J Plant Ecol ›› 2017, Vol. 10 ›› Issue (5): 822-830 .DOI: 10.1093/jpe/rtw089

• Research Articles • Previous Articles     Next Articles

Phosphorus does not alleviate the negative effect of nitrogen enrichment on legume performance in an alpine grassland

Fei Ren1,2, Weimin Song3, Litong Chen1, Zhaorong Mi1, Zhenhua Zhang1, Wenyan Zhu1,2, Huakun Zhou1, Guangmin Cao1 and Jin-Sheng He1,3,*   

  1. 1 Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, 23 Xinning Rd., Xining 810008, People's Republic of China; 2 University of Chinese Academy of Sciences, 19A Yuquan Rd., Beijing 100049, China; 3 Department of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, 5 Yiheyuan Rd., Beijing 100871, China
  • Received:2016-02-25 Accepted:2016-08-31 Published:2017-09-27
  • Contact: He, Jin-Sheng

Phosphorus does not alleviate the negative effect of nitrogen enrichment on legume performance in an alpine grassland

Abstract: Aims Nitrogen (N)-fixing legumes, despite being highly phosphorus (P)-demanding, constitute an important plant functional group and play key roles in N-poor ecosystems such as alpine grasslands. However, legume performance, including biomass, abundance and species richness, is expected to change, because anthropogenic activities have drastically increased soil N and P availability worldwide. We conducted a field experiment to assess the effects of N and P addition, alone and in combination, on legume performance in an alpine grassland, and identified and clarified the mechanisms underlying these changes.
Methods A three year field experiment of N addition (10g N m ?2 year-1), P addition (5g P m ?2 year-1), and N + P combined addition (both N and P, same amounts as solo treatments) was conducted in an alpine grassland on the Tibetan Plateau in China from 2011 to 2013. Effects of nutrient addition were assessed at the community level (above-ground net primary production (ANPP), height and light intensity), functional group level (biomass, species richness, relative height, relative coverage and relative density of legumes) and species level (foliar N, P concentration of two legumes).
Important findings Overall, adding N alone significantly increased ANPP by 20.82%, but adding P alone did not; whereas, addition of N and P together resulted in a large increase in ANPP (+37.03%) than addition of either alone, indicating potential co-limitation of alpine grasslands. In contrast, adding P alone significantly promoted legume performance as measured by 65.22% increase in biomass and 58.45% increase in relative abundance, while adding N alone reduced legume performance as measured by 39.54% decrease in biomass and 50.36% in relative abundance. Combining P and N addition did not mitigate the negative effect of N addition on legume performance and, surprisingly, suppressed legume biomass by 53.14% and relative abundance by 63.51%. N and P addition altered the balance of light competition between grasses and legumes as indicated by the changes in light levels, plant heights and litter accumulation. However, there were no obvious changes in legume species richness in response to N and P within our experimental timeframe. This study provides further evidence of the importance of P as a co-limiting nutrient in alpine grasslands, contrary to the traditional view that N limitation predominates in such regions. The contrasting effects of N and P addition on legume performance provide important insights into potential changes in legume performance in nutrient-limited grasslands following N and P enrichment under climate change, with implications for nutrient management in alpine grasslands.

Key words: Tibetan Plateau, nutrient addition, soil-nutrient interactions, legume productivity, species richness

摘要:
Aims Nitrogen (N)-fixing legumes, despite being highly phosphorus (P)-demanding, constitute an important plant functional group and play key roles in N-poor ecosystems such as alpine grasslands. However, legume performance, including biomass, abundance and species richness, is expected to change, because anthropogenic activities have drastically increased soil N and P availability worldwide. We conducted a field experiment to assess the effects of N and P addition, alone and in combination, on legume performance in an alpine grassland, and identified and clarified the mechanisms underlying these changes.
Methods A three year field experiment of N addition (10g N m ?2 year-1), P addition (5g P m ?2 year-1), and N + P combined addition (both N and P, same amounts as solo treatments) was conducted in an alpine grassland on the Tibetan Plateau in China from 2011 to 2013. Effects of nutrient addition were assessed at the community level (above-ground net primary production (ANPP), height and light intensity), functional group level (biomass, species richness, relative height, relative coverage and relative density of legumes) and species level (foliar N, P concentration of two legumes).
Important findings Overall, adding N alone significantly increased ANPP by 20.82%, but adding P alone did not; whereas, addition of N and P together resulted in a large increase in ANPP (+37.03%) than addition of either alone, indicating potential co-limitation of alpine grasslands. In contrast, adding P alone significantly promoted legume performance as measured by 65.22% increase in biomass and 58.45% increase in relative abundance, while adding N alone reduced legume performance as measured by 39.54% decrease in biomass and 50.36% in relative abundance. Combining P and N addition did not mitigate the negative effect of N addition on legume performance and, surprisingly, suppressed legume biomass by 53.14% and relative abundance by 63.51%. N and P addition altered the balance of light competition between grasses and legumes as indicated by the changes in light levels, plant heights and litter accumulation. However, there were no obvious changes in legume species richness in response to N and P within our experimental timeframe. This study provides further evidence of the importance of P as a co-limiting nutrient in alpine grasslands, contrary to the traditional view that N limitation predominates in such regions. The contrasting effects of N and P addition on legume performance provide important insights into potential changes in legume performance in nutrient-limited grasslands following N and P enrichment under climate change, with implications for nutrient management in alpine grasslands.