Understory vegetation altered soil CO2 and N2O emissions and the correlation with plant and soil stoichiometry following N and P addition in Chinese fir plantations

Background and aims Increased nitrogen (N) deposition may exacerbate soil phosphorus (P) deficiency, which alters soil greenhouse gas (GHG) emissions by changing soil properties and understory vegetation in subtropical forests. However, the effects of N addition, P addition, and understory vegetation interactions on soil carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) emissions in forest ecosystems and their underlying mechanisms remain unclear. Methods We conducted a continuous N and P addition experiment in a subtropical Chinese fir plantation. The effects of N and P addition on soil CO 2 and N 2 O emissions with different understory vegetation were examined using a structural equation model. Results The addition of N and P did not directly affect soil CO 2 emission of the understory, which was affected by understory species ( F = 2.86; p = 0.05). N indirectly and positively affects soil CO 2 emission through plant elements, and directly affect N 2 O emission of understory soil. Compared with CK, the addition of N2 promoted the N 2 O cumulative emission by 74.3%. N has a direct positive effect on soil N 2 O emissions, while P addition indirectly exerts a negative influence on N 2 O emissions through its impact on soil properties. Plant elements and soil properties were explained in 26.3% of soil CO 2 emissions, of which 17.6% and 16.0% variations were explained by plant elements and soil properties, respectively. Leaf total N was the most important factor for predicting CO 2 emissions. Conclusions Our results suggested that soil CO 2 emission was more dependent on plant elements, and soil N 2 O emission was directly dependent on N addition rather than plant elements. Thus, different patterns of soil GHG emissions and associated controls following N and P addition provided novel insights into predicting the effects of understory vegetation on climate change mitigation outcomes.