title: Response to non-uniform salinity in the root zone of the halophyte Atriplex nummularia: growth, photosynthesis, water relations and tissue ion concentrations.
abstract: OBJECTIVE
  Soil salinity is often heterogeneous, yet the physiology of halophytes has typically been studied with uniform salinity treatments. An evaluation was made of the growth, net photosynthesis, water use, water relations and tissue ions in the halophytic shrub Atriplex nummularia in response to non-uniform NaCl concentrations in a split-root system.
  
  
  METHODS
  Atriplex nummularia was grown in a split-root system for 21 d, with either the same or two different NaCl concentrations (ranging from 10 to 670 mm), in aerated nutrient solution bathing each root half.
  
  
  RESULTS
  Non-uniform salinity, with high NaCl in one root half (up to 670 mm) and 10 mm in the other half, had no effect on shoot ethanol-insoluble dry mass, net photosynthesis or shoot pre-dawn water potential. In contrast, a modest effect occurred for leaf osmotic potential (up to 30 % more solutes compared with uniform 10 mm NaCl treatment). With non-uniform NaCl concentrations (10/670 mm), 90 % of water was absorbed from the low salinity side, and the reduction in water use from the high salinity side caused whole-plant water use to decrease by about 30 %; there was no compensatory water uptake from the low salinity side. Leaf Na(+) and Cl(-) concentrations were 1.9- to 2.3-fold higher in the uniform 670 mm treatment than in the 10/670 mm treatment, whereas leaf K(+) concentrations were 1.2- to 2.0-fold higher in the non-uniform treatment.
  
  
  CONCLUSIONS
  Atriplex nummularia with one root half in 10 mm NaCl maintained net photosynthesis, shoot growth and shoot water potential even when the other root half was exposed to 670 mm NaCl, a concentration that inhibits growth by 65 % when uniform in the root zone. Given the likelihood of non-uniform salinity in many field situations, this situation would presumably benefit halophyte growth and physiology in saline environments.
authors: School of Plant Biology (M084), The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia.
authors: Nadia
authors: N
authors: Bazihizina
authors: Timothy D
authors: TD
authors: Colmer
authors: Edward G
authors: EG
authors: Barrett-Lennard
mesh_terms: D027466:Atriplex / Q000187:drug effects* / Q000254:growth & development* / Q000502:physiology; D018533:Biomass; D000431:Ethanol; D005740:Gases / Q000378:metabolism; D007477:Ions; D009928:Organ Specificity / Q000187:drug effects; D009995:Osmosis / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects*; D053147:Plant Exudates / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology; D054712:Salinity; D055051:Salt-Tolerant Plants / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D012995:Solubility / Q000187:drug effects; D014867:Water / Q000502:physiology
chemical_list: D005740:Gases; D007477:Ions; D053147:Plant Exudates; D014867:Water; D000431:Ethanol; D012965:Sodium Chloride