Pablo Castro Sánchez-Bermejo: Tree and mycorrhizal fungal diversity affect leaf functional traits in trees 

Pablo Castro Sánchez-Bermejo: Tree and mycorrhizal fungal diversity affect leaf functional traits in trees 

In this blog post, Pablo Castro Sánchez-Bermejo presents his work ‘Tree and mycorrhizal fungal diversity drive intraspecific and intraindividual trait variation in temperate forests: Evidence from a tree diversity experiment’. He discusses the effects of tree and mycorrhizal fungal diversity on leaf functional traits, the challenges of leaf sampling in tall trees, and how his love for the outdoors has led to an interest in the patterns of intraspecific variation in trees.

About the paper:  

Biodiversity is more than mere number of species, but it has strong impact on ecosystem functioning and species performance. For instance, the same tree species can adopt different strategies in the way it uses the resources depending on the interactions with other species in the forest. Yet, our understanding is mostly limited to the responses of species to the tree diversity species in the stand, but we know little about the interactions with other organisms. For example, mycorrhizal fungi are a key component of forests that establish a mutualistic interaction with trees: the tree provides carbon to the fungi in exchange from nutrients. As a result, mycorrhizal fungi are able to provide trees with a substantial amount of essential nutrients that trees need for living and growth. However, despite their importance, we do not understand the diversity effects of these organisms on tree functioning. As it is challenging to disentangle the effects of diversity and confounding variables in natural systems, we studied the diversity effects of trees and mycorrhizal fungi on leaves, a key organ of nutrient acquisition in plants via photosynthesis, in the MyDiv experiment, an experimental setup which encompasses plots with different tree diversity and different combinations of tree species with the same or different preferred type of mycorrhizal partner. 

Instead of acting interactively, we found that tree and mycorrhizal fungal diversity affected different functional traits in the leaves. For example, tree richness causes an increase in the specific leaf area, reflecting resource acquisitiveness, while arbuscular mycorrhizal fungal diversity alters the ratio between leaf carbon and leaf nitrogen, suggesting higher leaf nitrogen content as a consequence of the efficiency in nutrient uptake on those trees interacting with a diverse community of fungi. What is extremely interesting is that we found that trees responded to the loss of tree species by producing dissimilar leaves in the canopy. This suggests that the variability in leaves within the individual, could be a key strategy for trees to adapt to forests with low tree diversity. 

Using a leaf cutter to access the crown of a of silver birch (Credit: Sylvia Haider) 

In this work we showed that the loss of tree diversity influences the leaf strategy of trees, with potential consequences on ecosystem functioning (e.g. growth, herbivory, etc.). The loss of species in forests due to different causes (e.g. favoring monocultures dominated by economically profitable tree species over mixed stands) can affect the resource-use of trees. In addition, our work emphasizes that it is not only about tree species, but the diversity of mycorrhizal fungi is also important for trees in terms of their leaf strategy. That is why, I believe that foresters and restoration practitioners should take in account that favoring tree and mycorrhizal fungi diversity is key to guarantee robust forest functioning. 

About the research:  

In the experiment, we collected 3,200 leaves from 640 trees for functional trait assessment. While most of the sampled trees were easily accessible due to their youth (the experiment was established six years before our sampling campaign), collecting leaves from the crowns of some tree species, such as the silver birch (Betula pendula) was often challenging due to the height of some of the individuals. That is why, essential equipment like ladders and leaf cutters aided our fieldwork during the campaign. Additionally, we measured the reflectance of every leaf and obtained spectral information that was key to assess the values of the functional traits in our leaves. Using spectroscopy has great potential for ecological research as it allowed us to process our large number of leaves. However, most of us had a background in biology and were new to this method, so it was a great challenge to get to know how our spectroradiometer worked and how we could extract ecologically meaningful information from it. 

From our research, we are fascinated that intraindividual trait variation responded to tree diversity and that is why we would like to further explore the adaptative value of this mechanism. To do so, last year we worked in BEF-China, another tree diversity experiment located in subtropical China, and collected data to explore the trends of intraspecific and intraindividual variation across different levels of tree richness. You can find more about our experiences during that fieldwork campaign in our post in the ‘postcards from the field’ blog series

About the author:  

I am a PhD student in TreeDì, a graduate school at the German Centre for Integrative Biodiversity Research (iDiv), Germany, which focuses on Biodiversity-Ecosystem-Functioning (BEF) research in forests. Specifically, I am quite interested in functional ecology and in my work I try to understand some of the responses of intraspecific variation of trees to diversity. 

The author, Pablo Castro Sánchez-Bermejo (Credit: Paula Isla García) 

It is not surprising that I developed interest in plant ecology because, as many ecologists, I am passionate about outdoor activities: hiking, climbing, bouldering, etc., and I always loved to spend time in nature. Additionally, during my first fieldwork experiences as a bachelor student, I felt fascinated by the diversity of different plant species and strategies that we can find in nature, and I developed curiosity about the ecosystem processes shaping the ecological communities. On top of this, I will always remember the first fieldwork campaigns where I was involved, in which we spent several days sleeping in a hut, performing tree inventories and taking core samples from trees in European beech (Fagus sylvatica) stands in central Iberian Peninsula. That was so motivating that made me considered starting a career in ecology… and ‘voilà’! Nowadays I am working on my PhD and trying to understand the patterns of intraspecific variation in trees in different systems, such as temperate or subtropical forests. 

Last, I understand functional ecology as a key tool to understand the causes and consequences of the ongoing biodiversity changes, and that is why, in the future I would be keen to continue working in this field. For instance, we are only starting to understand the patterns of intraspecific variation, but there is a lot of work to do about it worldwide, especially as this variation seems to underlie many ecological processes and could be, among others, a key mechanism for species to adapt to global change.  

Enjoy the blogpost? Read the research here.

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