André Franco: root herbivory, water availability and above and belowground biomass

In our this new Insight, André Franco, a research scientist at Colorado State University presents his last work “‘Root herbivory controls the effects of water availability on the partitioning between above and belowground grass biomass”, shows the strong connection between above- and belowground processes and tells us how a soil scientist arrived to ecology.

André working at the experiment
André working at the experiment

About the paper

A group of us (soil ecologists from Colorado State University and plant ecologists from Arizona State University) collaborated to investigate belowground controls on plant responses to drought. Droughts are becoming more frequent, severe, and longer lasting than in recent decades in many places, and ecological theory suggests that certain plant species may respond to drought by producing less leaves because they lose water, and instead allocating more production to roots, which capture water. These patterns are important in the context of ecosystem responses to climate change as they set limits on ecosystem carbon assimilation and biomass production.

Plants interact with many other organisms in ecosystems, and the response of those to drought may also affect plant responses. Our previous multi-site grassland field study showed that more frequent extreme droughts can increase populations of root-feeding soil nematodes (roundworms) in sub-humid grasslands by suppressing their predators. These root parasites limit plant biomass production in grasslands, and their increased abundance under drought led us to ask whether high levels of root herbivory by nematodes would prevent the high grass biomass allocation to roots expected in response to drought.

Multiple samples of 'blue grama' experiment
Multiple samples of ‘blue grama’ experiment

In order to find out, we set up an experiment in which we exposed a dominant shortgrass steppe species, blue grama (Bouteloua gracilis), to extreme low and high amounts of water under a variable amount of root feeders. The results showed that the effects of drought on grass biomass allocation depend on the abundance of root-feeding nematodes. High abundance of those nematodes impeded grass responses that otherwise allocated relatively more biomass to roots than leaves under drought conditions to benefit water uptake. This indicated that when the root-feeding nematodes thrive, they undermine an important plant mechanism that buffers grasses and ecosystems against the effects of drought.

The findings presented in our paper challenge current predictions of increasing plant biomass allocation belowground in water-stressed grasslands, and can be of special interest to ecosystem modelers. Terrestrial biosphere models still have a low capacity in reproducing the magnitude of vegetation responses to temporal changes in annual rainfall at a given ecosystem. Our findings in this paper give support to the idea that including soil biota parameters (specifically those related to belowground primary consumers) will enhance the predictive capacity when modelling vegetation responses to drought. Accurately modelling vegetation responses to changes in rainfall is crucial to project water and carbon cycles into the future, and to enable solid scientific guidance to management decisions in grasslands.

Our next step is to investigate this nematode control on plant responses to drought in different grassland sites (arid to mesic). We have already completed field experiments in this regard, and are currently processing the dataset. We expect that the importance of this nematode control will be greater in mesic compared to arid environments where root-feeder populations seem to be primarily regulated by resource availability rather than predation pressure. Another emergent question is how this phenomenon affects carbon fixation in grassland soils, given that root inputs contribute more to soil organic matter than aboveground litter.

About the Author

I am a soil scientist by training, but realized early during my doctorate that the ecological interactions among soil organisms, and of those with plants, are crucial for our understanding of soil functioning. I currently hold a position as research scientist at Colorado State University’s Department of Biology. As many colleagues in the same position, I am actively prospecting tenure track jobs for the near future.

Apart from the project that resulted in this publication, I am currently working on a dataset from Antarctica that promises to shed light on how soil invertebrate communities responded to climate-driven changes since the last glacial maximum (~18,000 years ago). I am also writing a research project to test hypotheses about environment-soil-plant interactions in US grasslands, while of course dealing with some less exciting bureaucracies of academia.

I find great joy and pride in all processes of science; thus, I feel extremely blessed for all the projects and discoveries that I have been involved in my still young career. That said, I feel like whatever my latest manuscript is, that is always the one fuelling my enthusiasm for the future. So, this paper in Functional Ecology is right now the one that I keep telling my colleagues and non-science friends and family about over and over.

To me, the most exciting thing about doing science in ecology is the challenge of finding consistent patterns in extremely complex, but yet orderly, organized, biotic systems. I also enjoy the fact that ecological thinking, no matter at which scale, always tend to cross multiple disciplines. Collaborating with folks from difference science realms is fascinating and very enriching to me. I am still to find a negative aspect of working in ecology. My experience with ecology and ecologists has been very stimulating, although I still hesitate to call myself an ecologist due to my training in a different discipline.

I can summarize what I do in my spare time as all things Brazil: Listen to and play Brazilian music on the drums; Practice and watch football, judo (yes, that’s pretty big there); Share the table (and some drinks!) for long hours with family and friends; Enter survival mode through North American winter, re-emerge to life on summer. My family and I also enjoy taking road trips through the fascinating western US whenever we can.

To close with one piece of advice for my fellow young scientists: role models help as guides, but trail your own path and don’t be afraid if on the way things look pretty different from what you envisioned as ideal in the beginning of the journey. And ALWAYS, as a good Italian friend repeatedly emphasizes, watch out for reviewer #2!

Read the paper in full here!

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