Effects of sand burial disturbance on seedling growth of Nitraria sphaerocarpa

Abstract

Nitraria sphaerocarpa Maxim. (Zygophyllaceae) is a desert shrub, emerged seedlings may easily be covered by sand, thus the influence of sand burial on seedling survival and growth was studied. The experiment was conducted under controlled greenhouse conditions. Seeds were sorted into three size-classes and buried at 2 cm depths in plastic pots filled with sand. Two weeks after seedling emergence, seedlings were buried in sand to various depths of 0, 33, 67, 100 and 133% of their mean height. Seedling survivorship, height, mass, relative height growth rate, absolute height growth rate, biomass allocation to root, biomass allocation to belowground stem and biomass allocation to aboveground stem were significantly affected by burial depth, however, seedling survivorship, mass, relative height growth rate were not significantly affected by seed size. In the unburied and partial burial treatments, individual seedlings exhibited high survivorship of approximately 85-100% for all size-classes seeds. However, only about 60, 39 and 43% seedlings survived when the burial depth reached 100% of their height, for large, medium and small sized seeds, respectively. When the burial depth increased to 133% of seedling height, no seedlings survived. Seedling height, mass and absolute height growth rate in partial burial treatments, were higher than those of the unburied and completely buried treatments. In each seed size class, with increasing burial depth, or in each burial depth, with decreasing seed size, there was a tendency that both biomass allocation to root and biomass allocation to belowground stem increased, while biomass allocation to aboveground stem decreased. The burial experiment of N. sphaerocarpa showed that partial burial at depth of 33 and 67% of seedling height increased seedling vigor, however, when burial depth reached the whole height of seedlings, it reduced the seedling vigor, and the burial at depth of 133% of their height, led to death of all seedlings.