Comment on Growth responses of trees and understory plants to nitrogen fertilization in a subtropical forest in China by Tian et al. (2017)

Abstract. Negative effects of over-fertilization have been long reported in agricultural field, which is known as fertilizer burn. A recent paper by Tian et al. (2017) reported a result of simulated nitrogen (N) deposition experiment and demonstrated that application of NH₄NO₃ solution significantly reduced small trees, understory saplings, shrubs, seedlings, and ferns, while large trees were not affected by the application. They discussed that the result was due to the reduced light availability and intensified N saturation. I challenge this view, because it is more likely that the negative effects were caused by the monthly application of NH₄NO₃ solution with high concentration (as high as 0.4 M and 0.8 M). Since experiments using liquid NH₄NO₃ are common, careful interpretations are also required for other experiments.