In this new blog post, Marion Boisseaux, a postdoc at California State University, presents her work ‘Shifting trait coordination along a soil-moisture-nutrient gradient in tropical forests’. She discusses the knowledge gaps in functional traits studies, presents the importance of looking at multiple components to understand plants responses, and shares her wish to transmit the relevance of ecophysiology to everyone.
A French translation of this blog post is available here.
About the paper
Within the framework of the niche theory, the environment acts as a filter, and selects for species in a local community. The concept of environmental filtering explains that not all organisms can establish and persist in all environments. Studies examining trait-environment relationships often support the idea that environmental gradients act as selective pressures filtering tree species and therefore their functional traits. For example, along a topographic gradient where water and nutrient availability vary, tree species position themselves differently, and their abundance fluctuates in regards to the resources. However, some studies also report weak or no trait-environment relationships. In our paper, we highlight three key points that explain why these mixed results.
First, many experimental designs study traits one by one, even though plant performance is controlled by the interaction of multiple traits at the whole-plant level. We believe that multivariate approaches are essential to capture how traits combine to build species strategies across environmental gradients. We decided to look into the strength of trait correlations, also known as trait integration, which may be as important as trait variances or ranges for understanding species distribution and community structure.
Second, many analyses focus on structural traits that are weak proxies for the processes underlying plant functioning. We here looked at physiological traits that offer more direct insights into plant responses to environmental pressures.
Third, previous studies often focus on trait means, but intraspecific trait variability is increasingly recognized as a key factor influencing species niches and distributions.
By considering these points, we aim to bridge gaps in understanding how environmental filtering at the local scale shapes functional traits, offering insights into tropical species strategies in different environments.
About the research
This research is part of the METRADICA project (funded by Labex CEBA), led by Clément Stahl (INRAE, UMR Ecofog) and Ghislain Vieilledent (Cirad, UMR AMAP), aimed at modeling and understanding species distribution across French Guiana in the context of climate change. This paper also constitutes the second chapter of my PhD, supervised by Clément Stahl, Heidy Schimann (INRAE, UMR Biogeco) and Sabrina Coste (Université de Guyane, UMR Ecofog). Conducting fieldwork, trait measurements, data cleaning, and analysis took up a significant portion of my PhD, and gathering data has been difficult as most of it was carried out during the COVID pandemic.
In this study, we measured nine leaf functional traits across 552 individuals belonging to 21 tropical tree species, categorized as either tree species generalists or specialists to habitats (ie. seasonally flooded forests and terra firme forests). Reaching a consensus on whether a tree species was a generalist or specialist required multiple rounds of discussions and meetings!
Our results revealed that environmental conditions, particularly water availability, influenced trait integration rather than individual traits alone. Contrary to our hypothesis, we found that species in seasonally flooded environments exhibited greater trait integration, suggesting that excessive water, found in waterlogged soils, imposes significant hydraulic constraint on plants. This finding challenges the traditional focus on drought as the main stressor for tropical trees, highlighting the importance of water excess as a significant driver of plant strategies in these habitats. Another surprising result was the observation that generalist species did not exhibit greater intraspecific trait variability, but instead modified their trait integration across environments, illustrating a flexible trait syndrome. While generalists are capable of thriving in a wide range of habitats, they seem to adapt by altering trait coordination, particularly under extreme environmental conditions.
Moving forward, it is crucial to further explore how species respond to environmental thresholds like waterlogging and investigate the physiological mechanisms that drive trait coordination across different habitats. These insights can be incorporated into species distribution models to predict how species will shift in response to climate change, providing critical information for biodiversity conservation.
About the author
I always had a deep interest in plant physiology, and my fascination only grew when I was introduced to tropical botany, captivated by the remarkable diversity of leaf forms. After completing my studies as a horticultural engineer in France, I was left wanting more—a deeper understanding of tropical ecology. This curiosity led me to pursue a PhD in French Guiana at UMR EcoFog, on the functional strategies and microbiota of tropical trees in the context of climate change. After successfully defending my PhD in December 2023, I am now a postdoctoral researcher at Christine Scoffoni’s Lab in California State University, Los Angeles. I am focusing even further into the world of plant ecophysiology, by studying the coordination of leaf and root hydraulic traits. Through both my research and my efforts in teaching and science communication, I strive to deepen our collective understanding of plant physiology and share that knowledge to better tackle the broader questions in forest ecology.
Like the blog post? Read the research here.
