A drought resistance index to select drought resistant plant species based on leaf water potential measurements

The water deficit in arid and semi-arid regions is the primary limiting factor for the development of urban greenery and forestation. In addition, planting the species that consume low levels of water is useful in arid and semi-arid regions that have poor water management measures. Leaf water potential(Ψ) is a physiological parameter that can be used to identify drought resistance in various species. Indeed, Ψ is one of the most important properties of a plant that can be measured using a pressure chamber. Drought avoiding or drought resistant species have a lower Ψ than plants that use normal or high levels of water. To determine drought resistance of species that are suitable for afforestation in arid urban regions, we evaluated twenty woody species in the Isfahan City, central Iran. The experimental design was random split-split plots with five replications. The species were planted outdoor in plastic pots and then subjected to treatments that consisted of two soil types and five drip irrigation regimes. To evaluate the resistance of each species to drought, we used the Ψ and the number of survived plants to obtain the drought resistance index(DRI). Then, cluster analysis, dendrogram, and similarity index were used to group the species using DRI. Result indicates that the evaluated species were classified into five groups:(1) high water consuming species(DRI>–60 MPa);(2) above normal water consuming species(–60 MPa≥DRI>–90 MPa);(3) normal water consuming species(–90 MPa≥DRI>–120 MPa);(4) semi-drought resistant species(–120 MPa≥DRI>–150 MPa);and(5) drought resistant species(DRI≤–150 MPa). According to the DRI, Salix babylonica L., Populus alba L., and P. nigra L. are high water consuming species, Platanus orientalis L. and Albizia julibrissin Benth are normal water consuming species, and Quercus infectoria Oliv. and Olea europaea L. can be considered as drought resistant species.

Investigation of rangeland indicator species using parametric and non-parametric methods in hilly landscapes of central Iran

This study aimed to identify indicator species and explore the most important environmental and management variables contributing to vegetation distribution in a hilly upper dam landscape in Zagros Mountain chain, Iran. A stratified random sampling method was used to collect topographic, edaphic, management and vegetation data. The density and cover percentage of perennial species were measured quantitatively. Indicator species were identified using the two-way indicator species analysis. Besides calculating physiognomic factors in sample sites, 24 soil samples were collected from 0 to 30 cm of soil depth and analyzed in terms of gravel percentage, texture, saturation moisture, organic matter, pH and electrical conductivity in saturation extract, lime percentage, soluble calcium and magnesium, available phosphorus, Cation Exchange Capacity(CEC) and soluble sodium and potassium. Multivariate techniques including Canonical Correspondence Analysis and Multi-Dimensional Scaling were used to explore the relationships of species with environmental and management variables. Seven plants were identified as indicator species due to being significantly correlated with management(grazing or non-grazing) and edaphic variables such as CEC, soil texture, pH, CaCO3 percentage and physiographic variable including slope, elevation, and convex and concave formations(p < 0.05). Overall, overgrazing and its subsequent effects on soil characteristics, loss of vegetation cover and trampling were found as the major causes of deterioration. Sustainable and integrated management practices such as the implementation of appropriate grazing systems were suggested to enhance soil quality and reduce the accelerated erosion in upper dam zones.

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.