In this podcast for Functional Ecology, Assistant Editor, Frank Harris, sits down with two Guest Editors—Pablo García-Palacios and Ji Chen— to discuss our recently published Special Feature on soil carbon storage. The Special Feature identifies emerging findings from soil microbial ecology and climate change research that can be used to reduce uncertainty if incorporated into theory and models.

Frank: Today, I have Pablo García-Palacios and Ji Chen with me. They are the Guest Editors for Functional Ecology’s Carbon Soil Special Feature, published in our June 2022 Issue. I’d just like to start with some introductions. Pablo, who are you, where are you from, and what are your research interests?

Pablo: Hello Frank, thanks for the invitation. My name is Pablo García-Palacios, I work at the Institute of Agricultural Science which belongs to the Spanish Research Council—the largest research institution in Spain— and I am located in Madrid. I lead the ecosystems ecology and agroecology lab. Here, we are conducting research at the interface between ecosystems ecology, biochemistry, and microbial biology, and we try to understand the different issues related with the influence of plants and/or organisms on carbon and nitrogen cycling, with a particular eye on the influence of global change (particularly climate warming). Using this research, we are addressing the emergence and dynamics of relationships in different systems. We are working particularly in urban systems, agroecosystems, and also natural systems such as drylands.

Frank: Thank you. And now I will ask Ji the same question.

Ji: My name is Ji Chen, and I am a researcher from Aarhus University, Denmark. My research aims to explore the underlining mechanisms associated with soil carbon and nitrogen cycling under global change and ecosystem disturbances. As a child, I enjoyed being outside and playing in the soil with plants and animals. That is why I chose to do research in ecology. Ecology is beautiful and I love what I do.

Frank: Pablo, can you discuss why you became an ecologist, do you have any advice for other ecologists, and where do you think the field of ecology should be moving towards. It’s a big question, but please do try to give it a go!

Pablo: Thank you Frank. It’s a big question but I’ll try to answer. My interest in nature generally started in summer trips with my parents—they liked hiking in forests and mountains in Spain, so I think my interest in nature came from there. Then, in high school, I continued to pursue my interest which led me to studying environmental studies in Rey Juan Carlos University in Madrid. With regards to advice, I think that in all research areas—ecology, physics, chemistry—things can be very competitive. We are all complaining about the lack of funding, so my main advice for anyone looking to enrol in PhDs would be to really love what you are doing. It’s going to be a lot of hard work, and it will be way easier to complete your PhD and keep your confidence high if you really like the research topic you have chosen. For the second part, it is quite difficult—where should ecology be moving towards? Well I just want to highlight that we are in a climate emergency right now. We have just been struggling with a massive heatwave here in Madrid where we experienced 42°C temperatures in the early June! We are living in the center of the Iberian peninsula, but we’ve never experiencing such early and harsh heatwaves. I think ecology should be helping at the grassroots/street level. We should be using our expertise to help different social movements and collectives. We must force our politicians to fight climate change.  

Frank: Well said. In this podcast, we are trying to unpack what can be quite heavy research and terminology, and we are trying to get this message out to a wider audience so that they can appreciate the importance of carbon soil storage. Let’s move on to my next question. You’ve both spoken about your backgrounds. How did you move into carbon soil as a subject area? Ji, how did that emerge as a really interesting and important topic for you?

Ji: I grew up with and around crops and soils which led me to pursue my degree at a top agricultural university in China. At that stage, I got the opportunity to learn about climate change and learned that we are living in an era where the climate is changing too fast—every year it is getting warmer and warmer. Because we have more CO₂ in the air, we want to store more carbon in soil because it is a massive carbon reservoir. This is where my interest in exploring carbon storage in soil comes from. We must learn how to increase carbon storage by utilising our human knowledge.

Frank: Pablo, can you, in plain terms, explain the importance of soil’s role as a repository for carbon (I.E., the mechanisms of carbon storage), and what is the role that microbial communities play in maintaining or affecting carbon storage in soil?

