Morphological characteristics of Fraxinus rotundifolia Mill, Morus alba and Acer negundo saplings under water stress in greenhouse and field in Robatkarim

One of the main limitations in arid and semi-arid regions is the allocation of water resources for green space development. Since water and drought stresses along with incorrect selection of species are the main factors that reduce seedling survival in the afforestation stages in arid and semi-arid regions, the aim of current study is to investigate the morphological characteristics of ash, Mullberry and ash leaved maple seedlings in the greenhouse and the feild under different water stress in Robat Karim town.

Robat Karim city is one of the towns of Tehran province with area of 275 square kilometers. To study the effect of water stress on morphological characteristics 20 saplings were planted in 4 repetitons in a completely randomized design. 5 saplings of each species were selected for water stress treatments. A total of 90 saplings including 5 repetitons and three drought levels (2, 4 and 6 days after reaching MAD point) were considered and tested for the above species in greenhouse and in field. The saplings that reached the MAD point were not irrigated immediately and were subjected to 3 drought stresses 2, 4 and 6 days after reaching the MAD point. Then the quantitative appearance characteristics of seedlings which include parameters of leaf numbers, leaf size, seedlings height, stem diameter, dry leaf weight, stem dry weight along with 2 qualitative characteristics of seedlings, which are leaf freshness and seedling health, were measured.

The results showed that the number of MAD period times in the greenhouse for Fraxinus rotundifolia Mill species was 29, Acer negundo 28 and Morus alba 32 and in the field for Fraxinus rotundifolia Mill species was 20, Acer negundo 20 and Morus alba 17 period times. Generaly, in all three studied species, in May, as the first month of research, the seedlings were in a very good condition. In other months, after being under different water stress (2, 4, 6 days), the number of leaves and leaf size have always decreased over time. In case of ash leaved maple, the number of leaves in the greenhouse area in August was zero (absolute defoliation).

Generaly, by increasing water stress, leaf number, leaf size, dry leaf weight, dry stem weight, leaf freshness and saplings health reduced. It seems that 6 days after reaching MAD point is the sutiable time to irrigate the saplings according to their Morphological characteristics. Considering to the appearance of seedlings during irrigation always helps to use water efficiently, prevent over-irrigation and under-irrigation of seedlings and save the relevant costs.