Different root strategies of perennial native grasses under two contrasting water availability conditions: implications for their spatial distribution in desert dunes

Abstract

The distribution pattern of perennial native grasses in the dune systems of the Monte desert might be determined by the ability of plant roots to acquire water under drought conditions in different topographical positions and soil substrates. This study examined differences in root traits of two species growing in sand dunes, Aristida mendocina and Panicum urvilleanum, and two species growing in interdune valleys, Pappophorum caespitosum and Leptochloa crinita, under different water availability conditions in a sand substrate. Grasses were grown in rhizotrons and the factorial design included species, irrigation treatments, days from sowing, and depth soil profile. Root length, total root length, number of root branches, length of root branches-to-number of root branches ratio (LB:NB), daily elongation rate (DER), root length density (RLD), root angles, aerial and root dry mass, and shoot-to-root ratio (S:R) were measured. The four species studied were affected by drought conditions causing a decrease in root growth and modifying root structure, partition of assimilates, root angles, and exploration of the soil profile. However, we found that species from sand dunes were less affected by drought and showed a deeper root exploration under drought conditions, mainly due to proliferation of longer and more lateral roots in the deepest soil layer. The different root traits and responses of the species under drought conditions would imply adaptations to the topographical position each species occupies and could explain their spatial distribution in desert dunes.