Atmospheric nitrogen (N) deposition continuously increases in decades under human activities, which exerts huge impacts on terrestrial forest ecosystems.

Researchers led by Dr. KUANG Yuanwen from the South China Botanical Garden (SCBG) of the Chinese Academy of Sciences found that nitrogen addition to canopy and understorey exerted different effects on leaf traits of understorey plants in a subtropical evergreen broad-leaved forest. The canopy and understorey N addition approach and N addition rate could affect leaf traits of understorey plants.

They found that understorey N addition led to significantly lower leaf construction cost, concentrations of leaf carbon, phosphorus, organic acids and total non-structural carbohydrate concentrations, but significantly higher leaf total structural carbohydrate than canopy N addition.

The increased N addition rate significantly decreased leaf lignin concentrations, but increased leaf lipids and total structural carbohydrates concentrations.

The results implied that the responses of dominant understorey plant species in subtropical forests to atmospheric N deposition may be different from those stemmed from understorey N addition experiment. For example, the understorey N addition may overestimate the response of leaf construction costs and carbon concentrations to N deposition, but underestimate the responses of leaf organic acids concentrations.

Long term experiments via both canopy and understorey N addition may provide more unbiased responses in ecological processes and functions of subtropical forests to atmospheric N deposition.