Photosynthetica covers wide range of photosynthesis research or research including photosynthetic parameters of both experimental and theoretical nature.

2,4-dinitrophenol (2,4-DNP) is a new kind of pollutant that is highly toxic and difficult to be biodegraded. In this study, the feasibility of using exogenous growth regulator salicylic acid (SA) to improve the purification ability of Salix matsudana (S. matsudana) seedlings to 2,4-DNP stress was investigated by a hydroponic simulation experiment. The main research results are as follows: (1) After adding exogenous SA, a high concentration of SA (1000 mg·L⁻¹) inhibited the photosynthetic process and the normal physiological process of the chlorophyll fluorescence system of S. matsudana seedlings to a certain extent. When adding a low concentration of SA (10 mg·L⁻¹) to treat S. matsudana seedlings, all exogenous treatment groups could alleviate the stress of 2,4-DNP on the photosynthetic system and chlorophyll fluorescence system of S. matsudana seedlings, and 10 mg·L⁻¹ SA (DNP + S1) was the best. (2) The addition of exogenous SA could alleviate the damage of 2,4-DNP to S. matsudana seedlings by enhancing the activity of its antioxidant enzymes to remove excess reactive oxygen species (ROS) in the body and reducing the level of membrane lipid peroxidation and the size of membrane damage. The treatment with 10 mg·L⁻¹ SA had the best effect. (3) Exogenous low concentration of SA (10 mg·L⁻¹) could alleviate the decline of biomass index of S. matsudana seedlings under 2,4-DNP stress, but a high concentration of SA (1000 mg·L⁻¹) could not alleviate the 2,4-DNP toxicity of S. matsudana seedlings leaves. Exogenous SA could effectively alleviate the growth damage caused by 2,4-DNP stress on S. matsudana seedlings and increase the tolerance threshold range of S. matsudana seedlings to 2,4-DNP (8.81–33.78 mg·L⁻¹). (4) Exogenous addition of SA could increase the removal percentage of 2,4-DNP in Salix matsudana seedlings. Among them, the removal percentage of Salix matsudana was the highest at 10 mg·L⁻¹ SA, which was 1.46 times (5 days) and 1.19 times (10 days) higher than that of the DNP treatment group, respectively. Overall, when SA reached 10 mg·L⁻¹, the photosynthetic productivity of S. matsudana was the highest, and S. matsudana had the best purification effect on 2,4-DNP in wastewater.

In this study, the effects of different concentrations of 2,4-dinitrophenol (2,4-DNP) stress on physiological parameters, as well as the uptake and removal of 2,4-DNP in Salix matsudana, were investigated using hydroponic simulation experiments to explore the potential of the use of Salix matsudana in the phytoremediation of wastewater polluted by 2,4-DNP. The results showed that P_N (net photosynthetic rate), T_r (transpiration rate), G_s (stomatal conductance), L_s (stomatal limitation value), F_v/F_m (maximal quantum yield of PSII photochemistry), and q_p (photochemical quenching coefficient) of Salix matsudana seedlings showed an overall decreasing trend, while C_i (intercellular CO₂ concentration) showed an increasing trend with the increase in 2,4-DNP concentration. The net photosynthetic rate and intercellular carbon dioxide concentration showed an opposite trend in the leaves with the increase in 2,4-DNP stress concentration, and the inhibition of net photosynthesis by 2,4-DNP on Salix matsudana seedlings was mainly based on non-stomatal factors. In the 15 d incubation experiment, the values of SOD (superoxide dismutase), POD (peroxidase), and CAT (catalase) indexes were higher at low concentrations of 2,4-DNP stress, and all three enzymes reached their maximum values at 10 mg L⁻¹ of 2,4-DNP and then decreased. Salix matsudana seedlings could tolerate 2,4-DNP stress well, which did not exceed 20 mg L⁻¹. The toxicity of 2,4-DNP solution was significantly reduced after purification by Salix matsudana seedlings. The removal rate of 2,4-DNP was higher than 80% in each treatment group by Salix matsudana purified after 15 days. When the concentration of 2,4-DNP reached 20 mg L⁻¹, the contents of MDA (malonicdialdehyde) were 55.62 mmol g⁻¹, and the values of REC (relative conductivity) and LD (leaf damage) were 63.51% and 59.93%, respectively. The structure and function of the cell membrane in leaves were seriously damaged. With the increase in 2,4-DNP concentration, the removal of 2,4-DNP by Salix matsudana seedlings showed a decreasing trend. When the 2,4-DNP concentration was 5 mg L⁻¹, the highest removal rate of 2,4-DNP by Salix matsudana seedlings was 95.98%, while when the 2,4-DNP concentration was 20 mg L⁻¹, the highest removal rate was 86.76%. It is noted that the suitable, recommended concentration for the phytoremediation of 2,4-DNP contamination by Salix matsudana seedlings is between 8.81 and 13.78 mg L⁻¹.

