Using the static chamber–gas chromatography method, this study investigates the flux characteristics of CO₂, CH₄, and N₂O in the soils of three typical island-like forests in the Sanjiang Plain during the growing season (May to September), as well as their relationships with environmental factors. The results indicate that the soils of the Broadleaf mixed forest, Quercus mongolica forest, and Betula platyphylla forest act as emission sources for CO₂ and N₂O, with average fluxes of 433.92, 452.41, and 358.17 μg·m⁻²·h⁻¹ for CO₂ and 12.48, 13.02, and 10.51 μg·m⁻²·h⁻¹ for N₂O, respectively. The differences among forest types are not significant. All three forest types serve as sinks for CH₄, with average fluxes of −22.52, −23.29, and −0.76 μg·m⁻²·h⁻¹. The Betula platyphylla forest has a significantly weaker absorption intensity compared to the other types (p < 0.01). The measured environmental factors collectively explain 66.58% of the variability in greenhouse gas fluxes in the island-like forests, with soil temperature, soil moisture, and total nitrogen content being the main influencing factors in the region. Rising temperatures favor the emission of CO₂ and N₂O and the absorption of CH₄ in all three forest types. Increased soil moisture inhibits the absorption of CH₄ in the Broadleaf mixed forest and Quercus mongolica forest, while higher levels of alkali-hydrolyzed nitrogen enhance the N₂O flux in the Quercus mongolica forest. Soil organic carbon and soil pH significantly influence only the greenhouse gas fluxes of the Betula platyphylla forest.

Using a static chamber-gas chromatography method, we investigate the characteristics of soil CO₂, CH₄, and N₂O fluxes and their relationships with environmental factors during the growing season in four typical Larix gmelinii forests (moss–Larix gmelinii forest, Ledum palustre–Larix gmelinii forest, herbage–Larix gmelinii forest, and Rhododendron dauricum–Larix gmelinii forest) in the Greater Khingan Mountains. Our results show that all four forest types are sources of CO₂ emissions, with similar average emission fluxes (146.71 mg·m⁻² h⁻¹–211.81 mg·m⁻² h⁻¹) and no significant differences. The soil in the moss–Larix gmelinii forest emitted CH₄ (43.78 μg·m⁻² h⁻¹), while all other forest types acted as CH₄ sinks (−56.02 μg·m⁻² h⁻¹–−28.07 μg·m⁻² h⁻¹). Although all forest types showed N₂O uptake at the beginning of the growing season, the N₂O fluxes (4.03 μg·m⁻² h⁻¹–5.74 μg·m⁻² h⁻¹) did not differ significantly among the four forest types for the entire growing season, and all acted as sources of N₂O emissions. The fluxes of CO₂, CH₄, and N₂O were significantly correlated with soil temperature and soil pH for all four forest types. Multiple regression analysis shows that considering the interactive effects of soil temperature and moisture could better explain the changes in greenhouse gas emissions among different forest types. The average Q₁₀ value (8.81) of the moss–Larix gmelinii forest is significantly higher than that of the other three forest types (3.16–3.54) (p < 0.05), indicating that the soil respiration in this forest type is more sensitive to temperature changes.

Salt stress restricts cucumber seedling establishment by impairing root development, photosynthesis, ion homeostasis, and redox balance. This study examined whether potassium silicate (K₂SiO₃) could partially alleviate these responses under hydroponic sodium chloride (NaCl) stress. Cucumber seedlings were exposed to six treatments: a nutrient-solution control, K₂SiO₃ alone supplying 1.0 mmol L⁻¹ silicon (Si), 75 mmol L⁻¹ NaCl, and NaCl combined with K₂SiO₃ supplying 0.5, 1.0, or 2.0 mmol L⁻¹ Si. Growth, root morphology, photosynthetic pigments, gas exchange, chlorophyll fluorescence, photosystem II (PSII) energy partitioning, oxidative injury, antioxidant enzyme activities, osmotic adjustment, and ion status were evaluated at 7 and 14 d. NaCl markedly reduced seedling growth, root development, net photosynthetic rate, PSII photochemical performance, and electron transport, while increasing leaf sodium (Na⁺), malondialdehyde accumulation, non-photochemical quenching, non-regulated energy loss, proline, and soluble sugar. K₂SiO₃ partially alleviated these changes. The treatment supplying 1.0 mmol L⁻¹ Si produced the strongest integrated recovery of growth, root activity, photosynthetic performance, PSII function, and oxidative status. The treatment supplying 2.0 mmol L⁻¹ Si resulted in the lowest leaf Na⁺ concentration and the highest leaf potassium (K⁺)/Na⁺ ratio among salt-stressed seedlings but did not produce the greatest growth recovery. These findings suggest coordinated changes in photosynthesis, photochemical energy use, redox status, and ion balance. Because K₂SiO₃ supplied both Si and K⁺, the results represent responses to K₂SiO₃ supplementation rather than Si-specific effects.

