Experimental study on effects of prometryn exposure scenarios on Microcystis aeruginosa growth and N and P concentrations.

Single exposure toxicity tests of herbicides like prometryn are commonly applied in studying ecological and environmental issues, but they are more likely exposed to microalgae through multiple applications of irrigation and water flow. The toxicity of prometryn towards Microcystis aeruginosa (M. aeruginosa) at different growth stages (different exposure period) was determined by single and multiple exposures (different exposure mode) through 39-day batch-experiment comparison study. Inhibition rates showed that M. aeruginosa growth was greatly inhibited by exposure to prometryn in a final concentration of 80 and 160 µg·L-1 (p < 0.05). Specifically, with the same prometryn exposure periods (lag or exponential phase) and concentrations, a single exposure displayed larger toxicity on M. aeruginosa than repetitive additions of prometryn in general according to inhibition rates. Moreover, with the same prometryn exposure modes and concentrations, inhibitory effect was higher with prometryn exposure in lag phase than that in exponential phase according to M. aeruginosa densities and inhibition rates. In general, variations of total dissolved phosphorus (TDP) and total dissolved nitrogen (TDN) with time responded negatively to M. aeruginosa growth, and added prometryn inhibits the utilization rate of both P and N. Logistic function was well used to describe algae densities (R2 = 0.979 ~ 0.995), growth rates (R2 = 0.515 ~ 0.731), specific growth rates (R2 = 0.301 ~ 0.648) and inhibition rates (R2 = 0.357 ~ 0.946) along with its combination with Monod function. In addition, results showed that shifts of limiting nutrients could be prompted by not only M. aeruginosa growth but also prometryn exposure scenarios. This study provides a basis for studying the potential harm of prometryn to the ecological environment.

Effect of different fish feeds on water quality and growth of crucian carp (Carassius carassius) in the presence and absence of prometryn.

Few data are available regarding comprehensive or quantitative assessment of fish feed considering both the environmental and feeding impacts. Aiming to fill the gap, an experimental study to investigate the effects of three fish feeds on concentrations of nutrients and crucian carp (Carassius carassius) growth was conducted in laboratory aquariums in the presence and absence of prometryn. Results showed that weight gain rates of crucian carp treated with Tong Wei (TW) feed were 106.3% and 2.0% higher than that of Zhong Shan (ZS) and Zhong Liang (ZL) feeds, a possible explanation was that the quality of protein in TW feed was highest as evidenced by the protein efficiency ratios. Meanwhile, TW feed posed relatively lighter effects on water qualities (between ZL and ZS). Prometryn significantly inhibited the growth of crucian carp and thus affected concentrations of nutrients in water indirectly. The relationships between weight gain rates of fish and concentrations of nutrients in water (R2 = 0.929-0.990) were developed. In sum, this study suggested that it is realizable to obtain better fish growth performance with lesser degrading effects on water qualities by producing and selecting appropriate feed regardless of prometryn existence, and the developed equations could be used as a basis for future studies.

Effects of fish feed addition scenarios with prometryn on Microcystis aeruginosa growth and water qualities.

The number of undesirable environmental impacts of fish feed has been reported widely. Although repeated fish feed exposures are more prospective to occur in water, previous studies were mostly conducted as a single exposure of fish feed. In order to fill these gaps, a 40 days incubator experiment was conducted to explore the effects of fish feed addition scenarios during the lag phase with prometryn on both Microcystis aeruginosa growth and concentrations of nutrients. The maximum algae densities in groups of single exposure were 6.0-26.2% and 8.8-74.4% higher than those in groups of double and triple exposures, respectively (P < 0.05). At the beginning of the experiment, concentrations of nutrients in groups with different feed exposure scenarios were significantly different. The pattern of nutrient limitation showed a transformation from phosphorus limitation to nitrogen limitation generally. Furthermore, the average inhibition rates of algae by prometryn in the case of a single fish feed exposure were 4.6-9.4% lower than those under double exposures, and 22.0-26.8% lower than those under triple exposures (P < 0.05). In addition, algae growth rates have been developed as a function of concentrations of consumed nutrients (R2 = 0.410-0.932). Based on the above results, we concluded that in terms of limiting algae growth multiple low-dosage additions of fish feed were considered as a better addition pattern. By optimizing feed addition scenarios, there is considerable potential to increase the environmental sustainability of aquaculture.

