EP 125 Jernigan

Last modified 3:43 PM, January 16, 45.59 MB, 33 min.

Hello and welcome to Field, Lab, Earth, the podcast that's all about past and present advances in the fields of agronomic, crop, soil, and environmental sciences. Today, we'll be talking to Dr. Ashley Jernigan. Microarthropods are little critters that can have a big impact on crop production, particularly when it comes to nutrient cycling and nutrient acquisition. However, there's still much to learn about how the work these little helpers do is affected when paired with different types of fertilizers. In this episode, Dr. Jernigan joins me to discuss how microarthropods get along with different fertilizer treatments. I'm your host, Abby Morrison. Let's talk about science. Hi, everyone. Welcome to the show.

Today, we have Dr. Ashley Jernigan with us. Dr. Jernigan has recently joined Virginia Tech as the assistant professor of organic and sustainable vegetable crops production. She earned her bachelor's degree in international agriculture and rural development from Cornell University. She also completed her PhD in entomology at Cornell University in 2023, where she investigated the role of soil microarthropods in multiple aspects of cropping system management. She has research experience within the field of soil science, weed science, plant pathology, horticulture, and entomology.

Her diverse research background informs her systems level approach to crop management. At Virginia Tech, her research program aims to increase the sustainability of vegetable cropping systems by improving our ability to capitalize on biological processes and ecological patterns. Her work bridges mechanistic and applied research to further integrate soil biological processes into crop management strategies. Hello, Ashley. Welcome to the show.

Hey, thank you so much for inviting me.

Yeah, we are so happy to have you with us today. So, we are going to be talking about microarthropods and how they can help plants do what they do. So, to start us off, can you tell us a little bit about microarthropods in general, what they look like, how big they are, just general information?

Yes. The soil microarthropods are a pretty understudied group of soil biota, and in terms of abundance, they're dominated by springtails and mites. They are about the size of a grain of sand. Their body width is about 100 micrometers to 2 millimeters. So, whenever you're looking at a handful of soil, you're not really going to see them, but they're there just like microbes doing important processes.

Yeah. I was going over your paper again a little bit this morning and I saw you had mentioned one species that you used in this research specifically. I looked it up. Listeners, I actually looked it up beforehand this time and springtails are so cute. They're just adorable. For people who don't know what these things look like, I don't know if you've ever seen the videos of a manatee and they smush their face against the tank and they just condense. It's like if an ant did that and they just compress their entire body, they're very, very cute. So, I encourage people to look them up, but I will chill on fangirling over these adorable little creatures, so that you can tell us a little bit more about what you were hoping to address in this study. So, what were you hoping to investigate?

Yeah, so we know that soil microarthropods, springtails and mites play really important roles in soil organic matter, decomposition, and nutrient cycling, but how their role in these biological processes manifest in plant growth and development is still pretty not well understood in our field. We're trying to figure out how their roles in the soil environment can be better utilized to enhance crop production.

So, you had two greenhouse experiments that you did as part of this. So, tell me about them. What were you hoping to address with those?

Yeah, so growers have a lot of options in terms of how they're feeding their soil biological communities and what inputs they're using to give the crops the nutrients that they need. So, we wanted to compare different fertilizer options that growers can use and see how they interact with our soil microarthropod communities and these biological processes and how that ultimately manifested crop growth. So, to do this, we had our first greenhouse experiment focusing on this model organism, the one you looked up, Isotomiella minor. It's a really ubiquitous springtail that you can find pretty much anywhere, and they're really easy to maintain in colonies.

So, we keep them in our lab. We were able to have three different abundance levels with a no collembola control, then a low abundance and a high abundance based on what we would see in a natural field setting. Then we had our four organic fertilizer treatments where we had no fertilizers control and alfalfa green manure that I got from a local farmer's field, a poultry litter compost bought commercially, as well as Chilean nitrate. So, these fertilizers were chosen specifically because they really differ in their chemical composition and complexity, and we were really interested in the fact that they have these different carbon and nitrogen ratios that would affect their decomposition over time.

So, once we had all of our treatments set up and the pots were the greenhouse, we went in each week and monitored the growth and development, did our growth staging, and then at two time points within the experiment, we went in and did destructive harvest to mimic a forage harvest for growers around the boot stage. So, there was no seeds yet, but if you were giving it to your livestock, and then once the oats had developed seeds when they would be harvested for grain at the soft-dose stage.

