Investigating cultivation strategies for enhancing protein content in Auxenochlorella pyrenoidosa FACHB-5.

This study investigated the influence of yeast extract addition, carbon source, and photoperiod on the growth dynamics of Auxenochlorella pyrenoidosa FACHB-5. Employing response surface methodology, the culture strategy was optimized, resulting in the following optimal conditions: yeast extract addition at 0.75 g L-1, glucose concentration of 0.83 g L-1, and a photoperiod set at Light: Dark = 18 h: 6 h. Under these conditions, the biomass reached 1.76 g L-1 with a protein content of 750.00 g L-1, containing 40 % of essential amino acids, representing a 1.52-fold increase. Proteomic analysis revealed that the targeted cultivation strategy up-regulated genes involved in microalgal protein synthesis. The combined effect of yeast extract and glucose enhanced both the glutamine synthetase-glutamate synthetase mechanism and the free amino acid content.

A modified cultivation strategy to enhance biomass production and lipid accumulation of Tetradesmus obliquus FACHB-14 with copper stress and light quality induction.

In this study, a two-stage culture strategy was refined to concurrently enhance the growth and lipid accumulation of Tetradesmus obliquus. The results unveiled that, during the initial stage, the optimal conditions for biomass accumulation were achieved with 0.02 mg·L-1 Cu2+ concentration and red light. Under these conditions, biomass accumulation reached 0.628 g·L-1, marking a substantial 23.62 % increase compared to the control group. In the second stage, the optimal conditions for lipid accumulation were identified as 0.5 mg·L-1 Cu2+ concentration and red light, achieving 64.25 mg·g-1·d-1 and marking a 128.38 % increase over the control. Furthermore, the fatty acid analysis results revealed an 18.85 % increase in the saturated fatty acid content, indicating enhanced combustion performance of microalgae cultivated under the dual stress of red light and 0.5 mg·L-1 Cu2+. This study offers insights into the potential application of Tetradesmus obliquus in biofuel production.

Study on the removal and degradation mechanism of microcystin-LR by the UV/Fenton system.

Microcystin-LR (MC-LR) is highly hepatotoxic and potentially carcinogenic to humans. Therefore, removing MC-LR from water bodies is of paramount importance. This study aimed to investigate the removal efficacy of the UV/Fenton system on MC-LR from copper-green microcystin and to explore its degradation mechanism in simulated real algae-containing wastewater. The results showed that at an initial concentration of 5 µg·L-1, a combination of 300 µmol·L-1 H2O2, 125 µmol·L-1 FeSO4, and 5 min of UV irradiation under average radiation intensity of 48 µW·cm-2 resulted in a removal efficiency of 90.65 % for MC-LR. The reduction of extracellular soluble microbial metabolites of Microcystis aeruginosa confirmed the UV/Fenton method's degradation efficiency for MC-LR, while the observation of the functional group CH and OCO in the treatment group indicated effective binding sites in the coagulation process. However, the presence of humic substances in algal organic matter (AOM) and some proteins and polysaccharides in the algal cell suspension competed with MC-LR for HO·, resulting in a decreased removal effect (78.36 %) in simulated actual algae-containing wastewater. These quantitative results provide an experimental basis and theoretical foundation for controlling cyanobacterial water blooms and ensuring drinking water quality safety.

Study on the inhibition mechanism of eucalyptus tannins against Microcystis aeruginosa.

Microcystis aeruginosa is the competitively dominant algal species in eutrophic waters and poses a serious threat to the aquatic ecological environment. To investigate the effects of eucalyptus tannins (TFL) and black water in eucalyptus plantations on M. aeruginosa, this study exposed M. aeruginosa to different concentrations (0 (control), 20, 50, 80, 110, and 140 mg L-1) of tannic acid (TA; hydrolyzed tannins, HT; reagent tannin), epigallocatechin gallate (EGCG; condensed tannins, CT; reagent tannin), eucalyptus tannins (TFL, complex tannin) and mixed TFL + Fe3+ solution (tannin: Fe3+ molar ratio = 1:10). The cell density, chlorophyll-a (Chl-a) content, superoxide dismutase (SOD) activity, malondialdehyde (MDA) and soluble protein (SP) contents of algae under tannin stress were determined, and the algal cell density treated with under the combination of TFL and Fe3+ was determined. The results showed a reduction in the Chl-a content of algal cells, which inhibited photosynthesis; leading to membrane lipid peroxidation; and the complexation of soluble proteins resulting in blocked protein synthesis were the main mechanisms by which tannins inhibited the growth of M. aeruginosa. TFL achieved the same inhibition of algal cells as the tannin reagent at the same concentration. At 4 d, TFL at 80 mg L-1 and above could achieve more than 54.87 % algal density inhibition. The inhibition rate of 80 mg L-1 and above TFL + Fe3+ on algal density was more than 75 %, indicating that TFL + Fe3+ had a stronger inhibitory effect on algal density. The results may facilitate the resource utilization of eucalyptus harvesting residues, explorations of the potential application of eucalyptus tannins in the control of M. aeruginosa, and provide new ideas for ecological algal inhibition in eucalyptus plantations.

