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Polychlorinated biphenyls (PCBs) are a common category of persistent man-made organic pollutants that are widespread in the ambient environment. Although Lemna minor L. is an extensively applied plant for aquatic remediation in ecotoxicology research worldwide, little is known regarding its responses to the potentially toxic effects of PCBs. For this study, a 14-day dissolved exposure was conducted to explore the effects of 2,4,4′- trichlorobiphenyl (PCB-28) on the growth, photosynthesis characteristics and antioxidant defense system of L. minor plants. We found that 100 and 200 μg/L of PCB-28 decreased the fresh weight, chlorophyll and protein content, and activities of superoxide dismutase, peroxidase, glutathione S-transferase, and nitroreductase, whereas plasma membrane permeability, and the malondialdehyde and reactive oxygen species concentrations were increased. However, it was observed that 5 and 20 μg/L of PCB-28 had no significant effects on these physiological indices. The ultra-structure of chloroplast demonstrated that 100 and 200 μg/L PCB-28 severely damaged the chloroplast structures. Moreover, correlation analysis revealed that the content of reactive oxygen species had negative correlations with the fresh weight, chlorophyll and protein content, as well as the activities of superoxide dismutase, peroxidase, glutathione S-transferase, and nitroreductase, but had positive correlations with the malondialdehyde content and plasma membrane permeability. This work provides valuable data toward elucidating the physiology and biochemistry of PCBs induced phytotoxicity. • PCB-28 at 100 and 200 μg/L has toxicity on L. minor. • 100 and 200 μg/L PCB-28 damage cellular structure of chloroplasts. • The toxic mechanism lies in the overproduction of ROS. [ABSTRACT FROM AUTHOR]

• Drought increased enzyme activity C:N and fungi:bacteria ratios. • Microbial C and N use efficiencies increased under drought. • The threshold elemental ratio values were larger than the soil C:N ratio. Drought has been observed to decrease the accumulation of carbon (C) and nitrogen (N) in forest ecosystems. The microbial C use efficiency (CUE) and N use efficiency (NUE) are critical to elemental cycling in terrestrial ecosystems, which can be calculated by the C:N stoichiometry of soils, microbial biomass, and extracellular enzyme activities. However, little is known about how drought affects microbial CUE and NUE. We extracted soil samples at different depths (0–15 cm, 15–30 cm, and 30–45 cm) in forest stands that were subjected to 30% and 50% throughfall reduction manipulation experiments, in contrast to those obtained from stands that were left undisturbed from July 2019 to April 2020 in a poplar plantation of Eastern China. Under drought conditions, we found that the soil moisture, soil C:N ratio, and C- and N-acquiring enzyme activities decreased; however, the soil pH, microbial biomass C:N ratio, ecoenzymatic activity C:N ratio, and fungi:bacteria ratio increased. Microbial CUE and NUE, which were calculated based on these C:N stoichiometric ratios, also increased. These responses were similar at different soil depths across sampling dates. Our structural equation models indicated that drought-induced increases in CUE and NUE were driven by changes in the soil moisture, fungi:bacteria ratio, and ecoenzymatic activity C:N ratio. Our results suggested that decreases in soil moisture and increases in the ecoenzymatic activity C:N and fungi:bacteria ratios could stimulate microbial CUE and NUE. [ABSTRACT FROM AUTHOR]

• Warming effects increased with warming duration and magnitudes. • Warming effects on C and N concentrations remain globally invariant. • [C] and [N] responded inconsistently to warming between above- and belowground. • Warming effects on [C] and [N] are linked to soil moisture and soil pH. Global warming has significantly affected the terrestrial C and N cycling processes. Whereas, it is unclear how global warming impacts the C and N concentrations in the above- and belowground ecosystems. We performed a meta-analysis with the results presented in 136 papers and 1886 observations. The data reveals that global warming increased C concentrations in leaf, shoot, and microbial biomass and N concentrations in the shoot. The C:N ratios of microbial biomass also increased under conditions of warming. However, the soil C concentration and soil C:N ratios decreased. Furthermore, these responses are more evident with longer warming duration and elevated warming magnitudes. The warming effects on C and N concentrations and C:N ratios never changed with warming methods, ecosystem types, or background climates. Also, in response to warming, soil moisture was negatively correlated with leaf C concentration as well as C:N ratio in microbial biomass. Soil pH response to warming was in a negative correlation with those of soil C concentration, soil C:N ratio, and microbial biomass C concentration. Our analysis has identified some key ecosystem processes that can be potentially implemented into the ecosystem models for predicting how warming affects future terrestrial C and N dynamics. [ABSTRACT FROM AUTHOR]

