Biostimulation effects of rosemary essential oil on growth and nutrient uptake -

Biostimulation effects of rosemary essential oil on growth and nutrient uptake

In this study, effects of two concentrations of rosemary essential oil was evaluated on growth characteristics and nutrient uptake of tomato seedlings in a relatively lime soil and under greenhouse conditions. Treatments were foliar spray of 500 or 1000 ppm oil, soil application of 500 μL oil/kg soil, and a no application control. The results indicate that rosemary oil has beneficial effects on nutrient uptake of tomato seedlings toward a better growth quality.

Material and methods

About 1 kg dry soil was placed in black plastic pots, and five tomato seeds (Lycopersicon esculentum var Green Supper) were sown 1 cm deep in each pot, and two weeks after germination they were reduced to one plant per pot. The greenhouse temperature was 27 ± 5 °C with 75–80% humidity and light intensity of 250 μmole m⁻²s ⁻¹. Pots were irrigated with tap water in a daily basis and to 80% soil field capacity.

Fresh rosemary foliages were gently washed with tap water and were dried in shade. Two hundred gram of dried materials was steam-distilled for 90 min in full glass apparatus, with 1.9% oil yield production. The rosemary oil extraction was performed for two hour, after four hour maceration in 500 ml water. The rosemary oil was separated via Clevenger, and oil was placed in dark glass bottles and in refrigerator for one week.

Treatments were various concentrations of rosemary essential oil as follow: foliar application of 500 or 1000 ppm, soil application of 500 μL essential oil per kg soil, and a zero application as control. Foliar applications of oil were started three weeks after seedling emergence and for each concentration (500 or 1000 ppm) three sprays was performed with one week intervals. For this purpose, the exact amount of 500 or 1000 μL oil was dissolved in one liter distilled water and sprays were performed using a portable sprayer at early in the morning, just one hour after sunrise. Soil application of rosemary oil was also done in relatively similar way, after addition of rosemary oil to distilled water that was applied to pots during growth period based on 80% soil field capacity. A final concentration of 500 μL/kg soil was applied in three split applications including; the first 200 μL/kg soil was applied three weeks after emergence, and two other applications of 150 μL/kg soil were done in one week intervals.

Plants were harvested after eight weeks after emergence in which the final records of morphophysiological traits were presented in the results. Just before final harvest, plant height (as cm) was recorded using a ruler, and leaf SPAD values were recorded using SPAD meter.

Plant shoots were cut at soil surface and shoot fresh weighs were recorded using a digital balance. For determination of root fresh weight the soils were gently washed out from the roots, and the fresh weight of collected roots after dewatering against tissue paper was measured using a digital balance.

The soluble carbohydrates of leaves were measured using anthrone method.

Leaf nutrient concentrations were determined with different apparatus. Nitrogen concentration of leaves was determined by the Kjeldahl method, K using flame photometry, and Mg, Fe and Zn were determined using atomic absorption spectrophotometer.

