Plant adaptations in desert dunes

Desert sand dunes are an unstable habitat in which plants suffer frequently from cover and exposure by sand moved by wind. Plants growing in a sandy habitat are adapted to specific stresses that differ from one habitat to another. The establishment of grasses that easily produce adventitious roots and rhizomes and develop new stems when covered by sand leads to a local decrease in wind velocity. Consequently, fine-grained particles are deposited, the amount of available water increases, and filamentous cyanobacteria become established. Aggregation of clay- and silt-sized particles by cyanobacterial filaments, and gelatinous polysaccharides excreted by their trichomes lead to trapping of these particles and to the formation of a microphytic crust. Consequent improvement of the soil moisture regime and increasing soil stability and fertility, through development of nitrogen-fixing cyanobacteria, lead to the development of different higher plant communities in the processes of plant succession. Destruction of the microphytic crust by trampling or during several consecutive dry years leads to wind erosion. Fine soil particles are carried away and only plants with thick bark on the roots or with special root anatomy may remain. Plants of sandy or non-sandy habitats may function as an obstruction to the movement of sand (saltation and creeping) and cause accumulation of phytogenic hillocks at their leeward side. Such hillocks may vary from a few centimetres to a few metres in diameter and height. Some hillock plants produce adventitious roots and use resources that accumulate in the hillocks, while others remain limited to their original rhizosphere.