The effects of saltwater intrusion on germination success of standard and alternative crops

Saltwater intrusion (SWI) is the landward movement of seawater, which can salinize coastal farmlands and affect crop yields. Germination is an especially vulnerable life history stage for crops. Salt stress reduces a seed’s ability to absorb water (osmotic stress) and causes an ion imbalance within the seed (ionic stress), ultimately inhibiting germination and preventing crop production. Therefore, growing standard crops in the face of SWI can risk crop failure. If alternative crops are more tolerant of osmotic and ionic stress, they may be more suited to withstand SWI. Our objectives were to (1) determine how salt stress (ionic and osmotic stress) and osmotic stress levels affect seed germination in standard and alternative crops in a controlled environment experiment and (2) compare germination rates in the controlled environment with field trials. In our study region of the Eastern Shore of Maryland, standard crop species include corn, soybean, and wheat; alternative species and varieties include sorghum, chloride-excluding soybean, barley, and quinoa. Seeds of these species were germinated under different levels of salt and osmotic stress ranging from 0 to −4 MPa (0–111.1 dS m−1, respectively) by manipulating concentrations of NaCl to alter salt stress and concentrations of polyethylene glycol to alter osmotic stress. Crop species differed greatly in germination tolerance to salt and osmotic stresses, however, there was no significant difference in percent germination between standard and alternative crop species. Standard soybean, chloride-excluding soybean, and quinoa were the only species to germinate in salt stress; standard soybean and chloride-excluding soybean had an equal tolerance during germination at -1.8 MPa (50.0 dS m−1) and quinoa successfully germinated at -0.5 MPa (13.9 dS m−1). However, wheat (standard) and barley (alternative) were the most tolerant of osmotic stress, successfully germinating at -2 MPa (55.6 dS m−1). We also examined germination of sorghum and chloride-excluding soybeans in previously-established field trials for two years on two salt-intruded farms on the Eastern Shore of Maryland. One of the farms showed greater germination success (measured as seedling emergence) in chloride-excluding soybean than sorghum despite a small difference in salt stress (Δ -0.05 MPa across the field). These results highlight the complexity of understanding how salt stress shapes germination processes in the real world and suggest temporal windows of low and high stress may have long-lasting consequences for crop performance.