Acid rain reduces plant-photosynthesized carbon sequestration and soil microbial network complexity

Simulated acid rain (SAR) induced alterations in plant morpho-physiology, leaf ultrastructure, cell viability, and yield - A case study on Mentha arvensis L. (Wild mint)

Acid rain (AR), a secondary pollutant, a product of sulfur and nitrogen oxides fusion with the atmosphere's water vapor, comes on earth in the form of rain, poses a significant environmental threat, and affects soil characteristics and plant morphology, ultrastructure, physiology, and yield. However, its effects on aromatic and medicinal plants remain insufficiently studied. Due to their low side effects and high efficacy, the use of herbal plants for disease remedy preparation is found globally and their consumption increases year after year. Mentha arvensis is such an aromatic crop, having great economic importance due to the essential oil present in its leaf. This research examines the influence of simulated acid rain (SAR) at varying pH levels (6.0, 5.0, 4.0, and 3.0) on morphology, growth, physiology, and yield parameters in M. arvensis. Results revealed that different concentrations of SAR exposure significantly (p ≤ 0.05) reduced growth and yield parameters, photosynthetic pigments and protein content, essential mineral composition, and phytochemical levels. Conversely, antioxidants activity such as catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), ascorbate peroxidase (APX), lipid peroxidation marker malondialdehyde (MDA), osmo-protectant proline content, hydrogen peroxide (H2O2) content, superoxide ions content (O2•-), and electrolyte leakage percent (EL) level increased significantly (p ≤ 0.05) as acidity intensified, particularly at pH 3.0. At pH 3.0, there was a notable reduction (p ≤ 0.05) in shoot length (55.63%), root length (55.42%), fresh weight (59.81% for shoots, 52.32% for roots), dry weight (62.88% for shoots, 55.56% for roots), number of leaves (56.13%), leaf area (60.53%), nitrate reductase (NR) activity (58.48%) and chlorophyll content (43.58% for chlorophyll 'a', 57.07% for chlorophyll 'b'). Phytochemicals such as menthol (12.08%), menthone Title page (40.07%), and menthyl acetate (33.63%) were significantly reduced while antioxidants activity such as CAT (144.71%), POX (260.37%), SOD (255.15%), APX (213.51%), MDA content (193.97%), proline content (607.18%), H2O2 content (163.69%), O2•- content (185.82%), EL percentage (57.23%) significantly (p ≤ 0.05) increased. The highest acidity level (pH 3.0) resulted in the most significant reduction in growth, yield, and the production of economically important phytochemical constituents, highlighting the harmful effects of simulated acid rain on the growth, productivity, biochemical characteristics, and commercial value of M. arvensis.

Assessing the interactive effects of microplastics and acid rain on cadmium toxicity in rice seedlings: Insights from physiological and transcriptomic analyses

In heavy metal-contaminated areas, the simultaneous occurrence of increasing microplastic pollution and persistent acid rain poses a serious threat to food security. However, the mechanisms of combined exposure to microplastics (MP) and acid rain (AR) on the toxicity of cadmium (Cd) in rice seedlings remain unclear. Our study investigated the combined effects of exposure to polyvinyl chloride microplastics and AR (pH 4.0) on the toxicity of Cd (0.3, 3, and 10 mg/L) in rice seedlings. The results showed that at low Cd concentrations, the combined exposure had no significant effect, but at high Cd concentrations, it alleviated the effects of Cd stress. The combined application of MP and AR alleviated the inhibitory effects of Cd on seedling growth and chlorophyll content. Under high Cd concentrations (10 mg/L), the simultaneous addition of MP and AR significantly reduced the production of reactive oxygen species (ROS), the content of malondialdehyde (MDA), and the activity of the superoxide dismutase (SOD). Compared with AR or MP alone, the combination of MP and AR reduced root cell damage and Cd accumulation in rice seedlings. Transcriptomic analysis confirmed that under high Cd concentrations, the combination of MP and AR altered the expression levels of genes related to Cd transport, uptake, MAPK kinase, GSTs, MTs, and transcription factors, producing a synergistic effect on oxidative stress and glutathione metabolism. These results indicate that co-exposure to MP and AR affected the toxicity of Cd in rice seedlings and alleviated Cd toxicity under high Cd concentrations to some extent. These findings provide a theoretical basis for evaluating the toxicological effects of microplastic and acid rain pollution on crop growth in areas contaminated with heavy metals, and are important for safe agricultural production and ecological security.

Diverse factors influence the amounts of carbon input to soils via rhizodeposition in plants: A review

Rhizodeposition encompasses the intricate processes through which plants generate organic compounds via photosynthesis, store these compounds within aboveground biomass and roots through top-down transport, and subsequently release this organic matter into the soil. Rhizodeposition represents one of the carbon (C) cycle in soils that can achieve long-term organic C sequestration. This function holds significant implications for mitigating the climate change that partly stems from the greenhouse effect associated with increased atmospheric carbon dioxide levels. Therefore, it is essential to further understand how the process of rhizodeposition allocates the photosynthetic C that plants create via photosynthesis. While many studies have explored the basic principles of rhizodeposition, along with the associated impact on soil C storage, there is a palpable absence of comprehensive reviews that summarize the various factors influencing this process. This paper compiles and analyzes the literature on plant rhizodeposition to describe how rhizodeposition influences soil C storage. Moreover, the review summarizes the impacts of soil physicochemical, microbial, and environmental characteristics on plant rhizodeposition and priming effects, and concludes with recommendations for future research.

