Koyro, Hans-WernerGharred, JihedJihedGharred2025-12-032025-12-032025https://jlupub.ub.uni-giessen.de/handle/jlupub/20901https://doi.org/10.22029/jlupub-20252This thesis investigates the responses of two forage species, M. ciliaris and M. polymorpha, to water deficit, both alone and in combination with salinity. Additionally, it explores strategies to enhance their productivity under these challenging conditions, focusing on approaches such as seed priming and the incorporation of biochar into the culture medium. In Medicago ciliaris, drought (36% water holding capacity) led to a significant reduction in plant growth and an increase in the root/shoot ratio. The growth response was accompanied by a decreased stomatal conductance and a reduction of the net CO2 assimilation rate and water use efficiency. The associated higher risk of ROS production was indicated by a high level of lipid peroxidation, high antioxidant activities, and high proline accumulation. Soil amendment with biochar (2%) enhanced the growth significantly and supported the photosynthetic apparatus of Medicago ciliaris species by boosting chlorophyll content and Anet both under well-watered and insufficiently watered plants and water use efficiency in case of water shortage. This increase in water use efficiency was correlated with the biochar-mediated decrease of the MDA and proline contents in the leaves, buffering the impact of drought on photosynthetic apparatus by increasing the activity of enzymatic antioxidants SOD, APX, GPOX, and GR and non-enzymatic antioxidants, such as AsA and DHAsA, giving the overall picture of a moderate stress response. These results confirmed the hypothesis that biochar application significantly reduces both the degree of stress and the negative impact of oxidative stress on Medicago ciliaris plants. These results implied that this species could be suitable as a cash pasture plant in the development of agriculture on dry wasteland in a future world of water shortages. This study aimed to evaluate the extent to which seed priming with ascorbic acid (0.2 mM) enhances the performance of M. polymorpha L. under osmotic stress induced by 50 mM NaCl (salinity) or 100 g/L PEG. Parameters related to growth and photosynthesis were assessed to understand the impact. Both NaCl-induced salinity and PEG-mediated osmotic stress significantly reduced plant biomass (-30% and -40%, respectively), leaf and ramification numbers, stem length, net CO₂ assimilation, and leaf water content. However, both treatments, particularly PEG, increased the root/shoot ratio and leaf proline content. Interestingly, seed priming with ascorbic acid alleviated these stress-induced effects, improving CO2/H2O gas-exchange and increasing plant biomass production. Water relations also improved, as indicated by reduced leaf osmotic potential, enhanced proline accumulation, and higher leaf water content. Additionally, ascorbic acid seed priming increased leaf carotenoid content by 65% and chlorophyll content by 45%, thereby enhancing photosynthetic activity. These improvements collectively contributed to better plant performance, particularly under salinity stress. Seed priming with ascorbic acid is an easy, cost-effective, and promising approach to mitigate the impact of osmotic stresses like drought and salinity, especially by improving plant water relations and photosynthetic efficiency. The effects of salinity, soil drying, and their interaction on the two forage species Medicago ciliaris and M. polymorpha were investigated. The results revealed that salinity and drought applied individually adversely affected growth, photosynthesis, and leaf water and potassium content in both species. However, the combined effects of both constraints were not significantly additive. Salinity affected the growth of both species to a similar extent. The major advantage of M. ciliaris under dry or saline conditions seems to be its higher water use efficiency and its corresponding positive impact on the ROS risk. Compared to M. polymorpha, M. ciliaris demonstrated superior biomass production under drought, salinity, and combined stresses, making it a strong candidate for forage production and soil rehabilitation in arid and semi-arid salinized regions.enAttribution-NonCommercial-NoDerivatives 4.0 InternationaldroughtsalinityMedicago ciliarisMedicago polymorphabiochargrowthphotosynthesisantioxidant capacitySeed primingwater use efficiencyddc:570