The Ordos Plateau is one of the major areas of desertification in Northern China. Aerial seeding has long been regarded as a successful and quick measure for vegetation rehabilitation in deserts and sand lands, but seedling emergence is low for four of the dominant psammophyte species inhabiting in Mu Us sandy land including Caragana korshinskii, Hedysarum laeve, Artemisia ordosica and Artemisia sphaerocephala. Experiments were conducted under controlled conditions to study the effects of one-time water supply and sowing depth on seed germination and seedling emergence of these four species, in order to understand how much one-time precipitation can ensure seed germination, seedling emergence, and the survival of emerged seedling until next rainfall.
For each species, a set of experiments were conducted under the combination of one of seven depths of sand burial (0, 0.5, 1, 1.5, 2, 3, 5 cm) and an one-time continual water supply regime (2.5, 5, 7.5, 10, 15, 20, 30, 40 mm and 2.5 mm/3d). Our results show that: (1) for two species (Caragana korshinskii and Hedysarum laeve), a relative large number of seeds emerged mostly at 0.52 cm sowing depth and under 1020 mm one-time water supply regime, and a few seeds also emerged at 5 cm sowing depth; (2) for another two species (Artemisia ordosica and Artemisia sphaerocephala), seeds emerged well only at 0.5 cm sowing depth and under 1020 mm one-time water supply regime, however, Artemisia ordosica and Artemisia sphaerocephala can not emerge at 1.5 and 2 cm burial depth, respectively. In general, a 0.5 cm sowing depth resulted in the highest seedling emergence and emergence rate. It was also found that after 30 days, all the emerged seedlings of Caragana korshinskii, Hedysarum laeve and Artemisia ordosica died under 5, 7.5 and 7.5 mm one-time water supply regime respectively, and the seedlings mortality of all four species was under 50% in most treatments when one-time water supply regime is higher than 10 mm. As water supply was increased, the mortality of emerged seedlings of these four species was decreased accordingly.
Based on our experiment results and precipitation characteristics of the Mu Us sandy land, 0.5 cm sowing depth and one-time water supply regime of more than 7.5 mm are the important conditions for seedling emergence and survival in field for all 4 species.