Acute toxicity of eucalyptus leachate tannins to zebrafish and the mitigation effect of Fe3+ on tannin toxicity.

Fish ponds polluted by the black water of eucalyptus forests (formed by the complexation of eucalyptus tannins with Fe3+) have experienced fish deaths. However, the toxicity of the components of black water is still unclear. To study the acute toxicities of eucalyptus leachate tannins to fish, their changes in the presence of Fe3+, and the underlying mechanisms, the static bioassay test method was adopted for acute exposure testing of zebrafish. Zebrafish were exposed to three kinds of tannins, namely, tannic acid (TA), epigallocatechin gallate (EGCG) and tannins from fresh eucalyptus leaf leacheate (TFL), and to solutions of these tannins with different molar ratios of Fe3+, under both no-aeration and aeration conditions. The results showed that the 48 h LC50 values of TA, EGCG and TFL were respectively 92, 47, and 186 mg·L-1, under no aeration, and 171, 86, and 452 mg·L-1 under aeration. When Fe3+ at 2, 1, and 6 times the molar amount of tannin was added to LC100 solutions of TA, EGCG and TFL, zebrafish mortality in 24 h was reduced to 0-33%. Acute fish death in eucalyptus plantation areas is related to high concentrations of eucalyptus tannins in the water. However, with increasing dissolved oxygen and Fe3+ levels, the acute toxicity of tannins to fish can be reduced. Thus, the black water in eucalyptus plantation areas reflects a water quality phenomenon that reduces the acute toxicity of eucalyptus tannins to fish. The mechanism of tannin toxicity to fish may be related to the impairment of oxygen delivery by fish blood, but the mechanism needs further study. These results provide a scientific basis for the prevention and control of fish suffering from acute eucalyptus tannin poisoning in eucalyptus plantation areas and for the protection of water resources.

[Effects of plantation on aggregate distribution and stability of lateritic red soil in south subtropical China]. / 南亚热带人工林种植对赤红壤团聚体分布及稳定性的影响.

We examined the stability of soil aggregates in five typical plantations, i.e., Eucalyptus urophylla × E. grandis plantation, Cunninghamia lanceolata plantation, Pinus massoniana plantation, Mytilaria laosensis plantation and Castanopsis hystrix plantation, in the south subtropical China by the Elliott wet sieving and Le Bissonnais (LB) methods. The results showed that the content of water stability aggregate (WR>0.25) was more than 62.2% after wet sieving. The mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates were 1.58-3.71 mm and 0.57-2.02 mm, respectively, which were the largest in C. lanceolata plantation and the smallest in E. urophylla × E. grandis plantation. Percentage of aggregate destruction (PAD) of five kinds of plantations ranged from 4.6% to 31.5%. The transfer matrix method was used to evaluate the soil aggregates, with the aggregate stability index (ASI) following the order of C. lanceolata plantation > C. hystrix plantation > M. laosensis plantation > P. massoniana plantation > E. urophylla × E. grandis plantation. Under the three treatments of LB method, the FW treatment was the most destructive to the stability of soil aggregates, indicating that dissipation played a major role in the disintegration of soil aggregates. The WS treatment had the least damage to the aggregates. The effect of slow wetting (SW) treatment was between the fast wetting (FW) and wet stirring (WS). Both the MWD and GMD values followed the order of WS>SW>FW, which gradually decreased with the increases of soil depth. The GMD value of aggregates under FW treatment by LB method of five plantations was significantly positively correlated with ASI, MWD and GMD of wet sieving method, indicating that the traditional wet sieving method had a good correlation with FW treatment and was feasible to determine the stability of soil aggregates in the subtropical red soil. Based on the aggregate stability indices of MWD, GMD, PAD and ASI, C. lanceolata plantation was more conducive to the improvement of soil aggregation level, with more stable soil structure than the other four plantations.