Okay. How does destructive harvesting work? Tell me about that.

Destructive harvests are really fun because you just basically tear everything apart and get it into a state where you're ready to analyze it. So, what we did was we would take our little clippers and clip the biomass at the soil surface level because we were interested in how nitrogen and nutrients were moving between the different types of plant tissue. So, we had our above ground biomass and we would separate our seeds at that grain harvest at the end from the shoot biomass as well. Then you get to flip over the pots, and I love getting to use a soil knife or soil sauce to just cut soil that's rebound in half.

The reason why we need to separate the soil is because we always want to validate our microarthropod treatments throughout an experiment because they're these living biological communities. They're going to change and grow or diminish over time depending on the environment. So, we would put half of that soil on our Berlese funnels, which we use to extract the microarthropods from soil. So, we can count them. Then the other half of the soil, we were able to remove the root tissue. So, we could weigh and analyze that just like the above ground biomass. Then with the remaining soil, we would do some analyses on that to determine our microbial characteristics and other points of interest in the soil.

Sure. Okay. I know I am getting it a little off track, but I am just obsessed with these tiny creatures that exist on this planet. So, tell me more about both having a colony of things that are so, so tiny and then also what is that counting process look like. I mean, are you just going in and counting them one by one? Are you just using a tool that approximates these things? How does working with something that is so small and so cute function in the lab?

Yeah, it's pretty challenging, but it's also a lot of fun. So, maintaining the colonies is actually really easy. The deli cup containers you would get from a takeout restaurant, we just use those with some plaster of Paris and charcoal at the bottom, and we put a little bit of soil in there. They're pretty hardy over time. As long as you keep the colony moist and you put in yeast, just regular baker's yeast from the grocery store works great, they are happy and content to continue reproducing. So, easy to manage, but they're fast. They're called springtails for a reason. They have this organ on their bellies called a furcula, and they use that to hit against the ground and literally spring up. They can jump the equivalent as if I were to just jump in one leap to the top of the Eiffel Tower.

So, they're pretty amazing. That makes them hard to work with in terms of trying to count them, because I was trying to get an exact number of Collembolas into our specific pots for our treatments. So, trying to handle living organisms that are so mobile and bouncy can be a little challenging. So, it takes a lot of patience and a lot of hand dexterity. We work with them under the microscope when they're living and dead. So, to count them from the colonies, it's much easier because they're not in a soil substrate. We don't have to extract them from anything. I like to just dump them out of the deli cup into a smaller clean container, and I can count them under a microscope.

However, whenever we're counting living microarthropods or dead ones from soil, they first have to go through an extraction procedure using modified Berlese funnels. What this funnel system does is it relies on the microarthropods' natural biological response to move away from the heat and dryness because they like to be moist and in the dark. They're soil dwelling organisms.

So, by having a light bulb that puts off heat and light, they will move from the soil that you sample or collect down and drop it to the funnel where they fall either into a container of ethanol if we're trying to pickle them, so we can count them easier under the microscope, or into another type of container where we can do a live extraction. So, we can use them for experiments like we did with the second greenhouse experiment when we wanted to have that diverse natural microarthropod community from a local field.

I love that, how scientists figure out how to approach just really weird specific problems that they encounter and just consistently wowed by the way that they're just like, "Oh, instead of trying to go in and pick them out, why don't we just make the animal move itself?" That is so smart. So, I love that description. So, you had the two studies and the difference between them was just that one of them was all springtails all day and the other one was a mix of microarthropods, so getting additional mites in there. Is that the main difference?

With our single species experiment, it was just one species, but in the native community we collected, there were dozens of different springtail species probably and lots of different mites. There was also other microarthropods. So, some of those critters like peripods, centipedes, millipedes that are still technically in that category due to their size classification, but they were in such low abundances. They don't really have as much of a biological effect in the environment like those springtails and mites because of their really high numbers.

You said there's these natural communities, but I also know you wanted a variety of a low volume to high volume of microarthropods in your pots. So, are you just going to a place that you know has a lot of them or are you taking natural samples and then just dumping extra ones, like collecting them and then dumping them into a smaller container of soil, or how does that work to get different volumes if it's just a natural or are you just ordering them in?

