Spatial analysis of fine root distribution on a recently constructed ecosystem in a water-limited environment

(1) to investigate the spatial distribution of fine roots and its correlation with selected soil properties on an artificial ecosystem dominated by woody vegetation species, and (2) to compare the root distribution to that predicted using a global model for natural ecosystems. Root diameter distribution (a parts per thousand currency sign5 mm), root biomass density (RBD), root length density (RLD), soil pH, soil electrical conductivity and dry soil bulk density were measured on soil core samples (217) collected from a trench wall using a 20 x 20-cm grid sampling. Approximately 90% of the RBD (mean +/- standard error: 0.27 +/- 0.027 kg m(-3)) and RLD (1.57 +/- 0.023 cm cm(-3)) occurred in the top 40 cm, decreasing exponentially to a maximum rooting depth of 150 cm. RBD exhibited a vertical spatial structure associated with soil pH (p <0.05; r(2) = 0.48), and a random lateral distribution. Coefficients of variation (CV) of RBD were high irrespective of orientation (vertical: 79-200%, lateral: 50-236%). The root extinction parameter beta (0.944) for the global model was lower (p <0.05) than that of woodlands (beta = 0.964-0.976), indicating a shallow root distribution resembling that of grasslands (beta = 0.943). The superficial root distribution indicated subsoil chemical constraints to root growth, while high lateral variability was attributed to sparse vegetation. The findings stress the need to account for both vertical and lateral variability of roots for accurate modelling of water use and productivity on certain artificial ecosystems with sparse vegetation.