Air and foliage samples (Eucalyptus spp. and Pinus massoniana Lamb.) were collected from e-waste and reference sites in South China and analyzed for Dechlorane Plus (DP) and two dechlorinated DPs. DP concentrations in the air were 13.1–1794 pg/m³ for the e-waste site and 0.47–35.7 pg/m³ for the reference site, suggesting the recycling of e-waste is an important source of DP to the environment. Plant DP, with concentrations of 0.45–51.9 ng/g dry weight at the e-waste site and 0.09–2.46 ng/g at the reference site, exhibited temporal patterns similar to the air DP except for pine needle at the reference site. The air-plant exchange of DP could be described with the two-compartment model. Anti-Cl₁₁ DP was measured in most air and plant samples from the e-waste site. The ratios of anti-Cl₁₁ DP to anti-DP in the air and plants may indicate the preferential uptake of dechlorinated DP by plant compared with DP.

The present study investigated the changes of δ15N values in the tip, middle and base section (divided by the proportion to needle length) of current- and previous-year needles of Masson pine (Pinus massoniana L.) from two declining forest stands suffering from air pollution, in comparison with one healthy stand. At the healthy stand, δ15N in the three sections of both current- and previous-year needles were found evenly distributed, while at the polluted stands, δ15N values in the needles were revealed significantly different from the tip to the base sections. The results implied that the distribution of δ15N among different parts or sections in foliages was not always homogeneous and could be affected by air pollution. We suggested that the difference of δ15N values among pine needle sections should be reconsidered and should not be primarily ignored when the needle δ15N values were used to assess plant responses to air pollution.

Twenty-six polycyclic aromatic hydrocarbons (PAHs) and four synthetic musk compounds (SMCs) accumulated by Masson pine needles from different areas of Shanghai were investigated in the present study. Concentrations of Σ26PAHs (sum of 26 PAHs) ranged from 234 × 10−3 to 5370 × 10−3 mg kg−1. Levels of Σ26PAHs in different sampling areas followed the order: urban areas (Puxi and Pudong) > suburbs > Chongming. Total concentrations of 16 USEPA priority PAHs ranged from 225 × 10−3 to 5180 × 10−3 mg kg−1, ranking at a relatively high level compared to other regions around the world. Factor analysis and multi-linear regression model has identified six sources of PAHs with relative contributions of 15.1% for F1 (vehicle emissions), 47.8% for F2 (natural gas and biomass combustion), 7.8% for F3 (oil), 10.6% for F4 (coal combustion), 15.7% for F5 (“anthracene” source) and 3.0% for F6 (coke tar). Total concentrations of 4 SMCs varied between 0.071 × 10−3 and 2.72 × 10−3 mg kg−1 in pine needles from Shanghai. SMCs with the highest detected frequency were Galaxolide and musk xylene, followed by musk ketone and Tonalide. The highest level of SMCs was found near industrial park and daily chemical plant. The results obtained from this study may have important reference value for local government in the control of atmospheric organic pollution.

Free amino acid concentrations and nitrogen (N) isotopic composition in new current-year (new), mature current-year (middle-aged) and previous-year (old) Masson pine (Pinus massoniana Lamb.) needles were determined to indicate atmospheric N deposition in Guiyang (SW China). In different areas, free amino acids (especially arginine) concentrations in new and middle-aged needles were higher than in old needles, and the variation of free amino acids (especially arginine) concentrations in new and middle-aged needles was also greater than in old needles. This indicate that free amino acids in new and middle-aged needles may be more sensitive to N deposition compared to old needles. Moreover, concentrations of total free amino acids, arginine, histidine, γ-aminobutyric acid and alanine in middle-aged needles exhibited a strong relationship with N deposition (P < 0.05). Needle δ¹⁵N values showed a strong gradient from central Guiyang to the rural area, with more positive δ¹⁵N (especially in old needles) in the city center (0–5 km) and more negative δ¹⁵N (especially in old needles) in rural area (30–35 km). These suggest that N deposition in the urban center may be dominated by ¹⁵N-enriched NOx-N from traffic exhausts, while it is dominated by isotopically light atmospheric NHx-N from agriculture in rural area. Soil δ¹⁵N decreased slightly with distance from the city center, and the difference in δ¹⁵N values between the soil and needles (especially for old needles) increased significantly with the distance gradient, indicating that atmospheric N deposition may be an important N source for needles. This study provides novel evidence that free amino acids in needles and age-dependent needle δ¹⁵N values are useful indicators of atmospheric N deposition.

