Test of relationship between nitrogen deposition and plant species responses in grassland ecosystem
Human activities have led to rapid acceleration of global nitrogen cycle, with increased nitrogen availability, leading to widespread plant biodiversity loss in terrestrial ecosystems. Greatest species loss are known to occur at low levels of nitrogen deposition, however, it is currently not clear whether such N-enrichment induced species loss function will be linear or non-linear responses to such global change drivers. Here, we examine the trajectory of species loss (or gain) along a gradient of nitrogen deposition (1, 5 and 10 g N m-1 yr-1) in grassland ecosystem in Minnesota over six years. Furthermore, we also examine patterns of aggregate species responses between addition of nitrogen alone and in combination with other nutrients (potassium and phosphorous). Using existing nutrient level manipulation data at Cedar Creek Ecosystem Science Reserve, we characterize plant diversity and shifts in plant species/community composition along a gradient of nitrogen addition rates and in combination with other nutrients.
Species loss was greatest at low levels of N input, with species diversity lowest at N input of 1 g N m-1 yr- compared to the 5 and 10 g N m-1 yr-1 through time. Furthermore, a doubling of species loss was also observed when nitrogen is added in combination with potassium (K), with phosphorous (P) and with both PK than with N alone after six years, potentially suggesting multiple nutrient co-limitation at local scale. Taken together, these results allow for a better mechanistic understanding of relationship between species loss function (biodiversity in general) and N deposition under environmental changes.