Growth responses of Melilotus siculus accessions to combined salinity and root-zone hypoxia are correlated with differences in tissue ion concentrations and not differences in root aeration

STRIKER GG; TEAKLE NL; COLMER TD; BARRETT-LENNARD EG

ENVIRONMENTAL AND EXPERIMENTAL BOTANY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 109 p. 89 - 98

0098-8472

Soil salinity and root-zone hypoxia often occur together in saline landscapes. For many plants,  this  combination of  stresses  causes  greater  increases  in  Na+ and  Cl in  shoots, and decreases in K+, than from salinity alone. These changes in ion concentrations from combined  salinity  and hypoxia  can  have  more  adverse  consequences  for  growth  than from salinity alone. The herbaceous forage legume  Melilotus siculus  naturally occurs in saline  soils  prone  to  waterlogging; however,  accessions  differ  in  their  tolerances, although  all  form  high  levels  of  aerenchyma.  We hypothesised  that  tolerance to combined  salinity  and  hypoxia  would  be  associated  with either  greater  aerenchyma formation  in  roots  or  the  innate  ability  of  the  accessions  to  regulate  tissue  ion concentrations.  Fifteen accessions of  M.  siculus were  grown  in  nutrient  solution  with two salinities (0 or 200 mM NaCl) and two aeration treatments (aerated or hypoxic) for 21 days. Dry mass (shoot and root), root porosity and ion concentrations (Cl-, Na+, K+) in shoots and roots were assessed. In the M. siculus accessions variation in the shoot dry mass under saline-hypoxic conditions was negatively correlated with shoot Cl and Na+, and positively correlated  with  the  shoot  K+.  Shoot  ion  concentrations  under  saline-hypoxic conditions were related to concentrations under saline-aerated conditions, but not  to  the  porosity  of  the  main  root,  which  was  relatively  high  (~18  to  25%). Differences in the tolerance of M. siculus accessions to combined salinity and root-zone hypoxia were mediated by variation in the plants‟ ability to regulate ions, and were not related  to  variation  in  root  porosity,  which  was  relatively  high  in  all  accessions.  The interaction between salinity and  hypoxia  was  not  detrimental  to  M.  siculus,  a waterlogging tolerant species.