[Characteristics of soil saturated hydraulic conductivity on different positions and their controlling factors of granite collapsing gullies]. / èŠ±å²—å²©å´©å²—ä¸åŒéƒ¨ä½åœŸå£¤é¥±å’Œå¯¼æ°´çŽ‡ç‰¹å¾åŠå ¶å½±å“å› ç´ .

Collapsing gully is a common phenomenon of hydraulic-gravity combined soil erosion in granite hilly area of south China. The study aimed to explore the relationship between soil hydraulics pro-perties and erosion mechanism and the intrinsic controlling factors. The active, semi-stable, and stable types of granite collapsing gullies in southeastern Guangxi were selected to examine the spatial variation of soil saturated hydraulic conductivity and identify the influencing factors. Main results were as follows: 1) Soil saturated hydraulic conductivity of collapsing gullies fluctuated on different positions, with the bottom of collapsing wall showing the minimum value, the top of colluvial deposit showing the maximum, and followed by the top of alluvial fan. 2) All the models being selected to model the soil saturated hydraulic conductivity, including Cosby, Compbell, Julià, and Hypre, performed poor. 3) Results of correlation analysis showed that soil saturated hydraulic conductivity was negatively correlated with capillary porosity and clay content, and positively correlated with non-capillary porosity and sand content. 4) Results of path analysis showed that sand content was the most influencing factor in controlling soil saturated hydraulic conductivity of collapsing gullies, followed by non-capillary porosity and soil bulk density, where sand content and non-capillary porosity exerted a positive effect and bulk density exerted a negative one. Our findings will provide theoretical basis for the mechanistic understanding and prevention of collapsing gullies erosion.

Occurrence patterns of black water and its impact on fish in cutover areas of Eucalyptus plantations.

Black runoff occasionally flows from cutover areas of Eucalyptus plantations, polluting rivers and ponds, and resulting in fish death in severe cases. However, the occurrence patterns and environmental impacts of this black water remain unclear. Herein, we analyzed the major characteristics of black water at the occurrence sites, tested the complexation reaction of ground eucalyptus leaves with a solution of Fe3+, and determined the color and absorbance of the complex solution. The results showed that the water was dark blue, with weak acidity and strong light absorbance. The water contained a high level of dissolved organic matter content, while its chemical oxygen demand, total N, total P, NO3--N, and NH4+-N concentrations were significantly higher than those in the stream water from Eucalyptus, Pinus massoniana Lamb., and Cunninghamia lanceolata stands during the growth period. Additionally, the tannic acid concentration in the black water was 1.0 mg L-1 higher than that in the stream water from the Eucalyptus stand. The input of black water increases the concentration of tannic acid and NH4+-N, and the degradation of organic matter consumes dissolved oxygen in downstream ponds, leading to fish deaths. The presence of fresh logging residues and hot, humid weather also enable black water formation. Field investigations and simulation experiments revealed fresh Eucalyptus residues decompose rapidly under high-temperature and rainfall conditions, releasing large amounts of tannic acid, which reacts with Fe3+ to form a dark blue tannic acid­iron complex and results in black water. These results indicate that the rich Fe3+ in runoff may be a key factor in the occurrence of black water. The logging of Eucalyptus plantations during the dry season or on non-rainy days and a reduction in the logging area could prevent the occurrence of black water or mitigate the extent of its environmental hazards.

[Stability and organic carbon characteristics of soil aggregates under different ecosystems in karst canyon region].

Soil aggregates and their organic carbon distributions were studied under six ecosystems, i. e., farmland (short for ST), dry land (HD), grassland (CD), shrubbery (GC), plantation (RGL) and secondary forest (CSL), in a karst canyon region of China by a combination of field investigation and laboratory analysis. The result showed that, soil aggregates were dominated by particles with sizes>8 mm in the ecosystems except HD under dry sieving, and basically presented a trend of decreasing firstly, then increasing and finally decreasing along with particle sizes decreasing; while soil aggregates were dominated by particles with sizes > 5 mm in the ecosystems except HD under wet sieving and decreased with decreasing of particle sizes. The mean mass diameter (MMD) was in the order of ST>CD>RGL>CSL>GC>HD and the geometric mean diameter (GMD) was ST>CD>RGL>CSL>HD>GC by dry sieving, and MMD was RGL>CSL>GC>CD>ST>HD and GMD was CSL>RGL>GC>CD>ST>HD by wet sieving. Therefore, MMD and especially GMD of wet sieving were more accurate than that of dry sieving to evaluate soil aggregates quality in the karst cannon region. The fractal dimension (D) of mechanical stability in soil aggregates followed the order of CD>HD>ST>RGL>CSL>GC and the water stability was in the order of GC>CSL>RGL>HD> CD>ST. The higher the SOC content was, the larger values of D, MMD, GMD became, and the more sense the soil structure made. Soil organic carbon content was highest in the aggregate particles with sizes ranging from 0.25 to 0.053 mm, and the content in some particles with sizes > 5 mm was lowest. However, the contribution rate of particles with sizes > 5 mm was largest to soil organic carbon, which gradually decreased with the decrease of particle size.

