Sphagnum response to nitrogen deposition and nitrogen critical load: A meta-analysis

Sphagnum plants are sensitive to nitrogen deposition changes. However, previous literature is inconclusive on the response of Sphagnum to nitrogen deposition, little is known about the nitrogen critical load for Sphagnum growth, and the factors that influence the response of Sphagnum plant growth to nitrogen deposition are still unclear. Therefore, we conducted a meta-analysis of 60 experiments with different gradients of nitrogen application to Sphagnum plants in 14 countries around the world, and the results showed that excess nitrogen reduces Sphagnum production. Mixed-effects models were established to analyze the nutrient, environmental and climatic factors that may affect the response of Sphagnum plants to nitrogen deposition, and the results indicated that the water table and cumulative nitrogen were the most important influencing factors. We compared AICc values to select an optimal model set. We used a meta-analysis combined with general additive models (GAMs) to estimate the nitrogen critical load for Sphagnum, and we concluded that this load in the mid- to high-latitude region is in the range of 5–40 kg ha−1yr−1