The ecosystems of the marine coasts of Iraq are known to be poor in vegetation. As these coasts are exposed to continuous erosion due to waves and the movement of ships in the navigational channels, with a shrinkage in their biodiversity. The study aims at finding out the possibility of cultivating the Iraqi coasts with mangrove trees of the gray mangrove type Avicennia marina (Forssk.) Vierh., in order to preserve these coasts from erosion by increasing the vegetation cover, which achieves an upsurge in the biodiversity of the coastal marine environment. Two sites were chosen to conduct the experiment, the first in the Khor Al-Zubair oil port, which speaks for one of the Iraqi internal coasts, and the second in the Al-Faw Grand port at the entrance to Khor Abdullah, which represents the outer coast open to the sea. The experiment was carried out by planting 50 seedlings in each site at 5 lines parallel to the coast, each line contains 10 seedlings for the period from March 2020 to February 2021, in order to study the possibility of acclimatization of gray mangrove plants in these environments. Experimental measurements of vegetative growth indicators, total chlorophyll content, and survival rates for four seasons were taken during the study period. The results demonstrated a normal growth of plants in the Khor Al-Zubair oil port site, as the increase in the rate of height of seedlings reached 93.8 cm during the study period (12 months) at a daily rate of 0.256 cm.day-1, and the total content of chlorophyll pigment in the leaves increased from 43.68 µg.cm-2 when transplanting to 52.10 µg.cm-2 after one year of cultivation, while achieving survival rates of 78% at the end of the experiment. Compared to the site of the Al-Faw Grand port, which achieved medium vegetative growth during the first six months of the experiment, after which the plants began to deteriorate, and thus to the destruction of all seedlings after 12 months of the experiment's life.
Also, two experiments were carried out on the gray mangrove plant, A. marina, in one of the private orchards in the Abu al-Khaseeb district of Basra Governorate, for a period of 180 days, from 9/11/2021 to 9/5/2022. First was to study the effect of salt stress on the growth gray mangrove seedlings, and second to study the response of gray mangrove seedlings to crude oil contamination and their resistance to petroleum hydrocarbon pollutants, using a tidal bioreactor as a model of environmental conditions in the sea coasts. In the saline concentrations experiment, two-month-old (2m) and 24-month-old (24m) seedlings were used at planting, and five salinity levels TS1 (9.9 ms.cm-1), TS2 (25.9 ms.cm-1), TS3 (41.0 ms.cm-1), TS4 (57.0 ms.cm-1), and TS5 (41.0 ms.cm-1). Four treatments for crude oil concentrations were used in the experiment of petroleum hydrocarbon pollutants, which are the control treatment TO1 (0.191 mg/l), TO2 (0.885 mg/l), TO3 (5.812 mg/l), and TO4 (11.181 mg/l). In this experiment 9 seedlings of gray mangrove plant for each oil concentration were used, 6 seedlings were two-month-old (2m), which were placed in two levels, the first level (FL) consisting of 3 seedlings so that the seedlings are completely covered during the flow of water in the bioreactor system, and the second level (SL) consisting of 3 seedlings that are higher than the water level and are not completely submerged, in order to study the potential to which these seedlings are affected by immersion in crude oil floating on the surface of the water. And 3 seedlings of the third level (TL) at the 24-month-old (24m) to find out the relationship of the effect of petroleum pollutants with the age of the plant. Two experiments were conducted using a completely randomized design of a factorial experiment with three replications, and the averages were compared according to the Least Significant Difference test (L.S.D). at a probability level of 0.05.
The results of the salt concentrations experiment showed the response of the gray mangrove seedlings to the medium salt concentrations, as the vegetative growth indicators increased in the TS3 treatment plants for both seedling ages, while the lowest values were recorded in the plants treated with the high concentrations of salt TS5. While the fresh weight and the percentage of dry matter increased in the high salt concentrations TS5, while the treatment TS4 recorded the lowest fresh weight, while no significant differences were observed in the percentage of dry matter for plants for all saline treatments. The results of the chemical properties indicators showed that there was no significant effect on the total content of chlorophyll in the leaves of gray mangrove plants treated with different salt concentrations, as the highest content was recorded in the TS3 treatment plants of 24m seedlings, which amounted to 62.4 µg.cm-2. Plants treated with high salt concentration TS5 recorded the highest content of Malondialdehyde (MDA) for seedlings 2m and 24m, while seedlings of 24m recorded the lowest content of (MDA) content at treatment TS3, and seedlings of 2m recorded the lowest concentration when treating TS1. The highest content of the chemical elements (N, P, Na, K, Ca and Mg) in the leaves and roots when treated TS3. The results of the levels of the amino acids under study (Ala, Asn, Asp, Glu, Gly, Pro, Met, Leu, Phe, and Ser) in the leaves and roots indicated an increase in the concentrations of each of the amino acids (Ala, Asn, Asp, Glu, Gly, Pro and Ser) in the leaves and roots of gray mangrove plants in the TS3 treatment plants, while the amino acids Met, Leu and Phe decreased in the same treatment.
Gray mangrove plants also showed tolerance to different crude oil concentrations TO1, TO2, TO3 and TO4 by measuring vegetative growth indicators and chemical characteristics of the plant, where the results of the oil concentrations experiment showed a decrease in vegetative growth indicators such as plant height, total number of leaves, total leaf area and number of side branches of the plant, while the total value of fresh weight of the plant increased with the increase in oil concentrations, while no significant differences were observed in the percentage of dry matter in crude oil treatment plants. Chemical characteristics such as the total content of chlorophyll in the leaves, the concentrations of chemical elements (N, P, Na, K, Ca and Mg) and the levels of amino acids in the roots decreased with the increase in oil concentrations in the medium, while the content of malondialdehyde (MDA) increased in the roots of the gray mangrove plant compared to control treatment TO1. The study showed the effect of crude oil immersion on the growth and survival of gray mangrove plants.