Genbao Li

Development of artificially induced biological soil crusts in fields and their effects on top soil

AimsBiological soil crusts (BSCs) could improve severe environment ecological conditions by increasing soil moisture, soil nitrogen concentration, and so on. In order to control desertification and recover the destroyed soil fertility utilizing a new means using BSCs, the soil surface was artificially inoculated with Microcoleus vaginatus and Scytonema javanicum. Relationships between the development of the artificially induced biological soil crusts and the distribution and dynamic changes of nitrogen and phosphorus in the soil crusts have been analyzed.MethodsCrusts of different ages were investigated by measuring soil physical and chemical factors, such as moisture, pH, total and available N content, and total and available P, which were correlated with the depths of the crusts.ResultsThis study found that the types of color, shape, and species components of the algal crusts increased with crust development. Soil moisture, total N, available N, and available P increased gradually with crust growth. Soil with crusts was wetter than the controlled naked sandy soil, and a significant correlation was observed between biomass and total nitrogen (r = 0.946, P = 0.015). Soil pH was lower than that of control. The scytonemin on the soil surface was exceptionally higher than the other pigments, and all the pigments were mainly distributed at the soil surface level. Though the crusts were mainly distributed on soil surface, the available P was mainly stored below the crust layer.ConclusionsPearson correlation tests indicated that artificially inoculated biological crusts could improve soil fertility and micro-environment of the top soil: The development of artificially induced BSCs was very well, and this was favorable to inducing the following crust succession.

Effects of gibberellin A(3) on growth and microcystin production in Microcystis aeruginosa (cyanophyta)

Environmental factors that affect the growth and microcystin production of microcystis have received worldwide attention because of the hazards microcystin poses to environmental safety and public health. Nevertheless, the effects of organic anthropogenic pollution on microcystis are rarely discussed. Gibberellin A(3) (GA(3)) is a vegetable hormone widely used in agriculture and horticulture that can contaminate water as an anthropogenic pollutant. Because of its common occurrence, we studied the effects of GA(3) on growth and microcystin production of Microcystis aeruginosa (M. aeruginosa) PCC7806 with different concentrations (0.001-25mg/L) in batch culture. The control was obtained without gibberellin under the same culture conditions. Growth, estimated by dry weight and cell number, increased after the GA(3) treatment. GA(3) increased the amounts of chlorophyll a, phycocyanin and cellular-soluble protein in the cells of M. aeruginosa PCC7806, but decreased the accumulation of water-soluble carbohydrates. In addition, GA(3) was observed to affect nitrogen absorption of the test algae, but to have no effect on the absorption of phosphorus. The amount of microcystin measured by enzyme-linked immunosorbent assay (ELISA) increased in GA(3) treatment groups, but the stimulatory effects were different in different culture phases. It is suggested that GA(3) increases M. aeruginosa growth by stimulating its absorbance of nitrogen and increasing its ability to use carbohydrates, accordingly increasing cellular pigments and thus finally inducing accumulation of protein and microcystin.

Zebrafish neurotoxicity from aphantoxins--cyanobacterial paralytic shellfish poisons (PSPs) from Aphanizomenon flos-aquae DC-1.

