Abstract This article aims at finding efficient hyperspectral indices for the estimation of forest sun leaf chlorophyll content (CHL, µg cm leaf − 2 ), sun leaf mass per area (LMA, g dry matter m leaf − 2 ), canopy leaf area index (LAI, m 2 leaf m soil − 2 ) and leaf canopy biomass (B leaf , g dry matter m soil − 2 ). These parameters are useful inputs for forest ecosystem simulations at landscape scale. The method is based on the determination of the best vegetation indices (index form and wavelengths) using the radiative transfer model PROSAIL (formed by the newly-calibrated leaf reflectance model PROSPECT coupled with the multi-layer version of the canopy radiative transfer model SAIL). The results are tested on experimental measurements at both leaf and canopy scales. At the leaf scale, it is possible to estimate CHL with high precision using a two wavelength vegetation index after a simulation based calibration. At the leaf scale, the LMA is more difficult to estimate with indices. At the canopy scale, efficient indices were determined on a generic simulated database to estimate CHL, LMA, LAI and Bleaf in a general way. These indices were then applied to two Hyperion images (50 plots) on the Fontainebleau and Fougeres forests and portable spectroradiometer measurements. They showed good results with an RMSE of 8.2 µg cm − 2 for CHL, 9.1 g m − 2 for LMA, 1.7 m 2 m − 2 for LAI and 50.6 g m − 2 for Bleaf. However, at the canopy scale, even if the wavelengths of the calibrated indices were accurately determined with the simulated database, the regressions between the indices and the biophysical characteristics still had to be calibrated on measurements. At the canopy scale, the best indices were: for leaf chlorophyll content: ND chl  = ( ρ 925  −  ρ 710 )/( ρ 925  +  ρ 710 ), for leaf mass per area: ND LMA  = ( ρ 2260  −  ρ 1490 )/( ρ 2260  +  ρ 1490 ), for leaf area index: D LAI  =  ρ 1725  −  ρ 970 , and for canopy leaf biomass: ND Bleaf  = ( ρ 2160  −  ρ 1540 )/( ρ 2160  +  ρ 1540 ).

Calibration and validation of hyperspectral indices for the estimation of broadleaved forest leaf chlorophyll content, leaf mass per area, leaf area index and leaf canopy biomass

Cadmium (Cd) is a major environmental contaminant due to its widespread industrial use. Cd contamination of soil and water is rather classical but has emerged as a recent problem. Cd toxicity causes a range of damages to plants ranging from germination to yield suppression. Plant physiological functions, i.e., water interactions, essential mineral uptake, and photosynthesis, are also harmed by Cd. Plants have also shown metabolic changes because of Cd exposure either as direct impact on enzymes or other metabolites, or because of its propensity to produce reactive oxygen species, which can induce oxidative stress. In recent years, there has been increased interest in the potential of plants with ability to accumulate or stabilize Cd compounds for bioremediation of Cd pollution. Here, we critically review the chemistry of Cd and its dynamics in soil and the rhizosphere, toxic effects on plant growth, and yield formation. To conserve the environment and resources, chemical/biological remediation processes for Cd and their efficacy have been summarized in this review. Modulation of plant growth regulators such as cytokinins, ethylene, gibberellins, auxins, abscisic acid, polyamines, jasmonic acid, brassinosteroids, and nitric oxide has been highlighted. Development of plant genotypes with restricted Cd uptake and reduced accumulation in edible portions by conventional and marker-assisted breeding are also presented. In this regard, use of molecular techniques including identification of QTLs, CRISPR/Cas9, and functional genomics to enhance the adverse impacts of Cd in plants may be quite helpful. The review’s results should aid in the development of novel and suitable solutions for limiting Cd bioavailability and toxicity, as well as the long-term management of Cd-polluted soils, therefore reducing environmental and human health hazards.

