Environmental tracers have been defined as widely distributed, natural or anthropogenic compounds or isotopes in the near-surface environment of the Earth, such that variations in their abundance can be used to determine pathways and timescales of environmental processes (Cook and Böhlke, 2000). Environmental tracers are typically used in hydrological investigations, but they can also be very useful in an ecohydrological context. This presentation will discuss examples of how environmental tracers can be used to better understand plant-soil interactions and the unique perspectives that they can bring. It is hoped that this discussion will spur greater use of these techniques.
Results/Conclusions
The stable isotopes δ2H and δ18O in plant- and soil-waters have been used for quite some time to understand where plants get their water in a soil profile. However, they can also provide a great deal of insight about evaporation (physical loss of plant available water) and, as will be discussed in this presentation, can be even more powerful when coupled to other environmental tracers such as chloride. It is well established that root uptake of water imposes little to no fractionation of δ2H and δ18O (in most cases) and so the main determinants of the isotopic composition in soil water is the isotopic composition of precipitation and physical evaporation. However, chloride in soil water is affected by both evaporation and transpiration which makes it possible to obtain a better understanding of the spatial variations of evaporation and transpiration at canopy/intercanopy scales when these tracers are used together. Understanding climate change effects on plant-soil interactions is also an area where environmental tracers can be useful. We are measuring nitrate and nitrate isotopes in soil waters in Arctic permafrost systems and results suggest permafrost degradation can have a major impact on Arctic nitrogen cycling resulting in major feedbacks that will likely affect ecosystem functioning. Environmental tracers are underutilized and the examples presented show just a few of the ways that they can be used to understand plant-soil interactions.