The Effect of Single Heating on Soil Microbial Activity and Nutrient Cycling

The effect of soil heating during forest fires (often >100 °C for several hours) on soil microbes and nutrient availability has been studied extensively. Less is known about the effect of fast-moving fires with low fuel load where soils reach 50 to 100 °C for a few minutes. In this thesis, the effect of heating soil to 60 °C within 1 h and then maintaining this temperature for 30 minutes was studied. Soils were rewetted after cooling to room temperature. Heating of soils usually induces drying, but it is unclear if the effect of heating is only due to this water loss or if other factors are also important. An experiment included heated soils, constantly moist controls and air-dried soils which were dried at 30 °C to the same water content as the heated soils. Heating increased cumulative respiration and available N after rewetting about three-fold compared to the constantly moist control and the air-dried soils. To assess how the effect of heating is influenced by amendment type or time between amendment application soil was amended with the same amount of total N and P as pea residue or inorganic N and P either eight or one day before heating. Heating only reduced respiration when residue was added one day before heating. Heating increased available N on day 10 in the unamended soil or with fertiliser by about 20% and in residue treatments about 10-fold, particularly when residue was added one day before heating. To assess the effect of a second heating event, soils were heated once on day 8 (H8) or heated again 4, 8 and 16 days after the first heating event (H8-12, H8-16 and H8-24). Compared to unheated soil, cumulative respiration was about 10 and 20% higher in H8 and H8-12 and H8-16, but 30% higher in H8-24. The first heating increased available N and P by 25%. The second heating induced a further increase in available N and P compared to the first heating. To assess the effect of plants, soil was planted with wheat for 4 weeks or left unplanted. The heatinginduced increase in initial respiration rate, available N and P was greater in previously planted soil than unplanted soil. The last chapter includes two experiments. In the first experiment, soils were constantly moist or exposed to a drying-rewetting event before heating. Prior drying and rewetting had no effect on the impact of heating on respiration and nutrient availability. In the second experiment, non-saline soil was salinised to EC1:5 1 and 4 ds m-1 (referred to as NS, S1 and S4). After one month and pea residue addition (10 g kg-1), soil was incubated for 5 days, then heated. In moist soil, S4 reduced cumulative respiration but increased available N and P compared to NS and S1. Heating reduced cumulative respiration more in S4 than NS and S1. Compared to unheated treatments, available N in heated NS was up to ten-fold higher, but only three-fold in S4.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 202

Feminization of Sri Lankan Doctors and Key Specialties: 2000 to 2020

The study focused on the feminization of Sri Lankan generalist doctors in all major and selected minor specialties between 2000 and 2020. The study analyzed all relevant documents by exploring Sri Lanka's male-to-female doctor and specialist ratio over 20 years. This was determined by analyzing state medical faculty records from 1990 to 2020. For better clarity, the researchers analyzed the gender ratio changes in every five-year block from 1990 to 2020. Focus groups filled PGIM's gender data fields. Five-year medical students surged from 43% to 63% between 1990 and 2020. Linear trend analysis predicts 68% of female medical students by 2025 and 72% by 2030. This study simulated generalist doctors with medical students. Until recently, men dominated medicine, surgery, obstetrics, and pediatrics. Female specialists have increased in all fields over the past 20 years. The feminization of medical doctors challenges national human resource policies and health sector reforms. They emphasize gender-sensitive health workforce planning that considers a country's economic development and healthcare system. Sri Lankan health policymakers should consider gender dynamics in national health HR planning for the next decade

Role of Bacterial-Fungal Interactions on Heavy Metal Phytotoxicity in Serpentine Soil

This study was conducted to understand the role of bacterial–fungal interactions on heavy metal uptake by Zea mays plants. A pot experiment was conducted for 90 days with Z. mays in serpentine soil inoculated with a Gram-negative bacterium, fungus (Aspergilllus sp.) and both microbes to determine the effects of inoculation on nickel, manganese, chromium and cobalt concentrations in plant tissue and soil. Soil nutrients and soil enzyme activities were measured to determine the effect of inoculations on soil quality. Inoculation of microorganisms increased shoot and root biomass, and the maximum biomass was in the bacterial–fungal inoculation. This could be due to the solubilisation of phosphate and production of indole acetic acid. Although the combination treatment contributed to an increase in heavy metal uptake in Z. mays plants, the lowest translocation was observed in the combination treatment. Moreover, the soil available nitrogen, available phosphorous and total organic carbon content were increased with the microbial inoculation. Similarly, the soil dehydrogenase activity was higher as a result of microbial inoculation, whereas the highest dehydrogenase activity was reported in the combination inoculation. This study confirms the synergistic effect of bacterial–fungal inoculation as a soil-quality enhancer and as a plant-growth promoter in the presence of heavy metals

Heavy Metal-Induced Oxidative Stress on Seed Germination and Seedling Development: A Critical Review

