Extended Abstract 
1.    Introduction: Tomato (Solanum lycopersicum) is one of the strategic vegetable products in the world and has a valuable place in the food basket of people in most countries. One of the most important stages of the growth of S. lycopersicum is the germination and establishment of seedlings, which determines the final yields. The germination of seeds and establishment of seedlings are strongly influenced by the culture medium used, and therefore, choosing the right culture medium can ultimately lead to the improvement of the final yield of the product. Thus, in the present study, the effects of different cultivation substrates on morpho-physiological traits and photosynthesis performance were studied.
2.    Materials and Methods: For this purpose, the randomized complete block design (three repetitions) with treatments of 100% cocopeat (CP100), 100% Nipeat (NP100), 50% cocopeat + 50% Nipeat (CP50NP50), 25% cocopeat + 50% Nipeat + 25% perlite (CP25NP50P25), 50% Nipeat + 50% perlite (NP50P50) and 70% Nipeat + 30% perlite (NP70P30) were used in the early spring of the crop year 2019-2020. Seed cultivation was done in pots and daily irrigation and Hoagland nutrient solution were used. Also, the cultivation beds will be sent to the Soil and Water Institute and analyzed for their components. At first, germination percentage and germination speed were calculated. Almost 20 days after cultivation, morphological parameters such as root length, stem diameter, stem length, number of leaves, fresh weight of stem and root, and dry weight of root and stem were measured. After measuring the morphological traits, the content of chlorophyll and carotenoids in the leaves were calculated using a spectrophotometer and reading the absorbance intensity at the wavelengths of A645, A663 and A470. Then, the antioxidant potential of the plant was measured and the activities of catalase, polyphenol oxidase, and superoxide dismutase enzymes were measured. Catalase enzyme activity was measured based on the reduction of hydrogen peroxide absorption at 30 seconds at 240 nm. The activity of polyphenol oxidase enzyme was measured according to the method of Asadi Sanam et al., (2015) and the activity of superoxide dismutase was measured according to the method of Gianopoulits and Reis (1977). The proline content of the leaves was used according to the method described by Zhang et al., (2010), and the relative water content of the leaves was measured by drying the leaves, and recording the fresh and dry weight of the leaves, and calculating their difference according to the method of Paknejad et al., (2007). Handy flourCam FC 100H, Photon (Systems Instruments, PSI, Czech Republic) was used to measure the maximum efficiency of the photosystem. Finally, the obtained data were analyzed in SAS software.
3.    Results and Discussion: The results indicated that morphological traits were influenced by the type of culture medium. So that the highest germination percentage of tomato seedlings was obtained in the CP100 treatment. In this treatment, other traits such as stem length, number of leaves, fresh and dry weight of stem, fresh and dry weight of root were at their maximum value. In terms of all physiological traits, significant differences were observed in different treatments of the culture medium, so that more chlorophyll a, b and total content was observed in the leaves of tomato seedlings cultivated in NP100 treatment. Nevertheless, the highest carotenoid content of leaves was observed in the treatments of CP100, NP100 and CP50NP50, and the lowest was observed in the NP50P50 treatment. Although the highest activity of catalase was obtained in the treatments of CP50NP50, CP100 and NP100. However, low activity of polyphenol oxidase enzyme was seen in these treatments. Also, the highest activity of superoxide dismutase and proline enzyme was obtained in the CP100 treatment and the lowest in the NP100 treatment.
4.    Conclusion: The treatment of CP25NP50P25 resulted in the highest relative water content of leaves. The highest intensity of variable fluorescence was obtained in the treatments of CP100, CP25NP50P25, NP50P50, and NP70P30 treatments. The relative variable fluorescence in the intermediate J stage was the maximum in the NP70P30 treatment and the minimum in the NP50P50 treatment. Nevertheless, the relative variable fluorescence in intermediate stage I was the highest in the CP100 treatment. The maximum efficiency of the photosystem II water decomposition system (Fv/F0) was obtained in the treatment of NP70+P30 and the lowest was obtained in the treatment of CP50NP50. However, the maximum photosystem II efficiency (ΦPO) and electron transfer quantum efficiency (ΦEo) were seen in the treatment of CP50P50. The quantum performance of energy loss (ΦDo) had its maximum value in the treatment of CP50NP50 and the lowest value in the treatment of NP50P50. In general, it can be concluded that one of the important factors in the cultivation of tomato seedlings is the type of culture medium, and cocopeat and Nipeat or their combination can be a suitable option.