(L.) Pers. relative to Sorghum bicolor(L.) Moench was associated with shoot Clconcentration [59].
Similarly, salt-tolerant tall wheatgrass accessions excluded Naand Clfrom shoots (while maintaining
fairly high Kcontents) to a greater extent than salt-sensitive crested wheatgrass [Agropyron desertorum
(Fisch. ex Link) Schult.] accessions [60]. In contrast, salt-tolerant weeping [Puccinellia distans(L.) Parl]
and Lemmon [P. lemmoni(Vasey) Scribn.] alkaligrasses were found to accumulate more Naand Clin
shoots than did moderately salt-tolerant creeping bentgrass (Agrostis stoloniferaL.) [61].
Saline ion exclusion also appears to be an important factor influencing intraspecies salinity tolerance,
i.e., at the cultivar or accession level. For example, salt-sensitive populations were found having, at a
given test salinity, higher shoot Naand Clthan coastal (or other saline site) salt-tolerant accessions in
chewings fescue [50], red fescue (Festuca rubraL.) [62], bermudagrass [45], and creeping bentgrass [63].
However, this was not the case for eight natural populations of brown beetlegrass. There was no correla-
tion between salinity tolerance and shoot saline ion concentrations or the soil salinity level of the original
collection sites [36]. Relative salinity tolerance of zoysiagrass (Zoysiaspp.) cultivars and accessions has
been successfully predicted on the basis of shoot Naconcentrations occurring under salt stress [64,65].
B. Osmotic Adjustment and Ion Regulation
Osmotic stress due to lack of osmotic adjustment, resulting in reduced water absorption and physiologi-
cal drought, has long been considered a major cause of salinity injury in plants [47,61,66]. Maintenance
of cell turgor and plant growth requires sufficient increase in sap osmolality to compensate for external
osmotic stress, the process of osmoregulation, or osmotic adjustment [66,67]. In a saline environment, os-
motic adjustment is needed to avoid osmotic stress, yet this may result in ion toxicity [56,68].
It has been noted that monocots (relative to salt-tolerant dicots), including Poaceae, tend to restrict
saline ion uptake. This has been suggested to cause cell dehydration and reduced growth under saline con-
626 MARCUM
Figure 2 Leaf Cland Nalevels of grasses exposed to increasing salinity levels in solution culture. Verti-
cal bars represent LSD (P.05) values for mean comparison at each salinity level.