Getting to the roots of forest sustainability Woody plants acquire nitrogen and other resources to maximise growth and enhance their reproductive fitness. Dr Judy Simon and her team aim to build a deeper understanding of the basic mechanisms behind plant interactions with regard to nitrogen acquisition and its internal allocation, research which could hold important implications for forest management. A lot of
attention in ecological research over the past few decades has been devoted to interactions between plants, yet the underlying processes that determine the competitive success of individual plants or species have largely been neglected. This is a topic central to the work of the project Woody PIRATS, an initiative based at the University of Konstanz in Germany. “The overall aim of this project is to gain a more detailed understanding on the basic processes and mechanisms underlying woody plant interactions, such as competition, facilitation, and/or avoidance of competition between plants and different players in forest ecosystems,” explains Dr Judy Simon, the project’s Principal Investigator. These are important issues in terms of plant health and the sustainability of forest ecosystems. The acquisition and allocation of resources, in particular nitrogen (N), plays a central role in maximising the growth and reproductive fitness of plants, especially longliving woody species. “In the daily competition for limited resources, different strategies have evolved in plants to enhance their chances of survival,” says Dr Simon (1). Her group is investigating how both inorganic and organic N are acquired from the soil, in particular organic N. “With the recent suggestion that tree growth is limited by nutrient availability, particularly N (2), it becomes even more important to understand how trees acquire N from the soil and allocate it at the whole plant level,” continues Dr Simon. A number of techniques from various fields are being utilised to study plant interactions in the rhizosphere, a region of soil which is of great interest with respect to plant interactions. To Dr Simon, the most interesting zone in the soil is where plant roots can be found and interact with not only each other, but also with soil microorganisms and mycorrhizal fungi. “Our research includes the rhizosphere, and in general those soil layers which are important for N cycling,” she outlines. A recently developed in situ microdialysis technique (3) is being adapted within the project to quantify nitrogen fluxes
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in the soil, which Dr Simon says has several advantages over conventional methods. “There is no disturbance of the natural system, and degradation of organic molecules over time can be excluded,” she explains.
Transparent soil The group is also adapting a system to visualise processes in the rhizosphere in 3D using ‘transparent soil’ (4). In this system, ‘transparent soil’ – a transparent substrate consisting of a matrix of solid particles with a pore network containing liquid and air – is used to help researchers gain deeper insights into how plants compete for N in the rhizosphere. “This The Plant Interactions Ecophysiology Group.
substrate, used in combination with cutting edge 3D live microscopy systems, will provide valuable new information on living plants and soil organisms. In particular the effect of the physical heterogeneity of the growth substrate compared to phytagel as a substrate which is commonly used,” outlines Dr Simon. This approach enables researchers to look more closely at complex processes such as avoidance of competition, or the exploitation of microsites. With transparent soil, Dr Simon and her colleagues can monitor root-rootinteractions live, in situ, in 3D, and so study them in greater depth. “It allows us to identify species responses to the presence and absence of nitrogen, and/or to other tree species in the rhizosphere,” she explains. “It will provide novel insights into how tree species communicate to exploit nitrogen sources more efficiently and identify micro-niches exploited by tree species that allow better nitrogen uptake.” The distribution of N across different regions is not uniform however, and levels of availability do vary. Studies have shown that as the level of N supply in the soil varies, the
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Woody PIRATS Woody Plants – Interactions and Resource AllocaTion Strategies Project Objectives nature of plant interactions changes, a topic of great interest to Dr Simon and her research group. “In a recent experiment, we looked at the interactions between native and invasive tree seedlings and how the response to different competitors might shift with varying N supply,” she says. “Our surprising result is that one cannot generalise the responses of different species, but rather they strongly depend on competitor identity. Some species cope better or have advantages over others.”
