Abstract:

Objective: The study aim to reveal the effects of soil physicochemical properties on the emission characteristics of biogenic volatile organic compounds from Cunninghamia lanceolata under forest fire smoke deposition. It further explores the post fire interactions among soil, vegetation, and the atmosphere, providing a scientific basis for ecological restoration and atmospheric environmental assessment after forest fires. Method: C. lanceolata seedlings from the state-owned forest farm of Youxi County, Sanming City, Fujian Province were selected as the research objects. A blank group, a low-concentration group, and a high-concentration group were set up to burn 0, 50, and 150 g of combustibles for flue gas treatment. At 7, 30, and 90 days after enclosed smoke exposure, the chemical composition and emission rates of plant volatiles were determined using a preconcentration system coupled with gas chromatography-mass spectrometry (GC-MS). Concurrently, changes in soil physicochemical properties were continuously monitored, and structural equation modeling (SEM) was employed to analyze the potential relationships among smoke concentration, the emission rates of biogenic volatile organic compounds from C. lanceolata, and soil physicochemical parameters. Result: 1) On day 7 after smoke treatment, smoke concentration had a significant positive effect on both nitrogen content and pH in the 10–20 cm soil layer. By the 30th day, it exhibited a significant negative effect on nitrogen content in that layer while maintaining a significant positive effect on pH. On the day 90, smoke concentration showed a significant negative effect on pH in the 10–20 cm layer. Over time following smoke treatment, with the exception of phosphorus in the 0–20 cm layer and carbon in the low concentration group of the 0–10 cm layer, which declined on day 30 and rebounded by day 90. The nitrogen content, pH, and electrical conductivity in the 0–20 cm layer, as well as carbon content in the 10–20 cm layer, all displayed a continuous downward trend. 2) Eight important olefins were released from C. lanceolata, including 1-butene, 1-hexene, trans-2-butene, cis-2-butene, 1-pentene, isoprene, trans-2-pentene and cis-2-pentene, among them, isoprene, 1-hexene, 1-pentene and 1-butene exhibited the highest emission rates. At 30 days post-treatment, the emission rates of biogenic volatile organic compounds from C. lanceolata showed differences among, which tended to converge by day 90. At 30 days post-treatment, smoke concentration exerted a significant negative effect on isoprene emission rate (P<0.01). By 90 days post-treatment, the emission rate of trans-2-butene was significantly lower than that of the control(P<0.01). In the low concentration treatment group, 1-butene emission rate was significantly elevated at 7 days post-treatment(P<0.01). 3) Forest fire smoke altered the physicochemical properties of the soil, among which nitrogen and phosphorus content, as well as soil pH, were closely associated with the emission of biogenic volatile organic compounds from C. lanceolata. Structural equation modeling showed that soil nitrogen content had a direct, significant positive effect on isoprene emission (P?<?0.001), while soil phosphorus content had a direct, significant negative effect (P?<?0.01). Additionally, soil pH exhibited a highly direct, significant negative effect on isoprene emission (P?<?0.001).【Conclusion】Under the context of forest fire smoke deposition, dynamic changes in soil physicochemical properties, especially soil nitrogen and phosphorus contents and pH, significantly regulate the emissions of biogenic volatile organic compounds such as isoprene from C. lanceolata. These findings enrich our understanding of the soil-plant-atmosphere interactions following forest fire and offer guidance for post fire ecological management: for example, moderate nitrogen supplementation can enhance plant antioxidant capacity, while judicious phosphorus application and pH adjustment help control biogenic volatile organic compounds emissions and mitigate regional air quality impacts.

Key words: forest fire smoke, Cunninghamia lanceolata, biogenic volatile organic compounds, soil physicochemical properties, structural equation model(SEM)