Iron (Fe) is a micronutrient that plays an important role in agriculture worldwide because plants require a small amount of iron for its growth and development. All major functions in a plant's life from chlorophyll biosynthesis to energy transfer are performed by Fe (Brumbarova et al., 2008;Gill and Tuteja, 2011). Iron also acts as a major constituent of many plant proteins and enzymes. The acquisition of Fe in plants occurs through two strategies, i.e., strategy I and strategy II (Marschner and Römheld, 1994). Under various stress conditions, Nramp and the YSL gene families help in translocation of Fe, which further acts as a mineral regulatory element and defends plants against stresses. Iron plays an irreplaceable role in alleviating stress imposed by salinity, drought, and heavy metal stress. This is because it activates plant enzymatic antioxidants like catalase (CAT), peroxidase, and an isoform of superoxide dismutase (SOD) that act as a scavenger of reactive oxygen species (ROS) (Hellin et al., 1995). In addition to this, their deficiency as well as their excess amount can disturb the homeostasis of a plant's cell and result in declining of photosynthetic rate, respiration, and increased accumulation of Na + and Ca − ions which culminate in an excessive formation of ROS. The short-range order hydrated Fe oxides and organic functional groups show affinities for metal ions. Iron plaque biofilm matrices could sequester a large amount of metals at the soil-root interface. Hence, it has attracted the attention of plant physiologists and agricultural scientists who are discovering more exciting and hidden applications of Fe and its potential in the development of bio-factories. This review looks into the recent progress made in putting forward the role of Fe in plant growth, development, and acclimation under major abiotic stresses, i.e., salinity, drought, and heavy metals.

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Diatom indices have gained considerable popularity in estimation of the trophic state and degree of pollution in lotic ecosystems. However, their applicability and efficacy have rarely been tested in Indian streams and rivers. In the present study, benthic diatom assemblages were sampled at 27 sites along the Chambal River in Central India. PCA revealed three groups of sites, namely, heavily polluted (HVPL), moderately polluted (MDPL), and least polluted (SANT). A total of 100 diatom taxa belonging to 40 genera were identified. Brachysira vitrea (Grunow) was the most abundant species recorded from the least polluted sites with an average relative abundance of 29.52. Nitzschia amphibia (Grunow) was representative of heavily polluted sites (average relative abundance 31.71) whereas moderately polluted sites displayed a dominance of Achnanthidium minutissimum (Kϋtzing) with an average relative abundance of 26.33. CCA was used to explore the relationship between diatom assemblage composition and environmental variables. Seventeen different diatom indices were calculated using diatom assemblage data. The relationship between measured water quality variables and index scores was also investigated. Most of the diatom indices exhibited strong correlations with water quality variables including BOD, COD, conductivity, and nutrients, particularly phosphate. Best results were obtained for TDI and IPS indices which showed a high level of resolution with respect to discrimination of sites on the basis of pollution gradients. Water quality maps for the Chambal River were hence prepared in accordance with these two indices. However, satisfactory results with respect to water quality evaluation were also obtained by the application of EPI-D and IGD indices. The present study suggests that TDI and IPS are applicable for biomonitoring of rivers of Central India. Diatom indices, which are simpler to use such as IGD, may be considered, at least for a coarser evaluation of water quality.

Graphical abstract The nexus of COVID-19 and environment is conspicuously deep-rooted. The roles of environmental factors in the origin, transmission and spread of COVID-19 and the mutual impact of the pandemic on the global environment have been the two perspectives to view this nexus. The present paper attempts to systematically review the existing literature to understand and explore the linkages of COVID-19 with environment and proposes conceptual frameworks to underline this nexus. Our study indicates a critical role of meteorological factors, ambient air pollutants and wastewater in severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) transmission-spread dynamics. The study also focuses on the direct and indirect impacts of COVID-19 on the regional and global environment. Most of the indirect environmental effects of COVID-19 were attributed to global human confinement that resulted from the implementation of the pandemic containment measures. This worldwide anthropogenic ‘pause’ sent ripples to all environmental compartments and presented a unique test bed to identify anthropogenic impacts on the earth’s natural systems. The review further addresses emerging sustainability challenges in the new normal and their potential solutions. The situation warrants critical attention to the environment-COVID-19 nexus and innovative sustainable practices to address the ramifications of short- and long-term environmental impacts of the COVID-19 pandemic.

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