LNG 2-4
Phosphorus addition prevent plant species richness loss with nitrogen deposition in Inner Mongolia grassland

Tuesday, August 11, 2015: 3:45 PM
311, Baltimore Convention Center
Qiang Yu, Department of Biology, Colorado State University, Fort Collins, CO
Xingguo Han, Institute of Botany, Chinese Academy of Sciences
Melinda D. Smith, Graduate Degree Program in Ecology, Colorado State University, Ft. Collins, CO

Increased atmospheric nitrogen (N) deposition due to excessive application of N fertilizer and combustion of fossil fuels has decreased plant species richness in grassland ecosystems. Several possible mechanisms have been proposed to explain the species loss with increased N deposition, e.g. competitive exclusion, preemption of light or space, and metal toxicity (Al3+, Mn2+ and Fe3+). Based on ecological stoichiometric theory, it is hypothesized that imbalanced nutrient conditions (especially N and phosphorus (P)) should be an important mechanism. Yet, this mechanism has never been tested. We conducted a N (0.2 mol N m-2 yr-1) and P (0, 0.05, 0.1, 0.2, 0.3, 0.4 mol P m–2 yr-1) addition experiment and a P (0.05 mol m-2 yr-1 P) addition experiment since 2006. Species composition and biomass data were collected each year in August to explore the dynamics of plant species richness and composition under imbalanced and balanced N and P conditions. We also did a long-term monitoring experiment to explore the dynamic of plant species richness in a native grassland undergoing natural N deposition.


The results of N and P addition experiment showed that N addition decreased plant species richness significantly. Similarly, the long-term data showed that with natural N deposition, species richness decreased significantly in the past 30 years. However, the results showed P addition increased species richness in grassland with both added N and natural N deposition. Nitrogen addition decreased relative biomass of species with foliar N:P > 12 and increase relative biomass of species with foliar N:P < 12, but P addition showed opposite trends. Nitrogen addition increased soil N:P significantly. However, with the addition of P soil N:P decreased significantly, i.e. P addition returned imbalanced N:P back to normal conditions. Thus, our results indicate that P addition counters plant species richness loss with N deposition in Inner Mongolia grassland, suggesting that the imbalanced N and P condition may result in the biodiversity loss in grassland.