title: NH4+ enrichment and UV radiation interact to affect the photosynthesis and nitrogen uptake of Gracilaria lemaneiformis (Rhodophyta).
abstract: Solar ultraviolet radiation (UVR, 280-400 nm) is known to inhibit the photosynthesis of macroalgae, whereas nitrogen availability may alter the sensitivity of the algae to UVR. Here, we show that UV-B (280-315 nm) significantly reduced the net photosynthetic rate of Gracilaria lemaneiformis. This inhibition was alleviated by enrichment with ammonia, which also caused a decrease in dark respiration. The presence of both UV-A (315-400 nm) and UV-B stimulated the accumulation of UV-absorbing compounds. However, this stimulation was not affected by enrichment with ammonia. The content of phycoerythrin (PE) was increased by the enrichment of ammonia only in the absence of UVR. Ammonia uptake and the activity of nitrate reductase were repressed by UVR. However, exposure to UVR had an insignificant effect on the rate of nitrate uptake. In conclusion, increased PE content associated with ammonia enrichment played a protective role against UVR in this alga, and UVR differentially affected the uptake of nitrate and ammonia.
authors: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian 361005, China; Mariculture Institute of Shandong Province, Qingdao, Shandong 266002, China. Electronic address: bigwide@163.com.
authors: Zhiguang
authors: Z
authors: Xu
authors: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian 361005, China. Electronic address: ksgao@xmu.edu.cn.
authors: Kunshan
authors: K
authors: Gao
mesh_terms: D000641:Ammonia / Q000737:chemistry* / Q000633:toxicity; D001673:Biodegradation, Environmental; D057486:Carbon Cycle; D005068:Eutrophication; D044724:Gracilaria / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D050901:Nitrate Reductase / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D058458:Nitrogen Cycle / Q000187:drug effects / Q000528:radiation effects; D055668:Photochemical Processes; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D000641:Ammonia; D050901:Nitrate Reductase; D009584:Nitrogen