Abstract:

Primulina is a genus containing typical “stone plants” or “cave plants” that show a high degree of edaphic specialization in the karst limestone regions of southwest China. Most species of the genus occur only on calcareous soils developed from carbonate bedrock, while a few species are found only on the red soil developed from the Danxia landform or acidic soil developed from sandshale bedrock. The aim of this study is to investigate the diversity and characteristics of calcium absorption and storage in Primulina from different soil substrates. Calcium in leaves was determined for plants sampled from 15 populations representing 11 Primulina species occurring on calcareous soil, red soil or acid soil. We analyzed the main types of calcium found in leaves, and compared the calcium content within and among species from different soil types. The results revealed a general high level of leaf calcium content in Primulina species compared with other plants from the karst regions of southwest China. However, we found a significant difference in calcium content among Primulina species from different soil types, with high average calcium content (2,285.6 mg/kg) in Primulina from calcareous soil relative to low levels present in Primulina from both acid soil (1,379.3 mg/kg) and Danxia red soil (1,329.1 mg/kg). The main form of calcium stored in most Primulina species (9 out of 11) was pectate calcium, which accounted for 31.6-64.2% of the total calcium in the leaves. In contrast, for two species, P. linearifolia and P. medica, which grow on soil with a pH > 8, the main calcium form was soluble calcium, which accounted for about 40% of the total calcium in plant leaves. In addition, differences in calcium amount and type were recorded within species from either the same or different soil types. These results suggest that there is variation in calcium speciation found in Primulina at both interspecific and intraspecific levels. Our findings provide a valuable basis for further studies on adaptive mechanisms of edaphic specialization in Primulina.

Key words: Primulina, karst plant, calcareous soil, acidic soil, calcium speciation, diversity