Evaluation of the efficiency of irrigation methods on the growth and survival of tree seedlings in an arid climate

Scarce and scattered precipitation in arid regions is detrimental for newly planted seedlings.It is essential to provide required water storage for seedlings in restoration projects in the first year of their establishment.The subsurface irrigation can be much more effective than the surface irrigation because of the regulation of water availability and reduction in water evaporation.We studied the effect of surface and subsurface irrigation methods on the growth and survival of four common tree species including heaven tree(Ailanthus altissima(Mill.)Swingle),China berry(Melia azedarach L.),white mulberry(Morus alba L.),and black locust(Robinia pseudoacacia L.)by installing underground clay reservoirs with different permeabilities in Isfahan City,Iran.Different amounts of animal manure and wheat straw were mixed with clay fraction and cooked in a pottery kiln at 900°C to produce reservoirs with different permeabilities.The experimental treatments consisting of irrigation and tree species were considered with a factorial arrangement in a completely randomized design with three replications in 2016 and 2017.Leaf water potential of seedlings,which is indirectly related to drought resistance,was measured by a portable pressure chamber.The results showed that saplings height,basal diameter,number of leaves,chlorophyll content and stomatal conductance were significantly(P<0.05)higher in the subsurface irrigation with low permeability than in the surface irrigation,but the number of branches of the studied species were not significantly(P>0.05)affected by the irrigation methods and different permeabilities of clay reservoirs.The clay reservoirs with low and medium permeabilities constantly provide better conditions for plant growth,and water with lower pressure and longer time intervals to the plant roots as compared with the reservoirs with high permeability.Analysis of variance of the data showed that year and interaction between year and permeability of reservoir had significant effects(P<0.05)on all growth parameters,except for the chlorophyll content.In addition,the highest percentage of survival was 100%associated with the subsurface irrigation and the control treatment had the lowest survival percentages of 60%,70%,80%and 100%for M.alba,M.azedarach,A.altissima and R.pseudoacacia,respectively.Finally,the values of leaf water potential showed that R.pseudoacacia was the most drought resistant species.

Interactions between vegetation dynamic and edaphic factors in the Great Salt Desert of central Iran

Investigating the relationships between vegetation dynamic and edaphic factors provide management insights into factors affecting the growth and establishment of plant species and vegetation communities in saline areas.The aim of this study was to assess the spatial variability of various vegetation communities in relation to edaphic factors in the Great Salt Desert,central Iran.Fifteen vegetation communities were identified using the physiognomy-floristic method.Coverage and density of vegetation communities were determined using the transect plot method.Forty soil samples were collected from major horizons of fifteen profiles in vegetation communities,and analyzed in terms of following soil physical and chemical characteristics:soil texture,soluble Na+concentration,sodium adsorption ratio(SAR),electrical conductivity(EC),pH,organic matter content,soluble Mg2+and Ca2+concentrations,carbonate and gypsum contents,and spontaneously-and mechanically-dispersible clay contents.Redundancy analysis was used to investigate the relationships between vegetation dynamic and edaphic factors.The generalized linear method(GLM)was used to find the plant species response curves against edaphic factors.Results showed that plant species responded differently to edaphic factors,in which soluble sodium concentration,EC,SAR,gypsum content and soil texture were identified as the most discriminative edaphic factors.The studied plant species were also found to have different ecological requirements and tolerance to edaphic factors,in which Tamarix aphylla and Halocnemum strobilaceum were identified as the most salt-resistant species in the region.Furthermore,the presence of Artemisia sieberi was highly related to soil sand and gypsum contents.The results implied that exploring the plant species response curves against edaphic factors can assist managers to lay out more appropriate restoration plans in similar arid areas.