بررسی اثر پخش سیلاب بر شاخص های تنوع، غنا، تراکم و یکنواختی گونه ای بانک بذر خاک در ایستگاه آبخوانداری کوثر

Introduction and Goal
In recent years, the use of flood spreading systems is one of the most effective ways to control surface water, especially in arid and semi-arid regions which In addition to the reduction of the harmful effects of floods, it results in the reduction of soil erosion, the strengthening ground water tables, the improvement of agricultural lands and the rehabilitation of rangelands vegetation. In flooded rangelands, there is little information about the characteristics of the soil seed bank. This, in turn, has cost and wasted a lot of time. The presence of many species in the seed bank can explain the effects of environmental and management factors in the past. Identification of this resource plays an important role in the protection and restoration of vegetation. In this regard, the aim of the current study is to assess the biological diversity indicators of the existing seed bank due to flood spreading in order to restore and improve the vegetation cover in such rangelands.
Materials and Methods
In order to investigate the effects of flood spreading on the composition, density, diversity, richness and evenness species of the soil seed bank in two areas with flood spread and without flood spread (Control) in Gareh Bygone Fasa region, seed bank research was carried out for three years from 2020. In June 2020, was done after the preliminary identification of the rangelands of the flood spreading area, the location of two representative areas inside and outside the flood spreading area (Control). Sampling of the soil seed bank in the fall of 2020, before the seeds in the soil began to grow. Inside the representative area (rangeland flooded in 6 strips) and Control (rangeland without flooding), 1 transect of 150 meters was established in the direction perpendicular to the slope of the land. At 10-m intervals along each transect, a 1-m² plot was randomly selected (total of 15 plots or repetitions). A pit with a diameter of 7 cm and a depth of 0 to 5 and 5 to 10 cm was dug in the four corners and center of each plot. Soils of each depth were combined separately in five points of one square meter plot and considered as a sample for planting in special trays in the greenhouse. The soil seed bank samples were kept in the refrigerator for four months to break the seed dormancy and then transferred to the greenhouse environment for one year for cultivation and by the seedling emergence method, the seeds in the soil which gradually they turned green, were identified and counted.
Analyzes related to the seed bank were performed based on the number of germinated seedlings and counted in the greenhouse. The density of species in the soil seed bank was calculated by calculating the total number of seeds of all species per square meter. The diversity, richness and evenness of species were assessed using PAST software. For species richness of the soil seed bank, Margalef and Menhinic indices were used, Shannon-Wiener and Simpson indices were used for diversity, and Hill index was used for evenness. To compare the properties of the soil seed bank (density, richness, diversity and evenness of species) was also used between two representative areas of flooded rangeland and non-flooded rangeland (control) independent t-test and paired t-test were also used to compare between two depths of 0-5 and 5-10 cm. The analysis was conducted via R software, employing one-way analysis of variance and Duncan's method for comparison of means.
Results and Discussions
The results of the greenhouse studies showed that a total of 5340 seeds germinated in the greenhouse, 3756 seeds germinated in the flood spreading area at a depth of 0-5 cm and 1190 seeds germinated at a depth of 5-10 cm. In the area without flooding (control), 329 seeds grew at a depth of 0-5 cm and 65 seeds grew at a depth of 5-10 cm. In the flood spreading area of Aquifer Management Kowsar Station, in terms of the average density of the seed bank, at a depth of 0-5 cm, a total of 113 seeds per square meter (from 18 plant families and 61 species) sprouted. At a depth of 5-10 cm, a total of 36 seeds per square meter (from 18 plant families and 56 species) germinated. In the control area, in terms of the average seed bank density, at a depth of 0-5 cm, the average of 9.96 seeds per square meter (from 10 plant families and 23 species) germinated. At a depth of 5-10 cm, the average of 1.96 seeds per square meter (from 8 plant families and 15 species) germinated. The average density of sprouted seeds in the soil depth of 0-5 cm was 3.14 times higher than that in the soil depth of 5-10 cm. In the control area, the average density of germinated seeds in the soil depth of 0-5 cm was 5.08 times higher than that of the soil depth of 5-10 cm. The results of variance analysis showed that in terms of biodiversity indices (density, number of species, diversity, and richness species evenness) between the strips of Bisheh Zard 1 and control flood spreading network at the depth of 0-5 and 5-10 cm of the bank, there is a significant difference between soil seeds at the level of 1% and 5%. The results of the t-test showed that in terms of biodiversity indices between the depths of 0-5 and 5-10 cm of the soil seed bank both in the flood spreading area and in the non-flooding area (control) there is a significant difference in there are 1% and 5% levels.
Conclusion and Suggestions
In general, it can be concluded that the implementation of flood spreading operations in the studied area has created a special ecosystem that has improved the environmental conditions such as sufficient humidity and suitable organic matter in the area. Also, it has a significant effect on increasing the density and diversity, richness and evenness of the soil seed bank species, as well as the species composition. Therefore, the potential of the existing seed bank can be used to rehabilitation this area and similar areas. In general, the results of this research showed that the soil seed bank of this region had a positive response to the implementation of the flood spreading operation, so that the highest density, diversity, richness and evenness of the soil seed stock was observed in the flood spreading area. It is suggested to carry out projects on the effects of flood spreading on biodiversity indices in forestry plots with different species of Eucalyptus, Acacia, as well as shrub planting plots with Atriplex species, as well as a control plot be compared in Gareh Bygone, Fasa. This research's findings can be used in preserving plant diversity, preserving genetic reserves, and revitalizing and managing vegetation in the region.