Yeah, so it's a lot of soil manipulation. There's a lot of phases we have to get to prepare our soil treatments. So, the first step is collecting the soil that we want to use for the experiment. Because we wanted to have native microbial communities as well, we decided to defaunate the soil and remove all the microarthropods by using this heating and cooling cycle that will get rid of all the microarthropods without altering the microbial community. Then what I did was I did a preliminary sampling in a local pasture grassland area near our research station, and I extracted all of the microarthropods from a set volume of soil and counted them and classified them. So, I could get an idea of what communities were in that area.

Then I put the defaunated soil into our three big bins to represent the no micro arthropod communities, low communities, and high communities. Then I went back out and I collected fresh soil and did our live extraction. I put in double the volume of soil for our high community compared to our low community, so that we could roughly calculate that we would have twice as many microarthropods come out into our high community treatment. We let those big bins that we had put the extracted microarthropods in and set for a couple of days, so that they were evenly distributed and mixed throughout the soil before we put them in the pots in the greenhouse.

How abundant are microarthropods? If I had a coffee mug full of soil, how many are in there? Because it sounds like a lot of intense counting if they're very, very abundant.

Yes, there are hundreds to thousands of microarthropods in a coffee cup of soil, really depending on the natural ecosystem they've come from. So, agricultural systems, fortunately for me, because that's what I study, have lower abundances compared to our forest or grass lands or more natural undisturbed ecosystems that we as humans are managing. But there's still a lot of microarthropods in our soils, and they're one of the few organisms that can be found on every continent including Antarctica. So, wherever you're standing, you're standing on thousands of these little critters.

Hi, everyone. I hope you're enjoying the show. Interested in learning more? Ashley's paper, Microarthropods Improve Oat Nutritional Quality and Mediate Fertilizer Effects on Soil Biological Activity, published in Agronomy Journal is always freely available. If you're a certified crop advisor or certified professional soil scientist, you can take a quiz for continuing education units for this episode, which can be found in our show notes or on certifiedcropadvisor.org.

Let's get back to the show. I knew that this would be a really fun conversation because anytime there's anything that is a critter, I'm very excited about it, but these are just wowing me on levels that I did not realize would occur within this conversation. So, this is very exciting for me. We still need to talk about results. So, what did you find?

Yeah, so like I mentioned, we measured a lot of different things throughout each of these experiments. In terms of our soil metrics, we were focusing on nitrogen cycling because that's really the dominant nutrient that growers are trying to manage. So, we measured our microarthropods again to validate our treatments. Microbial biomass, so trying to get an estimate of the size of the community, we do that by measuring the carbon and nitrogen in them. Then microbial enzymes, our way that we can assess the activity of the microbial community. We chose five different enzymes, all of which are important in breaking down different elements like chitin, lignin, cellulose, et cetera, all of which are important within the nitrogen cycle.

Then the total soil carbon and nitrogen were of that elemental state that we would find. Then in terms of plant metrics, we had our biomass that I mentioned. We also counted and weighed the seeds. So, we could get an idea of reproduction of that grain harvest. Then for each of those three different types of tissues, the root shoots and seeds, we had our carbon and nitrogen content that we wanted to assess to see how nitrogen was moving through the plant tissues. So, one of the really unique and cool things about this study was that we were really focused on the big picture of how the soil environment overall affects crop growth and development overall, in this case for the oats that we were producing.

So, the way that we were looking at this was with really cool multivariate statistics that was able to say, "Okay, this is everything we measured in our soil environment related to our biological communities and nitrogen cycling. How is this entire data set affecting growth and development over time?" Because we had our weekly checks, where we were measuring their growth stages and how they were developing, and then we had our reproductive and biomass measurements as well as how the nitrogen and carbon was being allocated throughout those tissues. What was really unique was that we were able to see which soil characteristics were specifically correlated to crop growth and development.

We saw initially at that first harvest where we were looking at the forage stage of the oats, there was this focus on the biological metrics, right? Soil microarthropods, microbial biomass, nitrogen, some of those key nitrogen cycling enzymes were really correlated to the crop metrics at that time point. But then as time went on and we got to the grain harvest at the very end of the experiment, we saw this shift where more of the chemical soil metrics, soil carbon and nitrogen itself, as well as some of those microbial enzymes were still correlated with the plant metrics.

Really highlighting and illustrating how oat growth and development was initially related to those interactions between the soil biota and the fertilizers. Then we saw that shift by the end of the experiment once the crops were fully mature to where the nutrients stored in the soil were really important later in the growing season. So, healthy soils with those diverse biological communities have the potential to regulate nutrient availability for plants throughout the entire growing season.

