Eight species of turfgrasses or turfgrass alternatives were examined for salinity tolerance by growing them in hydroponics culture in a greenhouse. Salinity tolerance decreased in the order of: alkaligrass (Distichlis spicata), alkali sacaton (Sporobolus airoides), 'Arizona common' bermudagrass (Cynodon dactylon), 'Meyer' zoysiagrass (Zoysia japonica), sand dropseed (S. cryptandrus), 'Prairie' buffalograss (Buchloe dactyloides), 'Haskell' sideoats grama (Bouteloua curtipendula), and black grama (B. eriopoda). Rooting parameters (depth and weight) were directly associated with salinity tolerance. Root weights increased under salinity in 2 grasses: alkaligrass and alkali sacaton. Leaf osmotic potential (a measure of the amount of saline ions and other solutes) was highest in the most salt-sensitive grasses, indicating that salt tolerance in turfgrass is associated with salt exclusion from leaves.

As fresh water is becoming more scarce, increasing use of brackish water sources and sewage effluent for irrigation has resulted in a increasing need for salt tolerant turfgrasses. Though there are broad differences in salt tolerance among turfgrasses, little is known about how grasses adapt to salinity. Also, there are some alternative grasses which may hold promise for use as turfgrasses in extreme environments (e.g. high salinity, extreme drought). This project was done to determine the relative salinity tolerances of a broad range of warm season grasses which are adapted to Arizona.

Grasses were grown in 5" diameter cups, overlying tubs containing constantly aerified Hoagland's solution. Solution salinity levels were gradually raised to final levels of 100, 200, 300, 400, 500, and 600 mM NaCl, equivalent to a range of 0 -46 dS m^-1 (mmhol cm^-1), or 0 - 35,000 ppm. At each salinity level salinity tolerance was measured as the percentage of leaf firing. Leaf firing is a good indication of the amount of tissue damage occurring under saline conditions. Root lengths were measured at each salinity level, and total root dry weights measured at the end of the experiments. Osmotic adjustment (a measure of the amount of saline ions and other solutes present in the leaves) was measured at each salinity level. The experiment was repeated twice.

Relative salinity tolerance decreased in the order of: alkaligrass (Distichlis spicata), alkali sacaton (Sporobolus airoides), 'Arizona common' bermudagrass (Cynodon dactylon), 'Meyer' zoysiagrass (Zoysia japonica), sand dropseed (S. cryptandrus), 'Prairie' buffalograss (Buchloe dactyloides), 'Haskell' sideoats grama (Bouteloua curtipendula), and black grama (B. eriopoda) (Table 1). Even at 750 mM NaCl (35,000 ppm) alkaligrass and alkali sacaton showed little to no leaf injury. This level is well above full strength sea water. These grasses are a bit too coarse for many turfgrass scenarios, but make good ground covers and golf course roughs. We are currently selecting strains of alkaligrass which are finer and denser. Rooting is an important salt tolerance mechanism in these grasses. The more salt tolerant grasses had greater rooting depth (Table 2), and greater total root dry weight (Table 3) under salinity stress. This indicates that well adapted plants have vigorous root systems which seek out water at greater depths while under salt stress. Perhaps this is an evolutionary mechanism to seek out less salty water occurring deep in the soil profile. Finally, in salt tolerant grasses, osmotic potential was controlled (kept at lower levels), than in susceptible plants (Table 4). This means that saline ions were excluded from shoots to a greater degree in salt tolerant grasses. Saline ions are toxic to plant tissues at high concentrations. Knowledge of this mechanism of tolerance will aid plant breeders in developing more salt tolerant turfgrass cultivars. Alkaligrass and alkali sacaton are suitable grasses to use as ground covers in extremely saline areas. However, bermudagrass and zoysiagrass can also be successfully grown using poor quality irrigation water under relatively high saline conditions.

Table 1. Relative percent leaf firing (a measure of injury) under increasing salinity stress. Relative leaf firing indicates the change in leaf firing relative to control plants. Higher numbers indicate more injury.

Table 2. Root lengths (cm) under increasing salinity stress.

Grass 100 200 300 400 500

Sporobolus cryptandrus 25.0 56.5 62.5 47.0 72.3

Bouteloua curtipendula 68.5 102.8 91.8 88.0 90.3

Bouteloua eriopoda 63.3 79.3 77.8 76.8 75.3

Buchloe dactyloides 31.3 40.0 36.0 39.5 40.0

Cynodon dactylon 42.0 113.5 126.3 101.3 122.8

Distichlis spicata 37.0 82.3 109.8 121.3 138.8

Zoysia japonica 0.0 18.0 35.0 17.5 34.0

LSD¹ 17.8 21.9 36.3 35.2 41.5

Table 3. Root dry weights (g), and relative root dry weights, at end of experiment. Relative root dry weights indicate the change in rooting relative to control plants, in g (negative values indicate a rooting decrease under salinity stress).

Sporobolus cryptandrus 0.027 -0.048

Bouteloua curtipendula 0.039 -0.192

Bouteloua eriopoda 0.067 -0.197

Buchloe dactyloides 0.008 -0.033

Cynodon dactylon 0.095 -0.030

Distichlis spicata 0.185 0.060

Zoysia japonica 0.004 0.003

LSD¹ 0.060 0.168

Table 4. Leaf sap osmolality under increasing salinity stress.

Grass 100 200 300 400 500 600

Sporobolus cryptandrus 669 1089 1972 2216 3508 2264

Bouteloua curtipendula 728 1740 3391 ---- ---- ----

Bouteloua eriopoda 685 1464 2874 ---- ---- ----

Buchloe dactyloides 699 1296 2050 2858 2717 ----

Cynodon dactylon 605 712 968 1169 1573 1916

Distichlis spicata 567 678 841 1015 1235 1169

Zoysia japonica 707 891 1072 1465 2392 2313

LSD¹ 96 314 576 602 816 815

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