Low soil nitrogen and moisture limit the expansion of the invasive grass, Megathyrsus maximus (Guinea grass) in semi-arid soils

Abstract

The goal of this study was to predict the range expansion potential of an invasive forage grass, Guinea grass (Megathyrsus maximus). We collected rhizosphere soil samples of M. maximus and coexisting species from 150 different locations and analysed them for soil properties. We estimated the probability of M. maximus presence as a function of soil moisture, organic matter, pH, salinity, total N, and CN ratio using logistic regression. Presence of M. maximus was associated with higher soil moisture, higher organic matter, pH, and nitrogen, but lower salinity and CN ratio. Soil nitrogen and moisture were key factors for predicting the presence of M. maximus. Our results show that while M. Maximus prefers high nitrogen soils, coexisting plants are better adapted to soils with low nitrogen availability. Wetter soil with high nitrogen concentrations gives M. maximus a strong competitive advantage over other species as more nitrogen reduces the effect of otherwise adverse environmental conditions and allows M. maximus to capitalize on moisture. We expect that a regional climate shift towards a wetter rainfall regime in semi-arid regions would facilitate a range expansion by M. maximus further into the rangelands, countering efforts to protect and restore native plant communities.