So, I know that microbial communities impact a lot of plant function and soil properties and things like that, but you were trying to study specifically how microarthropods are assisting in breaking down the fertilizer, getting it where it needs to go, helping these communities thrive. So, how do you separate out what the microbial community is doing versus what the microarthropod community is doing? Is it just because you know that the microbial communities should be pretty standard across your samples? So, if they're affecting things, they should be affecting them at the same level, so you can take that out of the equation. How does that work?

Yeah, so in the case of this experiment, when we were preparing our soil treatments, as I mentioned, when we did our defaunation process, we left that soil just as it was in terms of the microbial community. Since we didn't alter the microbial community between our different pots that we were looking at, we're able to assume that any of the changes we observe in the microbial community was due to either our microarthropod or fertilizer treatments.

Okay, that makes sense to me. As you're describing what you were measuring, I was like, "Oh yeah, I think the prefix of micro is just making them the same thing in my brain." So, I have to keep being like, "No, these are two separate types of thing that exist." So, you were measuring a lot of these things. So, what did you find as far as how these microarthropod communities are doing it at the different volumes?

Yeah, so overall, just looking at the big picture, we saw that our microarthropods, both in that single species and diverse community greenhouse experiment, stimulated nitrogen cycling within the soils and these pot systems and enhanced our crop nutrition pretty much just indirectly through their effects on soil biological processes and what they're doing with the microbial communities, not this direct relationship between the microarthropods and the plants, but that makes sense, right?

We know in the nitrogen cycle that microbes are the dominant organism that's affecting nitrogen movement through the soil, especially bacteria. So, I think of microarthropods as the big brother of microbes where they're keeping them in line and helping to regulate those communities. So, they are affecting their processes, but anything that we're seeing in terms of nutrient management is definitely funneled through that interaction between the microarthropods and the microbes.

Nice. So, did you notice a difference in their impact depending on the fertilizer type, or was it just because they're in that helper role, it doesn't really matter which one you use?

Yeah. So, interestingly with the fertilizer treatments, we had again chosen fertilizers with vastly different compositions, some that would need more work to be decomposed, broken down, that alfalfa green manure in particular versus the Chilean nitrate, which is already a plant-available form of nitrogen that plants can quickly absorb once it's added. So, the type of fertilizer ended up being an interesting effect that we were looking at. In both experiments, the effects of the microarthropods seemed to diminish over time from those initial fertilizer additions, which really showed us that those initial interactions of the nutrients or the fertilizers entering the soil environment was an important stage of the microarthropods role in nutrient cycling.

It's basically if you were to take an alfalfa leaf, just a whole leaf and throw it on the soil, the microbes can only access what's on the surface because they're tiny, even compared to the microarthropods. So, having those shredding and grazing organisms in the soil that are able to break down these larger resources into more bite-sized chunks for the microbes where they can release the nutrients is really important. We saw that the indirect influence of microarthropods on crop production through their effects on the microarthropod communities was really significant.

As our abundance and diversity increased in the microarthropod communities, they were exerting a greater number of effects on the soil microbial community's activity, those enzymes I mentioned, which is a direct impact on plant nutrient availability. So, through these impacts, they were able to narrow the effects of the fertilizers because they were helping with that pre-processing. If you don't have that first step of the process, so the microbes can release the nutrients, then those more recalcitrant, less plant-available nutrient sources that farmers may choose aren't going to get into the plants as quickly or as easily. So, it definitely helps with nutrient management decisions if you have a healthy biological community.

Nice. So, it seems like having more of them in the soil is a helpful thing based on your results. Is that something that the average farmer like outside a research setting can just... How would you do that? Is there a way that you can manage your land to encourage a healthy community? Can you order them to just add them to the land? How does that work?

Well, the great thing about microarthropods, as I mentioned, is they're everywhere. So, you don't have to order them, you don't have to pay for them. They're living organisms. You can think of them just like your pet. They want a healthy, happy environment where they are safe and sheltered from the negative environmental elements, and they have plenty of food to eat. So, in terms of agricultural management, that looks like putting in high-quality nutrient resources like green manures, compost, things that are really nutrient-rich into your soil compared to those quick-fix chemical fertilizers like the Chilean nitrate that doesn't have a lot of bulk for your soil biota to feed on.

