Plant tolerance of a high calcium environment via foliar partitioning and sequestration

Our purpose in this study was to assess whether a range of plant species tolerate a very high-calcium (Ca) environment by chemically sequestering excess Ca in a physiologically unavailable form, thus maintaining labile foliar Ca at appropriately low levels. Calcium concentration within the cytoplasm of cells must be maintained at low levels to avoid toxicity, and to allow for Ca-based cellular signaling in response to numerous environmental cues. We assessed Ca partitioning and sequestration in foliage from six plant species growing at White Sands National Monument, a site with primarily gypsum (calcium sulfate) substrate, which supplies very high plant-available Ca in the soils. Chemical components of foliar Ca were separated by sequential acidic extractions and assessed using a colorimetric Ca analysis. We found substantial variability among species in their uptake and retention of Ca, especially in their ability to sequester the Ca they absorb. Of the six species we evaluated, four sequester large portions (40-90 percent) of their foliar Ca in a chemically-unavailable form, and one of these appears to substantially limit Ca uptake. The other two species maintain over 90 percent of their foliar Ca in labile forms, which may enable exudation of excess Ca via salt glands. This work provides new insights into the physiology of foliar Ca tolerance in plants growing in high-Ca conditions, as well as the physiological and ecological processes that occur in the unique ecosystems found at White Sands National Monument.

► Foliar Ca tolerance strategies are described for plants growing at a high-Ca site.
► Four of six species chemically sequester a large proportion of their foliar Ca.
► One species substantially limits Ca uptake into foliage.
► Two species maintain substantial labile foliar Ca, allowing exudation.