Physiological Behavior of the Aquatic Plant Azolla sp. in Response to Organic and Inorganic Fertilizers

Effects of nutrient enrichment on freshwater macrophyte and invertebrate abundance: A meta-analysis

External nutrient loading can cause large changes in freshwater ecosystems. Many local field and laboratory experiments have investigated ecological responses to nutrient addition. However, these findings are difficult to generalize, as the responses observed may depend on the local context and the resulting nutrient concentrations in the receiving water bodies. In this research, we combined and analysed data from 131 experimental studies containing 3054 treatment-control abundance ratios to assess the responses of freshwater taxa along a gradient of elevated nutrient concentrations. We carried out a systematic literature search in order to identify studies that report the abundance of invertebrate, macrophyte, and fish taxa in relation to the addition of nitrogen, phosphorus, or both. Next, we established mixed-effect meta-regression models to relate the biotic responses to the concentration gradients of both nutrients. We quantified the responses based on various abundance-based metrics. We found no responses to the mere addition of nutrients, apart from an overall increase of total invertebrate abundance. However, when we considered the gradients of N and P enrichment, we found responses to both nutrients for all abundance metrics. Abundance tended to increase at low levels of N enrichment, yet decreased at the high end of the concentration gradient (1-10 mg/L, depending on the P concentration). Responses to increasing P concentrations were mostly positive. For fish, we found too few data to perform a meaningful analysis. The results of our research highlight the need to consider the level of nutrient enrichment rather than the mere addition of nutrients in order to better understand broad-scale responses of freshwater biota to eutrophication, as a key step to identify effective conservation strategies for freshwater ecosystems.

Evaluating growth-dependent enhanced carbon dioxide sequestration potential of Azolla pinnata using cattle wastes (cow dung and cow urine)

The increasing rate of carbon dioxide (CO₂) emissions and its impact on global warming are a tremendous problem globally. To control these problems, the present research attempted to employ the Azolla pinnata for growth-dependent enhanced CO₂ sequestration using cattle waste (cow dung, CD and cow urine, CU). Two experiments of A. pinnata growth using six different percentages of CD and CU (0.5, 1.0, 5.0, 10, 20 and 40%) were conducted to determine the optimum doses of CD and CU for the maximum growth of A. pinnata and to assess the growth dependent enhanced CO₂ sequestration of A. pinnata using CD and CU. The maximum growth of A. pinnata was achieved at the doses of 10% CD (weight 2.15 g and number 77.5) and 0.5% CU (weight 2.21 g and number 79.5). The highest rate of CO₂ sequestration was found in the treatments of 10% CD (346.83 mg CO₂) and 0.5% CU (356.5 mg CO₂) in both experiments. Due to possessing the huge biomass production and high CO₂ sequestration properties of A. pinnata within a short span of time using the cattle waste (cow dung and cow urine), therefore, it can be concluded that the explored mechanism would be a simple and potentially novel approach in order to sequester the CO₂ and transform into useful plant biomass for the minimization of CO₂ emitting problems in the current global warming scenario.

Potentiality of Azolla pinnata R. Br. for Phytoremediation of Polluted Freshwater with Crude Petroleum Oil

The pollution of freshwater resources with crude petroleum oil is a major environmental issue in oil-producing countries. As a result, the remediation of polluted aquatic ecosystems using eco-friendly and cost-effective technology is receiving increased global attention. In this study, the ability of Azolla pinnata R. Br. to remediate petroleum-polluted freshwater was assessed. The remediation potentiality was determined by evaluating the total petroleum hydrocarbon degradation percentage (TPH%) and changes in the molecular type composition of saturated and aromatic hydrocarbon fractions. TPH% was estimated gravimetrically, and changes in the molecular type composition of saturated and aromatic fractions were measured using gas chromatography and high-performance liquid chromatography, respectively. The results reveal that A. pinnata has the potential to phytoremediate freshwater polluted with low levels (up to 0.5 g/L) of petroleum hydrocarbons (PHs). After seven days of phytoremediation, the degradation rate of total PHs was 92% in the planted treatment compared with 38% in the unplanted positive control. The highest breakdown of PHs for the normal paraffinic saturated hydrocarbon fraction occurred in the presence of A. pinnata combined with Anabena azollaea (A-A), which showed a moderate degradation capacity toward total aromatic hydrocarbons (TAHs) and total polycyclic aromatic hydrocarbons (PAHs). The results indicate that A. pinnata effectively removed C18, a saturated PH, and acenaphthene (Ace), an aromatic PH. Therefore, this study suggests that A. pinnata is a useful tool for the remediation of freshwaters contaminated with low pollution levels of crude oil.

Variations of Structural and Functional Traits of Azolla pinnata R. Br. in Response to Crude Oil Pollution in Arid Regions

In oil-producing countries, water pollution by crude petroleum oil frequently occurs and causes many environmental problems. This study aims to investigate the effect of crude petroleum oil on the growth and functional trails of the economically important freshwater plant Azolla pinnata R. Br. and to report on the plant’s resistance to this abiotic stress. Plants were raised in an open greenhouse experiment under different levels of crude oil pollution ranging from 0.5 to 2.0 g/L. Plant functional traits were monitored over a three-week period. Plant cover of A. pinnata was decreased with the increased levels of oil pollution. The total chlorophyll content decreased from 0.76 mg/g fresh weight under 2 g/L oil treatment after 21 days of growth. The chlorophyll a/b ratio exceeded the unity at crude oil treatments above 1 g/L, with values reaching 2.78 after seven days, while after 21 days, the ratio ranged from 1.14 to 1.31. The carotenoid content ranged from 0.17 mg/g in the control to 0.11 mg/g in the 2 g/L oil treatment. The carotenoid content varied over time in relation to DNA% damage, which increased from 3.63% in the control to 11.36% in the highest oil treatment level of 2 g/L. The crude oil stress caused severe damage in the frond tissues and chloroplast structure of A. pinnata, including a less compacted palisade, the malformation of the epidermis, the disintegration of parenchyma tissue, and the lysis and malformation of the chloroplasts. Since A. pinnata cannot withstand high concentrations of crude oil pollution, it is for use in the remediation of slightly polluted freshwaters up to 0.5 g/L.

Hydrogen Peroxide Supplementation in Irrigation Water Alleviates Drought Stress and Boosts Growth and Productivity of Potato Plants

The present investigations aim to decipher the beneficial role of hydrogen peroxide-supplemented irrigation in imparting drought tolerance and promotion plant growth and yield of potato plants grown under two different irrigation regimes. Hydrogen peroxide injection (oxygenation) was applied at 0, 300, and 600 ppm through subsurface irrigation regimes on potato performance grown in heavy clay soil. The results indicated that oxygenation of irrigation water boosted the plant′s vegetative growth and productivity, especially at 600 ppm hydrogen peroxide coupled with deficit irrigation. Root respiration, leaf biomass, chlorophyll content, and leaf osmotic status was observed to be improved in the presence of oxygenated irrigation. A similar trend was recorded on macro-elements (nitrogen, phosphorus, potassium and calcium content), proline, and soluble carbohydrates content of leaf along with catalase enzyme activity. Individual tuber weight, tuber number and tuber yield per plant and hectare recorded higher values as responding to oxygenated irrigation (300 and 600 ppm) of water within the optimum irrigation level. While the highest value of water use efficiency (WUE) was obtained by pairing deficit irrigation with 600 ppm oxygenated water. Thus, the present work provides new insights into the importance of oxygenated irrigation in obtaining optimum yield and field performance in potato plants subjected to deficit irrigation in clayey-loamy soils.