WHY ARE HAIRY ROOT CLUSTERS SO ABUNDANT IN THE MOST NUTRIENT-IMPOVERISHED SOILS OF AUSTRALIA

Rootlets, covered in long root hairs, are aggregated into distinct clusters in many groups of Australian plants. They are almost universal in the family Proteaceae, and some members of the Papilionaceae, Mimosaceae, Casuarinaceae, Cyperaceae, Restionaceae and Dasypogonaceae. These families have their centres of distribution in the oldest, most leached sands and laterites of the continent. Root clusters are almost confined to the uppermost 100 mm of the soil profile, often penetrating into the raw litter. These horizons are the major sources of mineral nutrients which are mobilized when these soils become moist. I argue that root clusters are an ideal solution for maximizing nutrient uptake in extremely impoverished soils, especially in seasonal climates.