Interaction effect of salinity stress and nitrogen on growth and activity of antioxidant enzymes of blue panicgrass (Panicum antidotale Retz.)

Salinity stress is one of the most important environmental stresses in arid and semi-arid regions of the world (Pandolfi et al., 2012) .It is reported that, salinity stress by decreasing dry weight and K concentration could be reduce growth and yield of different crops. Generally, salt stress causes a number of changes in plant metabolism. Of them, ion toxicity, osmotic stress and production of reactive oxygen species (ROS)such as singlet oxygen (O2), superoxide radical (O–2), hydrogen peroxide (H2O2), and hydroxyl radical (OH–) are the most prominent responses in plant tissues. The generation of ROS could be limited or scavenged by antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) (Apel et al., 2004). Blue panic grass (Panicum antidotale Retz.) is distributed through out the Indo-Pakistan region. It is found growing in a variety of soils and climatic conditions with a predominant distribution in arid and semi-arid regions. Blue panic is a highly productive grass with considerable nutritional value that can produce 150–180 tons of fresh biomass per hectare per year with 15-18% protein content (Sarwar et al., 2006). Some studies indicated that decrease of photosynthesis is the main damage of salinity stress that its result is reducing the dry matter production (Netondo et al., 2004).Grattan et al (1999) reported that application of nitrogen fertilizer improved growth and/or yield of different cops in stress conditions.Some studies also indicated that corn (Aalipour et al., 2011) and sorghum (Esmaili et al., 2008) dry matter decreased by increasing salinity but,using nitrogen fertilizer could reduce the negative effect of salinity stress. In most of these studies, the fact that applied nitrogen improves the growth under extreme saline conditions suggests that applied nitrogen increased plant salt tolerance.On the other hand, in comparison to higher levels of nitrogen application, salinity stress in lower levels of nitrogen application, had higher detrimental effect on decrease of dry and fresh weights (Grattan et al., 1999).This study aimed at finding out what amount of nitrogen fertilizer must be applied in saline soils and, furthermore, its main objective was to investigate the interactive effects of salinity and nitrogen fertilizer on growth and antioxidant activity of blue panicgrass.
This experiment was conducted at green house of College of Agriculture, Shiraz University, in 2014. The experiment was carried out in factorial arrangement based on completely randomized design with four replicates. Treatments included nitrogen at four levels (0, 10, 20 and 30 mg kg-1 soil) and three levels of salinity (0.4, 9 and 18 dS m-1). Studied features were included plant height, leaf area, root and shoot dry weight, root and shoot fresh weight at flowering stage, as well asthe activity of antioxidant enzymes (SOD, POD and CAT), proline and Sodium/potassium ratios in stem and root were measured. Analysis of variance of the data was carried out using SAS (2002) software. LSD test was applied to compare means of each trait at 5% probability level. Excel (2010) software was used to draw figures.
Results showed that effect of nitrogen, salinity and their interaction were significant on all traits (except for leaf fresh weight, leaf dry weight and leaf number). Salinity stress decreased stem fresh weight, leaf fresh weight, root fresh weight, plant height, leaf area and root/stem dry weight ratio. In comparison with control treatment, the activity of antioxidant enzymes (SOD, POD and CAT) and proline increased 13.78, 6.17, 7.44 and 26 times in high levels of salinity (18dS­m-1) and nitrogen (30 mg kg-1), respectively. Sodium/potassium ratio in stem and root were significantly decreased under nitrogen treatment.Generally, 20 mg/kg nitrogen could reduce the negative effects of salinity stress but, application of 30 mg/kg nitrogen significantly decreased all traits under salinity levels.The results also indicated that, soil salinity reduced K uptake and increased Na concentrations in plant tissues,as a result,stem fresh weight, leaf fresh weight, root fresh weight, plant height, leaf area and root/stem dry weight ratio were decreased.
In general, the obtained results indicated that in high salinity levels, application of nitrogen fertilizer in dose of higher than 20 mg/kg may cause more salinity and osmotic pressure, as well as may decrease water and nutrients uptake and plant growth. In other words, under low salinity level, nutrients deficiency can be the main limitation factor for plant growth.