Pablo: First of all, it is important to understand that the soils are made up of soil organic matter—the accumulation of plant residue like roots, stems, and leaves. Over time, with the help of different actors such as soil microbial communities and fauna, soil is formed. Soil is a sink of carbon. The carbon that is stored in the soil is the same carbon that resides in the atmosphere with other greenhouse gases. Therefore, all carbon that is stored in the soil is, importantly, not in the atmosphere promoting climate change. That is an important first point to highlight and clarify.

Next, soil stores a massive amount of carbon—it is the largest terrestrial reservoir of carbon. It is stores almost 3 times the amount of carbon in the atmosphere, and 2 times the amount of carbon stored in plants! Even a small release of carbon from the soil would mean a significant contribution to the carbon that is stored in the atmosphere, thus further promoting climate change.

Soil carbon is simply the net effect of the soil carbon gains from plant inputs or from plant productivity. Balance is maintained with regards the soil carbon losses to the atmosphere via decomposition of the soil organic matter by soil microbial communities. This is balanced finely, but climate warming can affect this balance. It can decouple this relationship between soil and microbial communities. This is called the carbon-climate feedback, which is a difficult name to remember, but the explanation is simple. Higher temperatures lead to higher microbial activity and decomposition of soil organic matter. Microbes need co2 from this biotic source, so microbes are heterotrophic organisms that respire and decompose soil organic matter, thus releasing CO₂ which then contributes to the further accumulation of greenhouse gases in the atmosphere. The higher the temperature, the higher the microbial decomposition and breakdown of soil, which then leads to higher carbon emissions. This is a positive feedback which is already incorporated in the ICPP projections, with the help of an abundance of studies from the last 20–30 years. However, a lack of consensus still remains with regards to magnitude. There is lots of uncertainty regarding the mechanisms that are driving this carbon feedback between soil carbon and climate systems. Much of this uncertainty comes from the role soil microbial communities will play in the wider picture of climate change.

Frank: Thank you. At present, if nothing is done to maintain carbon storage at the very least, and ideally enhance it, what is our current understanding of the projected effects of this feedback loop? In addition, why is it that we are seeing particularly worrying effects in colder climates? Can you tell us what a would a world look like if we allow a positive carbon-climate feedback to develop uninhibited?

Pablo: Good question. It’s important to say that all the carbon that we lose from soil will be added to the current ‘stock’ of fossil fuels in the atmosphere (I.E., in addition to current levels). It is very important to keep soil carbon in the soil for as long as possible to prevent a positive carbon-climate feedback. Cold systems are important because they store the largest amount of carbon per unit of area compared to other systems. In cold systems, plants grow very slowly due to low temperatures; however, microbial respiration and soil decomposition is even slower, so, in time, the carbon accumulates (over centuries and millennia) and is stored stably. On the other hand, you have tropical systems where microbial activity is very high because warm temperatures and high moisture aids decomposition, causing loss of stored carbon. But, tropical systems also have high plant productivity, leading to a finely tuned balance with low accumulation as compared to arctic and subarctic regions. These colder regions are very sensitive to climate warming, and, if we release all the soil carbon that has been accumulated in cold systems, a massive amount of fossil fuels will be further added to the atmosphere, leading to increased global warming effects on ecosystems. Soil carbon has two important points. We must try to keep the carbon in the soil for as long as possible, but we could also try to enhance it with different management practices in agricultural, urban, and natural systems. We must try to incorporate more carbon and keep it there. This is called the natural climate solution—soil carbon sequestration. Soil microbial communities will play a major role in the climate of the future. In this special feature, we are trying to shine some light on this topic.

Frank: This moves me forward to my next question. How did this special feature come to be? Where did the ideas come from, and why did you feel compelled to share this research with the ecological community?

Pablo: A few years ago, I think in 2018, at the British Ecological Society Annual Meeting, held in Birmingham, UK, I was co-chairing with professor Mark Bradford from the Yale School of Forestry & Environmental Studies on a thematic session for this topic. We looked at different, and even sometimes contradictory, views on the role of soil microbial communities pertaining to soil carbon storage and climate change. We did this thematic session, published a perspective paper which summarized the main findings; however, there were a lot of issues that we couldn’t cover. Therefore, we kept thinking about the subject, which then lead me to team up with Ji Chen, an expert in the physiological mechanisms of soil microbial communities and soil carbon cycling. From here, we suggested the idea to the Functional Ecology Editorial Board. We were in conversation with Chuck Fox and Katie Field who were super helpful in developing our ideas. We then got feedback from 6 of Functional Ecology Associate Editors who were very positive, but suggested lots of changes that turned out to be vital for the resulting quality of the special feature.

