الفهرس 
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Abstract
To investigate the effect of form of N on response of Rumex dentatus and R. pictus to P nutrition and water stress, plants were grown on washed sand with N either as nitrate or ammonium and P levels of 0.01-1.5 mM P or moisture content of 100% -5% field capacity. Rumex spp. preferred nitrate with lower optimum P supply than ammonium. R. dentatus exhibited less number of leaves but longer and wider blades compared with R. pictus. Allocation of plant biomass to root was favored under ammonium nutrition and P deficiency. P supply increased pigment concentrations. Soluble sugars, phenolics and DPPH scavenging activity were high under nitrate nutrition but the reverse was true for proline. Increasing P supply increased phenolic concentration and DPPH scavenging activity but reduced malondialdehyde content. The shoot mineral content was non-significantly affected by N form. P supply marginally affected shoot K+ concentration but reduced Na+ concentration. Shoot N was higher in R. dentatus than R. pictus, particularly under nitrate. Shoot P was higher in R. pictus than R. dentatus under ammonium but the reverse was true under nitrate. Water stress enhanced root growth but reduced shoot growth, number of leaves and leaf dimensions particularly under ammonium, with N-dependent effect on leaf pigments. Leaf protein was high in R. pictus under ammonium but the reverse was true in R. dentatus. Water stress reduced foliage protein particularly under ammonium. The foliage phenolics were comparable in the two species and under the two N forms. Water stress reduced the DPPH scavenging activity particularly in R. dentatus. Foliage sugar was higher in R. pictus than R. dentatus and under nitrate than ammonium with mild effect of water stress. Water stress increased proline content but reduced N and P contents of the foliage. Shoot K and Na were higher in R. dentatus than R. pictus under nitrate but the reverse was true under ammonium. In R. dentatus, water stress increased shoot K content under nitrate without effect under ammonium. In R. pictus, only severe water stress reduced shoot K. Water stress increased shoot Na content particularly in ammonium-fed R. dentatus.