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
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