Severe effects of long-term drought on calcareous grassland seed banks

Climate change models project shifts in precipitation patterns at regional and global scales. Increases in dry areas and the occurrence of drought predicted in future scenarios are likely to threaten grassland ecosystems. Calcareous grassland seed banks have proven to be resistant to short-term drought, but their responses to long-term drought are unknown. Here we show that 14 years of summer drought changed calcareous grassland seed bank composition, reducing its size and richness, and that these responses do not simply reflect patterns in the above-ground vegetation. Moreover, the effect of drought was larger on seed banks than on vegetation, and above-ground responses mediated by soil depth were less evident in the seed bank than in the vegetation. These results demonstrate that the severity of drought effects on calcareous grasslands is larger than previously thought, and show that this ecosystem is highly vulnerable and has low resilience to predicted decreases in soil moisture

Effect of Salinity on Seed Germination and Seedling Growth of Native Populations of Tall Fescue in Iran

Introduction: Worldwide, more than one-third of irrigated land is salinized, and in many regions, fresh water shortage has resulted in restrictions on the use of potable water for landscape irrigation. On the other hand, rapidly expanding population growth is occurring in many arid regions, where soil and water salinity are problems and there are increased demands on limited fresh water resources (9). In the turf grass industry, with the increased use of saline and non-potable water, the development of turf grass landscapes in arid and seashore regions where saline soil is common, and with the use of salt for deicing roadways, the need for salinity tolerant turf grasses is very important (16).Seed germination and early seedling growth is usually the most critical stage in plant establishment, and determining successful crop production (23). Tall fescue (Festuca arundinacea Schrub.) is an important perennial cool-season grass in temperate regions and it is widely used for both forage and turf purposes (25). There is no study on the evaluation of salinity on tall fescue native populations in Iran. The major objective of this study is to determine the relative salt tolerance and growth response of native populations of tall fescue to salinity in germination stage. Materials and Methods: In this experiment, seeds of some native populations of tall fescue (TF) (F. arundinacea Schreb) including: Semirom, Mashhad, Sanandaj, Sanajan, Yasuj, Yazd Abad, Daran, Kamyaran, Gandoman, Borujen, Nasir Abad, Alborz and commercial TF (C. TF) seeds were used. Four replicates of 25 seeds were germinated on filter papers with 5 ml of NaCl concentrations placed in 9 cm Petri dishes. NaCl concentrations included: 0, 45, 90 and 135 milimolar. The Petri dishes were transferred to germinator at 23°C.Germinated seeds were counted on the3rd, 5th, 8th, 11th and 14th days. Germination was considered to have occurred when the root length was 2 mm long. The seedling with short, thick, and spiral formed hypocotyls and stunted primary root were considered as abnormally germinated. Then, the total germination percentage, germination rate, root length and shoot length were calculated on Day 15. The vigor index was calculated as VI= (RL+SL)×GP, where for the VI, RL is the root length, SL is the shoot length and GP is the germination percentage. Root length and shoot length were measured manually with a ruler. The experimental design was a completely randomized design with 4 replications and 25 seed per replicate. The data were statistically analyzed by JMP 8.0. The difference between the means was compared using LSD values (P < 0.01). Results and Discussion: The results indicated that the increase of salinity level leads to a significant decrease in germination percentage, germination rate, length of shoot, root and vigor index in all genotypes. Also, interaction of salinity and genotype was significant for germination percentage, germination rate, and vigor index. The highest germination percentage was related to Mashhad population at 45 milimolar, and Daran population at 90 and 135 milimolar. Also, the lowest germination percentage was related to Kamyaran population at 45 and 90 milimolar and Commercial tall fescue at 135 milimolar. Mashhad population at 135 milimolar, Daran population at 90 and 135 milimolar had the highest germination rates. The lowest germination rate was recorded at 45, 90 and 135 milimolar in Commercial tall fescue, Kamyaran and Sanandaj populations, respectively. The highest root length was seen in Commercial tall fescue at 90 and 135 milimolar, and Mashhad population at 45 milimolar. For shoot length factor, Mashhad population, Commercial tall fescue and Mashhad population had the highest lengths at 135, 90 and 45 milimolar, respectively. The highest vigor index was related to Mashhad, Daran and Mashhad populations, at 45, 90 and 135 milimolar, respectively. NaCl has an inhibitory effect on seedgermination and its effect on germination showed time course dependence for absorption of Na and Cl by thehypocotyls (28).Increasing salinity levels caused delays in seedlingemergence as a result of reducing cell division and plant growth metabolism (28). The negative effect of salinity on seed germination and early growth could be due to the toxic effects of NaCl on seeds, or to the osmotic effect, that prevents the seeds from imbibitions (21). Conclusion: Major grasses mentioned above could tolerate 45 milimolar salinity without noticeable changes in germination traits. Mashhad and Brujen populations were least affected by 135 Mm Nacl at germination rate and percentage. Also, Daran and Mashhad populations were least affected by different salinity levels in all germination factors compared to other populations and could be suggested as salt-tolerant genotypes at germination stage