Germination and establishment of halophytes on brine-affected soils.
1. Contamination of soils with oilfield brines is a significant environmental problem in many oil-production areas. This study tested the feasibility of using different salt-accumulating halophyte species to remediate brine-contaminated soils at a site in south-eastern Ohio, USA, and tested whether planting season affected the germination, yield and sodium uptake of selected species. 2. Atriplex prostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina and Suaeda calceoliformis were sown in October 1992 (autumn sowing) and March 1993 (spring sowing). For A. prostrata and Spergularia marina, spring-sowing produced greater germination and survival, while H. jubatum exhibited greater germination and survival in autumn sowings. Germination and survival of Salicornia europaea and Suaeda calceoliformis were not significantly affected by sowing season, but Salicornia europaea germinated and survived poorly in both seasons. 3. Spring-sown A. prostrata and Suaeda calceoliformis and autumn-sown H. jubatum and Spergularia marina produced the greatest yields. 4. High soil conductivities negatively affected the survival and yield of spring-sown A. prostrata, H. jubatum and Spergularia marina, but did not significantly affect autumn sowings. 5. Root biomass allocation was greater in autumn-sown H. jubatum, Spergularia marina and Suaeda calceoliformis. We hypothesized that autumn-sown seeds of these species have earlier root development that facilitates avoidance of extreme salinity and moisture fluctuations found at the soil surface. 6. All species accumulated higher amounts of Na+ and Cl- than other ions. Autumn-sown A. prostrata and Suaeda calceoliformis accumulated significantly more Na+ than when spring-sown. Ash content (a measure of accumulated inorganic matter) ranged from 15% to 35% in the various plant tissues. Hordeum jubatum had significantly more Na+ in its roots than in its shoots, making it less suitable for site remediation than A. prostrata or Suaeda calceoliformis. 7. With the exception of Salicornia europaea, all species reduced soil salinity significantly compared with paired control plots, ranging from 4% in H. jubatum to 17% in A. prostrata. Leaching following precipitation resulted in a 44% reduction in Na+ from control plots over a 4-year period. However, there was a 59% reduction in Na+ from plots vegetated with halophytes over the same period. 8. The results indicate that establishment of salt-accumulating halophytes on salt-affected sites can sufficiently remediate the soil to the point where it can be returned to agricultural productivity or where native plants can invade and become established. The phytoremediation process can be facilitated by tailoring plant selection to site conditions, using inputs of fertilizer and water to enhance the growth of the halophytes, and by harvesting the plants on a regular basis.