Antagonistic effect of nitrogen additions and warming on litter decomposition in the coastal wetland of the Yellow River Delta, China

Human activities have changed global nitrogen (N) cycling in the last decades. Global warming has potential to alter the decomposition of organic carbon. At the moment the effects of inorganic and organic N additions on litter decomposition, alone and in combination with increasing temperature, are not well known. A filed experiment of N addition (nitrate, ammonium and organic N) was conducted in the reed (Phragmites australis) wetlands in the Yellow River Delta, China. At the end of second growing season, the standing litter (leaf and stem) of reed were collected, and were incubated (90 days) to determine the combined effects of N forms and increasing temperature on litter decomposition. The CO2 production was defined as litter decomposition. The results showed that increasing temperature accelerated stem litter decomposition, and had no effect on leaf litter decomposition. Nitrogen additions inhibited leaf and stem litter decomposition due to the decrease in C/N ratio. Ammonium and organic N additions had larger inhibitory effects on stem litter decomposition compared with nitrate addition. This highlights the importance of differentiating the effects of N forms on litter decomposition. Moreover, the combined effect of N additions and increasing temperature on both litter decomposition was antagonistic due to the decreased Q(10) value of litter decomposition after N additions. Our results suggest that the negative effect of N addition on litter decomposition may be enhanced by increasing temperature in the near future.