ROOT ARCHITECTURE OF SHRUBS AND SAPLINGS IN THE UNDERSTORY OF A TROPICAL MOIST FOREST IN LOWLAND PANAMA

Entire root systems of 2-3m tall plants in tropical moist forest near Barro Colorado Island were excavated, looking at the canopy and subcanopy species Trichilia tuberculata (Meliaceae), Prioria copaifera (Caesalpinoideae), Hirtella triandra (Chrysobalanaceae) and Tetragastris panamensis (Burseraceae); the immature treelet Faramea occidentalis (Rubiaceae); and the mature shrubs Piper cordulatum (Piperaceae), Psychotria horizontalis (Rubiaceae) and Hybanthus prunifolius (Violaceae). Shrubs had shallower root systems with a higher proportion of total surface area at 0-20cm depth than tree saplings. Shrubs also had greater root surface area, both absolutely and relative to leaf area. Reproduction may create greater nutrient demands in shrubs than in saplings. A well developed, superficial root system increases nutrient absorption from the relatively richer upper stratum. The tradeoff appears to be reduced resistance to water stress in shrubs compared with tree species. -from Authors