Effects of soil moisture profile on seedling establishment in the psammophyte Hedysarum laeve in the semiarid Otindag Sandland, China

In the Otindag Sandland of China, the moist soil layer from which plants can absorb water moves down gradually after rain. Thus, to absorb water from the moist soil layer, the rate of root extension may exceed the rate at which the moist soil layer moves downward. Responses of seedling survival of Hedysarum laeve to different soil water content (SWC) were studied. In the field, seeds of H. laeve, a dominant semi-shrub and major sand-binding species in the Otindag Sandland, were artificially sowed at five microsites on a sand dune, and then root depth of seedlings and SWC were monitored. The minimum SWC for seedling survival was 3%. Seedlings of H. laeve could successfully establish on lower and middle slope of windward side of sand dunes, but they had difficultly doing so on the top of dunes and on the middle and base of the leeward slope, since rate of root extension did not keep up with decreased moist SWC layer. The results suggested that rapid root extension rate of early seedling stages of H. laeve is an adaptation that may explain why this psammophyte can establish and dominate the windward side of sand dunes of semiarid Otindag Sandland.