Drought impacts on the efficacy of invasive grass control by clipping: A study on Johnsongrass (Sorghum halepense)

Abstract

Climate change has intensified drought conditions, aiding the spread of some invasive plant species. However, the impact of drought on invasion control, such as clipping, remains largely unexplored. Therefore, we conducted a greenhouse experiment to investigate the growth of an invasive non-native grass, Johnsongrass (Sorghum halepense), under drought and non-drought conditions, coupled with clipping and non-clipping treatments. We measured above- and belowground biomass and eco-physiological parameters of photosynthesis, plant water and nutrient status, and arbuscular mycorrhizal (AM) fungi-related factors. We also developed a theoretical model simulating the population dynamics of a hypothetical invasive grass species, enabling us to generalize the effects of clipping across a broad gradient of drought conditions. We found that: (1) The differences in aboveground biomass between clipped and non-clipped grasses were significant under the condition of non-drought, but became non-significant under drought; (2) Our model also showed a decrease in the clipping-caused population difference with increasing drought severity; (3) The clipped grasses exhibited a higher carbon assimilation rate and lower water stress compared to non-clipped ones under drought, but these differences were non-significant without drought; (4) The difference in leaf phosphorus concentration and AM fungal abundances between the clipped and non-clipped grasses were consistent across both drought levels. Taken together, the clipping efficacy was diminished under drought likely due to the low water stress experienced by clipped grasses. Furthermore, the AM fungi-related factors are unlikely to drive the reduced clipping efficacy. Therefore, the implementation of control treatment could consider climate conditions to improve the control efficacy.