In this new post Angela Illuminati, postdoc at University Rey Juan Carlos, Spain, presents her work ‘Functional differences between herbs and woody species in a semiarid Mediterranean plant community: a whole-plant perspective on growth, nutrient-use and size’. She talks about the many gaps existing in dryland plant ecology, shows the amazing distances that roots systems cover, and shares how science strengthens her family bonds.
About the paper
Even if you were a plant ecologist with expertise in arid environments, when the word ‘aridity’ comes to mind the first picture you probably would imagine is a desert with dry soil, high temperature and dusty horizons such as in the famous movies of the dollar trilogy directed by Sergio Leone.
Contrarily to this common perception, many environments included in the ‘arid range’ present very high species diversity (Figure 1) and their contribution to key ecosystem processes is of crucial importance at global level. Since environmental filtering exerts a very strong selective pressure on these environments, only species that can adapt to limited water and nutrient availability, or quickly exploit soil resources during rare water pulses, are able to survive. But what do we know about the interactions among coexisting species that shape plant community assembly at neighbourhood spatial scales?
A pioneering hypothesis about species coexistence in arid environments was proposed by Walter (1939) who suggested a vertical belowground segregation between trees and grasses in savannas. The development of plant functional ecology has raised to question whether, beyond spatial segregation, species interacting in arid environments at neighbourhood spatial scales may segregate functionally as an alternative way to avoid belowground competition. Woody and herbaceous species are two broad functional groups known to present key differences to aboveground growth and nutrient use strategies. However, whether herbs and woody species also differ in their belowground growth and nutrient use strategies is still under debate (Figure 2).
In dry environments, where most plant-plant competition centres on soil resources, we might expect a belowground functional differentiation between herbs and woody species, particularly in plant communities where both groups are very abundant and interact intensely. This led us to the following question: “Do herbs and woody species coexisting in the same plant community in a dry environment differ in their belowground growth and nutrient use strategies?”
About the research
To answer this question, we conducted our research in a semiarid Mediterranean shrubland, where herbs and woody species are both abundant in the plant community. We considered two possible approaches: measuring root traits directly in the field or cultivating all target species under controlled experimental conditions.
What approach would be most effective?
While it’s true that exact field conditions cannot be replicated in experimental settings, measuring functional traits in common garden experiments is valuable to compare species under uniform conditions, removing the effects of both environmental heterogeneity and biotic interactions. We thus chose the second approach and built up an experiment with a total of 23 species representing approximately 97% of the total plant cover in the community (Figure 3, 4).
One challenge we encountered during our research was the ambitious decision to sample the entire root system of each individual plant. For some species, such as Koeleria vallesiana (Honck.) Gaudin, this meant measuring root lengths as extensive as 300 m! In total, the root length we scanned for all the plants in the experiment added up to over 8 km.
In our research, we found that both above- and below-ground growth rates are strongly associated to root traits in all the species characterizing the semiarid Mediterranean community, emphasizing the critical role of root nutrient-use strategies for plant growth in this kind of environments. Our investigation also led us to point out key functional differences between herbs and woody species at whole-plant level, but the special novelty of the work is to the functional differences detected in the root nutrient-use strategies and their relationships to belowground growth. The competitive pressure for water and nutrients typical in these environments could explain the belowground differences observed between herbs and woody species, still future studies will be necessary to demonstrate this hypothesis.
About the author
I am a postdoctoral researcher at Rey Juan Carlos University (Madrid, Spain). I am especially interested in studying plant-plant and plant-soil interactions in arid environments, particularly Mediterranean shrublands and mountainous forests. A long time ago, when I had recently started my bachelor’s degree, a university colleague asked me what I was doing there. He did not see me fitting very well in that University career and, at least at the beginning, he was right. I was just a teenager who wanted to do something good for the planet, but did not know exactly how. I was totally unaware then that the complex world of plants would later intrigue me so much. I am so grateful to my grandmother and grandfather who were both scientists, and every day I spend doing research makes me feel closer to them.
