Nitrogen deposition does not alleviate the adverse effects of shade on Camellia japonica (Naidong) seedlings

Camellia japonica (Naidong), a Tertiary relict species with a unique biological and cultural characteristic, is a special ecotype of C. japonica and is the northernmost distributed populations of C. japonica in the world. This study investigated the interactive responses of C. japonica (Naidong) to shade and nitrogen deposition focusing on seedling growth, leaf morphology and leaf physiology under two light regimes (15% and 65% of full sunlight to represent deep shade and slight shade respectively) and three nitrogen deposition regimes (0, 6 and 12 g N m(-2) year(-1)) in a greenhouse. After 123 d of treatment, the results showed that the deep shade reduced the growth of seedlings significantly compared to slight shade, but improved the specific leaf area, leaf water content, chlorophyll content and F(v)/F(m) of plants. Moderate nitrogen (6 g N m(-2) year(-1)) supply increased the crown area, specific leaf area, leaf water content, chlorophyll content and water use efficiency of seedlings. However, high nitrogen (12 g N m(-2) year(-1)) supply reduced the basal diameter, crown area, specific leaf area and leaf water content. No significant interaction of shade and nitrogen deposition on C. japonica (Naidong) was found. There is a threshold of nitrogen deposition for the growth of C. japonica (Naidong). Camellia japonica (Naidong) populations should be protected by collecting of germplasm resources and carrying out the ex situ conservation.