As you know, water stress, as salt stress, causes osmotic imbalances in the plant tissues. However, in the case of salt stress, the presence of excess salts (normally Na+ and Cl-) causes direct nutritional effects and toxic effects.

In the first case, the ion unbalance of nutrients is due to the fact that the excess of Na + and Cl- provokes a decrease in the uptake of other ions (K+, NO3-, H2PO4-, etc.) or alters the internal distribution of one or more of these.

In the second case the toxic effect is caused by the specific toxicity of the ions Na + and Cl-.

Then, a method for distinguishing the water stress from the salt stress in the plant, it is firstly to determine the content of Na + or Cl-, or the nutrient deficiency "antagonists", such as K + and Ca2 + (better if you can make these determinations in the sap flow!). In a word, you have to focuses on the toxic effects of Na + and Cl-, which distinguish the salt stress from drought.

 I think that the more efficient method to distinguish the 2 stresses is this: monitoring the presence of ion (Na+, Cl-) toxic effects. I hope that my explanation do not be too obvious and above all, useful.

Best regards.

Because of NaCl, the following disorders appear:

(•) ionic disbalance;

(•) osmotic problems;

(•) ROS formation.

All of these except ionic disbalance is characteristic also for water shortage. In order to discriminate between these two types of environmental problems, one needs to analyze possible sensors and following adaptations. Lack of water is sensed both in roots and in shoots, salinity is sensed as increased transport of Na through plasmatic membrane. This ewokes clearly different primary adaptation responses. However, at later stages, secondary responses might be common. For example, antioxidative systems gaining protection against the both types.

Of course, to my mind, there is no strightforward answer to your question, it is necessary to analyze facts. I should say, that the difference is substantial at all levels of plant responses.

Because of NaCl, the following disorders appear:

(•) ionic disbalance;

(•) osmotic problems;

(•) ROS formation.

All of these except ionic disbalance is characteristic also for water shortage. In order to discriminate between these two types of environmental problems, one needs to analyze possible sensors and following adaptations. Lack of water is sensed both in roots and in shoots, salinity is sensed as increased transport of Na through plasmatic membrane. This ewokes clearly different primary adaptation responses. However, at later stages, secondary responses might be common. For example, antioxidative systems gaining protection against the both types.

Of course, to my mind, there is no strightforward answer to your question, it is necessary to analyze facts. I should say, that the difference is substantial at all levels of plant responses.

Probably salinity involves several reactions after ion uptake, whereas water stress is less invasive, but a large family of genes are shared. Specific cases of salinity resistant species that are sensitive to water stress like mangroves makes difficult to draw a general model. Whole conferences were about, as https://www.grc.org/programs.aspx?id=12419

In the case of water stress withering is the direct symptom due to lack of water which consequently leads to mineral deficiency, closure of stomata and inhibition of photosynthesis. Since there is no adequate water available, plant regulates water losses by closing stomata, slowing down biosynthetic processes and finally completely ceasing growing processes and getting into senescence conditions.

On the other hand, salinity stress results as already has been stressed out in ion imbalances due to ion toxicities (excessive Na, Cl, Ca) and deficiencies (K, Mg). Plant usually can adapt by changing morphological features such as leaf thickening, leaf abscision etc. As the conditions get worse, plants finds difficult to absorb water from the soil which results in withering as a secondary symptom. 

Sometimes, when stress is mild is difficult to distinguish the actual cause and effect and plant tissue and soil analyses are required to define the original stressing factor.

Water stress

Water stress is mineral deficiency and salt stress isis change in morphological change in plant.

if you have two plants of the same species, one is growing in salt media while the other in a drought stressed medium for the same period you can calculate the root to shoot ratio, water stressed plant must have greater ratio than salt stressed one. then analyze the content of both Na and K ratio which is greater in the salt stressed plant

Perhaps you find this useful?

http://www.ncbi.nlm.nih.gov/pubmed/16101905

Prof Rana Munns made  clear the experimental criteria for distinguish the two types of adaptation to salinity and drought which share a common trait in short term reactions but differ on steady state for ionic unbalance and tolerance mechanism, in PCE2002 http://faculty.ksu.edu.sa/Al-Whaibi/mhw%20documents/Coarses%20for%20the%20first%20tem%2031-32/671%20Bot/671%20Bot%20Course%20assignment/Translation%20assignment-1st%20Term-31-32/Assigned%20papers/10-Munns%202002%20comparativ%20d%20and%20s.pdf

salt stress and water stress that the main different in available water of gross:sat stress   have a lot of available water , but water stress defict water .

perhapes you find this useful,

http://onlinelibrary.wiley.com.sci-hub.org/doi/10.1046/j.0016-8025.2001.00808.x/pdf

i have some experience and i think Trachyspermum ammi(ajowan) is one of specific cases of salinity resistant species that is sensitive to water stress and Althea officinalis is one of specific cases of water stress resistant species that is sensitive to salinity stress.