Microorganisms have a major influence on soil biogeochemical processes and vegetation establishment. However, their long-term succession patterns and short-term turnover are not well-understood in artificial forest ecosystems. The aim of the present study was to investigate the effects of stand ages and seasons on soil bacterial community in a chronosequence of Chinese Pinus massoniana plantations, in 3, 19, and 58-year-old plots. Soil physicochemical properties were measured in three stand ages between two seasons (dry-rainy). The soil bacterial community composition was determined by 16S rRNA Illumina HiSeq sequencing. The results showed that soil bacterial community diversity and structure significantly differed among three stand ages, but was not different between two seasons. The diversity of soil bacterial community increased with an increase in stand age. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla in the three stands. The soil bacterial community structure in all the stands was influenced by soil pH, available phosphorus content, and litter phosphorus content. With the accumulation of available phosphorus, the relative abundance of Acidobacteria decreased, while that of Proteobacteria increased. These shifts suggested that dominant microbial communities transitioned from oligotrophic to copiotrophic with increasing stand age. Extending rotation periods could increase soil bacterial diversity, and in turn help improving soil quality of P. massoniana plantations.

Manganese (Mn) pollution in soil, especially around mining areas, is a serious environmental problem worldwide. Generally, plant remediation technology needs to select species with high Mn tolerance, and exploring the Mn tolerance mechanism of tree species with high ecological and economic benefits is of considerable significance for the effective identification and efficient utilization of Mn phytoremediation species. Masson pine (Pinus massoniana) is one of the main afforestation tree species, exhibiting high ecological and economic value in subtropical areas and also a plant with high Mn accumulation. To reveal the mechanisms governing the tolerance of this species for Mn stress, the morphological, physiological, and biochemical responses of seedlings grown in sand cultures under different Mn stress (0.0009~30 mmol·L⁻¹) were analyzed. The results showed that despite the chlorosis of leaves under high Mn stress (30 mmol·L⁻¹), the height of plant seedling, the diameter of ground and the root morphology was not significantly inhibited (p < 0.05), and a high level of Mn accumulated (translocation factor = 1.10). With increasing Mn concentration, malondialdehyde (MDA), soluble protein, and soluble sugar increased, and superoxide dismutase (SOD) and catalase (CAT) increased at first and later decreased. Under Mn stress, net photosynthetic rate, transpiration rate, stomatal conductance, total chlorophyll, chlorophyll a, and carotenoids increased first and subsequently decreased, and intercellular CO₂ concentration and chlorophyll b decreased, but chlorophyll fluorescence characteristics did not change significantly. Taken together, these results indicate that Masson pine can tolerate Mn stress by increasing its antioxidant enzyme activity and non-enzyme metabolite content. In addition, Masson pine can maintain photosynthesis by changing its gas exchange parameters, photosynthetic pigment content, and chlorophyll fluorescence, which is another important mechanism for coping with high Mn concentrations in the environment. In conclusion, the above results show that Masson pine can be effectively used for phytoremediation of Mn-contaminated soil.

Ground-level ozone (O₃) pollution has affected carbon metabolism in tree species, which becomes one of the top environmental issues in China. In this paper, 1-year-old seedlings of Phoebe bournei and Pinus massoniana Lamb. were grown under field conditions at a rural site near the city of Taihe (Jiangxi Province). The plants were exposed in open-top chambers either to charcoal-filtered air or nonfiltered ambient air for 145 days. At the end of the growth season, the plants were harvested and the major nonstructural carbohydrates in leaves and roots were determined. Exposure to nonfiltered ambient air compared with filtered air controls caused an increase of sucrose, glucose, fructose, starch, and total nonstructural carbohydrates (TNCs) in fine roots of Ph. bournei, while there is no change in carbohydrate contents in Pi. massoniana roots. Compared with filtered air, in Ph. Bournei, starch and TNCs in leaves were reduced by 48 and 7 %, respectively, in ambient O₃. While, ambient O₃ just increased TNC content by 8.9 % in Pi. massoniana needles compared to filtered air. In summary, ambient O₃ affected carbohydrate metabolism of these two subtropical tree species in China, and Pi. massoniana was less sensitive than Ph. bournei. O₃ induced much greater changes in the amounts of carbohydrates in roots than in leaves.

