XVI International Botanical Congess

Studies of plant competition often define the belowground neighborhood (the horizontal zone where plants compete) but rarely include competition at different soil depths. The lack of secondary thickening in roots of grasses places a morphological limit on their rooting depth. The two-layer model of deep and shallow resource partitioning, first proposed by Walter, is one offshoot of this observation, 40 years later the model remains useful but exceptions are common. This talk summarizes experiments of competition and resource uptake from different soil depths. Examples also include relatively deep resource uptake. On the Edwards Plateau of central Texas, at least six tree species grow roots from 5 to 25 m deep. The cave systems where this research is performed, the molecular tools for identifying the roots, and the stable isotope data showing water and nutrient uptake from 10-20 m underground will be described.