Relationships between emergence and soil water content for perennial cool-season grasses native to Iran

Native cool-season grasses are important for improvement of arid and semiarid rangelands in Iran. However, germination and seedling emergence of these species is a critical phase in these areas and are not well understood. The objective of this study was to evaluate the effect of low soil moisture on emergence of 36 populations of native cool-season grasses from 15 species of seven genera including Elymus, Agropyron, Secale, Hordeum, Bromus, Festuca, and Dactylis that were collected from different locations of Iran. A pot experiment was conducted in a greenhouse using a completely randomized design with three replicates. The populations were evaluated under field capacity (FC, -0.33 MPa), 75, 50, and 25% FC. Decreasing soil water content from FC to 25% FC reduced overall mean emergence from 69.3% to zero. Significant differences occurred among species and soil moisture levels for all characters except root/shoot dry weight ratio. Seedling emergence rate and root and shoot growth were decreased by limiting soil water content, while root-to-shoot length ratio (43%) was increased. Minimum water requirement for seedling emergence of all species except Dactylis glomerata L. was 50% FC (-0.6 MPa). Cluster analysis and canonical discriminant analysis separated the populations into five clusters. Populations in Clusters I and III had intermediate, Cluster II the greatest, and Clusters IV and V the least tolerance to low soil moisture. Cluster I and III had greater root and shoot biomass and rapid emergence, whereas decreasing soil moisture caused a severe reduction of root growth of 60% compared with the control. In response to low soil moisture, Cluster II showed high final emergence and the greatest stability (low sensitivity index) of root growth. Clusters IV and V had delayed emergence, low growth potential, and high sensitivity index for shoot and root growth under low soil moisture. In response to low soil moisture, there were differences among species and accessions of the same species collected from different ecological regions. These results suggest that the genetic diversity of Cluster II could be used for plant breeding programs and renovation of pastures in arid and semiarid regions of Iran.