Tingyu Sun

To reveal the relative effects and interaction mechanism of soil acidification and nitrogen regulation on the growth of Chinese fir (Cunninghamia lanceolata) and to provide a scientific basis for the prevention and control of Chinese fir plantation decline, we conducted an 18-month greenhouse pot experiment using 1-year-old Chinese fir saplings. The experiment combined three acid solution spraying gradients to simulate soil acidification (control S0, distilled water; low acidification LS, acid solution pH 4.5; high acidification HS, acid solution pH 3.5; the initial soil pH was 6.3; acidification was simulated by spraying a mixed acid solution of H₂SO₄ and HNO₃ at a molar ratio of 5:1) with three nitrogen application levels (no nitrogen N0, 0; low nitrogen LN, 50 mg N·kg⁻¹ dry soil; high nitrogen HN, 200 mg N·kg⁻¹ dry soil), forming nine treatment groups in total. Correlation analysis and a structural equation model (SEM) were used to analyze the influencing pathways. Soil acidification significantly reduced soil pH and nitrate nitrogen content, inhibited sapling growth, impaired the function of the photosynthetic system, and excessively activated superoxide dismutase (SOD) activity, which showed an extremely significant negative correlation with growth rate (−0.83). The total inhibitory effect of soil acidification on sapling growth reached 0.792, operating through direct growth inhibition, impaired nutrient supply, and enhanced antioxidant defense responses. Nitrogen application significantly increased soil available nitrogen content and alleviated stress under low acidification conditions by improving chlorophyll synthesis and photosynthetic efficiency; however, it had no significant direct effect on growth rate (0.15) and slightly exacerbated soil acidification (−0.45). The alleviating effect of nitrogen was completely lost under high acidification treatment with acid solution pH 3.5. The structural equation model showed a good fit (p = 0.379, GFI = 0.940, RMSEA = 0.051), confirming that soil acidification was the core dominant factor restricting Chinese fir growth. These results provide theoretical support and technical reference for precise nutrient management and decline control of Chinese fir plantations in southern China.

Pinus thunbergii Parl. is an economically and medicinally important plant, as well as a world-renowned horticultural species of the Pinus genus. Pine wilt disease is a dangerous condition that affects P. thunbergii. However, understanding of the genetics underlying resistance to this disease is poor. Our findings reveal that P. thunbergii’s resistance mechanism is based on differential transcriptome responses generated by the early presence of the pathogen Bursaphelenchus xylophilus, also known as the pine wood nematode. A transcriptome analysis (RNA-seq) was performed to examine gene expression in shoot tissues from resistant and susceptible P. thunbergii trees. RNA samples were collected from the shoots of inoculated pines throughout the infection phases by the virulent Bursaphelenchus xylophilus AMA3 strain. The photosynthesis and plant–pathogen interaction pathways were significantly enriched in the first and third days after infection. Flavonoid biosynthesis was induced in response to late infestation (7 and 14 days post-infestation). Calmodulin, RBOH, HLC protein, RPS, PR1, and genes implicated in phytohormone crosstalk (e.g., SGT1, MYC2, PP2C, and ERF1) showed significant alterations between resistant and susceptible trees. Furthermore, salicylic acid was found to aid pine wood nematodes tolerate adverse conditions and boost reproduction, which may be significant for pine wood nematode colonization within pines. These findings provide new insights into how host defenses overcame pine wood nematode infection in the early stage, which could potentially contribute to the development of novel strategies for the control of pine wilt disease.

Pine wilt disease (PWD) is a devastating disease that threatens pine forests worldwide, and breeding resistant pines is an important management strategy used to reduce its impact. A batch of resistant seeds of P. thunbergii was introduced from Japan. Based on the resistant materials, we obtained somatic plants through somatic embryogenesis. In this study, we performed transcriptome analysis to further understand the defense response of resistant somatic plants of P. thunbergii to PWD. The results showed that, after pine wood nematode (PWN) infection, resistant P. thunbergii stimulated more differential expression genes (DEGs) and involved more regulatory pathways than did susceptible P. thunbergii. For the first time, the alpha-linolenic acid metabolism and linoleic acid metabolism were intensively observed in pines resisting PWN infection. The related genes disease resistance protein RPS2 (SUMM2) and pathogenesis-related genes (PR1), as well as reactive oxygen species (ROS)-related genes were significantly up-expressed in order to contribute to protection against PWN inoculation in P. thunbergii. In addition, the diterpenoid biosynthesis pathway was significantly enriched only in resistant P. thunbergii. These findings provided valuable genetic information for future breeding of resistant conifers, and could contribute to the development of new diagnostic tools for early screening of resistant pine seedlings based on specific PWN-tolerance-related markers.