economically and ecologically valuable forest ecosystems. Forests provide vital ecosystem services, and Dr Simon hopes the results of the group’s research will help to improve management and boost sustainability over the longer term. “For example, a better understanding of the competition for N between trees could contribute to a more efficient use of fertiliser in forest plantations,” she says. “Also, our biodiversity work on invasive species and how natives respond to their ‘occurrence on
The overall aim of this project is to gain more detailed knowledge on the basic processes and mechanisms underlying woody plant interactions, such as competition and facilitation. Climate change A further important consideration is the impact of climate change on plants and interactions in the rhizosphere. The effects of higher temperatures, increased levels of atmospheric N deposition and longer periods of drought are all taken into account in the group’s research. “For example, plant N acquisition is strongly linked to soil water availability, thus with increasing periods of drought, it is to be expected that the availability of soil N pools to plants will be reduced,” outlines Dr Simon. The impact of climate change on N distribution in the soil depends on a variety of different factors that might also influence each other though, and Dr Simon says with the current knowledge it is difficult to draw wider conclusions in this area. “More research is still needed to study these interactions and especially their combined effects, which might even be stronger than the single impact, on forest ecosystems,” she continues. This research holds important implications for a sustainable forest management, helping to build a deeper picture of the functioning of
the scene’ provides insights that can be used for conservation and restoration.” Research in this area is ongoing, and Dr Simon is keen to stress that she views plant interaction and ecosystem ecophysiology as the continued focus of attention for her group. The new approaches that are being established within the group will be applied in future projects. “Using transparent soil and microdialysis as new tools provides unique solutions to study root-root interactions,” stresses Dr Simon. While the focus of the Woody PIRATS project has been on plant-plant interactions, Dr Simon plans to broaden out the scope of research in the future. “I plan to extend our research to also include other players in the rhizosphere, such as free-living soil microorganisms and mycorrhizal fungi, and their influence on plantplant interactions,” she says. “We are currently only at the beginning with this research and more work definitely needs to be done to really gain a fundamental understanding of plant interactions with regard to N cycling in forest ecosystem functioning, including the response to abiotic and biotic stressors.”
Capturing animal movement in the forest plots. February (left), May (right).
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Woody PIRATS investigates tree-tree interactions as a fundamental process promoting the establishment of specific nitrogen acquisition and allocation strategies across species (and biomes) as well as altered responses of nitrogen metabolism to biotic and abiotic stressors at different levels: the whole plant, the community, and the ecosystem.
Project Funding
The Heisenberg Fellowship and the project “Consequences of competition and abiotic stress on the acquisition and internal allocation of nitrogen in temperate woody species” are both funded by the German Research Foundation (DFG) – total amount: c. 500,000€. Part of this project is the development of a new approach in which to use “transparent soil” to visualize processes in the rhizosphere. This project is funded by the VolkswagenStiftung – total amount: 108,000€.
Contact Details
PD Dr Judy Simon (PhD, University of Melbourne, Australia) Heisenberg Fellow / Group Leader “Plant Interactions Ecophysiology” Department of Biology University of Konstanz Universitätsstrasse 10 D - 78457 Konstanz Germany T: +49 7531 88 4322 E: judy.simon@uni-konstanz.de W: www.plantinteractionsecophysiology.com 1 Reich et al. (1997) Proc Natl Acad Sci USA 94, 13730-13734 2 Körner (2003) J Ecol 91, 4-17, Millard & Grelet (2010) Tree Physiol 30, 1083-1095 3 Inselsbacher et al. (2011) Soil Biol Biochem 43, 1321-1332 4 Downie et al. (2012) PLoS ONE 7, e44276
Dr Judy Simon, PhD
Dr Judy Simon, PhD studied biogeography at Saarland University (Germany) and obtained her PhD on tree ecophysiology at the University of Melbourne (Australia). She worked as a postdoc at the University of Freiburg (Germany). From there she went to the University of Konstanz where she is currently a group leader and DFG Heisenberg Fellow.
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