The effect of soil physicochemical properties on intraspecific variability of pollen morphology in Staphylea pinnata L.

Soil properties influence various aspects of plant growth, development and reproduction. Despite the importance of the gametophytic phase in the plant life cycle, its response to soil factors remains poorly understood, particularly in wild plants. This study showed intraspecific variability of pollen morphology in Staphylea pinnata L., with its response to physicochemical soil properties examined under natural conditions in forest ecosystems. Staphylea pinnata is a locally rare species in Central Europe and is considered to be a shrub that prefers carbonate soils. The pollen of S. pinnata was sampled from 55 natural sites at the northern edge of its geographical range. Eleven morphological features in a total of 1620 pollen grains were analysed in relation to 15 soil parameters. The main objective was to establish a link between the habitat conditions, particularly contents of selected elements in the soil, and pollen grain morphology. Our results indicate a potential influence of Cu, Zn, and CaCO₃ on pollen morphology in S. pinnata. The interaction between pollen morphology and these three nutrients was manifested in pollen size, shape, and exine thickness. We show that in the wild, exine thickness (Ex) is positively correlated with CaCO₃ content. In addition, the length of the polar axis (P) and equatorial diameter (E) are correlated with Cu, while the P/E ratio - with Zn contents, respectively. Our results suggest that these ions play an important role in the formation of pollen grains. There is a lack of research linking the morphological features of pollen grains with such environmental parameters as nutrient contents. This study provides evidence for the role of soil micronutrients in shaping pollen morphology. This is the first comprehensive analysis linking wild soil chemistry and natural pollen variation in a rare European species. Further research should focus on the relationship between the mineral contents in the soil, contents of individual elements in pollen grains, pollen viability, as well as selected plant physiological parameters, such as photosynthetic activity. This will provide insight into the role of each element and the physiological state of the plant in the formation of mature pollen grains under natural conditions.