How Precipitation affects Prairie Plants and Plant Pathogens

Maria Losito: Welcome to another episode of Interview with a Biologist. I'm your host, Maria Losito and I'm joined today by Dr. James Bever, who is a KU Foundation Distinguished Professor of Ecology and Evolutionary Biology and a senior scientist at the Kansas Biological Survey and Center for Ecological Research. How has your week been so far?

James Bever: It's been wonderful, thank you. 

Maria Losito: Good, yeah, it's two days into daylight savings time, so personally, I am struggling.

James Bever: I can relate to that, yeah, It's a rough adjustment every year.

Maria Losito: One of these years it'll eventually go away and it'll just be beautiful. Could you tell us a little bit about your research interests?

James Bever: Yeah, I'd love to. So, I study plants and all the microbes that they interact with. Plant roots grow down in the soil and they're interacting with thousands of different kinds of microbes simultaneously and some of them help plants grow, and some of them eat the plant and have a strong negative effect --How do we understand that net effect and the dynamics of that system and how plants try to balance all of the beneficial and the non-beneficial interactions? That's sort of what we study.

Maria Losito: Along with all of your research work I believe you also teach some courses at KU. Can you tell us a little bit about those courses?

James Bever: Yeah, I teach Lab and Field Ecology, and I teach upper-level course on Concepts in Ecology and they are a lot of fun. 

Maria Losito: Yeah, I believe the Field Ecology classes mostly take place at the KU field station or simply around Lawrence?

James Bever: It's the KU Field Station. We use that a lot- We use other resources around Lawrence as well. It's traveling, taking students around in the van and doing exercises to do that.

Maria Losito: That sounds amazing. As you got started was there something that really drove your research and that interest in soil ecology?

James Bever: Yeah, that's a good question. So, I was starting out trying to think about how plants-- whether plants from a local environment would do better because they're reinforcing the beneficial microbes or would they do worse because the microbes would overwhelm them? --That simple question was just something that all gardeners might relate to--actually developed into a whole avenue of research where I evaluate the net effect of how microbes impact plant growth and how that relates to the structure of plant communities and the productivity of plant communities. It's been a lot of fun, and it's been a sort of an evolving adventure.

Maria Losito: You recently published a paper titled“Pathogen dilution, resource partitioning, and precipitation generate productivity benefits from plant diversity.” Would you tell us about what this publication is about?

James Bever: Yeah, I'd love to. So, this was where we're reporting the results of the first six years of this large experiment, where we manipulated the number of plant species in prairie plants. We [look at] the composition of those plants-- Plants from the same family versus plants from different families, and then the level of precipitation-- and we have all the plants in the shelters, and then we removed all the rain, and we put it back on with a sprinkler system and so, the goal is to evaluate what is the value of plant biodiversity.

Why are there so many plants and what is their impact on productivity and functioning of our communities. One major thing that came out of that is that interactions with pathogens can play a major role in the productivity of these systems in high diversity communities.

Maria Losito: Okay. So, I had been up to the field station, and I believe I had seen some of your grid system for these plants. If I remember correctly, you had some plants in a monoculture and some that were a polyculture.  With those two sorts of different setups did you really see big differences between the two?

James Bever: Yeah, they're exactly right. The monocultures were consistently low productivity. The total amount of plants in the plots was much less than the productivity of these plots in polyculture. So, productivity is something that we can all value as it relates to agricultural productivity. All of these things that we want, desirable or desirable properties of ecosystems increases dramatically with the diversity of plant--with the number of kinds of species in those plots.

Maria Losito: For the pathogens, if it was a negative pathogen, I suppose, would you see more of them in the mono-system versus the poly-system?

James Bever: Yes. So, the pathogen impacts are greatest in these monocultures. The pathogens are specialized and so they are able to eat some plants but not others. In a monoculture where it's all plants that a single group of pathogens can eat, they get to go from one plant to the next plant. They're always able to consume everything around them and that suppresses the plant productivity. But when you have lots of different kinds of plants near each other then there still may be pathogens in that system, but they are not amplified by their neighbor. So, when they disperse to their neighbor, they are not able to thrive.

Then the overall density of the pathogen, the overall impact of the pathogens in the community is much less. So, the diverse plant community suppresses the pathogen impacts and that allows for greater productivity in the system.

Maria Losito: That makes a lot of sense. I know you hear about orange tree blights and how these huge farm systems that are just orange trees, how they'll all be wiped out by one disease showing up. So, in a way it makes sense having more diversity of plants is a way kind of make a wall against [pathogen] spread.

