Can eDNA be an indicator of tree groundwater use? A perspective

A major challenge of managing groundwater-dependent ecosystems is determining when and where plants are accessing and using groundwater. Addressing this knowledge gap is particularly pertinent where remnant stands of old growth trees reside within areas where groundwater is being used at an unsustainable rate. The aim of this paper is to investigate what it means to find tree DNA in the groundwater and provide a perspective on whether the detection of tree DNA in groundwater could provide an indicator of groundwater use by trees. This idea arose from recent DNA-based surveys that routinely detected tree DNA in groundwater samples, which may be unexpected given the general absence of plants in dark, subsurface environments. We discuss the likely sources and fate of tree DNA in groundwater and the knowledge needed to progress the development of tree DNA as a robust indicator. If successful, such an indicator would help managers better understand the water requirements of groundwater-dependent vegetation, meet legislative obligations for monitoring and assessment, and improve the conservation and management of groundwater-dependent ecosystems.