Aphanizomenon flos‐aquae (A. flos‐aquae), a cyanobacterium frequently encountered in water blooms worldwide, is source of neurotoxins known as PSPs or aphantoxins that present a major threat to the environment and to human health. Although the molecular mechanism of PSP action is well known, many unresolved questions remain concerning its mechanisms of toxicity. Aphantoxins purified from a natural isolate of A. flos‐aquae DC‐1 were analyzed by high‐performance liquid chromatography (HPLC), the major component toxins were the gonyautoxins1 and 5 (GTX1 and GTX5, 34.04% and 21.28%, respectively) and the neosaxitoxin (neoSTX, 12.77%). The LD50 of the aphantoxin preparation was determined to be 11.33 μg/kg (7.75 μg saxitoxin equivalents (STXeq) per kg) following intraperitoneal injection of zebrafish (Danio rerio). To address the neurotoxicology of the aphantoxin preparation, zebrafish were injected with low and high sublethal doses of A. flos‐aquae DC‐1 toxins 7.73 and 9.28 μg /kg (5.3 and 6.4 μg STXeq/kg, respectively) and brain tissues were analyzed by electron microscopy and RT‐PCR at different timepoints postinjection. Low‐dose aphantoxin exposure was associated with chromatin condensation, cell‐membrane blebbing, and the appearance of apoptotic bodies. High‐dose exposure was associated with cytoplasmic vacuolization, mitochondrial swelling, and expansion of the endoplasmic reticulum. At early timepoints (3 h) many cells exhibited characteristic features of both apoptosis and necrosis. At later timepoints apoptosis appeared to predominate in the low‐dose group, whereas necrosis predominated in the high‐dose group. RT‐PCR revealed that mRNA levels of the apoptosis‐related genes encoding p53, Bax, caspase‐3, and c‐Jun were upregulated after aphantoxin exposure, but there was no evidence of DNA laddering; apoptosis could take place by pathways independent of DNA fragmentation. These results demonstrate that aphantoxin exposure can cause cell death in zebrafish brain tissue, with low doses inducing apoptosis and higher doses inducing necrosis.

Characteristics and kinetic studies of Hydrilla verticillata pyrolysis via thermogravimetric analysis

The pyrolysis characteristics and kinetic of Hydrilla verticillata (HV) have been investigated using non-isothermal thermogravimetric analysis. The results showed that the pyrolysis behavior of HV can be divided into two independent stages. The kinetics of Stage I was investigated using a distributed activation energy model (DAEM) with discrete 99 first-order reactions. Stage II was an independent stage which corresponds to the decomposition of calcium oxalate, whose kinetics was studied using iso-conversional method together with compensation effect and master-plots method. The activation energies ranged from 92.39 to 506.17 and 190.42 to 222.48 kJ/mol for the first and second stages respectively. Calculated data gave very good fit to the experimental data.

Dianchi Lake macroinvertebrate community succession trends and retrogressive analysis

Historical records and data from yield surveys conducted in 2009 and 2010 were used to investigate macroinvertebrate community succession trends in Dianchi Lake. Species richness has declined from 57 in the 1980s to 32 in 2010, representing a species loss of 44%. Among the major benthic groups, the highest rate of loss was recorded for mollusks (75%) and aquatic insects (39%). Surveys in 2009 and 2010 across the lake revealed that the total density was 1776 ind/m2, comprising oligochaetes (1706 ind/m2) and chironomids (68 ind/m2). Over a nearly twenty-year span (1992-2010), the density and biomass of oligochaetes first increased sharply (1992-2002) and then declined gradually (2002-2010). Further, chironomids have decreased gradually while the proportion of abundant species has increased. Limnodrilus hoffmeisteri became the sole dominant species with an average relative abundance of 74.1%. Cosmopolitan species, such as Einfeldia sp., disappeared across the lake; instead, tolerant species such as Chironomus plumosus, Ch. attenuatus and Tanypus chinensis became the common. Mollusk community structure has become simpler and many native species have gone extinct. Species of concern include Margarya melanioides, M. mondi, M. mansugi and Cipangopaludina dianchiensis, all rated as critically endangered by the IUCN. We found that the Shannon-Wiener index declined in Dianchi Lake, particularly in Caohai Lake, from 2.70 in the 1950s to 0.30 in 2009 and 2010. Species richness and biodiversity was significantly negative correlated with total phosphorus and total nitrogen. Factors responsible for the benthic community retrogression described here include habitat destruction, lowering of water quality, outbreaks of blue-green algae, extinction of submerged plants and lack of germplasm resources.

