Response of functional traits of Deyeuxia angustifolia to nitrogen addition in Sanjiang Plain Wetland

Deyeuxia angustifolia is a dominant plant in typical marshy wetlands in Sanjiang Plain. Through in situ field control experiments, the adaptability and response law of the species to the nitrogen addition level and nitrogen form were studied, providing a scientific basis for predicting the change in the wetland vegetation population after an increase in the atmospheric nitrogen deposition flux and the change in the nitrogen form. Three nitrogen forms were tested in the experiment with nitrate nitrogen, ammonium nitrogen, and organic nitrogen, with three nitrogen addition levels 4, 8, and 12 g·(m²·a)⁻¹, and a control (no nitrogen added). A total of ten treatments were used to analyze the differences in the functional properties of D. angustifolia. The results showed that, under the action of nitrate nitrogen and ammonium nitrogen, the basal diameter, internode length, leaf number, aboveground biomass, and stem and leaf biomass of D. angustifolia increased with the increase in the nitrogen application rate. Under the medium and high nitrogen levels, ammonium nitrogen mainly promoted stem growth, nitrate nitrogen had a significant impact on leaf growth, and organic nitrogen had a significant impact on the branch number and leaf number of D. angustifolia (P < 0.05). The number of internodes, branches, leaves, and biomass increased with the increase in inorganic nitrogen, while organic nitrogen followed the opposite trend. After applying nitrogen, the leaf biomass of D. angustifolia increased. Conclusion: The tolerance range of D. angustifolia to organic nitrogen is small, but that to inorganic nitrogen is large. Nitrogen application can promote the growth and biomass accumulation of D. angustifolia in Sanjiang Plain, increase the proportion of leaf biomass, and decrease the proportion of stem and tassel biomass.