Unlocking the potential of plant growth-promoting rhizobacteria on soil health and the sustainability of agricultural systems.

The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.

Fish Feed Quality Is a Key Factor in Impacting Aquaculture Water Environment: Evidence from Incubator Experiments.

The effect of fish feed quality has gained increasing attention to alleviate the harmful environmental impacts induced by intensive aquaculture. In current research, we have conducted an incubator experiment to highlight the effect of fish feed quality on aquaculture water environment. Fish feed from three manufactures with two different dosages (0.1000 g, 0.2000 g) was added to the culture medium with and without Microcystis aeruginosa. Treatments with Microcystis aeruginosa were named as MHT, MHP and MZT; while the treatments without Microcystis aeruginosa named as HT, HP and ZT. Microcystis aeruginosa densities and nutrients concentrations were measured in the study. Results have shown that fish feed quality (manufactures) has a great effect on nutrients concentrations in the absence of Microcystis aeruginosa (P < 0.05). Meanwhile, fish feed can stimulate Microcystis aeruginosa growth that is also influenced by fish feed quality excluding lag phase (0~12 day) significantly in general (P < 0.05). The maximum Microcystis aeruginosa density (Nmax) is 1221.5, 984.5, 581.0, 2265.9, 2056.8 and 1766.6 1 × 104 cells mL-1 for MHT 0.1 g, MHP 0.1 g, MZT 0.1 g, MHT 0.2 g, MHP 0.2 g and MZT 0.2 g, respectively. In treatments with algae, fish feed quality affect total phosphorus (TP) concentrations (except the difference between MHT and MHP) and total nitrogen (TN) concentrations significantly (P < 0.05). For most of consumed nutrients, the obvious differences among all treatments were observed excluding lag phase in general (P < 0.05), which suggest that the nutrient utilization is also dependent on fish feed quality. Keeping in mind the above facts it is concluded that fish feed quality is a key factor in impacting aquaculture water environment.

Induction of tolerance to salinity in wheat genotypes by plant growth promoting endophytes: Involvement of ACC deaminase and antioxidant enzymes.

Plant growth-promoting endophytes (PGPEs) can colonize the internal tissues of plants and are capable of promoting plant growth. These bacteria can improve plant tolerance against various biotic and abiotic stresses via the expression of antioxidant enzymes and the production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Two salt-tolerant PGPEs, Kocuria rhizophila: KF875448 (14ASP) and Cronobacter sakazakii: KM042090 (OF115), with ACC deaminase activity were investigated for their potential to ameliorate plant salinity stress. The wheat varieties Pasban 90 and Khirman were subjected to two levels of salt stress (80 and 160 mM NaCl) under greenhouse conditions by using a completely randomized design. Analyses of plant growth parameters, antioxidant enzyme activities, chlorophyll and plant mineral contents were conducted to investigate the stress tolerance induced by the PGPEs. The ACC utilization by the PGPEs directly relates to the promotion of plant growth due to the lowering of excess ethylene production under salt stress. High levels of NaCl exhibited negative effects in both varieties. However, inoculation with PGPEs increased the morphological traits and antioxidant activities of the plants while decreasing the Na+ contents in all treatments compared to uninoculated treatment. Wheat variety Pasban 90 was more tolerant than Khirman in to salt stress in all the measured morphological and biochemical parameters, while the bacterial strain OF115 performed significantly better in all morphological and biochemical parameters, such as fresh dry weight, root shoot length, proline and chlorophyll contents, compared to strain 14ASP. The K+/Na+ ratio in the tissues of bacterial treated plants was higher than the control, probably in order to maintain the nutrient balance. The results of our study revealed that the inoculation of plants by ACC deaminase-producing PGPEs is a potential tool for the enhancement of plant growth and stress tolerance. Moreover, endophytic bacteria allied with host plants are capable of enduring high saline conditions and can interact with plants in a very efficient way.