Variability of Life form and chorology of soil seed bank of Gamasiab river riparian with distance from the river

Background and objectives: Riparian vegetation along the river is one of the most sustainable aboveground covers that is a good source of food for livestock. Considering the degraded riparian areas, studies on soil seed bank is important and, necessary for restoration goals. Methodology: The present study was conducted to investigate the soil seed bank in the riparian region of the Gamasiab river in Nahavand city, Hamadan province. First, using Earth Google maps, 5 sampling sites on both sides of the river were identified. Soil sampling was performed to study the seed bank systematically using transects and quadrates. At each site, a transect perpendicular to the river flow was installed along the transect of at least 6 plots of 4 square meters (three on each side of the river) and soil sampling was performed from two depths of 0-5 and 5-10 cm in each quadrat. The seed bank samples were then transferred to the greenhouse for the experiment. Seed bank was examined by germination method. Plants in terms of annual and perennial, herbaceous and woody, life form (cryptophyte, trophyte, camophyte, hemicryptophyte, phanrophyte) and phytochorology of Iran-Turanian (IT), cosmopolitan (COSM), Siberian Europe (Polyregional or more than two vegetative regions (PL) Mediterranean (M), Turanian-Mediterranean Iran (IT, M), Irano-Tourani -Siberian Europe (IT, ES) Irano-Tourani -Siberian-Mediterranean (IT, ES, M) and Irano-Tourani - Europe, Siberia - Sahara (IT, ES, SS) were studied. Then, each of the above cases was analyzed along distance from the center of the river in three intervals (0-10), (10-20) and (20-30) meters from the river using one-way ANOVA analysis. Results: A total of 84 species including of 20 family and 65 genera, most of which belong to the family Gramineae (29) species and Compositae (18) species, were observed. Annuals, perennials, herbaceous and woody plants occupied 67.91%, 32.08%, 98.68% and 1.31%, respectively at the first soil depth. In the second depth, annuals created 65.42%, perennials 34.57% and in terms of life form, herbaceous were 100%. Also, trophytes with 63.90% and hemi-cryptophytes with 26% had the highest percentage of soil seed bank. In terms of colorology, COSM (35.83%), IT (24.01%) and PL (11.91%) were the highest. Annuals at the upper soil depth (0-5 cm) had the highest value at a distance of 0-10 m from the river and the lowest value at the distance of 10-20 m. In the second depth (5-10 cm), annual and herbaceous plants have the highest value at a distance of 20-30 m from the river and the lowest value at a distance of 0-10 m. In terms of life form, at the first depth, and in the second depth the therophytes had the highest value at a distance of 20-30 m and the lowest value at a distance of 0-10 m.  Regarding the corology of the first and second soil layers, the poly-regional had the highest value at a distance of (0-10) m and the lowest value at a distance of 20-30 m, and then the elements of Irano-tourani at the first depth and second depth had the highest value at a distance of 20 -30 m and the lowest value at the distance of 0-10 m. Conclusion: Being higher the number of gramineae species increased the soil seed bank density of annuals and, woody plants were observed only at the first depth of the soil seed bank which could be due to the large seeds of the trees that remain at the first depth and can not penetrate to the deeper depths, where it has deteriorated or decayed or eaten by seed-eaters (transient seeds of trees). Therophytes had the highest amount of life form, which can penetrate with more chances due to the production of very large number and small seed size. The high presence of poly-regional elements in the soil seed bank composition can be due to the abundant presence of pioneer plants and the early stages of the succession, which are present in a wide range of plant lands due to low need and extensive ecological range. These species do not indicate a specific affiliation to a particular climate or plant corology. The highest amount of Polyregional elements in the river riparian was due to the high percentage of Cynodon dactylon species. The results indicated that restoration of degraded riparian could rely on soil seed bank. More precisely, recovery of degraded vegetation through soil seed bank of palatable species such as Aloppecurus myosuroides, Trifolium repens and Bothriochloa ischaemum is feasible.