Liesbeth van den Brink & Rafaella Canessa: Microbial communities prefer high quality food, not specifically the food available “at home”

In this new post, post-doctoral friends Liesbeth van den Brink and Rafaella Canessa from the University of Tübingen, Germany, present their recently published paper “No home-field advantage in litter decomposition from the desert to temperate forest.” They discuss the importance of litter characteristics for decomposition, share their experiences with rodents, and celebrate the joy of working with friends.

Una versión en Español de esta publicación de blog está disponible para leer aquí!

About the paper

We tested the home-field advantage (HFA) hypothesis for litter decomposition (the decay of fallen leaves) across four different climates in Chile. This hypothesis suggests that microorganism communities that decompose litter may be locally adapted to litter types that they typically encounter, resulting in accelerated decomposition of local compared to non-local litter. So far, we don’t know in which situations microorganisms can develop this local adaptation and the results of previous studies are extremely variable. To test under which conditions this hypothesis was valid, we collected leaves of different species at different localities, and presented them to soil microorganisms from all these localities. After a year, we measured litter mass loss. In doing so, we distinguished how much the microorganisms had degraded the litter (microbial breakdown) and how much was gone due to the physical loss of nutrients by dissolution in rainwater (leaching), as this separation is key for identifying the effects of local adaptation of microorganisms across climates. We used a novel method, focusing on differential nutrient losses: nitrogen and phosphorus, that are actively released by microorganisms, were contrasted against potassium that leaches with rain so that we could calculate HFA based only on microbial decomposition. Overall, we did not find HFA effects in any of our sites, meaning that the microorganism communities were not specifically adapted to break down their local plant material. Instead, the quality of the leaves (decomposition was quicker when the plant material was easy to break down) and the general ability of the microorganism community to break down different litter types mainly determined the decomposition speed.

The idea for this paper came up while studying litter decomposition in Chile during our PhDs. We had established large decomposition experiments, translocating litter across four different ecosystems. We decided to analyze nutrient and element data from the initial litter and the litter after decomposition in order to look into stoichiometric changes in the litter. Although interesting and worth looking into for another manuscript, Yvonne Oelmann—one of our collaborators—suggested looking at the HFA hypothesis. She had recently read publications by Palozzi & Lindo and Wallenstein et al. and realized that most of studies only use litter decay as a proxy for microbial decomposition—whereas litter decay involves both microbial decomposition AND physical leaching. If we wanted to contrast ecosystems differing in precipitation, leaching could affect the calculations of microbial effects. Because we measured both leaching (potassium) and microbially released (nitrogen and phosphorus) elements during decomposition, it would be possible to disentangle these two losses across ecosystems, and thereby look for HFA effects.

Filling of the litter bags (credit: Ana Karen Sanhueza)

The method we describe in this paper is interesting for fellow researchers who have tested, or would like to test for, HFA effects for litter decomposition across different ecosystems. Additionally, the results are interesting for carbon cycle and decomposition models that account for the role of microorganisms, vegetation and climate, particularly under climate change scenarios.

About the research

After the first experiment with litterbags, we realized that the litterbags attracted curious rodents and bunnies. Specifically, these animals were attracted to litter bags in the mediterranean site where there is more than enough appropriate food. Bunnies (and perhaps degus as well) were trying out all the different food (leaves) that we translocated from the other sites. Although this was really annoying, it also illustrates the fact that it is not only micro-organisms that might prefer “food” from a different origin. In the end, food taste and quality is more relevant than its origin!

Bunny-proof experiment with litterbags to study HFA in litter decomposition (credit: Liesbeth van den Brink)

When collecting litterbags from the field, we quickly noticed that the succulent leaf litter from the arid desert was further decomposed compared to other litter types. This was surprising because the plant species from our coastal desert site are usually very salty. However, we later found out that they also had the highest litter quality (e.g., low C/N ratios), which explained the preference of the micro-organisms.

The lack of HFA effects across ecosystems suggest that bacterial and fungi communities are dynamic and resilient to changes in their resources. Moreover, our results also suggest that vegetation (litter quality) is one of the most important drivers of microbial breakdown. Thus, any changes in plant community composition may affect nutrient cycles and the decomposition process. Considering the many contradicting results in HFA studies, it is clear that HFA effects in litter decomposition are very context dependent. Thus, further studies contrasting different climate and vegetation conditions are necessary to unravel when and how HFA may occur.

About the author

Liesbeth van den Brink (left) and Rafaella Canessa (right) (credit: Liesbeth van den Brink)

We started our PhD in 2016 under the frame of the EarthShape project. This opportunity led not just to an important scientific collaboration, but also to a beautiful friendship. It is not often that you find your best friend in the field, but when it happens it makes work so much more fun!

Although we grew up in two different corners of the Earth (Chile and the Netherlands), we both loved to play outside as kids and wanted to understand how nature works in different parts of the world. We realized it was impossible to choose between microbes, plants or animals, which led us to study biology and dedicate our careers to ecosystem ecology. We were interested in understanding how all parts are connected and function, and thus, ended up studying soil-plant-animal interactions. Now, after finishing our PhDs, we are both working as PostDoc researchers at the University of Tübingen, and love to do fieldwork in remote areas. We like working in interdisciplinary environments, since we have learned that different points of view (although often super confusing) are necessary for better perspectives. We also like working with local non-scientists and have learned (and keep on learning) so much from them. Their knowledge and questions inspire us every day, and keep us grounded as scientists. When listened to, their input can make fundamental studies applicable without losing research interest.

Enjoyed the blogpost? Read the research here!

One thought on “Liesbeth van den Brink & Rafaella Canessa: Microbial communities prefer high quality food, not specifically the food available “at home”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s