and everything was going great for the time being. At one rock, I decided I wanted some pictures, for the memories! Mid mini photo shoot, I realized that the sole of my hiking boot had come clean off. Luckily, TWO very prepared people in my class happened to have waterproof adhesive tape and offered for me to use it to fix my boots. I was so thankful (and impressed that they had it in the first place) for the tape and used it to wrap my sole back to my boot and reinforce my second one because I noticed that the sole was starting to come off. The taped boots almost got me through to the end of the second day but I had to do some careful, soleless walking to get back to the van. I was able to go to the store near our hotel to get some replacement boots for the third, and final day in the field. 

Image 6. Realization of broken boot
Image 7. The final product of taped boots

Day 3

Image 8. Shale sample taken from outcrop along the Virginia Creeper Trail

The last day in the field was spent at the Virginia Creeper Trail in Damascus, Virginia. This specific trail serves almost entirely as a 34 mile cycling trail; by almost entirely, I mean entirely a cycling trail with the exception of a class full of geology students. Our day consisted of identifying rock types in outcrops along the trail and receiving a wide range of looks from cyclists passing by as our lookouts at the front and back yelled out for us to get out of the way. We walked around 1.5 miles of the trail, all while taking notes and pictures while our professor and teaching assistants were explaining each outcrop. Once we reached a certain point, our professor informed us that they would be leaving to get the vans and we would be walking back the way we came plus a half mile or so and identifying each outcrop while counting our steps and noting our bearings. So we measured our strides and got into groups to commence the journey. The goal of this was to eventually be able to create a map of our own that indicated each outcrop type and where they were on the path we took. 

Image 9. Mudstone displaying “varves”, which are a seasonal bedding pattern that develops in high latitude lakes. The thicker deposits develop in the summer and the thinner ones develop in the winter (please ignore my nailpolish-it is not a good idea to paint your nails before a geology trip).

This all sounds relatively simple, right? The answer is well, not really. The entire venture took around 4 or 5 hours and honestly made some people a little grumpy. I was happy though, because among the rhyolites and basalts, we were also able to see some really cool sedimentary rocks. Along the way we saw some awesome shale (Image 8) which we were told had some fossils in it if you looked hard enough. Of course, being interested in sedimentary geology I would’ve stayed forever chipping away at the shale to find a fossil but we were quickly ushered along by one of our professors. Shale is a type of sedimentary rock that is formed from packed silt or clay and easily separates into sheets. This type of rock is formed under gentle pressure and heat which allows organic material to be preserved easier as opposed to igneous or metamorphic rocks. As we continued along the trail we also saw mudstones and sandstones, diamictites, and conglomerates. After reaching the end of our journey, my group might have gone a little overboard and recorded 51 different outcrops. The outcrops we recorded could be reduced to: basalt, rhyolite, diamictite, conglomerate, sandstone/mudstone, and shale. The last field day was now concluded with tired feet but happy hearts as we listened to Fleetwood Mac in the van on the way back to the hotel.

Image 10. Diamictite (type of conglomerate) with poorly sorted grains suspended in a clay matrix. This specific rock was likely created by glacial activity and/or volcanic activity.

Day 4

We had a very early morning, skipped the hotel breakfast (they put out fruit and pastries for us though), and piled into the vans for a long journey back to Tampa, Florida. This trip was everything I had hoped it would be and made me fall in love with geology even more than I already was! I hope to go on many more adventures like this in the future. 

Bonus images of cool finds:

Image 11. Swallowtail feldspar (basalt) contains epidote and quartz. Lava cooled very quickly which caused rapid crystallization
Image 12. Rhyolite with pyrite (fool’s gold) clasts visible under hand lens

A fossil-rich rock formation at the Cretaceous-Paleogene Boundary in Mississippi, USA indicates environmental changes before mass extinction

A fossiliferous spherule-rich bed at the Cretaceous–Paleogene (K–Pg) boundary in Mississippi, USA: Implications for the K–Pg mass extinction event in the Mississippi Embayment and Eastern Gulf Coastal Plain

James D.Witts, Neil H.Landman, Matthew P. Garb, Caitlin Boas, Ekaterina Larina, Remy Rovelli, Lucy E. Edwards, Robert M.Sherrell, J. KirkCochran

Summarized by Mckenna Dyjak. Mckenna Dyjak, who is an environmental science major with a minor in geology at the University of South Florida. She plans to go to graduate school for coastal geology; once she earns her degree, she plans on becoming a research professor at a university. Mckenna spends her free time playing the piano and going to the gym.

What data were used? A fossil and spherule-rich rock formation in Union County, Mississippi exposed by construction. The formation contains the Cretaceous-Paleogene (K-Pg) boundary, which marks the end of the Cretaceous and the beginning of the Paleogene, estimated at ~66 million years ago. This boundary is characterized by a thin layer of sediment with high levels of iridium which is uncommon in Earth’s crust, because it is almost exclusively from extraterrestrial sources.  The K-Pg boundary is associated with a mass extinction: a significant, widespread increase in extinction (ending of a lineage) of multiple species over a short amount of geologic time. The iridium indicates that the extinction was likely caused by an extraterrestrial impact; the spherules found support this idea as well, as spherules are formed from ejecta after an impact. 

Stratigraphic (ordered) section of the rock formation showing the rock units, type of
sedimentology (sand, silt, clay), and fossil type. The K-Pg boundary is marked by the horizontal
dashed line. The black arrows point to calcareous nannofossils and the white arrows point to
dinoflagellate cysts.

Methods: The fossils present in the rock formation were identified and compiled into a complete list. In order to find out the composition of the rock formation. 14 sediment samples were collected; these samples were used to construct a biostratigraphic analysis: corresponding relative rock ages of different rock layers to the fossils found within them. The mineral composition and grain size were determined to construct this analysis. The mineral composition (mineral percentages present) of the sediment samples were determined by using a Scanning Electron Microscope (SEM) and a Diffractometer (type of X-ray). The grain size analysis of the sediment samples was determined by using a sieve (mesh strainer) to sort into different sizes. The Carbon-13 levels of the sediment samples were analyzed: Carbon-13 can be used to determine the amount of plants that were present at the time.The data collected was used to construct the stratigraphic section shown in the figure below.

Results: There was a significant decrease in the amount of micro and macro fossils present. Along with the decrease of fossils there was a positive shift of Carbon-13. The positive shift of Carbon-13 indicates that there was an increase in plant matter buried in the rock record. Sedimentary structures such as weak cross-bedding and laminations (indicates flowing water and fluctuating energy levels) An important layer was analyzed: 15–30 cm thick muddy, poorly sorted sand containing abundant spherules (sphere pieces) that were likely a product of  the Chicxulub impact event.

Why is this study important? The findings suggest that there was a quick, local change in sediment supply and possibly sea level due to the significant variation in facies (body of sediment), fossil changes, and different geochemical data that coincided with the extinction event. 

Big Picture: This study helps us understand how different areas were affected locally before the mass extinction event, which can help us understand how recovery from mass extinctions take place. 

Citation: Witts, James, et al. “A Fossiliferous Spherule-Rich Bed at the Cretaceous-Paleogene (K-Pg) Boundary in Mississippi, USA: Implications for the K-Pg Mass Extinction Event in the MS Embayment and Eastern Gulf Coastal Plain.” 2018, doi:10.31223/osf.io/qgaj