© 2004 Heron Publishing—Victoria, Canada
Accretion, partitioning and sequestration of calcium and aluminum in red spruce foliage: implications for tree health
Catherine H. Borer (1, 2), Paul G. Schaberg (3), Donald H. DeHayes (1) and Gary J. Hawley (1)
1. The University of Vermont, Rubenstein School of Environment and Natural Resources, 81 Carrigan Drive, Burlington, VT 05405,
USA / 2. Corresponding author (cborer@uvm.edu) / 3. USDA Forest Service, Northeastern Research Station, 705 Spear Street, South Burlington, VT 05403, USA / Received September 19, 2003; accepted February 8, 2004; published online July 1, 2004
Summary
Calcium (Ca) is an essential macronutrient in plants and is an important component of many cellular structures and physiological
processes as well as overall forest function. Aluminum (Al) in soil solution can inhibit Ca uptake by plants and disrupt many
Ca-dependent metabolic and physiological processes of plants. The ratio of Ca to Al in soil solution can be an important indicator
of forest health, especially on acid soils. We used sequential chemical extractions (water, acetic acid and hydrochloric acid)
to assess the chemical availability of Ca and Al in foliage from mature red spruce (Picea rubens Sarg.) trees growing under ambient environmental conditions. In plants deficient in Ca and with intermediate total foliar
Ca concentration ([Ca]), Ca preferentially accrued in labile and physiologically available forms (water- and acetic acid-extractable).
In plants with total foliar [Ca] above a “sufficiency” threshold, Ca also accrued in a chemically sequestered form with low
solubility (HCl-extractable), suggesting that Ca sequestration is an inducible process in response to excess foliar Ca. Because
it has low solubility, it is likely that sequestered Ca is unavailable for Ca-dependent physiological processes. Immobilization
of Al in foliage was related to Ca sequestration, suggesting that Ca sequestration may provide a passive mechanism for Al
tolerance in the foliage of these trees. Aluminum immobilization was evident based on the ratio of HCl-extractable Al to the
more labile (water- and acetic acid-extractable) forms of Al. Sufficient labile Ca combined with Al sequestration was associated
with plant health, including enhanced foliar accretion of Mg and Mn, greater tree growth, enhanced foliar cold hardiness and
reduced winter injury. These findings demonstrate that not all chemical forms of foliar Ca and Al are of equal physiological
significance and underscore the importance of assessing the biologically significant element forms in biogeochemical research.
Keywords:
acid rain, Ca:Al, foliar extractions, membrane associated Ca (mCa), nutrient availability, Picea rubens
.
