Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2003
Publication Date: 3/1/2004
Citation: Lovelock, C.E., Wright, S.E., Clark, D.A., Ruess, R.W. 2004. Soil stocks of glomalin produced by arbuscular mycorrhizal fungi across a tropical rainforest landscape. Journal of Ecology 92 (2):278-287.
Interpretive Summary: Belowground productivity of tropical forests is of great interest because accurate assessments of net productivity is likely to affect whether these forests are categorized as sources or sinks for atmospheric carbon. Tropical forests are highly dependent on arbuscular mycorrhizal fungi (AM fungi) that form a beneficial association with roots. Tropical trees are unable to grow beyond the seed reserves if the roots do not form an association with these fungi. We used the recently discovered glycoprotein, glomalin, exclusively produced by AM fungi, to provide the first estimates of activity of these fungi in a tropical forest. The site is in Costa Rica in a forest with a strong fertility gradient. Less fertile soils had more glomalin than higher fertility soils, and we hypothesize that turnover of the fungus is enhanced in the more fertile soil. These are preliminary results to be extended to a thorough examination of fine root and AM fungal production and turnover of important belowground carbon storage products.
Technical Abstract: Glomalin is a glycoprotein produced only by symbiotic arbuscular mycorrhizal (AM) fungi. Arbuscular mycorrhizal fungi utilize photosynthetically derived carbon for growth, and could account for a significant portion of belowground primary production. They also may be responsible for a significant fraction of the soil carbon stocks in forest soils. In this study we made a first assessment of the standing stocks of glomalin in a tropical lowland rain forest (the La Selva Biological Station, Costa Rica). Mean levels of glomalin in the top 10 cm of the La Selva soils were 3.94 ± 0.16 mg cm-3 (1.45 Mg C ha-1). We found that glomalin accounted for approximately 3.2% of total soil carbon and 5% of soil N in the 0-10 cm soil layer. We tested whether the glomalin concentrations varied over the strong fertility gradient in this forest. The soils with higher concentrations of Ca and Mg had less glomalin, while the less fertile soils, those with high C:N ratio, and high levels of Fe and Al had more glomalin. Younger, recently produced glomalin is immunoreactive. We found higher levels of immunoreactive glomalin in the soils with higher concentrations of P and K. We hypothesize that AM fungal turnover, as indicated by a greater proportion of immunoreactive, recently produced glomalin, is enhanced in the more fertile soils within this tropical rainforest landscape.