Absorption and distribution of root, fruit, and foliar-applied ⁴⁵ Ca in 'Clemenules' mandarin trees

The mechanisms of calcium (Ca) absorption and transport in plants are still poorly understood. This study focused on assessing the absorption and distribution of Ca in different plant organs after root (soil), foliar, or fruit application to 6-year-old 'Clemenules' mandarin trees, grown in pots, using ⁴⁵ Ca as a tracer.

The rate of ⁴⁵ Ca absorption and transportation in plant tissues varied according to the treatment method. The fruit and shoot Ca supply led to a rate of 97% to 98% ⁴⁵ Ca retention in such organs. In Ca-treated fruits, 22% of the applied ⁴⁵ Ca moved to the pulp and 78% remained in the flavedo and albedo. The fruit peel was examined by scanning electron microscopy and transmission electron microscopy (SEM and TEM) and variations were observed during fruit development. Following ⁴⁵ Ca soil treatment, approximately 56% of ⁴⁵ Ca activity was measured in the soil, with 19.5% determined in the roots, 14.6% in the trunks (90% in bark and sapwood and only 10% in heartwood), 9.6% in shoots, and 0.3% in fruits.

Calcium mobility in 'Clemenules' mandarin trees is limited and depends on the mode of Ca fertilizer application. The distribution of Ca to and within the fruits may be limited during development because of structural and functional constraints. © 2020 Society of Chemical Industry.