A new paper in Global Change Biology from the Wardlow Hay Cop LTE outlines how phosphorus and nitrogen interact with elevated carbon dioxide in limestone and acidic grassland ecosystems to lead to community composition changes.

 

Since the onset of the industrial revolution, humans have increased atmospheric CO₂ concentrations to their highest level in over 3 million years, and doubled the amount of fixed nitrogen (N) in the global nitrogen cycle. Such large and simultaneous increases in CO₂ and N availability are likely to have substantial consequences for plant communities. Yet their combined impacts are seldom studied together, especially in ecosystems where phosphorus (P) limits productivity. Here, we combine long-term N and P additions with elevated CO₂ (eCO₂) in two contrasting P-limited grasslands: one limestone and the other acidic both extracted from the Wardlow LTE.

 
 

An example of an ambient CO2 treatment block at the Bradfield Environmental Laboratory Research station, in the Peak District National Park. Mesocosms were extracted from the Wardlow LTE, also in the Peak District, and translocated into a miniFACE system at Bradfield to commence elevated CO2 treatment. Mesocosms from the limestone grassland are labelled in blue, and acidic mesocosms I red. Nutrient treatments include a distilled water control (0N), a low N treatment (LN, 3.5 g m−2 year−1) and a high N treatment (HN, 14 g m−2 year−1) and a P treatment (P, 3.5 g m−2 year−1). Photo credit: Ben Keane

The paper shows that after just 3 years of eCO₂, plant communities in mesocosms from both grasslands significantly changed compared to ambient CO₂ treatments. Nutrient additions also led to substantial shifts in community composition and reductions in species richness and diversity. However, in the limestone grassland, eCO₂ interacted with nutrients to significantly alter functional composition; leading to a replacement of grasses with sedges as the dominant functional type under eCO₂ and N addition, and a tripling of legume cover under eCO₂ and P treatment. The results therefore show that eCO₂ can modify the response of plant communities to increased nutrients in P-limited grasslands.