Aluminum phytotoxicity in acidic environments: A comprehensive review of plant tolerance and adaptation strategies.

Aluminum (Al), a non-essential metal for plant growth, exerts significant phytotoxic effects, particularly on root growth. Anthropogenic activities would intensify Al's toxic effects by releasing Al3+ into the soil solution, especially in acidic soils with a pH lower than 5.5 and rich mineral content. The severity of Al-induced phytotoxicity varies based on factors such as Al concentration, ionic form, plant species, and growth stages. Al toxicity leads to inhibited root and shoot growth, reduced plant biomass, disrupted water uptake causing nutritional imbalance, and adverse alterations in physiological, biochemical, and molecular processes. These effects collectively lead to diminished plant yield and quality, along with reduced soil fertility. Plants employ various mechanisms to counter Al toxicity under stress conditions, including sequestering Al in vacuoles, exuding organic acids (OAs) like citrate, oxalate, and malate from root tip cells to form Al-complexes, activating antioxidative enzymes, and overexpressing Al-stress regulatory genes. Recent advancements focus on enhancing the exudation of OAs to prevent Al from entering the plant, and developing Al-tolerant varieties. Gene transporter families, such as ATP-Binding Cassette (ABC), Aluminum-activated Malate Transporter (ALMT), Natural resistance-associated macrophage protein (Nramp), Multidrug and Toxic compounds Extrusion (MATE), and aquaporin, play a crucial role in regulating Al toxicity. This comprehensive review examined recent progress in understanding the cytotoxic impact of Al on plants at the cellular and molecular levels. Diverse strategies developed by both plants and scientists to mitigate Al-induced phytotoxicity were discussed. Furthermore, the review explored recent genomic developments, identifying candidate genes responsible for OAs exudation, and delved into genome-mediated breeding initiatives, isolating transgenic and advanced breeding lines to cultivate Al-tolerant plants.

Biochar impacts on carbon dioxide, methane emission, and cadmium accumulation in rice from Cd-contaminated soils; A meta-analysis.

Climate change and cadmium (Cd) contamination pose severe threats to rice production and food security. Biochar (BC) has emerged as a promising soil amendment for mitigating these challenges. To investigate the BC effects on paddy soil upon GHG emissions, Cd bioavailability, and its accumulation, a meta-analysis of published data from 2000 to 2023 was performed. Data Manager 5.3 and GetData plot Digitizer software were used to obtain and process the data for selected parameters. Our results showed a significant increase of 18% in soil pH with sewage sludge BC application, while 9% increase in soil organic carbon (SOC) using bamboo chips BC. There was a significant reduction in soil bulk density (8%), but no significant effects were observed for soil porosity, except for wheat straw BC which reduced the soil porosity by 6%. Sewage sludge and bamboo chips BC significantly reduced carbon dioxide (CO2) by 7-8% while municipal biowaste reduced methane (CH4) emissions by 2%. In the case of heavy metals, sunflower seedshells-derived materials and rice husk BC significantly reduced the bioavailable Cd in paddy soils by 24% and 12%, respectively. Cd uptake by rice roots was lowered considerably by the addition of kitchen waste (22%), peanut hulls (21%), and corn cob (15%) based BC. Similarly, cotton sticks, kitchen waste, peanut hulls, and rice husk BC restricted Cd translocation from rice roots to shoots by 22%, 27%, 20%, and 19%, respectively, while sawdust and rice husk-based BC were effective for reducing Cd accumulation in rice grains by 25% and 13%. Regarding rice yield, cotton sticks-based BC significantly increased the yield by 37% in Cd-contaminated paddy soil. The meta-analysis demonstrated that BC is an effective and multi-pronged strategy for sustainable and resilient rice cultivation by lowering greenhouse gas emissions and Cd accumulation while improving yields under the increasing threat of climate change.

Assessment of Cd availability in rice cultivation (Oryza sativa): Effects of amendments and the spatiotemporal chemical changes in the rhizosphere and bulk soil.

