Responses in growth, physiology and nitrogen nutrition of dragon spruce (Picea asperata) seedlings of different ages to enhanced ultraviolet-B

In the southeast of the Qinghai-Tibetan Plateau of China, dragon spruce ( Picea asperata) is a key species and widely used in reforestation processes in the area. The paper mainly studied the effects of ultraviolet-B ( UV-B) on growth, physiology and nitrogen nutrition of 3- and 6-year-old dragon spruce seedlings. The experimental design included ambient UV-B ( control) and enhanced UV-B (+UV-B, a 30% increase). Enhanced UV-B significantly decreased growth, needle and root nitrogen concentration, needle nitrate reductase activity and increased UV-B absorbing compounds and malondialdehyde ( MDA) content of two old dragon spruce seedlings. Glutamine synthetase activity was not affected by enhanced UV-B in two old dragon spruce seedlings. On the other hand, different old seedlings also exhibited different physiological responses to enhanced UV-B radiation. Chlorophyll content, carotenoids content and soluble protein content in 3-year-old seedlings significantly reduced by enhanced UV-B, but those in 6-year-old seedlings were not affected by enhanced UV-B. Proline content of 6-year-old seedlings were increased by enhanced UV-B. Compared with the 3-year-old seedlings, the 6-year-old seedlings showed lower reduction of growth and MDA content, and accumulated more proline and UV-B absorbing compounds for protecting seedlings under enhanced UV-B. The results implicated that 3-year-old seedlings were more sensitivity to enhanced UV-B than 6-year-old seedlings