Allelopathic effects of the invasive species (Prosopis juliflora) on seedlings of two common arid plants: Does free proline play roles?

Prosopis juliflora is an invasive plant, representing a threat to native flora of arid lands. Its invasion appears to be driven by allelopathy. Arid plants have been reported to express increased content of proline when stressed by various ecological circumstances, but little is known about this when they are subjected to P. juliflora invasion. Here, allelopathic effects of P. juliflora were investigated in two common arid plant species (Prosopis cineraria and Vachellia tortilis). Seedlings of P. cineraria and V. tortilis were germinated in soils with P. juliflora leaves/pods powders and observed for 28 days. There were no demonstrated differences in growth parameters (i.e., root length, fresh mass, and length-to-fresh mass ratio) and chlorophylls content between the two species. Unlike V. tortilis seedlings, proline content of P. cineraria seedlings was profoundly augmented after exposure to P. juliflora powders, likely indicating a stressful condition imposed by the invasive species. Our findings support the inclusion of measurement of free proline, as an ecophysiological marker, in the future studies on P. juliflora invasion.