Test of soil extractants for their suitability in predicting Ca/Sr ratios in leaves and stems of sugar maple seedlings

Abstract

Differential uptake and translocation of Ca and Sr in organisms have been reported, calling into question the use of Sr to track Ca cycling in the environment. We investigated the relationship between Ca/Sr ratios in soil extracts of various strengths (H 2 O, NH 4 Cl, and NH 4 EDTA) and seedlings of sugar maple (Acer saccharum Marsh.) grown from natural regeneration on 37 sites. Our objectives were to determine if Ca/Sr ratios in soil extracts are correlated with those in sugar maple tissues, and what soil extractant best duplicate plant tissue Ca/Sr ratios. Leaves had higher Ca/Sr ratios than stems and the extractants did not produce equal Ca/Sr ratios: H 2 O had the lowest Ca/Sr, and NH 4 EDTA the highest. The relationships between soil extract Ca/Sr ratios and leaf and stem Ca/Sr ratios were significant and linear, but the slopes differed among extractants. The lowest slope (0.45) was observed for the water extract/leaves and the highest (2.15) for the NH 4 EDTA extract/stem with discrimination factors ranging from 0.22 with NH 4 EDTA to 1.59 for water. Leaf extracts were more strongly correlated with soil Ca/Sr than stem extracts (R 2 of 0.57-0.7 vs. R 2 of 0.45-0.6, respectively). These findings support the use of Ca/Sr ratios in plants to track their source of soil Ca, but they highlight the need to calibrate the relationships for the plant tissue and soil extractant used.

Partitioning of the source of leaf calcium of American beech and sugar maple using leaf Ca/Sr ratios: a predominantly surficial but variable depth of Ca uptake

“…This is consistent with the observation of others ( behave similarly in the soil plant systems, the large differences in soil Ca/Sr ratios observed in different soil fractions (Beauregard and Côté 2008;Bélanger et al 2012;Blum et al 2002) suggest otherwise. Lefevre et al (1996) showed that Ca and Sr are retained with the same strength by mineral soil particles whereas Baes and Bloom (1988) …”

“…Thus, typical increases in Ca/Sr range from 1.0 to 1.9 in plant tissue compared to the soil available fraction (Åberg et al 1989;Beauregard and Côté 2008;Blum et al 2000Blum et al , 2012. Wood Ca/Sr along the bole of European beech (Fagus sylvatica L.) (Drouet and Herbauts 2008) and red pine (Picea rubens Sarg.)…”

“…The small root system of seedlings allow for a limited soil volume to be explored that makes for a more accurate characterization of the Ca/Sr ratio of the pedogenic source of Ca. A similar approach was used successfully with sugar maple in a previous study (Beauregard and Côté 2008). Seedlings were sampled from 40 locations in natural forest stands located in HW and MA.…”

“…Relationship between leaf and soil Ca/Sr ratios of seedlings As for sugar maple in Beauregard and Côté (2008), a linear regression was used to describe the relationship between leaf and soil Ca/Sr ratios of beech seedlings (Figure 1). The use of this approach was deemed necessary to facilitate comparisons of levels of preferential uptake and depth of Ca uptake between the two species.…”

“…Except for the F horizon, SOM was higher at HW at all depths with SOM remaining above 1% throughout the whole soil profile whereas SOM was less than 1% below the 30 cm depth at MA. A secondary peak in SOM was Using the equation published in Beauregard and Côté (2008) describing the relationship between leaf and soil Ca/Sr ratios of sugar maple at HW, its corrected leaf Ca/Sr ratio (mean ± SE) intercepts the F, B 20 and B 30 horizons, and the L horizon is also included when the full variation in Ca/Sr ratios is considered ( Figure 5). …”