沙埋与水分对科尔沁沙地主要固沙植物出苗的影响

蒿属半灌木乌丹蒿(Artemisia wudanica)、白沙蒿(A. sphaerocephala)、差不嘎蒿(A. halodendron)是科尔沁沙地的主要固沙植物。其中乌丹蒿和差不嘎蒿是科尔沁沙地的本土植物,白沙蒿为来自于库布齐沙漠、毛乌素沙地的飞播植物。设置了 5个沙埋深度(0.5、1.0、1.5、2.0和3.0 cm)和 4个水分梯度(86、171、257和 342 mL,分别模拟每月25、50、75和100 mm的降雨量),以探讨3种植物幼苗出土对沙埋和水分的响应。结果表明,沙埋与水分均显著影响着3种蒿属植物的幼苗出土(P < 0.001)。3种植物最适沙埋深度在0.5-1.5 cm范围内,萌发出土时适宜水量要高于当地种子萌发期的平均降水量(50 mm/月)。两种固沙先锋植物乌丹蒿和白沙蒿的种子出苗率均显著高于差不嘎蒿,乌丹蒿较白沙蒿也明显为高,尤其在水分缺乏时,表现出两种先锋植物种子出苗对干旱有更好的适应性。协方差分析表明,乌丹蒿幼苗死亡率显著高于白沙蒿和差不嘎蒿(P < 0.05),在达到75 mm/月降水量时,3种植物的出苗较好,但不能满足乌丹蒿幼苗生长对水分的需求,而实际种子萌发期的降水量平均只有50 mm/月。因而降水的缺乏导致乌丹蒿种群更新出现问题,加之飞播植物的竞争,使得近几年科尔沁沙地较多乌丹蒿种群出现衰退。

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

Semi-shrubs, Artemisia wudanica, A. halodendron and A. sphaerocephala, are major sand-fixing plants in Horqin Sandy Land. A. wudanica is a native pioneer species growing in shifting,semi-shifting sandy land and A. halodendron is the dominant species in semi-shifting, semi-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-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-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). 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-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.wudanica, water stress combined with competition with aerial seeding plants, A.wudanica populations degraded in Horqin Sandy Land.