Water and salinity stress generally have a major influence on the variation in crop phenology. Water stress(especially terminal drought stress) reduces crop duration and the reduction found to be much higher in reproductive phase compared to the vegetative phase. Conversely, salinity stress extends the vegetative growth duration (delayed flowering) providing a narrow window of reproductive duration leads to a forced maturity of crop and therefore reduce crop yield. Under those stress conditions, traits/plant functions such as partitioning coefficient, deep root system and efficient water use could be a benificial for crop adaptation.

Some good points have been presented by experienced researchers. The symptoms of both the stresses are almost the same because salt stress affects water potential and also induces artificial water stress, even though water may be present in the root zone. This is called physiological unavailability of water. Plants cannot uptake water and consequently many nutrients (dissolved in water). That is why salinity stress also disturbs ion balance within the plant. Plant show withering in case of water stress and in addition paleness when there is salinity stress. The moisture content and EC of soil very easily differentiate between two stresses. 

As you know, water stress, as salt stress, causes osmotic imbalances in the plant tissues. However, in the case of salt stress, the presence of excess salts (normally Na+ and Cl-) causes direct nutritional effects and toxic effects.

In the first case, the ion unbalance of nutrients is due to the fact that the excess of Na + and Cl- provokes a decrease in the uptake of other ions (K+, NO3-, H2PO4-, etc.) or alters the internal distribution of one or more of these.

In the second case the toxic effect is caused by the specific toxicity of the ions Na + and Cl-.

Then, a method for distinguishing the water stress from the salt stress in the plant, it is firstly to determine the content of Na + or Cl-, or the nutrient deficiency "antagonists", such as K + and Ca2 + (better if you can make these determinations in the sap flow!). In a word, you have to focuses on the toxic effects of Na + and Cl-, which distinguish the salt stress from drought.

 I think that the more efficient method to distinguish the 2 stresses is this: monitoring the presence of ion (Na+, Cl-) toxic effects. I hope that my explanation do not be too obvious and above all, useful.

Best regards.

Drought (water stress or water deficiency) cause wilting for plants and if increased it will perform to drying all parts of plants and finally death. When investigate root zone you'll notice increase in proliferation and depth in soil as trying to reach to water.           Salinity stress or irrigation by saline water irrigation differ according to salt concentration used. Low concentrations may lead to improve plant growth and increase amino acids, proteins etc. High concentrations make plants hurry to complete its life cycle and shortage in time. Very high concentrations lead to toxicity that show on leaves ( yellowish, dryness of peripheral parts ) symptoms often correspond to salt or group of salts that exist in the saline solution. Also, regard to mineral analysis on atomic absorption and flame photometer you can distinguish between water stress or salt stress as compared to normal plants. Increases in minerals refer to salt stress. 

         With My Best Regards

               Omaima

Water-deficit stress can be defined as a situation in which plant water potential and turgor are reduced enough to interface with normal functions. Water stress is considered to be a moderate loss of water, which leads to stomatal closure and limitation of gas ex‐change. Desiccation is a much more extensive loss of water that can potentially lead to gross disruption of metabolism and cell structure and eventually to the cessation of enzyme catalyzing reactions. Water stress is characterized by reduction of water content, turgor, total water potential, wilting, closure of stomata, and decrease in cell enlargement and growth. Severe water stress may result in arrest of photosynthesis, disturbance of metabolism, and finally death .The term ‘salinity’ refers to the presence in soil and water of electrolytic mineral solutes in concentrations that are harmful to many agricultural crops. Except along seashores, saline soils seldom occur in humid regions, thanks to the net downward percolation of fresh water though the soil profile, brought about by the excess of rainfall compared with evapotranspiration. In arid regions, on the other hand, there may be periods of no net downward percolation and hence no effective leaching, so salts can accumulate in the soil. Hence the combined effect of meager rainfall, high evaporation, the presence of salt-bearing sediments, and – in many places, particularly river valleys and other low-lying areas – the occurrence of

shallow, brackish groundwater which gives rise to saline soils .

Salinity in soil or water is one of the major stresses and, especially in arid and semi-arid regions, can severely limit crop production. 

Some very good explantions have been presented by Hashmat and the subject under discussion has been clarified extensively.

Dear Maher,

In addition to delivered information, for further clarifications, it is compulsory to consult:

1.   BARTELS DOROTHEA, SUNKAR R., 2005 – Drought and salt tolerance in plants. Crit. Rev. Plant Sci., 24: 23-58.

2.   MUNNS R., 2002 – Comparative physiology of salt and water stress. Plant Cell and Environ., 25: 239-250.

Hopefully, these would help you to answer your questions.

Please fallow M.N.Grigore for clarifications.