Immobilization is widely used to decrease the availability of heavy metals, such as Cd and Pb, in contaminated soils. However, the spatial and temporal changes in the immobilization of soil by amendments combined with planting effects have not been studied well. In this study, unplanted and planted (with rice plants) pot experiments were used to assess the spatial and temporal changes in water-soluble Cd, Fe, Mn, and Ca. Soil properties, such as pH, redox potential (Eh), and dissolved organic carbon (DOC), were continuously recorded in both the rhizosphere and bulk soil using non-invasive rhizon samplers and a microelectrode system (Unisense). In unplanted soil, pH and Eh varied with time, but showed little radial variation from the rhizosphere to the bulk soil. The addition of hydrated lime (Ca(OH)2) sharply increased the pH, DOC, and Ca content; decreased the Eh, Fe content, and Mn content; and gradually decreased the water-soluble Cd content in the soil profile. Hydroxyapatite showed no obvious effects in reducing Cd concentrations in different soil zones. The water-soluble Fe, Mn, Ca, and DOC content did not differ significantly between soil zones over time and a non-significant correlation with water-soluble Cd was shown. In planted soil, the pH increased while the Eh value decreased with an increase in the distance from the roots, regardless of the soil amendments used during the rice growth period. Hydroxyapatite gradually increased but hydrated lime decreased the water-soluble Cd in the rhizosphere. The concentration of water-soluble Cd in the rhizosphere was higher than that of the other soil zones during rice growth. These changes lead to more Cd uptake by roots and induced Cd accumulation in rice tissues. In addition, Cd and Fe concentration in iron plaque showed a significant positive correlation with Cd in rice, indicating that iron plaque promotes the uptake and accumulation of Cd in rice with soil amendments. Compared with the control, hydroxyapatite did not significantly affect the Cd content, while Ca(OH)2 significantly reduced the Cd content in iron plaque and rice tissues. In conclusion, the application of hydrated lime can significantly reduce the risk of Cd accumulation by rice in Cd-contaminated soils under flooding conditions.

Tungsten (W) bioavailability in paddy rice soils and its accumulation in rice (Oryza sativa).

The aim of this study was to investigate the accumulation characteristics of tungsten (W) by different indica rice cultivars from the soil and to assess the potential risks to human health via dietary intake of W in rice consumption. A total of 153 rice (ear) samples of 15 cultivars and the corresponding surface soil samples were collected from 7 cities in Fujian Province of southeastern China. The available soil W were extracted using H2C2O4·2H2O-(NH4)2C2O4·H2O at pH 3.3). Results showed that the total soil W ranged from 2.03 mg kg-1 to 15.34 mg kg-1 and available soil W ranged from 0.03 mg kg-1 to 1.61 mg kg-1. The W concentration in brown rice varied from 7 µg kg-1 to 283 µg kg-1 and was significantly correlated with the available soil W. The highest mean TFavail (transfer factor based on available soil W) was 0.91 for Te-you 627 (hybrid, indica rice), whereas the lowest was 0.08 for Yi-you 673 (hybrid, indica rice). The TFavail decreased with the increase in available soil W, clay content, and cation exchange capacity. The consumption of the brown rice produced from the investigated areas in some cultivars by the present study may cause risks to human health.

Spatiotemporal investigation of near-surface CH4 and factors influencing CH4 over South, East, and Southeast Asia.

