Glomalin in Ecosystems

Abstract

Glomalin is an abundant soil glycoprotein that could sequester substantial amounts of C and N on a global scale. Nevertheless, major controls over the distribution of this compound in ecosystems are little understood. We reviewed shifts in the production, decomposition, and standing stocks of soil glomalin in response to arbuscular mycorrhizal (AM) communities, plant dynamics, inorganic resources (e.g., N, P, and atmospheric CO2), and land use regimes. We also conducted a literature survey of glomalin concentrations from 22 ecosystems to test for relationships between standing stocks of glomalin and net primary productivity (NPP) and AM abundance. Globally, glomalin stocks were positively correlated with NPP but not with AM abundance. Rates of NPP may impose an upper bound for C available to AM fungi for glomalin construction. Availability of C to AM fungi appears to consistently influence glomalin dynamics in individual studies as well. Glomalin stocks are often greater where AM host plants are more abundant or are more effective hosts for the fungi (implying that more C is allocated to the fungi). In addition, elevated CO2 frequently increases glomalin concentrations in soil. Other inorganic resources and land use change produce inconsistent effects on glomalin stocks. Overall, glomalin dynamics appear to be linked to C dynamics, and this relationship may allow us to better predict the contribution of glomalin to ecosystem feedbacks on global change.