Effect of Salinity and Drought Stresses on Rhizome Bud Sprouting of Giant Reed (Arundo donax) under Different Temperature Conditions

The competition of different weed species with native species for ecosystem resources is a serious threat to reduce global biodiversity. Among the invasive species, Arundo donax is considered one of the most invasive invasive plant species in coasts, rivers and temperate regions. Knowing the relationship between changes in environmental conditions and climate change and Arundo donax with respect to the growth of native coastal species, as well as understanding the water wastage by this plant compared to native coastal plants, is vital to eliminate this plant in the current situation where there is drought in most areas.

In order to investigate the effect of drought and salinity treatment on the sprouting stages and growth time of rhizomes of Arundo donax an experiment was performed using rhizomes collected from Gorgan ecotype and in a completely randomized design with 4 replications in the growth chamber separately at 5 temperature levels (5, 10, 15, 20, 25 and 30 °C) at Ferdowsi University of Mashhad in 2020. Experimental treatments included different levels of drought stress {0 (distilled water), 0.4, -0.8 and -0.12 MPa} and different levels of salinity stress {0 (distilled water), 4, 8 and 12 dS. m}.

The general results of the experiment showed that increased levels of salinity and drought decreases the sprouting rate of rhizomes. The results also showed that sprouting of the rhizomes of the reed plant is possible from 5 °C to 30 °C, but the greatest sprouting rates occurred with the control treatment (no stress) at 15 °C (75%) and 20 ° C (66%) respectively. The lowest sprouting percentage (4%) was observed with 15 and 30 °C under the maximum salinity and drought levels. Sprouting percentage and other corresponding indices decreased with decreasing temperature from 15 °C to 5 °C, the same trend was observed with increasing temperature from 20 °C to 30  C, which shows that the best The temperature for the growth of reed rhizome buds is between 15 and 20 °C. The effect of salinity and drought on sprouting at different temperatures showed that with increasing salinity and drought stress level, the sprouting rate decreases, but with increasing drought level, the sprouting percentage decreased more than the salinity level and decreased the growth of reed rhizome buds more. Was affected by increasing soil dryness. The results of sprouting rate and sprouting percentage under environmental stresses also indicated that drought stress more than salinity stress can affect the growth of reed rhizome buds, in other words, this plant is more sensitive to drought stress. It is somewhat resistant to salinity stress, and perhaps this is why the abundance of this plant in the northern regions of Iran is higher than other regions. The triple interaction effect of salinity, dryness and temperature was significant in all parameters except the adjusted germination rate at the 99% probability level, which shows that the germination of the rhizome of Arundo donax plant is strongly affected by dryness, salinity and different temperatures and the existence of each of these treatments in natural conditions, it can disrupt its germination.

The results of the cultivation of Arundo donax rhizome at different temperatures and under salt and drought stress conditions showed that the growth of the rhizome of this plant was greatly affected by the stresses and the increase in the amount of stress led to a decrease in germination percentage. Also, rhizome cultivation at different temperatures led to determining the optimal germination temperature for the Arundo donax plant related to the ecotype in the northern regions of Iran and showed that the suitable temperature for the rhizome germination of this plant is 15 to 20 degrees Celsius. The results of the germination rate and the germination percentage under the applied environmental stresses also indicated that drought stress can affect the growth of Arundo donax rhizome buds more than salt stress, and in other words, this plant is more sensitive to drought stress and to some extent It is resistant to salt stress, and this is probably the reason why the abundance of this plant is more in the northern regions of Iran than in other regions. It grows best in well-drained soils where plenty of moisture is available and can spread from the water's edge to the shore far beyond the area previously occupied by woody coastal vegetation. It grows well in places where the water level is close to the soil surface or near it, which may be due to the sensitivity of this plant to drought stress, and on the other hand, small colonies of this plant can tolerate excessive salinity, but in conditions of widespread presence in one area, their tolerance to salinity decreases.