• C:N in plants-soils-microorganisms increased under elevated CO 2. • CO 2 effects increased with CO 2 concentrations and duration. • CO 2 effects were similar across ecosystems and background climates. The stoichiometry of carbon to nitrogen ratio (C:N) plays an important role in biogeochemical cycling in terrestrial ecosystems. As time goes by, the increase in atmospheric CO 2 levels is expected; however, the impact of elevated atmospheric CO 2 on the C:N stoichiometry of soils, plants, and microorganisms remains largely unclear. The results of the meta-analysis that included 174 studies with 1009 observations demonstrated that above- and below-ground C concentrations and C:N ratio increased under elevated CO 2 regimes, whereas N concentrations decreased. Importantly, these responses were more pronounced with rising CO 2 concentrations and longer experimental durations. Moreover, the responses of C, N, and C:N to elevated CO 2 were similar across croplands, forests, and grasslands ecosystems with varying climates. Our results revealed that the C:N stoichiometry of soils, plants, and microorganisms responded consistently to the rising global CO 2 levels, which indicated that terrestrial ecosystems might have the capacity to mitigate increased atmospheric CO 2 concentrations by increasing C sequestration in plants, soils, and microorganisms in future. [ABSTRACT FROM AUTHOR]

Biologists have extensively investigated the toxicity of polybrominated diphenyl ethers (PBDEs) on plants in ecosystems, where experiments revealed that PBDEs can promote, inhibit, or have no significant effects on the physiological and biochemical functionality of plants. These studies have stimulated many theoretical works that aimed to elucidate the differences in the toxicity of PBDEs on various plants. However, there has been no quantitative attempt to reconcile theory with the results of empirical experiments. To close this gap between theory and experiments, we conducted a hierarchical meta-analysis to examine the toxicity of PBDEs on plants and confirmed potential sources of variation across numerous studies. Through the analysis of 1299 observations garnered from 41 studies, we revealed the significant toxicity of PBDEs on plants. This result was verified to be robust and showed no signs of bias. Our study affirmed that functional indexes can contribute to variations that lead to the toxicity of PBDEs on various plants. Furthermore, we found that lower congeners PBDEs were more toxic to plants than higher congeners PBDEs, and higher plants were more resistant to PBDEs induced phytotoxicity than lower plants. For interactive effects, only specific PBDEs concentrations had significant effects on glutathione S-transferase activities, and experimental durations had no significant impacts on any functional indexes. These results reconciled empirical studies and assisted us with elucidating the ecotoxicology of PBDEs induced phytotoxicity. • PBDEs treatments initiated significant toxicity to plants. • Lower congener PBDEs were more toxic to plants than higher congener PBDEs. • Higher plants were more resistant to PBDEs induced phytotoxicity than lower plants. • GST activities showed a positive trend with increasing PBDEs concentration. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs), represent one of the new types of persistent organic pollutants (POPs) that are currently found in ambient aquatic ecosystems. Lemna minor L. is a floating freshwater plant, which is widely employed for phytotoxicity studies of xenobiotic substances. For this study, we investigated the growth, physiological functions, and antioxidant capacities of L. minor , which were exposed to 0–20 mg L−1 decabromodiphenyl ether (BDE-209) for 14 days. A logistic model was suitable for describing the growth of L. minor when the BDE-209 concentration was in the range of from 0 to 15 mg L−1. When exposed to 5 and 10 mg L−1 BDE-209, the growth of L. minor was significantly increased, where the intrinsic rate (r) and the maximum capacity of the environment (K) of L. minor were significantly higher than those of the control. In this case, the chlorophyll content and soluble proteins were also markedly increased. Moreover, the photosynthetic function (Fv/Fm, PI) was enhanced. However, for 15 mg L−1 BDE-29 treated group, the growth of L. minor was significantly inhibited, with decreases in chlorophyll and the soluble protein content, until the L. minor yellowed and expired under a concentration of 20 mg L−1. Photosynthetic functions were also negatively correlated with increasing increments of BDE-209 (15 and 20 mg L−1). The malondialdehyde (MDA), superoxide anion radical (O 2 ̄ · ) content, and permeability of the plasma membranes increased with higher BDE-209 concentrations (0–20 mg L−1). The superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities of L. minor increased when the BDE-209 concentration ranged from 0 to 10 mg L−1; however, the activities of SOD and POD were decreased. Only the CAT activity remained higher in contrast to the control group under 15–20 mg L−1 BDE-209. These results demonstrated that 15 mg L−1 BDE-209 imparted high toxicity to L. minor , which was a consequence of the overproduction of reactive oxygen species (ROS), which conveyed oxidative damage to plant cells. This study provided a theoretical understanding of BDE-209 induced toxicity as relates to the physiology and biochemistry of higher hydrophytes. • BDE-209 at 5–10 mg L-1 has a "hormesis effect" on L. minor. • 15 mg L-1 BDE-209 has high toxicity to L. minor. • The toxic mechanism lies in the overproduction of reactive oxygen species (ROS). [ABSTRACT FROM AUTHOR]

