Effects of water supply and sand burial on seed germination and seedling emergence of three sand-fixingArtemisiaplants in Horqin Sandy Land

Abstract

Semi鄄shrubs, Artemisia wudanica, A. halodendron and A. sphaerocephala, are major sand鄄fixing plants in Horqin Sandy Land. A. wudanica is a native pioneer species growing in shifting,semi鄄shifting sandy land and A. halodendron is the dominant species in semi鄄shifting, semi鄄fixed and fixed sand dunes. A. sphaerocephala, sown by aerial seeding to Horqin, was imported from Qubqi Desert and Mu Us Sandy Land as a sand鄄fixing pioneer plant. Seed germination and seedling establishment are critical to the recruitment of individuals into plant communities, and therefore studies on seed germination and seedling emergence characters of the three sand鄄fixing plants are of great significance to vegetation restoration in Horqin Sandy Land. Seedling emergence is closely related to sand burial depth and soil moisture in sandy land. In this study, five sand burial depths (0.5, 1.0, 1.5, 2.0 and 3.0 cm) and four water supply levels (86, 171, 257 and 342 mL) were adopted to investigate the responses of three plants to sand burial and water supply during seedling emergence. Water treatments are equivalent to mean monthly precipitation of 25, 50, 75 and 100 mm, respectively, and the average monthly precipitation during grass germination period (late May to early June) in the study area is about 50 mm. The results showed that, sand burial depth and water supply quantity had significant effects on seedling emergence in three plants (P<0.001). http: / / www.ecologica.cn The optimum depth for three species was 0.5-1.5 cm, suitable water supply at seed germination stage was higher than local monthly precipitation level (171 mL,i. e. 50 mm per month) , which resulted in a very low emergence rate. Within the scope of water supply in this study, the emergence and germination rates were the highest at 342 mL (100 mm per month) in most conditions, and the highest rates in three species was all appeared at 342 mL water supply and 1.5 cm burial depth, showing that water supply contributed to seed emergence from slightly deep soil. Seedling emergence rates of two sand鄄fixing pioneer plants (A. wudanica and A. sphaerocephala) were significantly higher than that of A. halodendron, especially under water deficient conditions, showing their higher adaptability to drought. Covariance analysis showed that, seedling mortality of A.wudanica was significantly higher than those of A. sphaerocephala and A. halodendron (P<0.05) , especially in 257 mL water treatment (P < 0. 01) , but the difference declined with the increase of water. That is to say, when precipitation reached 75 mm per month, it met the requirements for seed germination of three plants, but not enough for A. wudanica seedling growth. In fact, average precipitation at seed germination stage is lower than this treatment. A.wudanica is mainly distributed over a very narrow region in western Horqin Sandy Land, and many populations disappeared in recent years, showing A.wudanica has been declining in Horqin. According to the results, rainfall deficiency led to regeneration difficulty for A.wudani...