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Maintaining a viable seed bank throughout the germination season is considered very important for plant recruitment in desert environments, where environmental conditions are unpredictable. Seeds from fully matured Seidlitzia rosmarinus Bunge ex Boiss and Halothamnus iraqensis Botsch. were collected in December 2016, then April, June, and September 2017 from both soil-surface and aerial seed banks. Both of the species were selected mainly by their capacity to rehabilitate saline coastal sites. Germination was analyzed under two photoperiods (0 or 12 h light per day), with winged or dewinged perianths. Seidlitzia rosmarinus had a shorter seasonal range in comparison with H. iraqensis (6 and 9 months, respectively), and the presence of a winged perianth reduced the germination rate of both species. A permanent winged perianth significantly inhibited the germination rate in both species. In the absence of perianth, the germination registered in December 2016 was mostly 100%, but declined to around 20% in September 2017. Seeds are thus more likely to germinate after scarification from wind mobilization, and do not require burial. Our results show that seeds of both the aerial and soil banks are transitory, and viable only during the winter months. Taken together, the combination of aerial and soil seed banks has greatly facilitated germination asynchrony in their environmentally unpredictable desert habitat.

Salsola schweinfurthii is a perennial branched halophytic shrub that inhabits arid environments in and around the Arabian Peninsula. Its tolerance to extreme drought renders it suitable for urban arid landscaping. Germinability of intact and de-winged seeds (winged perianth removed) was determined under two photoperiods (0 and 12 hours light per day), three thermoperiods (daily low/high of 15/25, 20/30 and 25/35°C) and five salinity levels (0, 100, 200, 400 and 600 mM NaCl). Germination was maximised (93%) by de-winging and incubation in 12 hours light at 25/35°C. Intact and de-winged seeds both exhibited positive photoblastism. Germination of intact seeds was entirely prevented by the lowest level of salinity, and only slightly less prevented in de-winged seeds. Ability to germinate returned after saline solution was replaced with distilled water. The ability for S. schweinfurthii seeds to remain viable through a temporary period of salinity indicates an adaptation to unpredictable soil surface conditions in arid environments. Artificial propagation rates might be increased by removing perianths and sowing before or after mid-winter.

Drones to manage the urban environment. Risks, rewards, alternatives.

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