Morphological and Physiological Response of Five California Native Grass Species to Moderate Salt Spray: Implications for Landscape Irrigation with Reclaimed Water

Abstract

Five California native perennial grass species including Melica californica (California melic), Nasella pulchra (purple needlegrass), Sporobolus airoides (alkali sacaton), Muhlenbergia rigens (deergrass), and Deschampsia caespitosa (California hairgrass) were examined for their response to salt spray. Vegetatively propagated plants were sprinkler irrigated with deionized water, 500 mg L− 1 and 1500 mg L− 1 sodium chloride (NaCl) under greenhouse conditions for 20 weeks. Percent leaf chlorosis, shoot dry weight, root dry weight, and inflorescence dry weight were measured to determine response of the plants to salt stress in regard to their relative tolerance to salt, biomass partitioning, sexual reproduction, and the relationship between root thickness and root dry weight distribution. Physiological responses including changes in expressed leaf sap osmolality and tissue Na+, Cl−, and K+ concentrations were also measured. In terms of plant shoot tissue biomass, no significant salt stress response was detected in four of the five grass species under 500 mg L−1 NaCl treatment, and S. airoides had greater shoot dry weight than its control treatment. Above that level, D. caespitosa, M. californica and N. pulchra showed significant reduction in dry weight and increased leaf chlorotic symptoms. Muchlenbergia rigens and S. airoides were not affected by the 1500 mg L− 1 salt treatment. The root dry weight partitioning (percentage of total plant biomass) was highest in D. caespitosa and lowest in N. pulchra, and was significantly different among the five grass species. However, no significant difference was detected among in response to the salt treatments. Deschampsia caespitosa, M. californica, and N. pulchra had 70% to 90% of their root biomass in the top 30 cm of soil, but M. rigens and S. airoides had only about 50% in the top 30 cm of soil and had greater root mass in the 60–90 cm soil depth than the other three species. The root biomass distribution along the soil depth was significantly different among the grass species but not significantly different according to salt treatments. When the root dry weight distribution was expressed as linear regression slope values, a positive relationship was found between the slope values and the root thickness values, indicating that the species with larger root size tend to have greater root mass in the deeper soil profile. Deschampsia caespitosa, M. californica, and N. pulchra had greater salt uptake in their leaf tissue and had greater reduction of K+/Na+ ratio than M. rigens and S. airoides and were significantly different among both the plant species and salt treatments. Melica californica was the only species that showed significant osmotic potential adjustment. The osmotic potential of the applied salt solutions was low (−0.04 and −0.12 MPa), and the salt stress symptom likely to be caused by toxicity effect (passive saline ion uptake) rather than osmotic stress. Nevertheless, all five California native grass species were found to be suitable for sprinkler irrigation with reclaimed water containing a NaCl concentration of 500 mg L− 1 or less.