The relative uptake of Ca and Sr into tree foliage using a whole-watershed calcium addition

Abstract

The use of strontium isotopes and ratios of alkaline earth elements (i.e., 87 Sr/ 86 Sr and Ca/Sr) to trace Ca sources to plants has become common in ecosystem studies. Here we examine the relative uptake of Ca and Sr in trees and subsequent accumulation in foliage. Using a whole-watershed Ca addition experiment at the Hubbard Brook Experimental Forest in N.H., we measured the uptake of Ca relative to Sr in foliage and roots of sugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), American beech (Fagus grandifolia), and red spruce (Picea rubens). Vegetation was analyzed for Ca and Sr concentrations and the 87 Sr/ 86 Sr ratio. A comparison of the Ca/Sr ratio in the vegetation and the Ca/Sr ratio of the applied mineral allows for the calculation of a discrimination factor, which defines whether Ca and Sr are incorporated and allocated in the same ratio as that which is available. A discrimination factor greater than unity indicates preferential uptake of Ca over Sr; a factor less than unity reflects preferential uptake of Sr over Ca. We demonstrate that sugar maple (SM) and yellow birch (YB) have similar and small discrimination factors (1.14 ± 0.12,1r and 1.16 ± 0.09,1r) in foliage formation and discrimination factors of less than 1 in root formation (0.55-0.70). Uptake into beech suggests a larger discrimination factor (1.9 ± 1.2) in foliage but a similar root discrimination factor to SM and YB (0.66 ± 0.06,1r). Incorporation into spruce foliage occurs at a much slower rate than in these other tree species and precludes evaluation of Ca and Sr discrimination in spruce foliage at this time. Understanding the degree to which Ca is fractionated from Sr in different species allows for refinement in the use of 87 Sr/ 86 Sr and Ca/Sr ratios to trace Ca sources to foliage. Methods from this study can be applied to natural environments in which various soil cation pools have different 87 Sr/ 86 Sr and Ca/Sr ratios. The results reported herein have implications for re-evaluating Ca sources and fluxes in forest ecosystems.

Decreased water flowing from a forest amended with calcium silicate

“…Yellow birch, comprising 21% of the W1 tree biomass, showed a similar pattern for foliar Ca concentration, with the exception of a secondary peak in 2006. These Ca accumulation patterns are similar to previous observations of other vegetation in W1 (27).…”

Use of foliar Ca/Sr discrimination and 87Sr/86Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

“…These data are plotted on Fig. 2 along with a line of slope = 1 and a wedge-shaped area defined by lines of slope = 1.14 ± 0.12, which is the previously determined ratio between the Ca/Sr ratio of sugar maple foliage and its nutrient source (DF foliage ) and the associated uncertainty in that relationship (Dasch et al 2006). Several important trends are apparent in Fig.…”

“…A more detailed description of methods of chemical separation and isotope ratio measurement of Sr can be found in Dasch et al (2006). Between 100 and 200 isotope ratios were measured for each sample, yielding a mean 87 Sr/ 86 Sr ratio with an analytical uncertainty of less than ±0.000030 (±2r).…”

“…In a recent whole-watershed CaSiO 3 addition experiment at the Hubbard Brook Experimental Forest, Dasch et al (2006) found that various plant species accumulate Ca and Sr in foliage and roots in a constant proportion relative to their nutrient source. They determined discrimination factors [DF = (Ca/Sr plant tissue )/(Ca/Sr nutrient source )] for foliage and roots of sugar maple and some other herb, shrub and tree species.…”

“…Sugar maple was found to discriminate for Ca over Sr in foliage (DF foliage = 1.14 ± 0.12, 1r) but to discriminate for Sr over Ca in root formation (DF root = 0.60 ± 0.07, 1r). Dasch et al (2006) suggested that once the discrimination factor is empirically determined for a particular plant species and tissue, Ca/Sr ratios could be used as a tracer of the sources of Ca for that species.…”