Effects of Sand Burial on Survival, Growth, Gas Exchange and Biomass Allocation of Ulmus pumila Seedlings in the Hunshandak Sandland, China

Solving the riddle of the sands

Plants able to grow in sand or in very sandy soils may play an important role in stabilizing the sand and even preventing desertification of adjacent vegetation zones. Thus, it is a matter of concern when a sandland species starts to decline. This has already happened with Ulmus pumila, a species that grows in the dunes of the Hunshandak Sandland, Inner Mongolia. Shi et al. (Beijing, China, pp. 553�560) proposed that an increased frequency of sand storms may be a factor promoting this decline because seedlings are buried more frequently as a consequence. They have tested this idea by burying seedlings to different depths for up to 6 weeks. In partial burial treatments, the basal 33 % or 67 % of the stems were under sand. In full burial treatments, the sand surface was either level with the shoot apex (100 %) or the apex was under a depth of sand corresponding to 33 % of total stem height (133 %). The overall effects were very clear. Partially buried plants all survived but fully buried plants started to die between 2 and 4 weeks after burial; 6 weeks after burial, 30 % of the �100 %� plants and 80 % of the �133 %� plants had died. Further, while partial burial stimulated growth of stems and shoots and the emergence of leaves and lateral branches, total burial inhibited all these. In physiological tests (carried out after removal of the sand), plants that had been previously partially or 100 % buried (these experiments were not done with the �133 %� plants) showed greater rates of net photosynthesis and transpiration, higher leaf water contents and greater water-use efficiency than control plants. Of course, these enhancements are not relevant when a plant is actually totally buried but they do indicate that U. pumilais adapted to survive partial burial and even short periods of total burial. However, longer periods of total burial are fatal.

Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk