Impact of Season on Chemical Composition of Some Medicinal Plants in Saudi Arabia

Wadi Al-Rummah is one of the most important geographical phenomena in the Najd region of Saudi Arabia and is considered to be the largest and longest valley in the Arabian Peninsula, with most of its basin located in the Qassim region. This valley is the habitat of diverse flora, including medicinal herbs, plants, and trees. Three plant species, namely, Capparis spinosa L., Haloxylon salicornicum, and Zygophyllum propinquum were selected for their phytochemical analyses. The effect of soil and climatic conditions on the plant metabolites was investigated. Plant samples were collected at the beginning of March (winter) and the end of August (summer) separately to evaluate the effect of climatic conditions on plant components and their medicinal value. Soil samples were also collected for analysis to find any correlation between plant components and soil composition. Soil and plant samples were collected during the late winter and late summer of the same year. Quantitative analyses of soil samples showed differences in soil phosphorus, iron, magnesium, and as well as pH. These elements were higher in winter than in summer. On the other hand, nitrogen and electrical conductivity were higher in summer. However, there were no significant differences between summer and winter for calcium, potassium, sodium, bulk density, and soil water content. Physiological and biochemical analyses on the aerial parts of the selected plants showed significant differences in carbohydrate content between summer and winter. In fact, they were higher in winter for all the plants studied. Lipid content was higher in summer than in winter. The protein contents of C. spinosa L. were 14% higher in winter, while those of H. salicornicum were 21% higher in summer. Z. propinquum proved to be the most salt-tolerant plant, followed by C. spinosa L. and H. salicornicum. The alkaloid and saponin content of the plants was higher in summer than in winter. There was no significant difference between summer and winter in the levels of phenolic compounds and flavonoids in the plants studied. Based on these results, seasonal changes appear to significantly affect certain medicinal compounds, while other compounds remain relatively constant throughout the year.