About Me and My Research:
I grew up in northern California, and as a child spent as much time outdoors as I possibly could. Hiking in the Sierra Nevada and on the Pacific coast sparked my interest in the natural world, particularly for the study of plants. Now, as a PhD student at the University of Pittsburgh, I study the movement of toxic heavy metals through ecosystems. Pollution resulting from coal and mineral mining has left many natural environments contaminated with heavy metals, which may negatively affect both plants and animals that live nearby. Some plants, however, are known to accumulate soil contaminants and thus may be used in efforts to clean polluted soils. Unfortunately, these metal-accumulating plants may negatively affect pollinators and herbivores, which feed on plant tissue, if they eat them. Understanding the fate of environmental contaminants is vital for land managers whose goal is to clean contaminated soils without negatively affecting surrounding wildlife.
My big greenhouse experiment is underway! In order to determine if soil metals negatively impact insect populations, I first need to document whether plants absorb metals from the soil and store them in tissues that insects eat, like flowers. In a separate experiment that I conducted last summer, I found that one nickel-hyperaccumulating plant species did indeed accumulate nickel into flowers, including nectar and pollen. However, I am interested in how soil metals affect plant-insect interactions generally, not only for metal hyperaccumulators. Therefore, in my current experiment, I am growing several species of plants (some hyperaccumulators, some not) in soils that I have added potentially toxic metals to, and will determine whether the plants are storing metals in different tissues, including reproductive structures.
Just finished analyzing some data from my work this past summer, and found some interesting results! I conducted two separate experiments during the summer to determine whether the presence of metals in floral tissues alters pollinator visitation. This is important for two reasons: (1) pollinators may be negatively affected by the presence of metals in nectar and pollen if they are consuming these resources, and (2) plant reproductive success may be reduced if pollinators avoid visiting plants that have metal-tainted pollen and nectar. Here’s what I found: while pollinators do not avoid plants that produce metal-tainted floral rewards (i.e., nectar and pollen), they tend to spend less time foraging on these plants compared to plants that do not have metal-tainted rewards. These findings suggest that pollinators may be negatively affected by plants that accumulate metals into floral tissues, and also that plants growing in polluted environments may have low reproductive success due to decreased pollinator visitation. The results of these studies are important when considering the consequences of phytoremediation, which involves growing metal hyperaccumulating plants in polluted soils in order to remove heavy metals from the soil environment. Because pollinators do not completely avoid plants that accumulate metals into floral tissues, local insect populations may be harmed by the introduction of metal hyperaccumulating plants.
My current greenhouse experiment is winding down, as all of my study plant species are now in flower. Now the hard part begins- collecting all of the various tissues, including flower parts like pistils and anthers, and preparing them for chemical analysis. This is a multi-stage process that is very time consuming, so there is no time to waste! First, I must remove plants from the greenhouse, bring them down to my lab work space, and then dissect apart the various tissues I need to collect. This process takes about 25 minutes per plant, and with almost 1,000 plants growing in the greenhouse, that’s a lot of time! Next, the tissues are rinsed and dried in the drying oven- all of the elemental analysis I will do will be at the parts per million level for dry wright, thus I need to get rid of all of the water weight in each tissue collection. When the tissues are dried and weighed, I will digest them in a small amount of concentrated nitric acid- this reduces the samples to their elemental components, and removes organic compounds. After this, the samples are ready to run in the inductively coupled plasma mass spectrophotometer (ICP-MS). This fancy machine will tell me exactly how much of a particular element, such as the heavy metal nickel, is present in each sample. This is the last step for this experiment, which aims to determine the effect of soil metals on metal concentrations in various plant tissues. I should have some data to share very soon!