James Bever: That's exactly right.  A common problem for agriculture is that it's easiest to plant monocultures of corn and soybeans here in Kansas or oranges in California or Florida but that ends up being a just a perfect situation for the pathogens and which creates very deleterious problems for big problems for farmers.

Maria Losito: Along with the pathogens, you had also mentioned that precipitation had an impact on growth and loss. So, breaking this down for the everyday person, why is it important that we research changes in precipitation and the loss of species diversity in grasslands or other sorts of cultures that you're growing?

James Bever: Yeah, we removed all the rain here in Lawrence, and then we put on one plot, in one house, we would put 50% of the rain back on and that sort of replicates the environment of the middle of Kansas where it's drier. Then in the other house, we put 150%. That replicates the more moist environment of eastern prairies in Illinois and further east.

What we find is that the eastern prairies have a lot more kinds of plants. They have a more diverse prairie community, really at a local scale than in central Kansas and what we found in our experiment is that the productivity benefits of diversity increase with precipitation and a major reason for that is that pathogens like it wet.

In these monocultures with a lot of water, the pathogens really build up to high densities and that suppresses the yield. So here we are in Lawrence and we're putting a lot more water on the plots and we're getting less productivity, but in the polyculture, we get the response that we expect. When we put a lot of water on the plots, we get more plants, and that's because they're able to control the pathogen impacts with the diversity of the communities and so that illustrates that as we in areas with higher moisture, then it's even more important. Plant diversity is functionally more consequential for productivity and for ecosystem function.

Maria Losito: What kind of methods did you utilize to find your results and where did your research take place?

James Bever: Yeah, so we were working at the KU Field Station, and we a lot of the maintenance of the plot composition is weeding and so we employed a lot of KU undergraduates over the summer,  who learned taxonomy-- plant taxonomy, had to learn to identify all the plants and then it was a lot of work weeding during the summer but they were involved in a lot of different dimensions of the research.

A lot of those students went on to grad school in the sciences. We also did sequencing. In order to determine the composition of the microbial community and the pathogens and other microbes, we would take soil samples and we would extract the DNA from those samples.

We were identifying all of the species present; all the microbial species present form by amplifying and sequencing the DNA, and that that involves a lot of bioinformatics, and a lot of technical challenges and interpreting that. But it's those two kinds of things: One is just like gardening, and the other one is lab work and putting those two things together is what allowed us to get the inference that these pathogens are the major drivers of that productivity increase with diversity.

Maria Losito: Just to reiterate, during this study, what kind of findings did you have? What will those findings mean for further research?

James Bever: The importance of plant species diversity for pathogen control and productivity gains has important consequences and we're still trying to understand how those consequences cascade through the ecosystem. So, we do see greater carbon accumulation in the core in the soil, so greater nutrients in the soil with higher diversity of plants, so that is one of the longer-term benefits and trying to work out exactly the mechanism driving carbon in soil is a major avenue for future research.

If we better understood how we sequester carbon in the soil in these grasslands, because grasslands hold lots and lots of lots of carbon in the soil-- that's why the soils are so black-- If we better understood that process, we would better be able to manage our communities to remove CO2 from the atmosphere and help balance the climate problem that we that we're all facing right now. 

But the other, more practical dimension of this, is just directly for agricultural production. Farmers are planting in monoculture. If it was possible to include more kinds of crops in the cropping system, what would be the benefits and how would that benefit of crop diversity, balance with the effort to breed resistance in individual crops?  

The value of crop diversity is that you can get resistance to many pathogens at once while breeding for resistance, you're targeting one pathogen at a time. It's a slow process, and the pathogen evolves and overcomes that resistance in in continually. So, it's possible that we could get greater productivity by incorporating those two things together and we're studying that now with a grant funded by the U.S. Department of Agriculture.

Maria Losito: Is there anything we haven't talked about yet that you think would be good to sort of touch on?

James Bever: I'll just add that, going back to how the plants are interacting with lots of microbes simultaneously-- one other avenue that we're exploring now is how interactions with the beneficial microbes might alter how the plants defend themselves against the pathogens and were actually finding really complicated interactions, which we're in the middle of working out and that’s something that I would enjoy talking with you in  in the future.

Maria Losito: I'd love to hear about it. Thank you so much for joining us, Dr. Bever. I really appreciate you taking the time and stopping by and for offering to come back again.

James Bever: Thank you so much. I really appreciate that you're taking the time to talk to me.

Maria Losito: Thank you for listening to Interview with a Biologist. You can check out the show notes for more information about Dr. Bevers work, as well as a link to the research paper discussed in this episode. A full transcript of this episode will be available at biology.ku.edu.