Then in terms of habitat, having good pore structure and the ability for these animals to actually move through the soil and access the resources and environmental conditions that they want. So, that can look like reducing your tillage or making sure you keep a living root in the soil that's able to open up forest base and not disturbing them because we do know that tillage can decrease the abundance of these communities.

I love how much on this show just comes back to soil health. It's usually the answer to a lot of things is just take care of the soil, which is great. So, as you mentioned, microarthropods are not super well-studied little critters out there. Where is this research going? What's next on the horizons? What other areas would be helpful to keep studying as regards to this kind of research?

Yeah. Well, like I mentioned this study and the work I'm continuing to do is looking at how the effects that the microarthropods are having in our soil environments is manifesting in plant growth and development. So, in terms of the future, I'm really interested in seeing if we can use the microarthropods' potential to release nutrients from organic matter amendments and the soil in terms of micronutrients, because we know that micronutrient deficiencies is a problem globally for humans. If we're able to foster healthier food by creating healthier soils, that would be amazing.

Oh, I love that. That's very promising. They're just taking on that helper role for everybody down to microbial communities our way to helping us. Lovely. So, I have three questions left for you then. First one, if people want to learn more about any of the topics that we've talked about today, where can they go?

So, there's a lot of great resources out there. I'll plug my extension resources I created at the same time I was doing this experiment in grad school. I have some fact sheets on soil fauna and a video I made that's aimed at growers that can sample their own fields and learn a little bit more about what's living in them. Also plug one of my favorite macro photographers from the UK, his name's Andy Murray. He has a website called A Chaos of Delight, and it's not only a beautiful artistic thing to look at, but it's a great educational resource. He really explains a lot of these categories of fauna.

He travels the world. So, a lot of the microarthropods we have here are a nice shade of beige. We do have some fun bright pops of blue and purple in our samples, but the ones near the equator and then the tropics are really exuberant and charismatic and just crazy looking. They're little aliens.

I'm so glad that you brought that site up because that's literally where I was looking at these pictures before our call. Yeah, in addition to the smush condensed ant that booped a wall too hard, there's also ones that look like sea cucumbers and they look like they could be big giant animal on a sci-fi movie. They're very, very cool. I encourage you to look that up if you have the opportunity, because I had a blast looking at them. So, second question then, if people want to then take the next step and get involved in either this research or applying these takeaways on their farm, I know you mentioned some of the extension resources to help walk them through, but what else can they do to get involved?

Yeah, so as you mentioned, everything just comes back to good soil stewardship. So, there are companies and organizations globally in your local area that are probably working hard to foster good soil stewardship in your community. So, any way you can support those are always great. If you own land yourselves, the NRCS, the USDA's Natural Resources Conservation Service has four key principles for improving soil health and sustainability that anyone can implement. So, the first is minimizing soil disturbance, the reduction of tillage.

As a homeowner, you can even think of mowing your lawn as a way of disturbing that environment or soil aeration. The second is maintaining living roots, so making sure that the ground's always covered and protected from erosion. The third is maximizing soil cover, which again goes hand-in-hand with the living roots. Then lastly, increasing biodiversity and slow microarthropods themselves are this great reservoir biodiversity, really, really unique in crazy communities.

So final question then, what is one fun fact about you that people would not know if all they had was your research?

I really enjoy doing crafts and art. I'm not an artist by any means, but I really enjoy painting. Now that we've finally settled down here in Virginia, I'm getting to paint all of these fun murals on different walls in our house and really make it our own. That's been a lot of fun.

Ooh, I love that. That sounds so fun. What kind of crafts do you do?

Well, in addition to painting, I really love doing resin art. There's not a lot of fun microarthropod gear. If you were to go to a conference for agronomy, your insects, you'll see people wearing all of these fun clothes and jewelry representing their study organisms. So, I got really into putting microarthropods in resin. You can hardly see them, but I know they're there. If I get the contrast just right with a good soil background or a leaf, then they pop, and everyone's always like, "Oh, what's in your earrings?" I'm like, "Oh, that's clearly a mite."

Oh, I love that. Oh, my gosh. Resin is not easy to work with, so kudos on getting that to work. Wow, impressed on so many levels today. As part of this conversation, loved learning about microarthropods and this research. Thank you so much for joining the call today and for doing the research that you're doing. We wish you all the best as you continue on in your study area.

Thank you so much.

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