Determination of foliar Ca/Sr discrimination factors for six tree species and implications for Ca sources in northern hardwood forests

Abstract

Discrimination during foliar uptake between the alkaline earth elements Ca and Sr must be understood to fully utilize Ca/Sr and 87Sr/86Sr ratios as a monitor of Ca sources to trees. The aim of this study was to determine Ca/Sr discrimination factors [DF = (Ca/Srplant tissue)/ (Ca/Srnutrient source)] for six tree species in a northern hardwood forest and use foliar chemistry to consider whether species access measurably different soil reservoirs of Ca and Sr. This was accomplished by measuring the Ca/Sr and 87Sr/86Sr ratios of foliage from individual tree species in mixed stands and comparing these ratios to those of soil extracts from soil pits co-located at six sites in the White Mountains, New Hampshire (USA). For three species for which DFs have been previously determined, the source of Ca and Sr in foliage can be traced predominantly to recycling of material from organic horizons. Foliar and soil chemistry is consistent with each of the tree species in these six sites deriving Ca and Sr predominantly from the Oie horizon. Thus we can estimate DFs (±1sd) for sugar maple (Acer saccharum Marsh.; 1.16 ± 0.13), yellow birch (Betula alleghaniensis Britt.; 1.31 ± 0.10), white birch (Betula papyrifera Marsh.; 1.30 ± 0.14), pin cherry (Prunus pensylvanica L.f.; 1.24 ± 0.09), American beech (Fagus grandifolia Ehrh.; 1.78 ± 0.17) and red maple (Acer rubrum L.; 1.90 ± 0.15). These estimates of discrimination factors allow refinement in the use of Ca/Sr and 87Sr/86Sr ratios of foliage to trace Ca sources to plants.