Lenka Plavcová

While my research is mainly centered on xylem water transport, I enjoy thinking outside the realm of my main expertise. There is a plenty of opportunities for that because plant science is an incredibly broad and diverse discipline that encompasses a wide range of problems spanning from molecular plant biology to ecosystem ecology. During my research career, I have been lucky to be involved in various interesting projects.

If you want to learn more about my past and present research, take a look below:

During my PhD studies, I spent a lot of time working with and thinking about xylem conduits. However, I also realized that xylem contains other types of cells, some of which are, in contrast to conduits, alive and metabolically active. These cells are called ray and axial parenchyma (RAP). It struck me that we know very little about them because most researchers in wood ecological anatomy, including me, have focused on xylem conduits. So I decided to do something about it. I designed a research project looking at RAP and applied for the Humboldt postdoctoral fellowship. The application was successful, so here I am studying the anatomy and function of living cells in wood.

RAP is structurally and functionally interwoven with xylem conduits and plays several important roles in wood physiology. A striking variation in RAP anatomy is observed across species and these differences likely have functional and evolutionary explanations. However, a thoroughly comprehensive explanation of these structure-function relationships has not yet been provided.

In order to shed more light on the functional, ecological, and phyletic significance of the various patterns in RAP anatomy that have evolved in woody plants, I will firstly carry out an analysis of a global dataset that encompasses variation in wood traits for thousands of species of a diverse taxonomic and geographical origin. Following this global-scale analysis, I will conduct a more detailed, quantitative assessment of RAP anatomy in selected model species using progressive imaging techniques. Good knowledge of anatomy is a useful prerequisite for understanding the physiological function. Thus, I envision that this research will pave the way for designing interesting physiological experiments and lead to a better understanding of the numerous functions that living cells have in wood. The spectrum of these functions is very broad, spanning from the storage of nutrients and water, through their role in wood senescence and pathogen resistance to their putative involvement in embolism refilling, so there definitely is a lot of room for new and exciting discoveries.

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After finishing my PhD, I relocated back to Europe and took up a postdoctoral position at the Institute for Hydraulic and Water Resources Engineering at the Vienna University of Technology. I became a member of an interdisciplinary team working on floods. My task was to decipher the roles of biological processes in flood generation.

Floods represent one of the most prevalent natural hazards in Europe and in many other areas throughout the world. There have been concerns that the frequency and/or magnitude of floods are increasing as a result of climate or land use change. However, providing solid scientific evidence for such a statement is not a trivial task. First of all, you need long reliable flood data series from a large number of catchments. Then, you have to apply robust statistical methods to detect trends or other types of change in your data series. Finally, you can try to attribute the detected change to a possible cause, for instance to a change in the timing of snow melt, perturbed precipitation regime or altered catchment response.

But what is the role of plants in all this? While plant scientists don't often think about it, vegetation is an important player in the hydrological cycle that can affect the landscape water budget and run-off generation by a number of direct and indirect mechanisms. Vegetation takes up water from the soil and transpires it back to the atmosphere. It intercepts precipitation and shelters the soil surface from heat and wind. Furthermore, plant roots and the associated activity of soil microbes and soil fauna substantially influence the water infiltration and storage capacity of soil. Thus, changes in vegetation can lead to changes in precipitation and temperature regimes as well as altered catchment response dynamics.

During the seven months I worked on this project, I conducted an extensive literature search and prepared a summary of vegetation-related processes that have the potential to affect run-off generation. I then grouped these processes into three categories relevant for the flood generation mechanisms (i.e. processes that affect effective precipitation, processes that change infiltration rates and processes that change infiltration capacity). Although I left Vienna in order to accept the Humboldt Research Fellowship, I keep in touch with my former colleagues and we are currently preparing a review paper summarizing the effects of land use and climate change on vegetation and soil characteristics that can potentially translate into changes in floods. So stay tuned! In the meantime you can have a look at our poster on this topic presented at the EGU 2013 conference.

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Vulnerability of xylem to drought-induced cavitation was the main research focus during my doctoral studies at the University of Alberta, Canada. The primary goal of my project was to evaluate the phenotypic plasticity of xylem traits, including xylem vulnerability, in a model tree Populus. Progressively, I've become more and more interested in the actual mechanisms underlying vulnerability to cavitation, and therefore studied interconduit pits in greater detail. You can read about these two aspects of my PhD work below.

Phenotypic plasticity
It is well known that structural and functional parameters of xylem differ between different species. In contrast, much less is known about the structure-function variation within a single species, although this intraspecific plasticity of xylem might be important for the species' ability to adjust its water use to different growing conditions. The intraspecific variability has two components - genetic and phenotypic.

During my PhD research, I focused on the phenotypic plasticity of xylem traits in hybrid poplar. I cultivated cuttings from a single poplar clone under different growing conditions such as shading, fertilization and reduced water availability. I then looked at plant growth parameters and measured the structural and hydraulic properties of their xylem. I found that xylem vulnerability and hydraulic conductivity are to a certain degree plastic in response to growing condition. However, I suspect that the growth plasticity, exhibited as the variation in leaf area to xylem area or the variation in root to shoot biomass, is a more important mode of plant hydraulic adjustment.

While I was studying xylem plasticity, I also ventured into the field of molecular biology. The aim was to expand our knowledge of molecular mechanisms involved in xylogenesis and identify interesting gene candidates that might be responsible for important xylem traits such as vessel diameter or wood density. We took advantage of the poplar genome being sequenced and conducted a microarray analysis of gene expression in the developing xylem of poplars grown under two contrasting levels of nitrogen availability. We found a number or differentially expressed genes, including genes putatively involved in nitrogen and carbohydrate metabolism and various aspects of xylem cell differentiation. We subsequently linked the differential expression profiles with the differences in xylem phenotype observed between the two groups of plants.

Bordered pits
Bordered pits are small openings in walls of xylem conduits that allow movement of water via the xylem network. However, they are also sites through which air can penetrate water-filled conduits and disrupt the long-distance water transport. Despite their critical importance, we know very little about the chemical composition of pits. Therefore, I employed specialized histological and immuno-labelling techniques to shed light on their chemical composition. Pectins, a group of polysaccharides known for their gelling properties, were traditionally believed to be present in pit membranes. Contrary to this expectations, the outcomes of my experiments showed that pectins were not abundant in the pit membranes of four heartwood species. Instead, pectins were restricted to only a limited area around the circumvent of the pit membranes. This unexpected result suggests that the previously proposed role of pectins in pit membrane functioning needs to be revisited.



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