[Litter decomposition of dominant plantations in Guangxi and its effects on leachate quality].

To understand the decomposition characteristics of the litters in different forest plantations and the effects of released substances during litter decomposition on the leachate quality, litter samples (leaf, shoot, and cortices) were collected from five forest plantations (1 year-old Eucalyptus urophylla x E. grandis, EU1; 4 year-old Eucalyptus urophylla x E. grandis, EU4; 7 year-old Acacia mangium x A. auriculaef, AM; 13 year-old Pinus massoniana Lamb, PL; and mixed broad-leaved softwood, BL), and incubated at 28 degrees C, using water leached for 255 days. In the first 105 days, the litter leachates of EU1 and EU4 had significantly higher coloration and N and P contents and lower pH than those of AM, PL, and BL. On the 255th day, the cumulative chemical oxygen demand (COD) in the leaf litters leachates of EU1 and EU4 was 193.9 and 212.8 g x kg(-1), being 4.2, 4.0, and 4.3 times and 5.3, 4.4, and 4.7 times higher than that of AM, PL, and BL, respectively. The mass loss rate and the N and P leaching rate of the leaf litter of EU1 were significantly higher than those of AM, PL, and BL. The mass loss rate of cortices of EU1 was significantly higher than that of PL. No significant difference was observed for the leaching rate of the shoot litters between AM, PL, and BL. Among the litter samples, leaf litter was easiest to be decomposed, while shoot litter was most difficult to be decomposed. The pH value of the litter leachates of Eucalyptus plantations was significantly negatively correlated with leachate chroma and COD, and the COD had significant positive correlations with the concentrations of total N and P in the leachates.

[Effects of water content on redox potential and carbon mineralization of wetland sediments].

To better understand the effect of soil water contents on redox potential (Eh), and their impacts on C mineralization in natural wetland, sediment samples from 3 types of wetlands (fen, humus marsh and marshy meadow) in the San-jiang Plate region of North China were incubated (25 degrees C) for 155 d under a range of reducing and oxidizing conditions by controlling water contents (varied from 24% to 232% of water holding capacity) (WHC). CO2-C evolved during incubation was measured at different time intervals. Results showed that Eh of sediments decreased significantly as water content increased from 24% WHC (lighted moisturized) to about 100% WHC, then decreased slightly as water content increased further to a level of submersed (about 2 cm water-depths). The accumulative amount of CO2-C evolved from the sediments indicated that the optimum water contents for mineralization of organic C are 32%, 48% and 76%-100% WHC for sediments of fen, humus marsh, and marshy meadow, respectively. The relationship between mineralization rates and redox potentials (Eh) were well fitted with second order parabola equations (p < 0.05). Mineralization rates and accumulative amount of organic C displayed a positive correlation with Eh up to 300 mV. However, a significant negative correlation was observed when Eh increased above 300 mV. Results demonstrated that low redox potential is the controlling factor of carbon accumulation of wetland in San-jiang Plate region.

[Relationship between organic carbon and water content in four type wetland sediments in Sanjiang Plain].

Characteristic and relationship were analyzed between organic carbon and water content in four types of wetlands (one cultivated wetland and three typical natural wetlands including fen, marsh and marshy meadow) in Sanjiang Plain of Northeastern China. Results show that there are distinct differences in the depths of organic carbon deposition, the organic carbon and water content in sediment profiles of these four type wetlands. There are significant positive correlations between organic carbon and water content in sediment profiles of the same type wetland (p < 0.01; R2 = 0.8276, 0.9917, 0.9916 and 0.9782 for cultivated wetland, fen, marsh and marshy meadow, respectively). The trend for evolution of ecological and environmental functions of wetland ecosystems is discussed based on the analysis of the relationship between soil organic carbon and water content. The results further illustrate the viewpoint that the protection and restoration of wetlands could lessen the global climate change caused by the increase in atmospheric CO2 concentration.