A critical review of soil algae as a crucial soil biological component of high ecological and economic significance.

Aero-terrestrial algae are ecologically and economically valuable bioresources contributing to carbon sequestration, sustenance of soil health, and fertility. Compared to aquatic algae, the literature on subaerial algae is minimal, including studies of distinctive habitats such as forest soils, agricultural fields, deserts, polar regions, specific subaerial zones, artificial structures, and tropical soils. The primary goal here was to identify the gaps and scope of research on such algae. Accordingly, the literature was analyzed per sub-themes, such as the "nature of current research data on terrestrial algae," "methodological approaches," "diversity," "environmental relationships," "ecological roles," and "economic significance." The review showed there is a high diversity of algae in soils, especially members belonging to the Cyanophyta (Cyanobacteria) and Chlorophyta. Algal distributions in terrestrial environments depend on the microhabitat conditions, and many species of soil algae are sensitive to specific soil conditions. The ecological significance of soil algae includes primary production, the release of biochemical stimulants and plant growth promoters into soils, nitrogen fixation, solubilization of minerals, and the enhancement and maintenance of soil fertility. Since aero-terrestrial habitats are generally stressed environments, algae of such environments can be rich in rare metabolites and natural products. For example, epilithic soil algae use wet adhesive molecules to fix them firmly on the substratum. Exploring the ecological roles and economic utility of soil and other subaerial algae could be helpful for the development of algae-based industries and for achieving sustainable soil management.

Optimization of environmental and the other variables in the application of arbuscular mycorrhizal fungi as an ecotechnological tool for sustainable paddy cultivation: a critical review.

Arbuscular mycorrhizal fungi (AMF) are effective natural alternatives to assist plants in improving crop productivity and immunity against pests and diseases. However, a comprehensive idea of the variables under which they show optimum activity, especially concerning particular soil, climate, geography, and crop characteristics, has yet to be adequately standardized. Since paddy is the staple food for half of the world's population, such standardization is highly significant globally. Research concerning determinants affecting AMF functioning in rice is limited. However, the identified variables include external variables such as abiotic, biotic, and anthropogenic factors and internal variables such as plant and AMF characteristics. Among the abiotic factors, edaphic factors like soil pH, phosphorus availability, and soil moisture significantly affect AMF functioning in rice. In addition, anthropogenic influences such as land use patterns, flooding, and fertilizer regimes also affect AMF communities in rice agroecosystems. The principal objective of the review was to analyse the existing literature on AMF concerning such variables generally and to assess the specific research requirements on variables affecting AMF in rice. The ultimate goal is to identify research gaps for applying AMF as a natural alternative in the sustainable agriculture of paddy with optimum AMF symbiosis enhancing rice productivity.

Lead accumulation, growth responses and biochemical changes of three plant species exposed to soil amended with different concentrations of lead nitrate.

Lead (Pb) contamination of soil is a serious environmental problem, adversely affecting ecosystems, globally. Phytoremediation is an alternative to conventional methods of soil remediation. The success of phytoremediation depends on the identification of suitable native plant species with high biomass to deal with metal contamination. In the present experiment, response of Eclipta prostrata (L.) L., Scoparia dulcis L. and Phyllanthus niruri L. to increase in concentrations of PbNO3·5H2O in the soil for a period of 30 days was tested to assess their suitability in phytoremediation. Pb accumulation in all the three plants was in a concentration-dependent manner. Although S. dulcis survived the soil metal concentrations, it exhibited a stunted growth; P. niruri was found susceptible to Pb toxicity; E. prostrata recorded a maximum uptake of 12484 µg/g dry weight in its root and 7229 µg/g dry weight in its shoot, without any adverse impact on growth traits. Bioconcentration factor and translocation factor of the three plants were also calculated, which revealed that E. prostrata has Pb accumulation potential. Therefore, enzymatic antioxidant activities and transmission electron microscopic analysis were carried out to determine the physiological adaptation and tolerance of E. prostrata to Pb stress. Overall, E. prostrata is identified as a tolerant plant showing Pb hyperaccumulation tendencies with essential features for phytoextraction.

Heavy metal contamination in "chemicalized' green revolution banana fields in southern India.

The present report is a general assessment of the level of nutrient and toxic heavy metals as an impact of "chemicalized" cultivation practices for decades in banana fields in the three south Indian states, Kerala, Karnataka, and Tamilnadu. The major objective was to critically analyze the status of metallic content in green revolution fields, where chemical fertilizers or plant protective chemicals remain the major source of heavy metal contaminants. Since soil series being a soil taxonomic category that includes slightly variant soils of similar origin and common parent materials, the 286 field samples of the broad south Indian region were further grouped into composite samples representing 47 different soil series for limiting the sample analysis. The quantitative assessment of ten metals done in these soils using the Atomic Absorption Spectrophotometer included Ca, Mg, Mn, Zn, Fe, Cu, Pb, Ni, Cr, and Co. The amount of Cu observed in many fields was higher than all the previous reports of the same in the "chemicalized" fields. Similarly, the amount of Co observed in 25 fields was above its threshold levels expected for normal soils. The amount of Pb observed in all the soils appeared quite normal. The amount of Ni observed in 14 soil series was higher than its threshold levels for normal soils, except in 4 soil series, where its amount exceeded the upper limit of contamination. Cr was detected in all the samples, but found higher than its threshold level in 31 soil series. Significant positive correlations were observed between the amounts of different metals in the study. PCA results indicated that variables were correlated to four principal components, and 74.36% of the total variance was justified.

Toxic heavy metals in human blood in relation to certain food and environmental samples in Kerala, South India.

Toxic heavy metals such as arsenic (As), lead (Pb), and mercury (Hg) are systemic toxicants that are hazardous to human health. However, as these elements are increasing in the environment due to fast urbanization, industrialization, and chemicalized agricultural activities, accumulation of the same in human body anywhere in the world is quite interesting to global assessment of environment quality. In this connection, random examination of blood samples of human population in Kerala, South India, was carried out to assess the threat of heavy metal contamination to humans in this part of the globe, especially in relation to the amount of such metals in food and other environmental samples. Except pure vegetarians, people of Kerala consume rice as the staple food with a lot of fish. Therefore, the amount of these three heavy metals in drinking water, fish, rice, and paddy soils was done. Heavy metals in the blood were examined in relation to age, gender, and dietary habits such as frequency of fish eating or vegetarianism. Influence of dental amalgam fillings on blood mercury levels was also analyzed. Quantitative assessment of metals in samples was done by inductively coupled plasma-mass spectrometry (ICP-MS). The levels of arsenic, lead, and mercury were found well below the reference values, though diet seemed to pull them up as the amount of metals in blood showed significant differences between vegetarians and non-vegetarians. Evidence to the influence of dental amalgam fillings on blood mercury levels could not be established with the present samples.