SEASONAL PATTERN OF FINE ROOT PROLIFERATION IN A TROPICAL DRY FOREST

The growth of fine roots (less-than-or-equal-to 2 mm diameter) in a tropical dry forest on recent dune sand has been monitored for 2 years during the dry season-wet season transition, using root-ingrowth bags buried for short time intervals. In both years, most root growth was concentrated in one brief period after the beginning of rains, and it is estimated that the fine root system of the forest can be fully re-deployed before the start of water percolation through the soil. In an accompanying field experiment, root-ingrowth bags were protected from rainfall and treated with distilled water or simulated throughfall solution. Root ingrowth did not occur in the absence of rainfall, indicating that endogenous cues were not involved in the initiation of root growth. Comparable proliferation was found in the presence of distilled water or nutrient solution, indicating that moisture rather than high nutrient concentrations in soil solution is the proximal cue to root proliferation at the start of the wet season. The root systems of the trees comprising this forest can respond rapidly and opportunistically to increased soil moisture, which probably represents an important component of their ability to survive at this hydrologically extreme site.