Chin J Plan Ecolo ›› 2014, Vol. 38 ›› Issue (2): 103-115.doi: 10.3724/SP.J.1258.2014.00010
• Research Articles •
BAI Xue1,2, CHENG Jun-Hui1,2, ZHENG Shu-Xia1, ZHAN Shu-Xia1,2, and BAI Yong-Fei1*
Aims The accelerated atmospheric nitrogen (N) deposition due to human activity and climate change greatly increases the availability of reactive N in terrestrial ecosystems, leading to limitations of other nutrient elements such as phosphorus (P). The effects of N and P additions on grassland ecosystems across different organizational levels, however, have rarely been studied; particularly the underpinning mechanisms remain unclear. Our objective is to examine the effects of N and P additions on aboveground net primary productivity and functional traits of Leymus chinensis, which is a dominant species in the typical steppe of Inner Mongolia, and to study nutrient limitations at different organizational levels in a L. chinensis steppe induced by N and P additions.
Methods We conducted a field manipulation experiment with additions of N (10.5 g N·m–2·a–1) and P (32 g P2O5·m–2·a–1) in a L. chinensis steppe ecosystem in Inner Mongolia in 2011 and 2012. The aboveground primary productivity, population biomass and density, whole-plant traits (e.g., individual biomass and stem-leaf biomass ratio), leaf physiological (e.g., photosynthetic rate, water use efficiency, and leaf N content) and morphological traits (e.g., leaf area and specific leaf area) of L. chinensis were investigated.
Important findings Our results showed that N and P additions had different effects on the aboveground biomass at different organizational levels. The aboveground net primary productivity was greatly enhanced by the combined N and P additions in 2011 (normal precipitation) and 2012 (above average precipitation), indicating the co-limitation of N and P at the community level. At the species level, N and P additions had no significant effects on population biomass, density, and relative biomass of L. chinensis in both years, indicating that this species could maintain population stability. The individual biomass of L. chinensis was increased by N addition in 2011; whereas it was not affected by either N or P addition in 2012. It is suggested that the growth of L. chinensis may be subjected to N limitation in the dry year, but not to any nutrient limitation in the wet year due to water mediation. Leymus chinensis exhibited high specific leaf area, leaf size and leaf N content, and high photosynthetic yield in response to N enrichment. In conclusion, our results indicate that the primary productivity of typical steppe in Inner Mongolia is co-limited by N and P availability. The functional traits of L. chinensis in response to N and P additions are dependent on the organizational level and mediated by interannual precipitation fluctuations.
BAI Xue, CHENG Jun-Hui, ZHENG Shu-Xia, ZHAN Shu-Xia, and BAI Yong-Fei. Ecophysiological responses of Leymus chinensis to nitrogen and phosphorus additions in a typical steppe[J].Chin J Plan Ecolo, 2014, 38(2): 103-115.
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