Glomalin concentrations of extra-radical arbuscular mycorrhizal (AM) hyphae were estimated by deploying hyphal in-growth cores containing glomalin-free sand in field soils in a tropical forest and in pot cultures. In field soils, glomalin was 0.044 +/- 0.013 microgram m(-1) hyphae. In pot cultures glomalin concentrations were lower (range 0.0068-0.036 microgram m(-1)), and varied significantly among species. Using this technique, preliminary estimates of extraradical AM hyphal production on Inceptisols were 1.91 Mg ha(-1)yr(-1) and on Oxisol were 1.47 Mg ha(-1) yr(-1), but they could range between 0.9-5.7 Mg ha(-1) yr(-1). These rates of hyphal production are approximately 10% (range 5-33%) of estimated above ground primary production of the forest.
