II. GROWTH RESPONSE AND RELATIVE SALINITY TOLERANCE
A. Shoot Growth Responses
Salt tolerance in plants depends not only on genotype but also on cultural and environmental conditions.
Therefore, salt tolerance can be determined not with certainty but only on a relative basis [13,16]. Rela-
tive salinity tolerance is generally quantified as the salt level resulting in a 50% reduction in shoot growth
(yield) or, alternatively, the threshold salinity, i.e., salinity level where yield begins to decline, followed
by the rate, or slope, of yield reduction [16,18].
Fifty percent shoot growth reduction occurred at 150 mM NaCl salinity (approximately 12 dS m^1
ECsoln) for buffalograss, 330 mM (26 dS m^1 ) for bermudagrass, and 600 mM (46 dS m^1 ) for desert
saltgrass (Figure 1). Reid et al. [19] also reported 50% shoot growth decline at 12 dS m^1 for three buf-
falograss cultivars. In another study, six natural populations of buffalograss had an average 50% shoot
growth reduction at 13 dS m^1 [20]. Previous data for bermudagrass are more variable, perhaps because
of the genetic diversity within this genus [21]. Fifty percent shoot growth reductions for bermudagrass
cultivars and/or accessions have been reported as 24 and 33 dS m^1 [22], 24 and 31 dS m^1 [23], and 17
to 22 dS m^1 [24]. The halophytic nature of saltgrass is apparent from other sources [15,16,25]. In sev-
eral studies, shoot growth of desert saltgrass was not affected by salinities up to 40 dS m^1 [26,27].
These results place buffalograss in the moderately salt-sensitive category [14], similar in tolerance
to Kentucky bluegrass (Poa pratensisL.) [28], various grama grasses (Boutelouaspp. Lag.) [17], chew-
ings fescue (Festuca rubraL.) [29], and bahiagrass (Paspalum notatumvar.sauraeParodi) [30].
Bermudagrass is considered salt tolerant [12–14,16]. Other studies have shown it similar in tolerance to
St. Augustinegrass [Stenotaphrum secundatum(Walt)) Kuntze] [31,32], tall wheatgrass [Thinopyrum
624 MARCUM
Figure 1 Relative shoot dry weight [(treatment/control) 100] and relative rooting depth (treatment minus
control) of three grasses exposed to increasing salinity levels in solution culture. Vertical bars represent LSD
(P.05) values for mean comparison at each salinity level.