Cytochrome P450 monooxygenases (CYP450s) play crucial roles in the regulation of plant growth and response to abiotic stress. However, their functions in woody trees are still largely unknown. Previously, we reported that expression of the rice cytochrome P450 monooxygenase gene OsCYP714D1 increased gibberellic acid (GA) accumulation and shoot growth in transgenic poplar. In this work, we demonstrate that expression of OsCYP714D1 improved the salt tolerance of transgenic poplar plants. Compared to wild type, plant height and K+ content were significantly higher, whereas plant growth inhibition and Na+ content were significantly lower, in transgenic plants grown under high salt stress condition. Transcriptomic analyses revealed that OsCYP714D1 expression up-regulated the expressions of GA biosynthesis, signaling and stress responsive genes in transgenic plants under both normal and high salt stress conditions. Further gene ontology (GO) analyses indicated that genes involved in plant hormone and ion metabolic activities were significantly enriched in transgenic plants. Our findings imply that OsCYP714D1 participated in the regulation of both shoot growth and salt resistance through regulating gibberellin and ion homeostasis in transgenic poplar, and it can be used as a candidate gene for the engineering of new tree varieties with improved biomass production and salt stress resistance. • Constitutive expression of OsCYP714D1 promoted growth and salt tolerance in transgenic poplar. • Expression of gibberellin synthesis and metabolism genes was affected in OsCYP714D1 transgenic poplar. • OsCYP714D1 transgenic poplar showed altered ion homeostasis and related gene expression. [ABSTRACT FROM AUTHOR]

• Fungi:bacteria ratio increased with drought stress. • Labile organic C and N contents influenced microbial communities greatly. • These responses kept consistent across different soil depths. Soil microbial communities are key to ecosystem processes in terrestrial ecosystems. Although droughts are projected to be more frequent with the intensifying effects of climate change, our understanding of the responses of soil microbial communities to drought remains incomplete. For this study, we employed 30% and 50% throughfall reduction manipulation experiments to simulate different drought intensities, and collected soil samples at three depths (0–15, 15–30 and 30–45 cm) for each season in a poplar plantation. We analyzed the physical and chemical properties of the soil samples (e.g., soil moisture, pH, total C, total N, and labile organic C and N contents represented by extractable organic C and N contents, microbial biomass C and N contents) and microbial communities, via phospholipid fatty acid (PLFA) and high-throughput sequencing methods, from November 2018 to August 2019. We found that drought significantly decreased soil moisture, the content of soil labile organic C and N, and total microbial biomass; however, it increased soil pH and microbial biomass C:N across all soil depths. Furthermore, fungi:bacteria and Gram+:Gram- bacterial ratios increased with drought treatments across all three soil depths. Drought reduced the relative abundance of Proteobacteria, but increased the relative abundance of Acidobacteria across the three soil depths. In contrast, drought had no significant influence on the relative abundance of fungal phyla. The changes in soil properties and microbial communities increased with drought intensity. Regression analysis demonstrated that changes in the total PLFA, fungi:bacteria and Gram+:Gram- bacterial ratios were significantly correlated with soil moisture, pH, and the soil labile organic C and N content. Redundancy analysis revealed that soil pH, extractable organic C and extractable organic N accounted for the majority of the variabilities in the bacterial communities. The patterns of fungal community structures in the drought treatment plots were not distinct from the control groups across three soil depths. Our results suggested that droughts induce significant increases in fungi:bacteria and Gram+:Gram- bacterial ratios in forest soils, primarily through changes in soil pH, moisture, and soil labile organic C and N content. [ABSTRACT FROM AUTHOR]