Possible role of soil alkalinity in plant breeding for salt-tolerance

Abstract

Bennett et al.[1] present the phylogenetic distribution of salt-tolerant species on a phylogeny of 2684 grasses in the context of plant breeding for salt-tolerance. Salt-tolerance, they conclude, is an evolutionary labile trait that has evolved a number of times across many lineages; this is at odds with the record of difficulty in breeding salt-tolerant crops.One potential explanation for this disconnect is the association between soil salinity and alkalinity; many saline soils are also alkaline due to the presence of sodium (Na)-carbonates (see [2] for a review of salt-affected soils). Combined alkaline and salt-stresses are more deleterious to plant growth than salinity alone [3][4][5]. Thus, the failure of laboratory-bred NaCl-tolerant cultivars to give good yields under field conditions may reflect combined soil sodicity and alkalinity. Indeed, Yang et al. [4] have shown that for even for Chloris virgata, a natural alkali-resistant halophyte, the inhibitory effects of alkali stress (from NaHCO 3 and Na 2 CO 3 ) on relative growth rate and stored energy were significantly larger than those of salt-stress (from NaCl and Na 2 SO 4 ). Other Chloris species are tolerant of alkaline pH (e.g. Chloris gayana [6] and Chloris barbata [7]), and it would be interesting to see whether there is any evolutionary relationship between alkali-and salt-tolerance in Chloris and more widely in the Chloridoideae. Has there been coevolution of alkali-and salttolerance in grasses? If yes, this may provide new avenues for plant breeding for salt-tolerance.Both alkali-and salt-stress impact photosynthetic productivity and metabolism, but they may involve different physiological and molecular processes ([8 -11] and references therein). However, plant breeding efforts continue to focus on NaCl-tolerance [12]. In Australia, where decades of research on plant breeding for salt-tolerance have been invested, 50% of soils are calcareous [13] and therefore contain significant concentrations of carbonate and bicarbonate ions (alkalinity). Sodic soils occupy about 27% of Australia [14], including large tracts of agricultural land; most have calcareous subsoils. This implies that a wider range of salts and their potential interactions need to be considered if we are to successfully breed salt-tolerant crops that are high-yielding under field conditions. It also suggests that new breakthroughs in food security are likely to arise at the intersection of disciplines (plant and soil sciences).

Soil alkalinity and salt tolerance: adapting to multiple stresses

“…We agree that, given the overlap of salinity and alkalinity on the landscape [1,9], it would be interesting to ask whether there has been co-adaptation to salinity and alkalinity. Although clear differences in tolerance to salinity and alkalinity exist for some species (e.g.…”

“…Although clear differences in tolerance to salinity and alkalinity exist for some species (e.g. rice [7]), shared underlying mechanisms in salinity and alkalinity tolerance have been suggested for some taxa, such as Eucalyptus [10] and Chloris [1]. This leads to a broader question of whether some lineages have characteristics that make them better able to adapt to a range of environmental stresses.…”

Soil Chemistry Factors Confounding Crop Salinity Tolerance—A Review

“…The failure of laboratory-bred NaCl-tolerant cultivars to perform well under field conditions may reflect the effects of sodicity and alkalinity [47]. In the field, crops are routinely subjected to a combination of different abiotic stresses [48].…”

Beneficial Effects of Potassium on Growth, Water Relations, Mineral Accumulation and Oxidative Damage of Beta vulgaris in Sodic-alkaline Condition

“…Many saline soils are also sodic-alkaline due to the presence of NaHCO 3 and Na 2 CO 3 , which resulted in high soil pH, usually greater than 8.5 (Lyubimova et al, 2009;Bui, 2013). Sodic-alkalinity is more deleterious to plant growth than salinity alone, and results in laboratory-bred NaCl-tolerant cultivars failing to achieve good yield in field conditions (Nishiuchi et al, 2010;Bui, 2013 influx, respectively, resulted in a concomitant elevation of cytosolic Ca 2+ activity and K + loss (Demidchik et al, 2003;Demidchik et al, 2007).…”

“…Sodic-alkalinity is more deleterious to plant growth than salinity alone, and results in laboratory-bred NaCl-tolerant cultivars failing to achieve good yield in field conditions (Nishiuchi et al, 2010;Bui, 2013 influx, respectively, resulted in a concomitant elevation of cytosolic Ca 2+ activity and K + loss (Demidchik et al, 2003;Demidchik et al, 2007). Alongside toxic Na + influx, cytosolic ionic homeostasis is seriously impaired, and cellular tissue damage occurs via a number of destructive processes following a rise in ROS levels (Ashraf, 2009;Velarde-Buendía et al, 2012).…”