Our current study investigated the impact of a wide range of ASA concentrations combined with biochar on emergence, and early seedling growth and physiological attributes of sorghum grown under salinity stress. We found that the combined application of ASA and BC at appropriate concentration increased salt tolerance by enhancing emergence, seedling growth and physiological activities of sorghum grown under salt stress. Root and shoot growth are often expressed with the vigorous growth of seedlings, which usually lays a solid foundation for a proper crop density, especially under saline stress 31. Poor seedling emergence is one of the main reasons limiting crop establishment under saline stress 32.
Emergence percentage(EP) and emergence rate(ER)
In our study, emergence and early seeding growth were decreased by increasing salinity level. Those findings are in agreement with previous reports in sweet sorghum (Sorghum bicolor)33, who founded that, The reduction in emergence and seedling growth under saline stress might be due to the combined effects of osmotic pressure34 and /or due to the effects of added chlorine ion that gave rise to osmotic stress35.
We observed that BC amendment successfully promoted emergence and early seedling growth. Similar results have also been observed by 36 who reported that BC promoted the growth of soybean (Glycine max) 37. This may be due to the application of to soils providing additional nutrients that facilitate plant growth. However, there are some studies in which BC was observed having negative effects on emergence of rice (Oryza sativa) 38. the addition of some biochars to agricultural soils may cause a spike in microbial activity resulting in net N immobilization, in some cases reducing plant-available N and plant yields.
In the present study, we observed that ASA caused positive influences on emergence under salt stress. Seed priming with appropriate plant growth regulators can increase metabolic and enzymes activities, which can facilitate the preparation of seeds for rapid germination 33. Similar finding was also remarked in Sunflower (Helianthus annuus L.) by39 ,who observed that, improved in emergence percentage and rate in seeds soaked with ASA may be due to improved oxygen absorption, increased α-amylase activity, and increased transfer of nutrients from cotyledons to embryos.
Seedling growth parameters
The growth of seedlings, such as shoot and root length, are most important parameters for salinity stress, because roots are the plant part that contact with the soil and absorb water from the soil and provide it to other plant parts 40. Root length and shoot provide important evidence for plant response to salinity stress 41. In the present study, salinity stress decreased seedling growth (Table.2). Our study is agreement with 40, who noticed that, a negative correlation between salinity and seedling growth (Root length, shoot length, total fresh and total dry weight) may be caused by the lethal influence of NaCl as well as by a deficiency of the nutrient amount 23.
In this investigation, BC application increased seedling growth (shoot length, root length, specific root length, total fresh and total dry weight) and alleviated adverse effects of salinity. Similar results were found by42 , was indicated that, BC had a positive effect on seedling growth by reduced transient sodium ions by adsorption and released mineral nutrients such as potassium, calcium, and magnesium into the soil solution under saline condition.
Seed soaking with proper plant growth regulators can ameliorative the negative effects of salt stress on the seedling growth parameters 43. In this investigation, exogenous ASA significantly increased the seedling growth (root length, shoot length, total fresh and total dry weigh) and ameliorative the effects of salinity (Table .2) and (Fig 3). This is in support of earlier studies by44 ,who mention that treatment with ASA significantly improved root length, shoot length, total fresh and total dry weight . The Improvement of seedling growth might be due to increased cell division within the apical meristem of seedling growth due to enhanced exogenous hormone level in the plant tissues.
Antioxidant enzymes
Superoxide dismutase (SOD) is a major scavenger of O2 – and its enzymatic action results in the production of H2O2 and O2. Then, H2O2 is scavenged by a variety of peroxidases (POD) or directly broken into water and oxygen by catalases (CAT) 45.
In our study, salt stress caused a significant reduction in the POD, SOD and CAT activities. A similar result was substantiated with the findings by 46,who noticed that POD, SOD and CAT activities were reduced under salt stress. Reduced enzymes activity in the stressed plants might have stimulated H2O2 accumulation in plant cells under stress, which are finally lead to damage biological systems 47. A dissimilar results has been reported by48,49 , they showed that salt stress increased POD, SOD and CAT activity. An increase in the anti-oxidative enzymes under salt stress could be suggestive of an increased result of ROS and improvement of a protective mechanism to decrease oxidative harm triggered by stress in plants. At 200 mM NaCl The highest activity of POD, SOD and CAT were observed in the high level of ASA, and the lowest POD, SOD and CAT were recorded in 0 μM level of ASA.
Biochar application under saline soil can improve seedling growth, physiological and biochemical process by hanged nutrient release, holding, or immobilization by its surface properties (cation exchange capacity and anion exchange capacity) 11 .Our results showed that the application of BC increased the activities of antioxidant enzymes such as CAT, SOD and POD in the sorghum seedlings. Similar result were finding by many investigators that the BC application was improving stress tolerance by increased activity of POD,SOD and CAT 50,51. The BC application can regulate the synthesis of antioxidant enzymes in plants and thereby ameliorate salt stress in plants. Nevertheless, there are some researches in which observed that application of BC reduced the activity of the POD , POD and CAT enzymes under salt condition49,52. The reduction on antioxidant enzyme activities can be associated to the concentration of heavy metals immobilization effect of BC followed by decreased metal translocation into plant tissues. The highest POD, SOD and CAT activity was observed in the 4% BC application.
The activity of antioxidant enzymes was increased with increasing of ASA when exposed to salinity stress. Our study revealed that exogenous ASA could improve POD, SOD and CAT activity under NaCl. A similar result observed that ASA improved POD, SOD, and CAT activities, which are significance for antioxidative defense required for the plants under saline condition 53-55. The improvement of the activity of antioxidant enzymes could be due to the regenerative nature of ascorbate which plays a key role in quenching intermediate/excited reactive forms of molecular oxygen either directly or through enzymatic catalysis 56.
Malondialdehyde enzyme
Malondialdehyde is a naturally and the end product occurring of membrane lipid peroxidation, its considered to be indicator of oxidative damage from stress. MDA content increased under salinity in sweet sorghum (Sorghum bicolor.L) 33.When NaCl was applied, the MDA content was substantially higher than the control in sweet sorghum 57. Similar results were reported by 58, who demonstrated that MDA content was increased by an increase in salinity in sunflower.
BC has the positive significant effect on the MDA content when sorghum plants exposed to salinity stress. The maximum content of MDA was appeared under highly salt-stressed at 4% BC application (Table .4). Similar report was observed by 59 ), who showed that MDA content under NaCl-stressed plants was increased significantly by applying a high level of BC.
In this study, the MDA content improved by ASA treatment. Our result disagreement with60,61,they mentioned that MDA content had significant decreased when the ASA Appling on sorghum plant. It was shown that exogenous application of AsA modified antioxidant enzymes and none nzymatic antioxidants in plants under different stress conditions and induced various defensive signaling mechanisms by interacting/stimulating the signaling of different plant hormones 62.Seed soaking by appropriate concentration of ASA improved seedling growth of sorghum seedling under salt stress. Under salt stress, mixing soil with 4% biochar alone or combine with ASA could also enhanced the antioxidant enzyme system, and improved photosynthesis by increased chlorophyll content. Farmers can use this technique to achieved strong seedling growth, good crop establishment and high yielding of dry matter accumulation.