Precipitation pattern alters the effects of nitrogen deposition on the growth of alien species Robinia pseudoacacia

Aims: Nitrogen (N) supply and precipitation pattern (amount and frequency) both affect plant growth. However, N deposition is increasing and precipitation regimes are changing in the context of global change. An experiment was conducted to access how the growth of Robinia pseudoacacia, a widely distributed and cultivated N₂-fixing alien species, is affected by both the pattern of precipitation and N supplies. Methods: Seedlings were grown in a glasshouse at four different N levels combined with different precipitation regimes, including three precipitation amounts, and two precipitation frequencies. After treatment for 75 days, plant height, biomass allocation, leaf and soil nutrient concentrations were measured. Results: Plants under high precipitation frequency had greater biomass compared with plants lower precipitation frequency, despite receiving the same amount of precipitation. Higher N supply reduced biomass allocation to nodules. Under low precipitation level, nodule growth and N₂ fixation of R. pseudoacacia was more inhibited by high N deposition compared with plants under higher precipitation level. Even slightly N deposition under higher precipitation inhibited N₂ fixation but it was insufficient to meet the N needs of the plants. Conclusions: Even at low levels, N deposition might inhibit N₂ fixation of plants but low N in soil cannot meet the N requirements of plants, and caused N₂ fixation limitation in plants during seedling stage. There was likely a transition from N₂ fixation to acquisition of N from soil directly with root when N supply was increased.