Chloride accumulation and partitioning in Barley as affected by differential root and foliar salt absorption under saline sprinkler irrigation

Abstract

Barley is a crop that has been classified as tolerant to soil salinity, but under sprinkler irrigation with saline water it can readily absorb salts through its leaves and develop injury. Experiments using a triple-line-source sprinkler system were conducted on barley between 1989 and 1991 to determine: (1) the specific effects of foliage wetting on the mass of different shoot components; (2) the relative contribution of root and foliar absorption processes to foliar Cl accumulation; and (3) the extent by which these processes affect Cl partitioning in the shoot at the end of the season. Some plants were covered with plastic during the irrigation process to prevent foliar wetting while others remained uncovered. Salinity affected the partitioning of dry matter in the shoots regardless of whether plants were covered during the irrigation process. The organs associated with reproduction, e.g., heads and peduncles, comprised a larger fraction of the total shoot biomass under high salinity than under low salinity, indicating that plants under salinity stress were able to redistribute their dry matter to favor reproductive growth. The Cl concentration of the young leaves sampled from uncovered plants was linearly related (i.e., r ²>0.71) to the Cl concentration of the irrigation water. Equivalent leaves from covered plants also contained a substantial amount of Cl but concentrations were weakly correlated (i.e., r ²<-0.41) with the concentration of Cl in the irrigation water. At low salinity, there were no differences in leaf Cl concentrations between covered and uncovered treatments. In young leaves, differences between these treatments progressively increased with increasing salinity, indicating that the relative contribution of Cl in the leaf from foliar absorbed salts increased with increasing Cl in the irrigation water. Only in the youngest leaves sampled at the end of the season from plants grown at high salinity was the Cl concentration in uncovered plants (foliar plus root-absorbed Cl) found to be more than twice that in covered plants (only root-absorbed Cl) indicating that most of the Cl in young leaves originated from foliar absorption. In addition, only in the youngest leaves (e.g., flag leaves) was the slope of the relationship between leaf-Cl concentration and Cl concentration of the sprinkling water of uncovered plants more than twice that of covered plants, also indicating that foliar-Cl absorption was more substantial than root-Cl absorption. At high salinity, the difference in leaf Cl concentration between covered and uncovered plants was maximum in the youngest leaf (flag leaf), but differences became progressively smaller with increasing leaf age until ultimately concentrations of chloride in leaves older than the flag leaf-2 were highest in covered plants. In older tissue, it was difficult to distinguish which process, foliar or root absorption, was most responsible for leaf-Cl accumulation. These processes may not be entirely independent of one another and much of the Cl in the oldest leaves of uncovered plants could have been derived from foliar sources during the first month of sprinkling, reaching maximal levels, and thereby restricting root-absorbed Cl. Furthermore, since these leaves at the end of the season are more injured and drier than those from covered plants, late-season sprinkler irrigations may have been responsible for leaching some of the Cl out of these necrotic leaves.