Victoria Luizzi: Is it worth it to smell nice? Allocation cost of plants floral fragrance under nutrient stress

In this post Victoria Luizzi, PhD candidate at University of Arizona, presents their work ‘Phenotypic plasticity in floral scent in response to nutrient, but not water, availability in the perennial plant Arabis alpina (Brassicaceae)’, discuss the importance phenotypic plasticity for plants and revisit their experience at Sweden before starting their PhD.

About the paper

Victoria outside their grandmother's house in Nyssa, OR, USA
Victoria outside their grandmother’s house in Nyssa, OR, USA

Animal-pollinated plants use a variety of strategies to attract pollinators to their flowers, one of which is fragrance. Previous research has shown that floral scent can both be crucial for attracting pollinators, and can be highly variable within species. A potential explanation for some of this variation that has received relatively little study is phenotypic plasticity, where traits change in response to environmental variation. In this paper, we tested the extent to which floral fragrance responds to resource availability.

Samples of floral volatiles waiting to be analyzed
Samples of floral volatiles waiting to be analyzed

We tested the response of the floral fragrance of alpine rock-cress (Arabis alpina) to nutrient and water availability by growing plants in the greenhouse under four treatments: 1) abundant nutrients and water, 2) abundant nutrients and limited water, 3) limited nutrients and abundant water, and 4) limited nutrients and water. We also tested whether A. alpina experiences an “allocation cost” of floral scent production—i.e., whether investing more in floral scent necessitates investing less in some other function—by hand-pollinating the plants that received limited nutrients and testing for a tradeoff between floral scent and seed production.

Sampling floral volatiles from A. alpina plants
Sampling floral volatiles from A. alpina plants

We found that plants grown with limited nutrients produced less scent per flower than did plants grown with abundant nutrients, though genetic factors were more important than nutrient environment in determining per-flower scent emission. Water had no effect on floral scent, and neither water nor nutrients affected the composition of scent (i.e., which compounds were present and in what amounts). While the effects of nutrients on floral scent were limited at the per-flower level, they were more dramatic at the level of the whole plant, thanks to a 10-fold increase in the number of flowers produced by plants that had access to more nutrients. Interestingly, even though plants decreased their floral scent production when nutrients were limited, suggesting that scent might be costly to produce, we did not find evidence of an allocation cost in the form of a tradeoff between scent and reproduction.

About the research

Victoria and their experimental plants undergoing vernalization
Victoria and their experimental plants undergoing vernalization

The fact that floral scent can be sensitive to resource availability—either at the per-flower level or at the whole-plant level—may complicate plants’ interactions with pollinators and/or other organisms like herbivores or nectar microbes that can also be affected by floral scent. Traits that are very important for fitness, presumably including floral traits that contribute to plants’ reproductive success, are generally expected to be highly stable across environmental conditions. Some recent research including our study has shown that this is the case for the composition of the compounds that are emitted from the flower, but our results also show that the strength of the floral scent signal is affected by the environment. It is yet not clear, however, to what extent this plasticity will affect the interaction between the plants and their pollinators. An important next step is therefore to place plasticity in floral traits like scent into context by investigating how it affects species interactions, both with pollinators and with other organisms. Since our study showed that the response of floral scent to resource availability can be different at the level of individual flowers vs. the whole plant, future research will need to carefully parse out the behavioral effect of scent on pollinators or natural enemies at long vs. short distances.

About the author

Like many ecologists, I was fascinated with the world of non-human organisms from a young age. I loved watching insects in the garden and relished even things that made others squeamish, like the parasitoid wasps that emerged from a tomato hornworm caterpillar I found on a tomato plant. I didn’t really know I wanted to be an ecologist, though, until I took a trip to Costa Rica during my undergraduate studies, as part of a tropical ecology course, and was stunned by the diversity of species and species interactions there. Since then, I continue to be inspired by time spent in the field watching the organisms I study in action.

Victoria enjoying the plants at Copenhagen Botanical Garden
Victoria enjoying the plants at Copenhagen Botanical Garden

This research was conducted during my time as a Fulbright grantee in Lund, Sweden, where I met my coauthors Magne Friberg and Hampus Petrén, then a doctoral student working with Magne. Being able to make these international connections was an incredible opportunity, and the collaborative nature of ecology is something I really enjoy.

After my time in Sweden, I moved back to the US and began graduate school. I am now a PhD candidate at the University of Arizona. I study plant-insect-microbe interactions, with an emphasis on investigating how microbial communities may alter their host’s interactions with other species. In my spare time, I enjoy hiking, playing French horn, and doing overly ambitious cooking and baking projects.

Read the research in full here

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