Effect of Seasonal Changes on Photosynthetic Pigments and Proline Contents of Some Plants Growing Naturally in Tayma Region, Saudi Arabia

The present study was undertaken to understand adaptive behavior and the possibility of osmotic adjustment adopted by three plant species to tolerate harsh environmental conditions during the winter and summer seasons based on some soil and plant variables as well as the relationships among them. The plant species studied are Hyoscyamus muticus L. (H. muticus), Anabasis setifera Moq. (A. setifera) and Teucrium polium L. (T. polium) and were collected from Tayma Governorate, Tabuk region, Saudi Arabia. ANOVA results showed that the plant species, depths, and their interaction significantly affected most physicochemical properties of the soil supporting three plant species. Also, the plant species, seasons, and their interaction highly significantly affected photosynthetic pigments and proline contents. The highest values for pH and Ec in A. setifera soil, for Na+, Mg++ and Cl- in H. muticus soil, and for other studied chemical properties in T. polium soil were recorded. Significantly increased water content % was observed in A. setifera soil at 20-40 depth across the winter season. Chlorophyll a (Chl.a), chlorophyll b (Chl.b) and Chl.a+b contents in H. muticus plants and Chl.a/b, total carotenoids, total pigment and proline contents in T. polium plants were significantly increased in comparison to the other plant species. Compared to the winter season, the amount of proline and photosynthetic pigments increased significantly in the summer season. The principal component and biplot analysis displayed that the three plant species were quite separated based on the variables studied, and showed positive correlations among most soil and plant variables, but these associations varied in their degree and consistency. The positive correlations were observed for PC1 with K+, Ca++, HCO3- and SO4-- in soil as well as Chl.a/b, total carotenoids, total pigment and proline in T. polium plants. While PC2 showed highly positively correlated to Na and Mg in soil as well as Chl.a, Chl.b and Chl.a+b in H. muticus plants. As a result, the above soil chemical properties are associated closely with the above plant variables in the two previous plant species. The statistical study shows that due to its adaptive behavior and potential for osmotic adjustment, T. polium type generally adapts better to the dry desert environment and seasonal changes.