Changes in their growth rate in response to natural can be studied. Parameters such as Relative Growth Rate (RGR), Net Assimilation Rate (NAR) and Leaf Area Ratio (LAR) can be calculated.

Sugar profile can tell about stresses in plant....

Also, polyphenolic profile....

You can study hormone level. transpiration rate, flavonoid content

You can study many characters, will depend of you equipment and interest. here some colleges had found in tomato that stomatic index can vary with water stress also the size of stomas.

Dear Enrio et Luis Carlos,

Thank you for interest aspect of water stress reactivity by morphogenetic changes, especially on the stomatal index. 

I studay not the damage of stress on survival, dut the role of some natural stress on the evolution trends in flowers formation 

Dear Marpha Telepova-Texier: If you want to check impact of abiotic stress (drought, salinity and pollutant) condition on plants, please check attached papers/Links. You will get plenty of ideas on – how to screen them at morphological (plant biomass, leaf area, width, length etc.), biochemical (leaf pigments, proline-accumulation, lipid-peroxidation rates, antioxidant enzymes etc.) and physiological (maximum quantum yield of PSII, stomatal conductance, net photosynthetic rate, transpiration rate, water-use efficiency etc.) levels. The question raised by Luis Carlos Ramos is most appropriate, thus first you have to identify the stress, i.e. biotic or abiotic. However, for quick observation, Fv/Fm (a non-destructive methods) can be used as a criterion for evaluating plant performance under stressful conditions (both abiotic and biotic) and is thus important to determine seedling-stock quality.

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I think you should be more specific, because it depend on what kind of plant it is, for example a cultivated plant or wild plant. The physic and biotic factors might be analyzed on different view