Physiological responses of Scirpus validus to nitrate stress were investigated. The experiment was conducted in an artificial greenhouse over a period of 35 days. The inhibitory effects of nitrate stress on S. validus growth were greater at concentrations higher than 10 mmol·L^-1. Greater than 10 mmol·L^-1 nitrate inhibited the growth of S. validus; specifically, the fresh weight, new stem height, Δroot length, surface area, and root average diameter and volume were reduced. The level of ammonium in the plants was constant, whereas total nitrogen and nitrate nitrogen levels were reduced. Under stress, nitrate damaged the photosynthetic system and strongly reduced the net photosynthetic rate, transpiration rate, quantum yield at LCP, LSP, and P_nmax. Furthermore, nitrate increased stomatal limitation and conductance and influenced spectral parameters, e.g., reduced both PRI and SDr/SDb. The inhibitory effect of nitrate was most pronounced at 20 mmol·L^-1, primarily due to penetration and non-stomatal limitation. This study identified the physiological responses of S. validus to nitrate stress. The observed changes in physiological indices for S. validus, including photosynthetic parameters and spectral indicators, suggest that nitrate can inhibit root growth, differentiation and photosynthesis in plants, leading to an overall reduction in growth.

Meta-cresol (m-cresol) is highly corrosive and toxic, and is widely present in industrial wastewater. As a pollutant, it adversely affects various aspects of human production and daily life. To evaluate the feasibility of using sunflowers to remediate m-cresol-contaminated wastewater, this study used Helianthus annuus L. as the test subject to analyze its tolerance and the wastewater purification efficiency under different m-cresol concentrations. The results showed that the net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), and light energy utilization efficiency (LUE) of Helianthus annuus L. exhibited an overall decreasing trend, while the intercellular CO₂ concentration (Cᵢ) initially increased and subsequently decreased with increasing m-cresol concentration. When m-cresol concentration reached or exceeded 60 mg·L⁻¹, the net photosynthetic rate and intercellular CO₂ concentration in the leaves showed opposite trends with further increases in m-cresol stress. The inhibition of net photosynthesis in sunflowers by m-cresol was mainly attributed to non-stomatal factors. The maximum photochemical efficiency (F_v/F_m), actual photochemical efficiency (ΦPSII), photochemical quenching coefficient (q^P), PSII excitation energy partition coefficient (α), and the fraction of absorbed light energy used for photochemistry (P) all decreased with increasing m-cresol concentration. In contrast, non-photochemical quenching (NPQ), the quantum yield of regulated energy dissipation [Y(NPQ)], and the fraction of energy dissipated as heat through the antenna (D) first increased and then decreased. Under low-concentration m-cresol stress, sunflowers protected their photosynthetic system by dissipating excess light energy as heat as a stress response. However, high concentrations of m-cresol caused irreversible damage to Photosystem II (PSII) in sunflowers. Under m-cresol stress, chlorophyll a exhibited strong stability with minimal degradation. As the m-cresol concentration increased from 30 to 180 mg·L⁻¹, the removal rate decreased from 84.91% to 11.84%. In conclusion, sunflowers show good remediation potential for wastewater contaminated with low concentrations of m-cresol and can be used for treating m-cresol wastewater with concentrations ≤ 51.9 mg·L⁻¹.

The leafhopper, Erythroneura sudra (Distant) is becoming a dominant insect pest, and usually can cause significant damage to fruit production in northern China. We studied the occurrence and density of E. sudra on three fruit tree species and its transcriptomic responses when it was fed on leaves of these tree species. A higher density and survival rate of E. sudra were recorded when it fed on leaves of peach (Amygdalus persica L.) (Rosales: Rosaceae) and cherry (Cerasus pseudocerasus Lindl) (Rosales: Rosaceae) than on apple (Malus domestica Mill) (Rosales: Rosaceae). Also, feeding on M. domestica induced the largest variation in transcriptomic profiles in E. sudra. In total, 166 genes were differentially expressed (89 upregulated and 77 downregulated) in E. sudra when it fed on M. domestica, compared to when it fed on the other two tree species. The upregulated genes were mainly related to ‘response to oxidative stress’, ‘stress-resistance’, and ‘xenobiotic metabolic process’. The downregulated genes were mainly related to ‘structural constituent of cuticle’, ‘biosynthetic process’, and ‘development regulation’. These results suggested that M. domestica significantly changed the expression of many genes and consequently caused lower occurrence and density of E. sudra. Such information could enhance our understanding of the leafhopper–host plant relationship. Additionally, it can contribute to the improvement of current control strategies for this pest.