Effect of Short-Term Nitrogen Addition on N and P Stoichiometry of Herbaceous Leaves and Roots in the Understory of Larix principis-rupprechtii Plantation in Northern China

Nitrogen (N) deposition in China remains high. However, the response of species-level plant elemental stoichiometry to N deposition is not comprehensive. This study aimed to investigate the N and phosphorus (P) stoichiometric response of understory herbaceous plants to N deposition at the species level. An addition experiment in Larix principis-rupprechtii plantation was conducted with multiple-gradient N addition (0, 5, 10, 20, 40, 80, and 160 kg N ha−1 yr−1). The N and P stoichiometry of the leaves and roots of nine representative herbaceous plants was determined. N addition significantly increased N concentration and N/P ratio in herbaceous plants. The changes in P concentration varied by species, with most plants reaching their highest P concentration at lower N addition levels. The availability of soil nutrients, such as nitrate nitrogen, driven by N addition, was the primary factor influencing N and P concentrations and the N/P ratio in plant leaves and roots. The response patterns of plants to N addition varied by species and organs, indicating that we should pay more attention to the differential response of different plants to nitrogen deposition.