Atmospheric N deposition is a serious problem in subtropical China where N is present in large amounts but P is deficient. Several studies hypothesized that N₂ fixers can overcome phosphorus limitation by trading fixed N₂ for soil phosphorus. In order to know whether N₂ fixers could invest fixed N₂ in extracellular phosphatase production and could stimulate arbuscular mycorrhizal fungi (AMF) to acquire soil P in N-rich subtropical China, an open-air greenhouse experiment was carried out. Two N₂ fixers (Acacia mangium and Ormosia pinnata) and two non-N₂ fixers (Schima superba and Pinus massoniana) were exposed to three levels of N addition: 5.6 kg ha⁻¹ a⁻¹ (ambient N), 15.6 kg ha⁻¹ a⁻¹ (middle N), and 20.6 kg ha⁻¹ a⁻¹ (high N). We found that the capacity of plants to acquire soil P in N-rich subtropical China is species specific. The higher P uptake rates were found for N₂ fixers than non-N₂ fixers under N addition, which were related to the greater soil APA and higher AMF (p < 0.01) in the soil of N₂ fixers. However, with time, high N addition decreased more significant quantities of soil microbial phospholipid fatty acids (PLFAs) in the soil of N₂ fixers than that of non-N₂ fixers (p < 0.05). We conclude that N₂ fixers have higher P uptake capacity than non-N₂ fixers under ambient N deposition in subtropical China. However, continuing N deposition in the future might affect P uptake ability of N₂ fixers as high N addition would decrease soil microbial PLFAs of N₂ fixers.

Biochars derived from Pinus massoniana and Cunninghamia lanceolata trunks (abbreviated as PB and CB, respectively) were used to investigate their potential capabilities to improve lead (Pb(II)) and antibiotic florfenicol (FLO) immobilization in soil. Results shows that, after incubation for 60 days, the maximum adsorption capacities (Q ₘ) of biochar-treated soils (soil-PB and soil-CB) for Pb(II) was increased by 27 and 14 %, respectively, compared with pristine soil sample. In the case of FLO, however, the Q ₘ of biochar-treated soils were enhanced by 266 and 206 % for soil-PB and soil-CB, respectively. The increased Pb(II) adsorption was mainly due to the enhanced interactions between Pb(II) and oxygen-containing functional groups and aromatic structures in biochars. Whereas, the improvement of FLO adsorption was achieved through electrostatic interaction, hydrogen bonding, and van der Waals forces interactions between FLO molecule and biochars. Regardless of the similarities in chemical compositions between two biochars, significantly higher surface area and total pore volume of PB than CB biochar may be the key factors accounting for the differences in adsorption efficiencies for Pb(II) and FLO between Soil-PB and Soil-CB.

Over-exploration of rare earth elements causes soil desertification and environmental degradation. However, the restoration of rare earth mine tailings requires the recovery of both vegetation and soil microbiota. Accordingly, the present study aimed to compare the efficacy of restoring mine tailings using organic compost and native plants (Miscanthus sinensis, Pinus massoniana, Bambusa textilis, or a mixture of all three). After three years, the mixed plantation harbored tenfold greater plant richness than that in the barren land. Among these, M. sinensis played a dominant role across all restored areas. The microbial communities of the soils were assessed using high-throughput 16S rDNA gene sequencing. A total of 34,870 16S rDNA gene sequences were obtained and classified into 15 bacterial phyla and 36 genera. The dominant genus across all the restored soils was Burkholderia, and the bacterial diversity of restored soils was greater than that of soils from either unrestored or natural (unexploited) areas, with the M. sinensis plantation yielding the greatest diversity. The effects of phytoremediation were mainly driven by changes in nutrient and metal contents. These results indicate that M. sinensis significantly improves phytoremediation and that mixed planting is ideal for restoring the soils of abandoned rare earth mines.