Three halophytes for saline-water agriculture: an oilseed, a forage and a grain crop. (Special Issue: Sustainable cultivation and exploitation of halophyte crops in a salinizing world.)

摘要

Greenhouse and field trials and nutritional studies are reviewed for three halophytes that are candidate species for salt-water crop production. Salicornia bigelovii is a leafless, C3, succulent annual salt marsh plant that produces an oilseed on seawater irrigation in coastal desert environments. Yields on seawater are similar to conventional oilseeds under ideal conditions but are reduced under mechanical harvest due to uneven seed ripening and shattering of seeds. Water management requires frequent irrigation to keep the shallow-root zone at field capacity and to ensure a leaching fraction to prevent accumulation of salts. Nutritional value of oil, seed meal and biomass are adequate to replace conventional animal feed ingredients in formulated diets, despite presence of saponins in the meal and high salt content of the biomass. A breeding program showed that this species is amendable to improvement using conventional breeding approaches. Atriplex lentiformis is a perennial C4 xerohalophyte shrub valued as a forage species in North American rangelands. Under cultivation it produces as much biomass and protein as alfalfa on salinities ranging from mildly saline (1.8 g L-1 TDS) to full seawater salinity (40 g L-1). Greenhouse trials show that salinity increases dry matter production and water use efficiency of A. lentiformis on drying soils, making it a good candidate for deficit irrigation for forage production. As with other Atriplex spp., its crop potential is currently limited by a tendency to become woody with successive cuts and with non-protein nitrogen and anti-nutritional compounds present in leaves. Distichlis palmeri is a perennial C4 saltgrass endemic to the delta of the Colorado River in the northern Gulf of California that produces a grain similar in size and nutrition composition to rice. It was a staple summer food source for the Cocopa people before upstream water diversions disrupted flood flows to the delta. It is productive on full-strength seawater and produces aerenchyma tissue allowing it to grow under flooded conditions similar to paddy rice. However, only limited experiments have been conducted with this plant, and therefore its ultimate agronomic potential is unknown. Despite initial pessimism about the production potential of halophytes, these examples show that euhalophytes can maintain high productivity of useful agricultural products up to a root-zone salinity of 70 g L-1 TDS, double the salinity of seawater.