Results

The result showed that tomato plant height was differently affected by essential oil treatments. Foliar spray of 1000 ppm but not 500 ppm oil has resulted in significantly shorter plants than control. Determination of plant leaf SPAD values showed that plants treated with foliar spray of 1000 ppm oil had the highest SPAD value (or chlorophyll index) that showed significant increase compared to control plants. Application of rosemary essential oil on tomato seedlings resulted in changes of seedling shoot fresh weight. All foliar and soil applications of oil showed an increasing trend in shoot fresh weight; however, only plants treated with foliar spray of 1000 ppm oil resulted in significantly higher shoot fresh weight than control plants. The changes in root fresh weight were more evident, as all essential oil treatments have significantly increased root fresh weight than control plants. In addition, the root fresh weight was significantly highest in plants treated with foliar spray of 1000 ppm oil and plants treated with 500 μL oil in soil application than those plants treated with foliar spray of 500 ppm oil. Only foliar application of oil in 1000 ppm level significantly increased leaf soluble carbohydrates than control plants. Determination of nutrients concentrations in tomato leaves revealed that foliar application of rosemary oil particularly at 1000 ppm level showed some changes compared to the nutrients concentrations in control plants. Nitrogen, iron and zinc concentrations in leaves of tomato seedling were increased by foliar sprays of rosemary oil; however, only foliar spray of 1000 ppm oil resulted in significantly higher concentrations of these nutrients than control plants. Leaf concentration of N, Fe and Zn was almost similar in control and soil applied oil treatments. On the other hand, potassium and magnesium concentration of leaves were significantly increased only under 1000 ppm foliar oil treatment than control plants. The analysis of the soil shows that the soil with nearly 9% carbonates of calcium and magnesium is characterized as a lime soil. These conditions as well as its high pH can face tomato plants to some growth restrictions, although tomato is a potent plant under lime soil conditions. In the present study despite plant height was reduced by 1000 ppm spray of rosemary oil; however, other traits including leaf SPAD value, shoot and root fresh weights and leaf soluble carbohydrates were increased by foliar application of oil or its soil application (root fresh weight). The reduction in plant height by 1000 ppm oil spray could be due to reduced cell division or cell enlargement. It seems that the applied essential oil has affected plant growth characteristics as a biostimulant.

In this study, the most evident effect of applied oil in either foliar or soil application was on root fresh weight. Soil application of 500 μL kg soil as well as foliar applications particularly at higher concentration of 1000 ppm has resulted in significantly higher root fresh weight of tomato seedlings than control plants. Increase in root biomass can be due to stimulation effect of applied oil on root growth characteristics. Root architecture, root volume, density and root length are probably changed by oil applications.

Higher nutrients concentration of leaves due to oil application of 1000 ppm can be due to better root growth and higher root biomass production. However, root fresh weight was increased by all oil treatments, whereas leaf nutrients concentrations were increased only by foliar spray of 1000 ppm than control plants. Such stimulating effects on root growth and higher nutrient uptake have been also reported under application of other organic compounds. Increase in root radicular surface causes a wider rhizosphere area that can results in improved root uptake of nutrients such as N, K and Fe. Foliar application of oil probably has resulted in higher release rates of proton, organic acids and natural chelators or to a lesser extent by altering the redox potential of soil in the relatively lime soil used in the present study.

In the present study, improve in seedling growth via essential oil application can also be due to possible signaling effects of the oil that induced systemic resistance or mild stress conditions. The perception of the oil by plant cells as a stress signaling molecule can also justify the observed results of reduced plant height, higher leaf SPAD value, and increased shoot and particularly root fresh weights and nutrients uptake.

Conclusion

In the present study, foliar and soil applications of rosemary oil showed some stimulation on the growth characteristics of tomato seedlings. However, the most pronounced effect was on seedling root system, as all oil treatments (foliar or soil applications) increased root fresh weight. The beneficial effects of essential oil on better root growth and higher nutrient uptake can help to improve nutrient use efficiency and reduce fertilizer application rates in cropping systems. The seedling growth was changed under essential oil applications particularly by 1000 ppm foliar spray. Foliar application of 1000 ppm essential oil reduced plant height, whereas it increased leaf SPAD value, shoot and root fresh weights, leaf soluble carbohydrates and nutrient concentration of nitrogen, potassium, magnesium, iron and zinc of leaves than control plants.  Many compounds behave as signaling molecule in the rhizosphere or within the plant, that help to up-regulate the genes involved in nutrients pathway. Such effects may also be attributed to results obtained in present study by rosemary oil application. Nevertheless, more studies are needed to investigate the detailed physiological and molecular aspects of rosemary oil effects on plant growth.

Reference:

Souri, M.K. and Bakhtiarizade, M., 2019. Biostimulation effects of rosemary essential oil on growth and nutrient uptake of tomato seedlings. Scientia Horticulturae, 243, pp.472-476.