Influence of Arbuscular Mycorrhizal Fungi and Drought Stress on Some Macro Nutrient Uptake in Three Leek Genotypes with Different Root Morphology

Drought stress is one of the main problems in agricultural productions in arid and semiarid regions such as Iran. Lack of water influences on most of plant physiological processes such as photosynthes, cellular development and uptake and transmission of nutrients in plants. Some approaches such as selection of resistance cultivars to drought stress, and selection of dripped irrigation have been applied in order to increase the irrigation efficiency. In recent years, biological approaches such as mycorrhizal symbiosis have been used to alleviate the detrimental effects of drought stress. Mycorrhizal symbioses increase the absorption of nutrients, especially phosphorus, and reduce the adverse effects of environmental stresses. It can also improve the host plant growth and yield. The percentage of mycorrhizal dependency of host plants depends on different environmental factors (such as light intensity, temperature, soil conditions), as well as morphological and physiological characteristics of plants. 1n 2010, a greenhouse pot experiment was conducted at University of Agriculture and Natural Resources Ramin. The effect of mycorrhizal inoculation on root morphology of three leek genotypes and uptake of phosphorous, calcium and potassium in shoot and root were studied. The experiment was conducted in a completely randomized design consisting of a 3×3×2 factorial combination. Experimental factors included three levels of soil moisture 40, 60 and 80% of available water in the soil), two mycorrhizal status (with and without fungus Glomus intraradices) and three leek genotypes including: Shadegan (with low root branching, short and thin root length), Esfahan (with abundant root branching and long root length) and Porrum (with low root branching, short and thick root length). The treatments were replicated four times. The soil was autoclaved at 121°C and15 PSI for 15 minutes and gently packed into PVC pots, 200 mm long and 150 mm in diameter. Leek seeds were sterilized with sodium hypochlorite (NaOCl) solution (10%) for 20 min. Two hundred grams of inoculum (spore, hyphae, mycorrhizal clover of root fragments and soil) were placed in deep of plant root. Each pot received cm-3 nutrients solution, free of P weekly. Plants equally watered for one mounth then, drought stresses were applied. Leeks were harvested 12 weeks after planting. Sub-samples of roots were taken for determination of root length were cleared in 10% (w/v) KOH solution and then were stained with trypan blue and root colonization was studied using modified Phillips & Hayman. The colonized root length was determined by binocular and gridline intersect method of Tennant. Phosphorus concentrations were measured by the method of colorimetery with a spectrophotometer. Potassium and calcium concentrations were determined by flame photometer and titration with vercin (Ethylene diamine tetra acetic acid: EDTA), respectively. The statistical analysis was performed using MSTAT-C statistical software and means were compared by Duncan’s multiple range test at the significance level of P<0.05. The results showed that the total content of phosphorus, potassium and calcium was reduced with increasing drought stress. The concentrations of phosphorus, potassium and calcium in root and leaves of three genotypes were different depending on genotype, morphological root characteristics of leeks. At all drought stress levels, the concentration and total content of three elements were greater in mycorrhizal treatments compare to non- mycorrhizal treatments. At all drought stress levels, the total content of three elements in unit root length were greater in mycorrhizal treatments compare to non- mycorrhizal treatments because of Mycorrhizal colonization significantly increased leeks root length and root dry weight in all drought stress levels. The results also revealed that Shadegan genotype with weak root system had high dependency on Glomus intraradices that ultimately led to a higher uptake of nutrients. These findings supported the Baylis’s hypothesis even in drought stress condition Clearly, the results of this study indicated that mycorrhizal fungi inoculation improved the nutritional status of leeks and the negative effects of drought stress were reduced by increasing the absorption of phosphorus, potassium and calcium. leek genotypes response to mycorrhizal symbiosis under drought stress was related to root morphology. Shadegan genotype with low root branching and short and thin root length (weak root system) had stronger symbiotic relationship with mycorrhizal fungi compared to the other genotypes which has ultimately led to a higher uptake of nutrients (phosphorus, potassium, calcium) in mycorrhizal Shadegan leeks.