Cytochemical changes in the developmental process of Nostoc sphaeroides (cyanobacterium)

There are several apparent developmental stages in the life cycle of Nostoc sphaeroides Kützing, an edible cyanobacterium found mainly in paddy fields in central China. The cytochemical changes in developmental stages such as hormogonia, aseriate stage, filamentous stage and colony in N. sphaeroides were examined using fluorescent staining and colorimetric methods. The staining of acidic and sulfated polysaccharides increased with development when hormogonia were used as the starting point. Acidic polysaccharides (AP) were most abundant at the aseriate stage and then decreased, while the sulfated polysaccharides (SP) were highest at the colony stage. Quantitatively, along the developmental process from hormogonia to colony, total carbohydrates first increased, then became stable, and then reached their highest level at the colony stage, while reducing sugars were highest at the hormogonia stage and then decreased sharply once development began. SP were not detectable in the hot water soluble polysaccharides (HWSP), and hormogonia had the lowest content of AP, while old colonies had the highest. The AP content of the aseriate stage, filamentous stage and young colony stage were very similar. The evolutionary relationships reflected in the developmental stages of N. sphaeroides are discussed.

Distribution and population dynamics of potential anatoxin-a-producing cyanobacteria in Lake Dianchi, China

The occurrence of cyanobacterial blooms is often accompanied by a variety of toxic secondary metabolites known as cyanotoxins. Anatoxin-a (ATX-a) is a highly toxic cyanobacterial neurotoxin synthesized by numerous species (e.g., Aphanizomenon, Anabaena and Oscillatoria) that has received much public attention. In this study, we used molecular methods (PCR and qPCR) to track the presence and dynamics of ATX-a-producing cyanobacteria, Aphanizomenon and Anabaena in Lake Dianchi, China based on the anaC and cpcBA-IGS genes over a 23-month period (from June 2010 to April 2012). Results revealed that Aphanizomenon was the major potential ATX-a producer in Lake Dianchi and that they were most abundant in early spring and least abundant in summer, coinciding with observed Aphanizomenon blooms. It was found that the proportion of ATX-a toxigenic cells was lower in the northern part of the lake (2.1%) than the middle (16.7%) and southern parts (19.2%). The information on the spatio-temporal distributions of ATX-a-producing cyanobacteria obtained in this study will help to build management strategies to improve water quality for public health.

Submerged vegetation removal promotes shift of dominant phytoplankton functional groups in a eutrophic lake

Historical data indicate that the dominance of submerged plants in Dianchi Lake in the 1960s was characterized by low algal density with dominance of non-toxic group J (Scenedesmus, Pediastrum, etc.). The removal of submerged plants, which began in the 1970s, resulted in the expansion of bloom-forming Microcystis (group M). Laboratory experiments suggested that Microcystis aeruginosa was inclined to grow and develop at elevated temperatures. The growth of Scenedesmus obliquus was slower than that of co-cultivated M. aeruginosa in the absence of Ceratophyllum demersum, especially at higher temperatures. The existence of submerged plant C. demersum could inhibit the growth of the harmful algae M. aeruginosa and this inhibitory effect by C. demersum was enhanced with an increase in temperature. Instead, with C. demersum, the growth of S. obliquus was not inhibited, but the co-cultivated M. aeruginosa was eliminated in a short time. Combined with the historical data and laboratory experiments, it was indicated that the submerged plants might play important roles in the dominance of the non-toxic group J in the historical succession. Consequently, the introduction of the submerged plant such as C. demersum might alter the dominant phytoplankton functional groups from M to J and benefit the restoration of the eutrophic lake.

The algae-lytic ability of bacterium DC10 and the influence of environmental factors on the ability.

A lysing-bacterium DC10, isolated from Dianchi Lake of Yunnan Province, was characterized to bePseudomonas sp. It was able to lyse some algae well, such asMicrocystis viridis, Selenastrum capricornutum, and so on. In this study, it was shown that the bacterium lysed the algae by releasing a substance; the best lytic effects were achieved at low temperatures and in the dark. Different concentrations of CaCl2 and NaNO3 influenced the lytic effects; the ability to lyse algae decreased in the following order: pH 4 > pH 9 > pH 7 > pH 5.5. It was significant to develop a special technology with this kind of bacterium for controlling the bloomforming planktonic microalgae.