Frank: I’d like to ask Ji, could you discuss the importance of review papers. This SF is made up entirely of review papers. Why are they important, why have you chosen this model.

Ji: Review papers can give an overview of the recent research themes. In this SF, we particularly focused on research from the last 10–20 years—the most recent findings in soil microbial research. Microbial studies is a fast moving subject area with updates happening all the time. Therefore, it is really important to provide an overview of the changes and movements in the past decades.

Frank: Pablo, can you discuss your perspective as a guest editor on this. How did it feel, were there any issues, were there things that went well? Any tips you can provide for future guest editors who would like to a compile a special feature?

Pablo: First of all, we included some of this information in our blogpost for Functional Ecology. Otherwise, I would say that you should have a good connection with the editorial board of the journal—they are always super helpful. They will suggest ideas that you might not have thought of, such as having a round of Internal revisions. This turned out to be the key for the success of the Carbon Soil Special Feature. I have to say, It was a lot of extra work. However, it helped us to avoid overlapping of topics between different reviews. It also helped us to focus and frame the reviews from the authors. It is just good practice for the argumentation and clarity of the topic. My top tip, go ahead with rounds of internal revisions.

Frank:

Yes, ensure the quality of the papers and lean on the Editorial Board for their perspectives, but also their connections. They can help to identify authors and groups that are working in the subject area that can provide useful contributions.

Ji, I’d like to ask you what makes this special feature unique? What are some of the novel contributions that one might be able to find?

Ji: This special feature has a particular focus on the emerging findings from the last few decades. Pablo chose the most active and famous authors to provide contributions. In this, we are working on the emerging findings from microbiology and climate change research. The research has the potential to be integrated into models for advancing our understanding of soil carbon storage and microbial mechanisms. In this feature, we have 8 papers from leading scientists in the field. All papers published are invited review papers, with a particular focus on new frameworks from soil microbiological and climate change research. These new frameworks have high potential to be incorporated into newer scientific models and studies. We hope authors will enjoy reading about the latest research on this subject.

Frank: Pablo, with regards to the special feature, what is unique about it? Something you wouldn’t find in other papers or collections pertaining to soil carbon storage. What is vital for people to know?

Pablo: The combination of approaches is vital. We have very mechanistic reviews that deal with specific mechanisms that are important in soil carbon storage (such as priming effect or the role of enzymes), and then we are also investigate novel (very recent) discoveries and frameworks such as the role of the interactions between microbial necromass, minerals, and plant residues. We also have a couple of studies that also suggest how microbial traits can be incorporated into different experiments and modelling frameworks to incorporate new findings and emerging concepts that have been found in the last ten years. The challenge now is, how do we incorporate all this information so that we can increase the predictability of our climate change models?

Frank: As we finish up, Pablo, is there anything else that you’d like to address? Is there something you’d like to say to our listeners, or anyone interested in the subject?

Pablo: A take home message—soil microbes do matter for addressing climate change and its effects on ecosystems! In this special feature, we are offering reviews on really important topics that are particularly relevant to emerging relationships between microbes and soil carbon cycling. If we can incorporate them into theory and models, we will be able to greatly increase the predictability of climate change effects.

Frank: Ji, is there anything else you’d like to add?

Ji: I want to express my appreciation and gratitude for the authors, reviewers, and editors for their great contribution to this special feature. It would not have been possible to create this special feature without their input. I hope that you will gain some knowledge from our work. Thank you.

Frank: To wrap up, I’d like to remind listeners that the special feature can be found on the Functional Ecology website, in our June 2022 Issue. Pablo and Ji have also published a blogpost on about how to do a special feature and about the feature itself. Furthermore, they have great tips for people interested in the subject, or in special feature curation in general. Thank you to both of my guests, Pablo García-Palacios and Ji Chen. It’s been wonderful talking to you. I hope the listeners have enjoyed listening to this talk, and I hope they’ll check out the special feature.

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