Heavy metal contamination in soils can influence plants and animals, often leading to toxicosis. Heavy metals can impact various biochemical processes in plants, including enzyme and antioxidant production, protein mobilization and photosynthesis. Hydrolyzing enzymes play a major role in seed germination. Enzymes such as acid phosphatases, proteases and α-amylases are known to facilitate both seed germination and seedling growth via mobilizing nutrients in the endosperm. In the presence of heavy metals, starch is immobilized and nutrient sources become limited. Moreover, a reduction in proteolytic enzyme activity and an increase in protein and amino acid content can be observed under heavy metal stress. Proline, is an amino acid which is essential for cellular metabolism. Numerous studies have shown an increase in proline content under oxidative stress in higher plants. Furthermore, heat shock protein production has also been observed under heavy metal stress. The chloroplast small heat shock proteins (Hsp) reduce photosynthesis damage, rather than repair or help to recover from heavy metal-induced damage. Heavy metals are destructive substances for photosynthesis. They are involved in destabilizing enzymes, oxidizing photosystem II (PS II) and disrupting the electron transport chain and mineral metabolism. Although the physiological effects of Cd have been investigated thoroughly, other metals such as As, Cr, Hg, Cu and Pb have received relatively little attention. Among agricultural plants, rice has been studied extensively; additional studies are needed to characterize toxicities of different heavy metals on other crops. This review summarizes the current state of our understanding of the effects of heavy metal stress on seed germination and seedling development and highlights informational gaps and areas for future research

Occurrence and cycling of trace elements in ultramafic soils and their impacts on human health: A critical review

The transformation of trace metals (TMs) in natural environmental systems has created significant concerns in recent decades. Ultramafic environments lead to potential risks to the agricultural products and, subsequently, to human health. This unique review presents geochemistry of ultramafic soils, TM fractionation (i.e. sequential and single extraction techniques), TM uptake and accumulation mechanisms of ultramafic flora, and ultramafic associated health risks to human and agricultural crops. Ultramafic soils contain high levels of TMs (i.e. Cr, Ni, Mn, and Co) and have a low Ca:Mg ratio together with deficiencies in essential macronutrients required for the growth of crops. Even though a higher portion of TMs bind with the residual fraction of ultramafic soils, environmental changes (i.e. natural or anthropogenic) may increase the levels of TMs in the bioavailable or extractable fractions of ultramafic soils. Extremophile plants that have evolved to thrive in ultramafic soils present clear examples of evolutionary adaptations to TM resistance. The release of TMs into water sources and accumulation in food crops in and around ultramafic localities increases health risks for humans. Therefore, more focused investigations need to be implemented to understand the mechanisms related to the mobility and bioavailability of TMs in different ultramafic environments. Research gaps and directions for future studies are also discussed in this review. Lastly, we consider the importance of characterizing terrestrial ultramafic soil and its effect on crop plants in the context of multi-decadal plans by NASA and other space agencies to establish human colonies on Mars

A preliminary study of the role of bacterial-fungal co-inoculation on heavy metal phytotoxicity in serpentine soil

This study was conducted to understand the role of bacterial–fungal interactions on heavy metal uptake by Zea mays plants. A pot experiment was conducted for 90 days with Z. mays in serpentine soil inoculated with a Gram-negative bacterium, fungus (Aspergilllus sp.) and both microbes to determine the effects of inoculation on nickel, manganese, chromium and cobalt concentrations in plant tissue and soil. Soil nutrients and soil enzyme activities were measured to determine the effect of inoculations on soil quality. Inoculation of microorganisms increased shoot and root biomass, and the maximum biomass was in the bacterial–fungal inoculation. This could be due to the solubilisation of phosphate and production of indole acetic acid. Although the combination treatment contributed to an increase in heavy metal uptake in Z. mays plants, the lowest translocation was observed in the combination treatment. Moreover, the soil available nitrogen, available phosphorous and total organic carbon content were increased with the microbial inoculation. Similarly, the soil dehydrogenase activity was higher as a result of microbial inoculation, whereas the highest dehydrogenase activity was reported in the combination inoculation. This study confirms the synergistic effect of bacterial–fungal inoculation as a soil-quality enhancer and as a plant-growth promoter in the presence of heavy metal

Role of Woody Biochar and Fungal-Bacterial Co-Inoculation on Enzyme Activity and Metal Immobilization in Serpentine Soil

Purpose In this study, we investigated the effect of biochar (BC) and fungal bacterial co-inoculation (FB) on soil enzymatic activity and immobilization of heavy metals in serpentine soil in Sri Lanka. Materials and methods A pot experiment was conducted with tomatoes (Lycopersicon esculentum L.) at 1, 2.5, and 5 % (w/w) BC ratios. Polyphenol oxidase, catalase and dehydrogenase activities were determined by idometric, potassium permanganate oxidisable, and spectrophotometric methods, respectively. Heavy metal concentrations were assessed by 0.01 M CaCl2 and sequential extraction methods. Results and discussion An increase in BC application reduced polyphenol oxidase, dehydrogenase, and catalase activity. The application of FB increased soil dehydrogenase activity, with the maximum activity found in 1 % BC700 + FB treatment. Moreover, the CaCl2 extractable metals (Ni, Mn, and Cr) in 5 % BC700 amended soil decreased by 92, 94, and 100 %, respectively, compared to the control. Sequential extraction showed that the exchangeable concentrations of Ni, Mn, and Cr decreased by 55, 70, and 80 % in 5 % BC700, respectively. Conclusions Results suggest that the addition of BC to serpentine soil immobilizes heavy metals and decreases soil enzymatic activities. The addition of FB to serpentine soil improves plant growth by mitigating heavy metal toxicity and enhancing soil enzymatic activities