Background Acid rain is a prominent problem in southern China. It can affect the chemical element balance of plant and soil. Among them, carbon(C), nitrogen(N) and phosphorus(P) are important elements required for plant growth and development. And the response mechanisms of different plants and soils to acid rain vary. The study was conducted in Jinyun Mountain, a typical acid rain area in Southwest China. Four plant seedlings were selected for simulated experiments under different concentrations of acid rain. The response mechanisms of plants and soils to acid rain stress were investigated by analyzing plant root and soil C, N and P contents and ratios, as well as changes in plant root morphology under different acid rain concentrations.

Methods The experiment took Chongqing native tree species Pinus massoniana, Cunninghamia lanceolata, Cinnamomum camphora and Phyllostachys edulis as the research objects, and conducted acid rain(SO₄^2-∶NO₃^-=1∶1) simulation experiment in May 2021, with four different treatments, namely CK(pH 7.0 distilled water), pH 4.5, pH 3.5 and pH 2.5, described as pH7.0, pH4.5, pH3.5 and pH2.5 below. The plant root morphology and soil and root C, N and P contents were measured after 4 months in simulated acid rain environment. SPSS Statistics 22.0 was also applied for univariate analysis, Canoco 5 for redundancy analysis, and Origin 2021 for correlation analysis and graphing.

Results 1) At pH3.5, the root total N content of C. lanceolata and C. camphorar was significantly inhibited(P < 0.05) and decreased by 18.86% and 35.66%, respectively, compared with the CK, and at pH4.5 the organic carbon stock of P.massoniana soil was elevated while the total N of P. edulis soil was lost. 2) Acid rain had different effects on each plant-soil C∶N∶P. The root C∶N of C. lanceolata and C. camphora increased significantly to 50.26 and 61.33 at pH3.5. The trends of root nitrogen and phosphorus changes were consistent under the acid rain treatment, and P. massoniana, C. lanceolata and P. edulis were limited by nitrogen elements. 3) Different plant roots behaved differently under the influence of acid rain, which promoted the root growth of P. massoniana and C. lanceolata and inhibited the root growth of C.camphora and P. edulis. 4) Root morphology was significantly positively correlated with root C∶N and root total carbon content, while it was significantly negatively correlated with root N∶P.

Conclusions Tree species may influence the overall plant-soil response mechanism to acid rain. Short-term acid rain has not yet disrupted the overall balance of each plant-soil, and the buffering capacity of C. lanceolata soils is stronger than that of P. massoniana, C. lanceolata, and P. edulis soils, and the root system responds more positively to acid rain.