In addition to studying metal accumulation in plant tissues, I am interested in understanding trophic transfer of soil metals. For example, are metals that are accumulated by plants transfered to animals that eat these plants, such as herbivores and pollinators? I am particularly interested in trophic transfer of metals to pollinators, as there is currently little available data to help us understand whether metal contaminated soil may harm pollinator populations, which are valuable both ecologically (help plants reproduce) and economically (help produce foods for humans). This past summer, I conducted a survey to determine if bees foraging in polluted environments are providing their offspring with contaminated food (nectar/pollen). Working at the Powdermill Nature Reserve in Rector, PA, I placed bee nesting materials in one polluted environment (a site contaminated with the metal Al due to previous coal mining activities) and one unpolluted environment. At the end of the season, I collected the boxes so I could determine whether or not bees produced in contaminated environments were themselves contaminated with metals. Recently I have sorted through all of the nests and removed the bee larvae in preparation for chemical analysis of their bodies. Soon I will have data that will provide valuable information for land managers seeking to understand the implications of soil metal contamination for both plants and animals in polluted environments.
There is only one task left to complete for my current greenhouse experiment: analyze all of the different plant tissues for their chemical composition. After growing plants in soils with various metals, I now want to know if plants are moving metals into tissues that may affect plant reproduction, such as anthers (which produce pollen) and pistils (which produce ovules). This will be done using Inductively Coupled Plasma Mass Spectrophotometry, which I have mentioned before, but I thought I would provide some additional details about how this machine actually works to provide elemental information relating to plant tissue samples. Modern technology is amazing, and ICP-MS allows for the determination of specific elements, like the metal Ni that I study, in very small tissue samples. For example, I can determine the parts per million (1 ppm = 0.0001% dry weight) concentration of Ni in a sample that is only 1/1000 of a gram! Pretty cool… Here’s how it works: after samples are dissolved in a solution, they are introduced into the machine. The samples are quickly heated so all molecular compounds are reduced to individual ions (for example, Ni or Ca ions). Ions of different elements vary in both their mass and their charge, and the ICP-MS is able to separate the elements out based on these differences. Thus, from running a single sample through the ICP-MS, a researcher can gain information on many elements simultaneously. This process differs from other methods, such as atomic absorption spectrophotometry, where samples have to be run separately for each element of interest. For the next month or so, I will be working daily to prepare samples for analysis on the ICP-MS. Ready… go!
It’s been a while since I’ve last posted, and that’s because I’ve been in the field collecting data! While much of my work is accomplished in greenhouse facilities at the University of Pittsburgh, I also study natural populations of metal hyperaccumulating plants in order to understand how metal accumulation may alter ecological interactions, such as plant-herbivore and plant-pollinator interactions. In this post, I’ve decided to share some photos of the beautiful field locations (and associated plants) where I spend my summers conducting field work. I mainly study two species of metal hyperaccumulating plants: Noccaea fendleri and Streptanthus polygaloides, both from the mustard family (Brassicaceae). Both can be found growing on serpentine soils in northern California. Over the past two summers, I have described pollinator communities associated with these unusual plants in order to determine whether metal hyperaccumulation in natural populations leads to differences in pollinator visitation, relative to closely related, non-metal-accumulating plant species. I’m currently working on identifying pollinators collected from these plants over the last two field seasons- more soon!
As the new year is fully underway, my PhD dissertation work is winding down. If all goes well, I only have a single experiment left before I will be able to defend my thesis and graduate next winter. Thus far, my graduate work has focused on understanding and describing metal accumulation into flowers and pollinator rewards in flowers (nectar and pollen), and determining the consequences of floral metal accumulation on plant-pollinator interactions. For my last experiment, I will determine the consequences of floral metal accumulation on plant reproduction more generally, by measuring how soil metals alter seed and fruit production. For this experiment, I will grow plants in four different treatments that represent different concentrations of soil metals. Half of these plants will be pollen donors, and the other half will be pollen recipients on which pollen will be applied to the female parts of the flowers. I will collect pollen from plants growing in each treatment, and use this pollen to pollinate flowers of plants also growing in the same four treatments. With this design, I can determine whether soil metals are more influential for plant reproduction when present in the soils of the paternal (pollen donor) or maternal (pollen recipient) plants. Results from this experiment will allow scientists to predict if plant populations can persist in soils with different levels of metal contamination.