Methane (CH4) is the second most abundant greenhouse gas after CO2, which plays the most important role in global and regional climate change. To explore the long-term spatiotemporal variations of near-surface CH4, datasets were extracted from Greenhouse gases Observing SATellite (GOSAT), and the Copernicus Atmospheric Monitoring Service (CAMS) reanalyzed datasets from June 2009 to September 2020 over South, East, and Southeast Asia. The accuracy of near-surface CH4 from GOSAT and CAMS was verified against surface observatory stations available in the study region to confirm both dataset applicability and results showed significant correlations. Temporal plots revealed continuous inflation in the near-surface CH4 with a significant seasonal and monthly variation in the study region. To explore the factors affecting near-surface CH4 distribution, near-surface CH4 relationship with anthropogenic emission, NDVI data, wind speed, temperature, precipitation, soil moisture, and relative humidity were investigated. The results showed a significant contribution of anthropogenic emissions with near-surface CH4. Regression and correlation analysis showed a significant positive correlation between NDVI data and near-surface CH4 from GOSAT and CAMS, while a significant negative correlation was found between wind and near-surface CH4. In the case of temperature, soil moisture, and near-surface CH4 from GOSAT and CAMS over high CH4 regions of the study area showed a significant positive correlation. However significant negative correlations were found between precipitation and relative humidity with GOSAT and CAMS datasets over high CH4 regions in South, East, and Southeast Asia. Moreover, these climatic factors showed no significant correlation within the low near-surface CH4 areas in our study region. Our study results showed that anthropogenic emissions, NDVI data, wind speed, temperature, precipitation, soil moisture, and humidity could significantly affect the near-surface CH4 over South, East, and Southeast Asia.

Divergent consequences of different biochar amendments on carbon dioxide (CO2) and nitrous oxide (N2O) emissions from the red soil.

Climate change due to greenhouse gas (GHG) emissions is one of the global environmental matters of the 21st century. Biochar (BC) amendments have been proposed as a potential solution for improving soil quality and to mitigate GHGs emissions. Therefore, we evaluated the influence of different BCs on soil CO2 and N2O emissions in an outdoor pot experiment. The soil was mixed with three different types of BCs; bamboo, hardwood, and rice straw BCs as BB, BH, and BR, respectively, and control as B0 with four levels (0, 5, 20, and 80 g kg-1 of soil). Gas samples were collected on a bi-monthly basis for six months. A polyvinyl chloride (PVC) static chamber was placed on each replicate to collect the gas samples at 15, 30, 45, and 60 min, respectively. Compared to B0, the lowest cumulative N2O emissions were observed in BH80 (11%) followed by BH20, BH5, and BR80. However, for cumulative CO2 emissions, B0 and BC treatments showed no significant differences except for BB80 (>11%) and BB5 (<2%). BC type and level both had a significant (P < 0.001) impact on the cumulative N2O emissions with a significant interaction (P < 0.001). However, cumulative CO2 emissions were unaffected by BC type but BC level showed a significant influence on cumulative CO2 emissions (P < 0.05) and there was a significant (P < 0.001) interaction between the BC type and level on cumulative CO2 emissions. Overall, higher doses of BR and BB showed a pronounced effect on soil pH over BH. The soil pH and moisture showed a negative correlation with N2O emissions whereas soil temperature showed a positive correlation with the cumulative fluxes of N2O. Our results demonstrate that BC incorporation to soil may help to mitigate GHGs emissions but its influence may vary with BC type and level under different conditions and soil type.

Chlorine weaken the immobilization of Cd in soil-rice systems by biochar.

Rice (Oryza sativa L.) was cultivated in a Cd-contaminated soils with rice straw biochar (BC) and water-washed rice straw biochar (W-BC) were applied to investigate the underlying mechanisms and possible reasons for biochar's weakening effects on the immobilization of Cd in soil-rice system. The results indicated that W-BC reduced the Cd concentration in pore water as well as in the roots and shoots of rice by 26.24%, 53.23% and 62.47% respectively. On the contrary, there was an increase in Cd contents by 50.27% in pore water, 2.32% in the roots, and 12.80% in the shoots of rice under BC treatment. Furthermore, Cd content in rice shoot was significantly and positively correlated with Cl- addition to the soil (P < 0.01). This phenomenon could be attributed to several combined effects: (1) the increase of Cl- in the soil decreased the soil pH, enhanced the dissolved organic carbon in soil pore water and increased the complexes of Cd2+ and Cl-, resulting in the release of Cd from solid phase into solution phase, (2) the chloride in the soil increased the uptake of CdCl+ instead of Cd2+ by the roots, thereby causing an increase of Cd in rice tissues. These results demonstrate for the first time that biochar with high chloride content could weaken its immobilization effects on soil Cd and even enhance Cd uptake by rice.

