In this Insight, Ximeng Li talks about his paper More than iso/anisohydry: Hydroscapes integrate plant water use and drought tolerance traits in 10 eucalypt species from contrasting climates, recently shortlisted for Functional Ecology’s Haldane Prize. Ximeng recently finished his PhD at the Hawkesbury Institute for the Environment, Western Sydney University and has now returned to China, where he hopes to continue his research.

Ximeng Li

About the research

What is the background behind your paper?

Plants differ enormously in their responses to drought stress. Nonetheless, there are many ways to simplify this complex picture. One approach is to use the iso-/anisohydry terminology, by which plants are positioned along a spectrum according to their degree of response to water stress. A number of metrics have been proposed to quantify the degree of isohydricity, but no consensus has been reached because many metrics are solely based on the measurements of plant water status, yet plant drought response strategy is multi-dimensional, incorporating various phenological, morphological or physiological features. This work aimed to identify a metric that integrates key aspects of plant water regulation and best quantifies isohydricity among species.  

How did you come up with the idea for it?

The idea for this work is largely inspired by the study of Hochberg et al. (2018). In this work, they compared several commonly-used metrics of isohydricty and concluded that one important reason underpinning species rankings was that variables typically used for calculating isohydricity are influenced by environmental factors including atmospheric water vapor deficit or soil moisture. Therefore, we wanted to test this conclusion under uniform environmental conditions and assess the source of variation.

Where you surprised by anything when working on it?

One thing that was really surprising was the lack of trade-offs between maximum stomatal conductance and species drought tolerance. According to the “fast-slow” spectrum, drought tolerant species should exhibit lower stomatal conductance, which is representative of an overall conservative resource acquisition strategy. But we observed the opposite. Given that drought tolerance species are mostly living in arid regions, we presumed that such features may enable plants to maximize the use of stochastic rainfall. However, we should confirm this assumption in the field.

Why is it important?

The word isohydricity is perhaps the most frequently used term in the literature to describe plant drought response strategies. Summarizing plant drought responses with the proper metric enables the comparison and characterization among diverse species, thus allowing us to answer some key questions in ecology such as the mechanisms responsible for community assembly or species distributional pattern at a certain spatial scale. Moreover, the correlation between the metric and many coordinated hydraulic traits will facilitate the modeling of plant dynamics with the traits-based approach.

What are the key messages of your article?

The foremost message is certainly about the best metric for characterizing species drought response strategy. It is crucial to realize that variables measured at single time points or under specific conditions might be insufficient to fully characterise the drought strategy of plants. In addition, the correlation between isohydricity and species home climate suggests that plant hydraulic strategy is at least partially genetically determined, thus plants may not be fully able to adjust rapidly to environmental change.

Does this article raise any new research questions?

Species used in this work are congeneric, so it is worth testing the correlation between metrics and traits using phylogenetically diverse species. Also, it will be valuable to see if the concept of isohydricity and associated metrics work for plants with different growth forms. 

About the Author

What are you currently working on?

My latest work looked at the plasticity of some key hydraulic traits of cotton plants in the context of global climate change.

What’s your current position?

I recently finished my study at Hawkesbury Institute for the Environment, Western Sydney University and returned home to China to seek an academic job.

What project/article are you most proud of?

Personally, my favourite paper comes from a related work, which looks at the hydraulic traits coordination and their relationships with provenance climate in Australian trees. 

What is the best thing about being an ecologist?

I think the best thing of being an ecologist is that it teaches me how to view the nature in a very different way. Questions concealed in our daily life such as why this organism lives here and do what it does are pretty fascinating, and answers to these questions, for me, reside in ecology. I am still in the early career phase, so I believe there are many interesting things awaiting to be discovered.

What would you like to do next?

There are many things I would like to do in the future but for now I am very interested in the water regulation strategy of desert plants. Given that species in dry regions show remarkable variation in terms of embolism resistance, it will be fun to see what the alternative strategies are.

What do you do in your spare time?

I am really into cooking and video games, especially real-time strategy.

You can find Ximeng’s paper here, along with our other shortlisted papers.