Can photosynthetic traits offer insight into the success of a widespread invasive grass?

Despite their presence in almost all global ecosystems, the underlying mechanisms contributing to the success of invasive plants remain largely unknown. Invasive plants cause broad ecological and economic damage and pose a growing threat with climate change. There has been recent interest in identifying plant functional traits (e.g. leaf and growth traits) that facilitate invasion. Less attention has been paid to the underlying physiology of invasive plants, despite them generally being shown to have faster photosynthetic rates than native plants. Intraspecific variation in photosynthetic traits may contribute to their success, with invasive plant performance linked to a population’s home climate, however no study to date has focused on the relationship between local climate variables and ecophysiological traits

In their new study published in AoBP, Kelly et al. evaluate photosynthetic trait variation among populations, ecotypes and home climates (i.e. the climates from the locations they were collected) of the widespread and expanding invasive Johnsongrass (Sorghum halepense). Johnsongrass has been described as one of the world’s worst weeds, including in the USA where it is one of the six most damaging agricultural weeds. Recent studies have shown that Johnsongrass populations are differentiating genetically and phenotypically into unique agricultural and non-agricultural ecotypes. Kelly et al. found maximum photosynthetic rate to vary among these diverse populations and ecotypes. They also found that populations from warmer home climates had lower dark respiration rates, light compensation points and water-use-efficiencies. As Johnsongrass expands across the US, biotic and abiotic factors are driving variation in genetics and physiology, and contributing to its invasiveness. This study demonstrates the importance of more accurately evaluating physiological traits in invasive plants, especially as they relate to home climates. The authors conclude by highlighting that they would like to investigate the underlying genetics underlying photosynthetic traits found to vary across populations. They hope that this would inform not only our understanding for invasiveness, but also the potential for range expansion in the face of a changing climate.