Effect of Some Inorganic and Organic Fertilizers’ Application and Drought Stress on Superoxide Dismutase and Peroxidase Activities and Total Soluble Protein of Bidane-Ghermez Grapevines

 Drought is the most important limiting factor for the yield and quality of products in the world. Fertilizer application can mitigate drought stress in plants. Most farmers prefer to use inorganic (chemical) fertilizers because of their fast impact on plant growth. The reasonable cost of inorganic fertilizers and their availability are the other reasons. However, the long-term effects of organic fertilizers on plant growth and soil fertility has been proved. The grapevines are one of the most important garden products in the world as well as in Iran. It has been reported that the application of biochar has significant effects on soil fertility as well as plant growth. Biochars have properties such as highly porous structure, high specific surface area, higher water holding capacity of the soil, the long-term stability in the soil. In addition, our previous study indicated that it could decrease the hazard of sodium in soil compared with compost. In Iran, the cultivation area of grapevines was the second grade after the pistachio cultivation area in 2019. According to statistical data on agriculture in 2019, the cultivation area of irrigated and rain-fed grapevines in Kermanshah province was 7710 and 1515 ha, respectively. According to this report, the production of irrigated and rain-fed grapevines in Kermanshah province in 2019 was 82718 and 1763 tons, respectively. The effect of application of some inorganic and organic fertilizers under drought stress on yield, water use efficiency, and some biochemical characteristics of the grapevine leaves cultivar Bidane-Ghermez has been previously studied. In this research, the effect of drought stress and the application of potassium sulfate, compost, and biochar on antioxidant activities of the grapevine leaves cultivar Bidane-Ghermez was investigated.
 
A greenhouse study with a factorial experiment based on a block of randomized completely design was conducted with fertilizer treatments including control, potassium sulfate (1250 mg kg-1), compost (5% w/w), and biochar (10% w/w) without and with drought stress conditions (80 and 40% FC, respectively) during 2017-2018. For this research, the biochar was produced from apple tree pruning under low oxygen conditions by slow pyrolysis at 400 ◦C. The compost was purchased from the municipal compost factory of Kermanshah province. To evaluate drought stress and inorganic and organic fertilizers' application on antioxidant enzymes activities, the superoxide dismutase and peroxidase activities and total soluble protein of grapevine leaves were determined. The data were analyzed by ANOVA and the mean of studied characteristics was compared by Duncan’s test at 5% probability level using SAS software.
the results indicated that the interaction effect of fertilizers treatments and drought stress on the superoxide dismutase and peroxidase activities as well as total soluble protein was significant (P<0.01). Under drought stress conditions, among fertilizers’ treatments, the activity of superoxide dismutase for potassium sulfate was significantly lower than compost and biochar treatments (P<0.01). The results also showed that the peroxidase activity for compost was significantly higher than potassium sulfate and biochar treatments (P<0.01). Besides, the highest total soluble protein amount was found for biochar treatment (P<0.01).
 
 according to the results of this study, it can be concluded that the increase of total soluble protein of grapevine leaves under drought stress conditions by biochar application contributed to the increase of superoxide dismutase and peroxidase activities also increasing the bioavailability of macro-and micronutrients. Biochar application increased significantly the potassium concentration of the leaves of the grapevines. Potassium regulates water movement at the plant and also provides a higher relative water content of grapevine leaves. Moreover, potassium decreases the non-stomatal effects are also attributed to stomatal closure during drought stress conditions. Furthermore, potassium contributes to protein synthesis. Biochar application also increased the phosphorus, copper, and magnesium of the leaves of the grapevine. Higher concentration of phosphorus under drought stress conditions caused the grapevine leaves to suffer less from phosphorus deficiency. Copper exists in superoxide dismutase and is considered a key player in superoxide detoxification. Under drought stress conditions, higher manganese concentration by biochar application resulted in more protection of the cellular membrane against Reactive Oxygen Species (ROS). For fertilizer recommendation in order to reduce drought stress effects on some antioxidant enzymes activities of Bidane-Ghermez grapevine leaves, the application of biochar is recommended first then potassium sulfate and compost.