In this post, Anna Abrahão, of the Universität Hohenheim, Germany, talks about how plants – and people – set roots on rocky terrain.
About the paper
Our paper is about plants that grow on rock outcrops in a very nutrient-poor ecosystem in mountaintops of Brazil called campos rupestres. Theseplantshave incredible roots that allow them to dissolve rock and mine phosphorus. We called these roots vellozioid roots, name after the plant family they belong to, Velloziaceae. The idea came when we were doing field work, Rafael Oliveira, Hans Lambers, Grazielle Teodoro and me. Campos rupestres are characterised by rock outcrops and plants from a few families are able to grow on rock.
Hans asked us: “Where do they get their nutrients from?” and I answered as if this was a simple question: “From the rocks.” Hans was skeptical, so we bought a hammer and a chisel and he started hammering the rocks and followed the roots growing into the cracks and observed them branching there. Then we noticed that the roots growing inside the rocks had a somehow different morphology. They were unusually sturdy and very hairy. We knew we were onto something different. The first step was then to describe the root morphology and physiology, which was part of Grazielle’s post-doc project. We found that these roots released carboxylates and that these carboxylates dissolved the rock and release phosphorus, a very scarce nutrient in campos rupestres. Root penetration in the rocks also accelerated soil formation and influenced the shape of the landscape and future plant establishment. So, this means that these plants are pivotal for the ecosystem.
In this study, we wanted to know if these special roots, or any other root or leaf functions, were essential for plants to grow on rocks. We compared 27 rock- or soil-dwelling species to understand which plant functions and structures were associated with the ability of the species to grow on each phosphorus-impoverished substrate. We found that these special roots are common in plants that grow on rocks and are rarely present in soil-dwelling species. These vellozioid roots are likely very costly in terms of carbon to acquire nutrients, and thus only advantageous where the gains in nutrient acquisition outweigh their costs, as likely occurs when growing on rocks. A similar but likely less costly strategy is found in soil-dwelling species, where there is no need to dissolve the substrate to access the phosphorus needed for growth. The nutrient-acquisition from phosphorus-poor soils is expected to usually depend on an association with mycorrhizal fungi. On the substrates that we investigated, the proportion of roots colonized by mycorrhizal fungi and other fungal root endophytes was negligible. Our study confirmed that in extremely phosphorus-impoverished substrates, mycorrhizas are inefficient to merit the formation of these symbiotic structures, while the vellozioid root specialisations are very effective. The leaf functions we investigated were similar for soil and rock-dwelling species, indicating that it is the roots, more specifically, the type of roots, which are pivotal in determining where each species can grow.
So far, we only investigated vellozioid roots on quartzitic rocks; however, representatives of the investigated Velloziaceae also grow on other rocks such as the very hard ironstones and granites from inselbergs. We don’t know if Velloziaceae growing on these rocks also have vellozioid roots, or perhaps another strategy to access nutrients there. As typical for interesting research, every project ends up raising new questions. An important point of this paper is that it shows how important it is to consider specific traits that are unfrequently surveyed but could play a major role in ecosystem functioning.
About The Author
During most of my Bachelor’ s at the University of Brasilia, I was planning to become a palaeontologist. I used to work on taxonomy of microcrustaceans from the upper Cretaceous. In my last year, I looked at my bookshelf and noticed I didn’t have a single palaeontology book, but only ecology books. I grew up in the savannah of central Brazil, and felt like I needed to understand more about how our natural world worked, so I left palaeontology and moved to a plant ecology lab. Why plants? Because they are the ones that are really always there and tell us the story of ecosystem processes. In that lab, I had two great female mentors, Professor Mercedes Bustamante and her PhD student, Luciola Lannes. They taught me how a research project was organised, and involved me in a project on plant nutrition and nutrient stoichiometry, which are still the main focus of my current research.
After I graduated, Professor Bustamante recommended me to switch labs and expand my horizons, and suggested me to get in contact with Professor Rafael Oliveira. After he agreed to supervise me and I passed the exam, I moved states and really got out of my comfort zone in many ways. However, the optimism and curiosity of Rafael were worth the move. He supervised me through my Master’s and PhD. He also introduced me to Professor Hans Lambers (the one that hammered away at the rocks) and we submitted a proposal that funded this research and allowed me to spend one year at the University of Western Australia, working with Hans and A/Professor Megan Ryan. Megan was a great supervisor, being able to follow every step of my experiments without suffocating me. I have been very lucky with all my supervisors so far.
I think that one of the best things of being an ecologist is that we can ask the same questions in different ecosystems and test the generality of theories in different parts of the world. My PhD thesis was a comparison of plant nutrient-acquisition strategies in the very nutrient-impoverished campos rupestres in Brazil and the kwongan, in south-western Australia. I discovered many mechanisms used by plants to acquire nutrients and contributed a little bit to that field. At the end of my PhD, I found that I wanted to understand better how nutrients cycle in the soil, and that would mean understanding the role of soil microbes. This led me to my current position, thanks to Hans Lambers’ network of collaborations. I am now working in Germany, at the University of Hohenheim, with Professor Ellen Kandeler, a celebrity in microbial ecophysiology.
After 14 years doing research, in the third country and fourth university, I had to discover how to make myself comfortable anywhere I moved. I had to find a home inside myself and this took me a while. Working as a scientist, I had to be flexible and grow short roots everywhere I lived. Before every move, I had to pull out these roots and put them in a pot. Getting myself out of the pot in the next destination also required preparation of a good well-watered substrate. Sometimes, I felt that the substrate was like a soft compost full of nutrients, and sometimes it felt as hard as the quartzite vellozioid roots dissolve. This substrate consists mainly of friendships I have now built all over the world. My advice for someone starting in my field would be to open their minds and allow themselves to experience different cultures and projects, despite the initial discomfort of feeling completely displaced. The initial distress gives place to very strong independence and initiative, which are both prerequisites for a good scientist.