Root systems of two Patagonian shrubs: A quantitative description using a geometrical method

Abstract

A method for mapping coarse root distribution suitable for stony soils was developed. Each root is considered as a broken line, whose segments are fairly straight root portions. The spatial location of end points of these segments is recorded in the field through 3 coordinates: its distance from plant vertical axis, its depth, and its distance to the foregoing point on the same root. With these data the roots' spatial arrangement is reproduced using a computer program including simple geometrical relationships. The main advantages of the method are: (a) it does not require sample harvesting and handling; (b) it considers root length instead of root biomass; and (c) its quantitative character allows statistically valid comparisons. Two species living in the Patagonian semidesert were studied: neneo (Mulinum spinosum, Umbeliferae) and mata mora (Senecio filaginoides, Compositae). In both shrubs, roots extend laterally more than 2 m and root length decreases exponentially as the distance from the canopy edge increases. Neneo was found to have its maximal root density at a depth of 0.4 m, whereas mata mora has most of its roots close to the soil surface. An interpretation of the differential response of these shrubs to grazing derives from these results.