Calcium oxalate crystal production and density at different phenological stages of soybean plants (Glycine max L.) from the southeast of the Pampean Plain, Argentina

Glycine max L. (soybean) is one of the major crops of the world. Although the process of biomineralisation has been reported in some organs of soybean, we now report the description and quantification of calcium oxalate crystals in vegetative and reproductive organs of soybean during its life cycle, as they act as an important source of calcium to the soil, once the harvesting is finished. Through diaphanisation, cross-sectioning, optical and scanning electron microscopy analysis of the organs, morphology, size and location of the crystals were identified. In addition, crystal density (no crystal.mm(-2)) and the input of crystals to soil (no crystals.ha(-1)) were calculated. Soybean produced prismatic calcium oxalate crystals in vegetative and reproductive organs, generally associated with vascular bundles, resulting in a potencial transfer to the soil of 81.4 x 10(7) crystals.ha(-1) throughout its life cycle. Pods were the organs with higher calcium oxalate crystal production (1112.7 +/- 384.6 crystals.mm(-2)), but with the smaller size (12.3 +/- 2.1 mu m long). However, cotyledons were the organs that produce the larger crystals (21.3 +/- 3.5 mu m long), but in lesser amounts (150.9 +/- 64.4 crystals.mm(-2)). In leaves, although crystal size did not differ from vegetative to reproductive stage (14.5 +/- 4.2 and 14.5 +/- 4 mu m in length, respectively), the crystal density increased (293.2 and 409 crystals.mm(-2), respectively). These results will contribute to knowledge of the amount of calcium oxalate crystals involved in the process of Ca recycling through cultivated vegetation in fields from humid plains at medium latitudes, which therefore have biological, botanical, biogeochemical and pedological relevance.