Soil liming effects on CH4, N2O emission and Cd, Pb accumulation in upland and paddy rice.

Keeping in view the expanding environmental pollution and irrigation water deficit, a pot experiment was performed for the upland (Huyou2, Hanyou737) and paddy rice cultivars (Taigeng8; Yixiang2292), to study soil liming effects on methane (CH4) and nitrous oxide (N2O) emission, bioavailability and accumulation of Cd, Pb in upland and paddy rice. Upland rice reduced 90% of soil CH4 emission as compared to paddy conditions. Soil CH4 emission decreased by 45% and 39% with dolomite, and it reduced by 35% and 33% with lime treatment both in upland and paddy conditions, respectively. Soil N2O emission decreased by 44% and 52% with dolomite, and with the lime application, it was reduced by 37% and 44% for both upland and paddy conditions respectively. Reduction in soil DTPA-extractable Cd was between 37-53% and 43-80% with dolomite and 16-37% and 24-72% Cd decreased with lime application in upland and paddy conditions respectively. Soil DTPA-extractable Pb reduced by 27-44% and 25-53% with dolomite and 16-40% and 11-42% with soil-applied lime in upland and paddy conditions, respectively. Cd accumulation in rice grain was decreased by 47-88% and 62-79% with dolomite and 31-86% and 45-52% reduction by lime application in upland and paddy rice respectively. Rice grain Pb reduced by 58-91% and 66-78% with dolomite application and 32-71% and 44-71% with lime in upland and paddy rice, respectively. Our results showed that soil liming significantly reduced soil N2O and CH4 emission and Cd, Pb accumulation in rice grain, but dolomite was more effective as compared to lime. Altogether, results of this study suggest that upland rice can be cultivated in CdPb polluted soils with least soil CH4 emission. Cd and Pb toxicity, accumulation, and N2O emission in upland rice can be minimized by soil liming of 3 g kg-1 and optimizing the nutrients composition of the soil.

Uptake, translocation, and accumulation of Cd and its interaction with mineral nutrients (Fe, Zn, Ni, Ca, Mg) in upland rice.

An analysis of the Cd and mineral nutrients accumulation of upland rice was performed in an experimental field with hard-ridged plots containing three soils with exogenous Cd addition at rates of 0, 0.25, 0.5, 1, 2, 4, 8, 16 mg kg-1 five years prior to commence this experiment. Aims of this investigation were to study uptake, translocation, and accumulation of Cd by an upland rice (Huyou2) and effects of Cd addition on the accumulation of Fe, Zn, Ni, Ca, and Mg. The results demonstrate the mean Cd content in the plant parts, from highest to lowest, were as follows: root, stem, leaf, and brown rice. The Cd content in the brown rice of the upland rice was below the limit of Cd in rice (0.2 mg kg-1) from China (GB 2762-2017) when the amount of Cd added was ≤ 1 mg kg-1. This observation can be attributed to lower TFsoil-grain of Cd in upland rice. Significant differences were observed between Cd concentrations present in brown rice from the three soils which can be mainly attributed to the differences in DTPA-extractable soil Cd because of different soil pH. Addition of high concentrations of Cd to soil was found to reduce Fe, Zn, Mg, and increased Ni uptake by the roots and their accumulation in brown rice. Altogether, results of this study suggest that it may be possible to cultivate upland rice in slightly Cd-polluted soils and Cd toxicity and accumulation in upland rice can be minimized by optimizing the macro and micronutrient composition of the soil.