Saline–alkali stress severely restricts leafy vegetable growth by impairing photosynthesis, ion homeostasis, and oxidative balance. This study investigated whether exogenous melatonin could alleviate saline–alkali stress in pakchoi (Brassica rapa subsp. chinensis) through coordinated protection of photosynthetic electron transport, ionic balance, and antioxidant defense. Pakchoi plants were subjected to four treatments: normal nutrient solution (CK), 100 μM melatonin (MT), 100 mM mixed saline–alkali stress with NaCl:NaHCO₃ at 2:1 (SAS), and saline–alkali stress plus melatonin (SAS+MT). After 7 d, growth traits, gas exchange, chlorophyll fluorescence, OJIP transients, ion contents, osmotic adjustment, oxidative damage, and antioxidant enzyme activities were analyzed. Saline–alkali stress markedly inhibited growth, reduced photosynthetic pigment contents and gas exchange, impaired PSII photochemical performance, disrupted ion balance, and increased ROS accumulation and membrane damage. Compared with SAS, SAS+MT increased net photosynthetic rate (Pn) by 66.2%, effective quantum yield of PSII [Y_(II)] by 56.0%, electron transport rate (ETR) by 57.9%, and the performance index on absorption basis (PI_ABS) from 0.80 to 1.80. Melatonin also reduced Na⁺ content by 38.7%, increased the K⁺/Na⁺ ratio from 1.0 to 2.2, and enhanced superoxide dismutase (SOD),peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activities by 20.5%, 24.4%, 29.2%, and 33.3%, respectively. These results indicate that melatonin alleviates saline–alkali injury in pakchoi by maintaining PSII electron transport, improving ion homeostasis, and strengthening antioxidant defense.

Soil microplastic pollution may affect woody plant establishment, but evidence for tree seedlings remains limited. Populus simonii × P. nigra ‘1307’ seedlings were grown for 45 d in soil containing an equal-mass PVC–PE–PS mixture at 0, 100, 500, or 1000 mg kg⁻¹ dry soil. Growth, root architecture and activity, photosynthetic traits, oxidative status, and soil chemical and enzymatic properties were measured. The 100 mg kg⁻¹ treatment produced limited, trait-specific changes and did not consistently inhibit growth. In contrast, 500 and 1000 mg kg⁻¹ reduced most growth and physiological traits. At 1000 mg kg⁻¹, total dry biomass, total root length, root surface area, root volume, root-tip number, and root activity decreased by 43.7%, 46.5%, 47.2%, 50.2%, 51.1%, and 50.9%, respectively. Net photosynthetic rate and PSII electron transport declined, whereas H₂O₂, O₂•⁻ production, thiobarbituric acid-reactive substances (TBARS), and electrolyte leakage increased. Under higher exposure, soil electrical conductivity was higher, whereas available nutrient levels and several soil enzyme activities were lower. These results indicate that medium and high concentrations of the tested mixture were associated with concurrent inhibition of root development, photosynthetic performance, and biomass accumulation under short-term pot conditions. Because concurrent impairment of woody-seedling performance and soil biochemical functioning may compromise vegetation establishment, these findings support the inclusion of mixed-polymer exposure in ecological risk assessments for soils used in forestry and ecological restoration.

High temperature can impair leaf water status, photosynthetic function, and membrane stability in ornamental woody seedlings. However, integrated evidence combining gas exchange, chlorophyll fluorescence, oxidative injury, antioxidant activity, and osmotic-adjustment-related responses in heat-stressed Syringa oblata remains limited. One-year-old seedlings from a single nursery batch were exposed for 7 d to 25/18 °C or 40/30 °C day/night conditions and sprayed with either a solvent solution or 0.5 mM salicylic acid. Growth, leaf water status, photosynthetic pigments, gas exchange, pulse-amplitude-modulated fluorescence, OJIP/JIP-test parameters, oxidative-injury markers, antioxidant enzyme activities, and osmotic-adjustment-related compounds were evaluated. Heat treatment reduced leaf relative water content, photosynthetic performance, and photosystem II function and increased reactive oxygen species accumulation, lipid peroxidation, and electrolyte leakage. Compared with heat treatment alone, seedlings receiving salicylic acid under heat showed an 82.2% higher net photosynthetic rate, a 12.2% higher maximum quantum efficiency of photosystem II, and a 116.4% higher performance index on an absorption basis. Hydrogen peroxide, malondialdehyde, and electrolyte leakage were 35.1%, 35.8%, and 32.5% lower, respectively. Antioxidant enzyme activities were also higher under heat plus salicylic acid than under heat alone, whereas additional increases in proline and soluble sugars were not statistically confirmed; soluble protein was partially maintained. Gas exchange was measured after treatment at a common leaf-chamber temperature of 25 °C and therefore represented retained photosynthetic capacity under standardized conditions. Overall, foliar application of 0.5 mM salicylic acid was associated with partial maintenance of photosynthetic function and lower oxidative injury during short-term heat exposure. Because one chamber was assigned to each treatment combination in a single experimental run, possible chamber-specific effects could not be statistically separated from treatment-related differences. Independent validation is therefore required.