Root morphology, root-hair development and rhizosheath formation on perennial grass seedlings is influenced by soil acidity

Perennial pasture species are important for sustainable pasture systems; yet some species display poor persistence on acid soils. This work investigated the effect of soil acidity on primary root length and root-hair and rhizosheath development of five perennial grass genotypes varying in acid-soil resistance. Plants were grown in three low-P acid soils that were limed (CaCO3) to modify soil pH (0.01 M CaCl2 extractable) from < 4.3 to > 5.0 and Al3+ concentrations from a parts per thousand yen 16 to < 4 mg kg(-1) (0.01 M CaCl2 extractable). Root morphology of tall wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C Wang), phalaris (Phalaris aquatica L.), cocksfoot (Dactylis glomerata L.) and weeping grass (Microlaena stipoides Labill. R. Br.) was assessed after 20-25 days growth. The root length of tall wheatgrass and phalaris cv Sirosa was sensitive to acidity, with lateral root length more sensitive to acidity than seminal root length. Lime increased the root-hair length and density of both acid-soil sensitive and resistant genotypes (cocksfoot and an acid-resistant line of phalaris) and root-hair length was positively correlated to an increase in rhizosheath size per unit root length. Restricted root length and poor root-soil contact of acid-soil sensitive genotypes may explain their low yield and relatively poor persistence on acid soils. The improvement to root-hair and rhizosheath development of genotypes that are acid-soil resistant in terms of root length demonstrates the benefit of using resistant genotypes in conjunction with liming to manage acid soils. Weeping grass was exceptional in its ability to maintain root length, root-hair and rhizosheath development in acid soil.