Physiological and Biochemical Yield-Related Response of Lallemantia iberica to Nitrogen Fertilizer Sources in Soil Salinity Conditions

The medicinal plant Dragon's head (Lallemantia iberica, Lamiaceae family), is more commonly known as “Gara Zayrah” in most parts of Iran, particularly in Azarbaijan region. It is one of the most important spring herbaceous plants in rainy and dryland farming areas cultivated in most parts of Azerbaijan. The ever-expanding soil salinity under the influence of human activities restricts crop production worldwide, especially in arid and semiarid regions. One of the strategies to enhance the crop yield is increasing in off-farm inputs like application of fertilizers. Managing or adding fertilizer can severely affect crop production in saline conditions. Therefore, nutrient addition can increase or decrease plant resistance to salinity or it may not be affected by salinity at all. Accordingly, due to the importance of Dragon's head as a climate-adapted medicinal plant in Iran, this study aimed to evaluate the effect of nitrogen fertilizer sources (urea and Azotobacter) on the morphological characteristics of Lallemantia under salinity conditions.

An experiment was conducted as factorial layout based on randomized complete block design with three replications in 2018 at Urmia University (latitude 44° 58' East, latitude 37 ° 39' North and altitude 1363 m above sea level). Treatments consisted of four levels of nitrogen fertilizer (urea fertilizer, 50 kg/ha), Azotobacter as a foliar spraying and Azotobacter as a seeds inoculant (population of 109 per g) and no-fertilizer as control), and two soil salinity (saline was 6.70 and non-saline was 0.91 dS.m-1). The seed yield, biological yield, leaf relative water content, leaf area, leaf perimeter, leaf area index, sodium, potassium and phosphorus content in root and shoot, glycine betaine, osmolytes (osmotic regulators), leaf chlorophyll and carotenoids of Dragon's head were measured. The analysis of variance (ANOVA) was performed using GLM procedure (SAS 9.1.3, SAS Institute Inc., Cary, NC, USA), with the means compared by LSD at P≤0.05.

The results showed that in non-saline conditions, the biological yield (regardless of root, as well as root included) treated by Azotobacter seed inoculant were decreased compared with control, while the biological yield of untreated control plants were identical with the application of other nitrogen treatments. However, biological yield increased by Azotobacter seed inoculant in saline soil. In contrast to the decrease in stem length in saline soils, especially with the Azotobacter foliar application, the flower weight gain was significantly higher with urea fertilizer even under saline conditions. The highest crop growth rate (regardless of root, as well as root included) was related to plants grown in saline soils without fertilizer application. In other words, except for seed treatment, Azotobacter had no significant effect on crop growth rate under salinity. Moreover, the greatest amount of root potassium was obtained from plants in non-saline conditions with urea fertilizer. Despite the decrease in aerial phosphorus under salinity stress, root phosphorus was not affected by salinity, whereas urea increased shoot and root phosphorus. The plants had the highest concentration of total chlorophyll and carotenoids under salinity and foliar application of Azotobacter. The highest reduction of carotenoid was observed in saline soils in control plants, urea and Azotobacter seed treatments, respectively. Despite increasing proline concentration in plants grown in saline soil, urea and seed inoculation lead to decreasing the leaf proline. Other osmotic regulators, glycinebeta and water-soluble carbohydrates were not affected by soil salinity and nitrogen fertilizer sources. Shoot and root sodium were increased in saline soils, and applying urea fertilizer caused more increases. Root potassium was not changed in saline soils, but potassium content of aerial parts was decreased. This resulted in a decrease in the potassium to sodium ratio of both aerial parts and the root.

In general, despite some minor changes, salinity caused decreasing the level of morphological and physiological responses related to the yield of Dragon's head plant. However, applying nitrogen fertilizers reduced salinity damages by seed inoculation of Azotobacter and urea, respectively. Azotobacter foliar application showed no advantage over saline and non-saline conditions over control treatment (without receiving fertilizer).