How do abiotic stresses influence the seed germination and vigor of tree species from the Pampa biome?

The Pampa biome is increasingly threatened by anthropogenic pressure and climate change, which intensify thermal extremes, water scarcity, and soil salinity, negatively affecting seed production and dispersal. This study evaluated the effects of thermal, water, and salinity stresses on the germination and vigor of Neltuma affinis and Vachellia caven, two ecologically and economically important Fabaceae species native to the Pampa parklands. The seeds were subjected to different temperatures (15, 25, 30, and 35 °C), polyethylene glycol (PEG) concentrations (0.0, -0.41, -0.58, and -0.79 MPa), and NaCl concentrations (0.0, -0.46, -0.92, and -1.37 MPa). Germination of N. affinis was not observed at 15 or 35 °C, whereas V. caven failed to germinate only at 15 °C. Under water stress, both species showed reduced germination and germination speed index (GSI). While V. caven demonstrated tolerance to salinity, N. affinis germination and GSI were inversely proportional to salinity. Overall, V. caven showed tolerance to thermal and saline stress, whereas N. affinis was significantly more sensitive to abiotic stresses. Given the limited distribution of N. affinis in Brazil, together with ongoing anthropogenic pressure and increasing climatic extremes, this species may be at risk of extinction due to reduced germination capacity and seed vigor.