Soil and plant chemical profiles of invasive Cyperus aromaticus (Cyperaceae) and co-occurring pasture species across land-use types: potential implications for invasion and plant–soil feedbacks

Abstract

Biological invasions diminish the structures of ecosystems and biological functions. In this regard, Cyperus aromaticus (Cyperaceae) (Navua sedge), a native of Africa, recently established along the coastal regions of north-eastern Queensland (NE-QLD), Australia, forming extensive monospecific stands and impacting both agricultural and natural landscapes. Aims: This study examined the changes in soil physico-chemistry and differences in plant tissue chemical profile of C. aromaticus and its co-occurring pasture species in invaded landscapes of varying land use types. Methods: Across many C. aromaticus invaded sites in NE-QLD (N=14), we collected above ground vegetation and soils in invaded and nearby non-invaded patches. We also set-up a microcosm trial in which C. aromaticus and a desirable pasture grass species (Urochloa humidicola) were grown individually in potted soils and changes in soil chemistry monitored for three years. Key results: Neutral effects of C. aromaticus invasion were detected in soils of active agricultural lands, but significant differences occurred in other land use types (roadside, riparian corridor, abandoned agricultural land) and in the microcosm trials. The plant tissues of C. aromaticus are higher in many micro-nutrients (e.g., S, Cu, Al, Fe, Zn) compared to co-occurring pasture species. Significantly higher lignin, but lower forage quality of fibre, cellulose, and hemicellulose were also detected in C. aromaticus. Conclusions: C. aromaticus invasion is associated with changes in soil processes and systems, but its effect can be obscured by land use (e.g., anthropogenic) practice. In invaded landscapes the changes in soil chemistry and observed differences in tissue composition between C. aromaticus and co-occurring pasture grasses might lead to positive plant-soil feedback, thus promoting the establishment and further spread of the weed. Additionally, C. aromaticus lower forage quality reinforces the need to manage the weed, especially in grazing landscapes.