UC Davis

Lepidium latifolium is an aggressive plant species that is invading both wetlands and uplands across a wide range of salinities. This study examined how salinity and moisture gradients influence the potential for invasion by L. latifolium. Three sites in the San Francisco Bay Delta with varying salinity and moisture levels were chosen as research sites. These sites corresponded to a dry (18.32%) freshwater (3.88‰) site, a wet (40.53%) brackish (23.16‰) site, and a moderately wet (38.33%) saline (32.33‰) site. Our results showed that inflorescence number and height were unaffected by salinity or soil moisture. Seed production was significantly affected by salinity (P = 0.0297) and moisture levels (P = 0.0004). Seed production at the high salinity site was reduced by 29% from the freshwater site. Seed production at the wettest site had an 87% reduction from the driest site. Seed viability was also reduced by both salinity (P < 0.0001) and soil moisture (P < 0.0001). Viability at the highest salinity site was reduced by 49% from freshwater sites and was reduced by 8% from the wettest to driest sites. Mean seed dispersal distance was 0.23 m greater at the freshwater site, which was not statistically significant (P = 0.1815). The deleterious effects of salinity and moisture resulted in reduced L. latifolium densities in high salinity and moisture locations, but only at the highest salinity site. With increased seed production and viability, drier freshwater sites experience greater propagule pressure, resulting in an increased invasion potential. Therefore, variability along salinity and soil moisture gradients serve as useful metrics for prioritizing control and eradication efforts of L. latifolium.