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tap into new soil calcium pool Acid rain depletes calcium from forest soils and may choke the growth of trees, which use calcium from the soil to form and maintain their cell walls. Bioavailable calcium in the soil is known to come from atmospheric deposition and from slow weathering of calcium-containing silicate minerals. Researchers led by geology professor Joel D. Blum of the University of Michigan have now shown that some trees are bypassing these sources and obtaining their calcium directly from the calcium phosphate mineral apatite [Nature, 417, 729 (2002)]. They analyzed calcium/strontium ratios and strontium isotope abundances in trees, soil, and water in the Hubbard Brook experimental forest in northern New Hampshire. The symbiotic mycorrhizal fungi that live on the roots of these trees are likely to help the trees access this alternative calcium pool, Blum says. These fungi can send out filaments that extract calcium ions directly from apatite. "This additional source of calcium will affect our estimates of how much acidity a forest soil can withstand and may help explain why some trees are more susceptible than others to acid rain," Blum tells C&EN. |
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