Redox potential model for guiding moderate oxidation of polycyclic aromatic hydrocarbons in soils

In-situ chemical oxidation is an important approach to remediate soils contaminated with persistent organic pollutants, e.g., polycyclic aromatic hydrocarbons (PAHs). However, massive oxidants are added into soils without an explicit model for predicting the redox potential (Eh) during soil remediation, and overdosed oxidants would pose secondary damage by disturbing soil organic matter and acidity. Here, a soil redox potential (Eh) model was first established to quantify the relationship among oxidation parameters, crucial soil properties, and pollutant elimination. The impacts of oxidant types and doses, soil pH, and soil organic carbon contents on soil Eh were systematically clarified in four commonly used oxidation systems (i.e., KMnO4, H2O2, fenton, and persulfate). The relative error of preliminary Eh model was increased from 48-62% to 4-16% after being modified with the soil texture and dissolved organic carbon, and this high accuracy was verified by 12 actual PAHs contaminated soils. Combining the discovered critical oxidation potential (COP) of PAHs, the moderate oxidation process could be regulated by the guidance of the soil Eh model in different soil conditions. Moreover, the product analysis revealed that the hydroxylation of PAHs occurred most frequently when the soil Eh reached their COP, providing a foundation for further microorganism remediation. These results provide a feasible strategy for selecting oxidants and controlling their doses toward moderate oxidation of contaminated soils, which will reduce the consumption of soil organic matter and protect the main structure and function of soil for future utilization. ENVIRONMENTAL IMPLICATIONS: This study provides a novel insight into the moderate chemical oxidation by the Eh model and largely reduces the secondary risks of excessive oxidation and oxidant residual in ISCO. The moderate oxidation of PAHs could be a first step to decrease their toxicity and increase their bioaccessibility, favoring the microbial degradation of PAHs. Controlling the soil Eh with the established model here could be a promising approach to couple moderate oxidation of organic contaminants with microbial degradation. Such an effective and green soil remediation will largely preserve the soil's functional structure and favor the subsequent utilization of remediated soil.

Acid rain reduced soil carbon emissions and increased the temperature sensitivity of soil respiration: A comprehensive meta-analysis

Soil respiration the second-largest carbon flux in terrestrial ecosystems, has been extensively studied across a wide range of biomes. Surprisingly, no consensus exist on how acid rain (AR) impacts the spatiotemporal pattern of soil respiration. Therefore, we conducted a meta-analysis using 318 soil respiration and 263 soil respiration temperature sensitivity (Q10) data points obtained from 48 studies to assess the impact of AR on soil respiration components and their Q10. The results showed that AR reduced soil total respiration (Rt) and soil autotrophic respiration (Ra) by 7.41 % and 20.75 %, respectively. As the H+ input increased, the response rates of Ra to AR (RR-Ra) and soil heterotrophic respiration (Rh) to AR (RR-Rh) decreased and increased, respectively. With increased AR duration, the RR-Ra increased, whereas the RR-Rh did not change. AR increased the Q10 of Rt (Rt-Q10) and Rh (Rh-Q10) by 1.92 % and 9.47 %, respectively, and decreased the Q10 of Ra (Ra-Q10) by 2.77 %. Increased mean annual temperature, mean annual precipitation, and initial soil organic carbon increased the response rate of Ra-Q10 to AR (RR-Ra-Q10) and decreased the response rate of Rh-Q10 to AR (RR-Rh-Q10). However, as the AR frequency and initial soil pH increased, both RR-Ra-Q10 and RR-Rh-Q10 also increased. In summary, AR decreased Rt but increased Q10, likely due to soil acidification (soil pH decreased by 7.84 %), reducing plant root biomass (decreased by 5.67 %) and soil microbial biomass (decreased by 5.67 %), changing microbial communities (increased fungi to bacteria ratio of 15.91 %), and regulated by climate, vegetation, soil and AR regimes. To the best of our knowledge, this is the first study to reveal the large-scale, varied response patterns of soil respiration components and their Q10 to AR. It highlights the importance of applying the reductionism theory in soil respiration research to enhance our understanding of soil carbon cycling processes with in the context of global climate change.

Ultrasound-assisted preparation of PdCo bimetallic nanoparticles loaded on beta zeolite for efficient catalytic hydrogen production from dodecahydro-N-ethylcarbazole

Research and development of high-performance catalysts is a key technology to realize hydrogen energy storage and transportation based on liquid organic hydrogen carriers. Co/beta was prepared using beta zeolite as a carrier via an electrostatic adsorption (ESA)-chemical reduction method, and it was used as the template and reducing agent to prepare bimetallic catalysts via an ultrasonic assisted galvanic replacement process (UGR). The fabricated PdCo/beta were characterized by TEM, XPS, FT-IR, XRD, H2-TPR, and H2-TPD. It was shown that the ultrafine PdCo nanoparticles (NPs) are evenly distributed on the surface of the beta zeolite. There is electron transfer between metal NPs and strong-metal-support-interaction (SMSI), which results in highly efficient catalytic dodecahydro-N-ethylcarbazole (12H-NEC) dehydrogenation performance of PdCo bimetallic catalysts. The dehydrogenation efficiency reached 100 % in 4 h at 180 °C and 95.3 % in 6 h at 160 °C. The TOF of 146.22 min-1 is 7 times that of Pd/beta. The apparent activation energy of the reaction is 66.6 kJ/mol, which is much lower than that of Pd/beta. Under the action of ultrasonic waves, the galvanic replacement reaction is accelerated, and the intermetal and metal-carrier interactions are enhanced, which improves the catalytic reaction performance.