/pdf/cadmium-phytotoxicity-tolerance-and-advanced-remediation-qk8hkw71.pdf

Cadmium Phytotoxicity, Tolerance, and Advanced Remediation Approaches in Agricultural Soils; A Comprehensive Review

Biochar is a carbonaceous material produced from the slow/fast pyrolysis of biomass under limited or no supply of oxygen. It has diverse uses from climate change mitigation to contaminant remediation from the environment. However, biochar's role in bringing these changes depends on its physicochemical properties, suggesting the use of function-specific biochar for achieving a specific target. This review summarizes the basic properties of biochar and how they are affected by different modification strategies. It also looks at remediation of heavy metal pollution using biochar, mitigation of heavy metal toxicity to plants including their impacts on physiological attributes, and human health mitigating effects. Biochar production conditions and feedstock is known to control the physicochemical properties of biochar. For instance, biochar's ash content increases with increasing pyrolysis temperature while there is a significant linear relationship between biochar's pH and pyrolysis temperature (r2 = 0.53, n = 112). Moreover, the cation exchange capacity of biochar decreases with the increase in pyrolysis temperature. When applied to soil, biochar interacts with soil and contaminants and can fix contaminants depending on their functionality. Biochars with positive surfaces (e.g. mineral doped biochars) have a large capacity to fix anionic contaminants while biochars with negative surfaces (e.g. acid-modified biochar) mostly fix cationic contaminants. The meta-analysis suggests that the overall effect of biochar application to polluted soils is the reduction of pollutant uptake by plants, with some exceptions for Fe and Mn. The reductions were estimated at 26.2% (Cd), 25.8% (Cu), 56.0% (Cr), 41.5% (As), 3.03% (Pb), 18.3% (Zn), 33.0% (Ni), and 22.8% (Mn). The underlying mechanisms for this reduction in the bioavailability of heavy metals in soils are diverse with charged metals being fixed through ion exchange, physical entrapment on biochar's surfaces and changes in soil chemistry. Amending heavy metal polluted soils with biochar reduced the overall daily intake of heavy metals (12.5%), hazard quotient (30.0%), and cancer risk (30.6%). However, these effects can be quite diverse depending on biochar properties, soil properties and the chemistry of concerned heavy metals. Altogether, our study provides a fundamental understanding of biochar mediated changes in heavy metal bioavailability in the contaminated soils and their subsequent effects on plants and animals. 

pdf/reduction-of-heavy-metal-uptake-from-polluted-soils-and-0flx5vm0k3.pdf

Reduction of heavy metal uptake from polluted soils and associated health risks through biochar amendment: A critical synthesis

Biochars provide several agricultural and environmental benefits, such as soil health improvement, better crop growth and yield, carbon sequestration, decreasing greenhouse gas (GHGs) emissions, and regulation of nutrient dynamics. This review highlights the role of biochar in transforming the soil’s physiochemical and biological properties, and their impact on improving seed germination and seedling growth, altering crop physiological attributes, enhancing crop resistance against biotic and abiotic stresses, improving crop productivity, curtailing GHGs, and controlling nutrient leaching losses. However, the type of feedstock used, pyrolysis temperature, application rate and method, soil type and crop species largely influence the biochar performance under different environmental conditions. Application of biochars at low rates help to promote seed germination and seedling growth. Biochar modified the abiotic and microbial processes in the rhizosphere and increased nutrient mineralization and enhanced the nutrient availability for plant uptake. Hence, biochar enhanced the plant resistance against diseases, reduced the availability of heavy metals and improved the plant resilience against environmental stressors. By providing a comprehensive analysis about the variable impacts of biochars on soil physicochemical properties, plant growth, development and productivity and mitigating environmental problems, this review is quite valuable for developing an efficient soil and crop specific biochar with desired functionalities. It could be helpful in improving crop productivity, ensuring food security and better management of environment. Furthermore, this review identifies the knowledge gaps and suggests future outlooks for the commercialization of biochar applications on large-scale.

https://www.frontiersin.org/articles/10.3389/fenvs.2023.1059449/pdf

Biochar-Soil-Plant interactions: A cross talk for sustainable agriculture under changing climate

Cotton straw biochar and Bacillus compound biofertilizer decreased Cd migration in alkaline soil: Insights from relationship between soil key metabolites and key bacteria.

