Flowering dogwood (Cornus florida L.) is an important tree species that is thought to enhance ecological calcium (Ca) cycling and soil Ca availability, through high Ca content and rapid decomposition of its leaf litter. Ca is an essential macronutrient in plants and is an important component of many cellular structures and physiological processes. It acts as an intracellular second messenger and can help plants sense and physiologically respond to numerous environmental cues. Previous research demonstrated that analyses of total foliar Ca concentrations in red spruce trees (Picea rubens Sarg.) are frequently not indicative of a plant’s true physiological Ca status, but that analyses of specific foliar partitions are more closely tied to Ca-dependent physiological processes. To investigate the role of foliar Ca partitioning and sequestration in the enhanced Ca cycling by flowering dogwood trees, we assessed specific pools of Ca in foliage from two tree species common to southeastern forests, flowering dogwood and white oak (Quercus alba L.). Grab samples of foliage were collected during the middle of the growing season, at sites in northwest Georgia. Foliage was flash-frozen, freeze-dried, ground to a fine powder, and tested for three physiologically relevant pools of foliar Ca, using sequential acidic extractions.
As expected, our results demonstrate that these species both accumulate substantial amounts of foliar Ca. However, we found that flowering dogwood foliage contains a significantly higher proportion of Ca in labile pools, and significantly less Ca in a chemically sequestered form. In contrast, white oak chemically sequesters a significantly greater proportion of its foliar Ca, with a much smaller proportion of labile Ca in its foliage. It is likely that the substantial proportion of labile Ca in the foliage of flowering dogwood is released more rapidly during decomposition of leaf litter, in comparison with chemically sequestered Ca. This study builds on our understanding of the relevance of foliar Ca partitioning, providing evidence for a role of Ca partitioning and sequestration in ecological Ca cycling. The decline of flowering dogwood, resulting from dogwood anthracnose, an invasive disease caused by the fungus Discula destructiva, thus may have important implications for nutrient cycling in affected forests.