Study on the effects of soil temperature,soil moisture content,sowing depth,and sand cover on seed germination and seedling growth of Reaumuria soongorica and Zygophyllum xanthoxylum

Reaumuria soongorica and Zygophyllum xanthoxylum are important ultra-xenomorphic shrubs in the northwest arid desert region of China.In 2001,seeds of the two species were collected at maturity in the Alshan Region,Inner Mongolia,and kept at-5℃ until use.Study on the effects of soil temperature,soil water content,sowing depth and sand cover on seed germination and seedling growth for the two shrubs was conducted in their native habitats.The results showed that during a simulating shower period(manned shower),the average soil temperatures of the sowing layers were too high for seed germination.This was especially so at noon,where the average temperatures at the soil depths of 1 and 4 cm sowing layer in the sand covered and non-sand covered plots were 43.2,37.3℃ and 38.0,33.6℃,respectively.These high temperatures,which could have lead to secondary seed dormancy,were the primary reason for seeds not germinating.Further,the soil water contents of sowing layers reduced acutely.This finding was especially so for soil water contents in the 1 cm sowing layer treatments of the two plots,where it decreased to 0.11% and 2.62%,and could also have been a cause for secondary seed dormancy,also leading to seeds not germinating.However during the continual nature raining period,the soil temperatures of the sowing layers were as expected,with the soil water contents of the sowing layers high and sustainable.As such,the basic conditions of seed germination of the two shrubs were met in this period.Thus,the accessorial sowing planting in arid desert region must depend upon continual rainfall.The highest seedling emergence percentage for Z.xanthoxylum was obtained in 2 cm sowing depth treatment in the sand covered plot,and was obtained in 1 cm sowing depth treatment in the non-sand covered plot.The highest above biomass for the Z.xanthoxylum seedling was obtained at the 2 and 3 cm sowing depths in both trail plots.Comparatively,the sand covered plots had an advantage for Z.xanthoxylum seed germination and seedling growth over the non-sand covered plots.In the first growing year,the above biomass of Z.xanthoxylum was significantly higher than that of R.soongorica(P 0.01),where it had 75～117 times of the biomass to R.soongorica.