Consistent use of large amounts of fertilizers, pesticides, and mulch can cause the accumulation of harmful substances in cotton plants. Among these harmful substances, cadmium (Cd), an undegradable element, stands out as being particularly highly toxic to plants. The objective of this study was to evaluate the ability of biochar (3%) and biofertilizer (1.5%) to decrease Cd uptake, increase cotton dry weight, and modulate the activities of photosynthetic and peroxidase (POD), superoxide dismutase (SOD), catalase enzyme (CAT) in cotton (Gossypium hirsutum L.) grown in Cd-contaminated soil (0, 1, 2, or 4 mg Cd kg-1 soil) in pots. These studies showed that, as expected, exogenous Cd adversely affects cotton chlorophyll and photosynthesis. However, biochar and biofertilizer increased cotton dry weight by an average of 16.82% and 32.62%, respectively. Meanwhile, biochar and biofertilizer decreased the accumulation of Cd in cotton organs, and there was a significant reduction in the amount of Cd in bolls (P < 0.05). Biochar and biofertilizer have a positive impact on cotton chlorophyll content, net photosynthesis, stomatal conductance, transpiration rate, and intercellular CO2 concentration. Thus, the addition of biochar and biofertilizer promote cotton growth. However, biochar and biofertilizer increased the SOD activity of leaves (47.70% and 77.21%), CAT activity of leaves (35.40% and 72.82%), SOD activity of roots (33.62% and 39.37%), and CAT activity of roots (36.91% and 60.29%), respectively, and the addition of biochar and biofertilizer decreased the content of MDA and electrolyte leakage rate. Redundancy analyses showed that biochar and biofertilizer also improved SOD and POD activities by reducing the heavy metal-induced oxidative stress in cotton and reducing Cd uptake in cotton organs. Therefore, biochar and biofertilizer have a positive effect on the growth of cotton.

/pdf/effects-of-biochar-and-biofertilizer-on-cadmium-contaminated-509d6u5gqd.pdf

Effects of biochar and biofertilizer on cadmium-contaminated cotton growth and the antioxidative defense system

Hyperspectral technology, which has been used in rapid and non-destructive monitoring of crop nitrogen status, is of great significance for the nitrogen fertilization management in modern agriculture. However, most researches collect hyperspectral data from the vertical angle, always leading to the inaccurate estimation of crop nitrogen. Studies have found that using multi-angle spectral data could improve the accuracy in estimating crop leaf nitrogen content (LNC). In this study, the LNC at different leaf positions of winter wheat under five nitrogen treatments was measured and the multi-angle spectral reflectance of leaves were collected. The results showed that the top third leaf were the most sensitive to nitrogen application rate. Correlation analysis showed that the correlation between LNC and spectral reflectance obtained at 0° was the highest, followed by that between LNC and spectral reflectance obtained at 10°, 30°, 40°, and 20°. Moreover, a model based on the multi-angle composite vegetation index (MACVI) for LNC estimation was constructed through combining the difference vegetable index (DVI), the normalized difference vegetable index (NDVI), and the ratio vegetable index (RVI) and using the spectral data obtained from multiple leaf inclination angles, finding that this model could improve the estimation accuracy. The accuracy of the model based on the spectral reflectance obtained at 0°, 10°, and 20° was higher than the others, and the coefficient of determination (R ²) for the MACVID,R-based model was the highest. The MACVI-based model proposed in this study could effectively improve the estimation accuracy of winter wheat nitrogen content, and provide scientific guidance for the nitrogen fertilization management in winter wheat cultivation.

Monitoring of leaf nitrogen content of winter wheat using multi-angle hyperspectral data

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Effects of biochar and biofertilizer on cadmium-contaminated cotton growth and the antioxidative defense system

Monitoring of leaf nitrogen content of winter wheat using multi-angle hyperspectral data