[Effects of Organic Fertilization on Bacterial Community and Maize Productivity in Dryland Red Soil].

Since 2002, a long-term field experiment has been conducted to determine the effects of different organic fertilization treatments on the bacterial community characteristics and maize productivity in dryland red soil using high-throughput sequencing technology. The experiment consisted of four treatments:no manure, M0; low manure, M1; high manure, M2; and high manure with lime addition, M3. Our results showed that the different organic fertilization treatments(M1, M2, and M3) significantly promoted maize productivity with the highest values of pH, soil organic matter(SOM), total nitrogen(TN), and total phosphorus(TP) compared to that under the M0 treatment, and the high manure with lime addition(M3) treatment had the highest level of maize production. The different organic fertilization treatments significantly increased the Shannon index, Evenness index, Chao1 index, and ACE index and significantly shaped the composition of the bacterial community. TP and pH were the main variables determining soil bacterial diversity index based on random forest modeling analysis, whereas pH, SOM, TP, and TN were the main variables determining the structure of the soil bacterial community. Correlation analysis and structural equation modeling determined that TP and SOM indirectly affected maize productivity by varying the bacterial diversity and community structure. The results of this study provide the scientific basis for ensuring food security and sustainable agricultural development by improving the fertility and bacterial diversity in dryland red soil.

[Effects of Ni2+ on physiological characteristics and submicroscopic structure of Salvinia natans leaves].

Influence of 0, 5, 10, 15, 20 mg/L Ni2+ on growth, mineral nutrition, chlorophyll, carotenoid, soluble protein, soluble sugar, superoxide (O2*-), hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents as well as the activities of superoxide dismutase (SOD), guaiacolperoxidase (POD), and catalase (CAT) were studied in the leaves of Salvinia natans plants on 10 days after treatment. With the increase of the Ni2+ concentrations, exposure of the plants revealed that, (1) the addition of Ni2+ affected the absorption of mineral nutrients, it mainly increased the absorption of Ca2+, Na+, Zn2+, Fe3+ and Mg2+, while reduced that of Mn2+, Mo2+, P and K+. (2) The content of chlorophyll, carotenoid, soluble protein and soluble sugar content as well as activities of SOD and CAT decreased gradually. That of O2*-, H2O2 and MDA content as well as POD activity increased, 383%, 168%, 207%, 131% of these controls, respectively. (3) In the leaves of Ni2+ -treated fronds, the polypeptide with apparent molecular weights 94000, was became visible in SDS-PAGE, and the nature of it remains to be determined. The amount and intensity of polypeptide band increased gradually with augment of Ni2+ was also observed, the polypeptide with apparent molecular weight 35,000 increased significantly in fronds. (4) Transmission electron microscope observation indicated that Ni2+ also imposed injury action on submicroscopic structure of leaf cells, disaggregation of nucleolus, agglutination and disappearance of chromatin of nucleus, disruption of nuclear membrane, swelling of thylakoids and breakage of chloroplast envelope, decreasing of cristae quantity and vacuolization of mitochondria. The conclusion could be reached that the plant death was resulted from destruction under structure foundation of physiological function, unbalance of ion equilibrium and disorder of physiological metabolism.

[Toxic effects of Hg2+, Cd2+ and Cu2+ on cell membrane system of Cabomba caroliniana A. Gray].

By the observation with electron- and confocal laser scanning microscopy and the determination of physiological and biochemical reactions, the toxic effects of Hg2+, Cd2+ and Cu2+ on the cell membrane system of Cabomba caroliniana A. Gray were investigated. The results showed that under the actions of the three heavy metal ions, the contents of reactive oxygen species (ROS) and malondialdehyde (MDA) in C. caroliniana leaf cells increased, activities of protective enzymes were in disorder, and lipid peroxidation happened. The cell membrane was damaged, membrane permeability increased, and plasmolysis occurred. Meanwhile, the chloroplast swelled or even disintegrated. The excitement of photosynthetic pigments on thylakoids membrane by light was inhibited, and the auto-fluoresent intensity was decreased. The cristae of mitochondria swelled and decreased, mitochondria membrane was damaged, and nuclear membrane was broken. The effects of Hg2+, Cd2+ and Cu2+ on the cell membrane system of C. caroliniana showed a definite dose-effect correlation, and the stability of membrane system played a key role in the resistance of C. caroliniana to the toxic effects of heavy metals. C. caroliniana was sensitive to Hg2+, and the lethal concentration of Hg2+ was ranged from 0.3 to 0.5 mg L(-1). C. caroliniana had relatively higher endurance to Cd2+ and Cu2+, and could be used as the resistant plant for biological control.

[Roles of exogenous spermidine in improving Salvinia natans tolerance towards cadmium stress].

In this study, the effects of foliar spraying different concentration (0.05-1 mmol L(-1)) spermidine (Spd) on the photosynthetic pigments, soluble protein content, antioxidant system, and mineral nutrition of Salvinia natans leaves under cadmium (Cd) stress were investigated, aimed to approach the action mechanisms of exogenous polyamines (PAs) in improving the adaptability of aquatic plants to heavy metals stress. The results showed that exogenous Spd could markedly mitigate the Cd stress to S. natans. It retarded the chlorosis, with chlorophyll a/b and total chlorophyll content increased by 18.97% and 43.96%, respectively, and increased the soluble protein content by 27.83%, compared with the control. SDS-PAGE revealed that the increase of soluble protein content was mainly of the expression increase of 5 polypeptides with apparent molecular weights 202.15, 77.67, 52.69, 41.83, and 25.35 kD. Exogenous Spd increased the activities of antioxidant enzymes SOD, POD and CAT and the contents of low molecular weight protective compounds AsA, GSH and Car, with an average increase of 12.44%, 66.90% and 51.23%, and 11.21%, 17.60% and 24.81%, respectively, and effectively maintained the balanced absorption of P, K, Fe, Na, Mg, Zn and Mn (with exception of Ca). In general, the optimum concentration range of exogenous Spd was 0.05-0.1 mmol x L(-1), which could enhance the resistance of S. natans to Cd toxicity by improving photosynthesis, stimulating the expression of protein, promoting the activity/content of antioxidant system, and keeping the balanced absorption of nutrient elements, etc.

[Effects of Cu2+ stress on leaf physiological indice and ultrastructure of Potamogeton malaianus].

With solution culture, this paper studied the toxic effects of different concentrations of Cu2+ (0, 2, 4, 6, and 8 mg x L(-1)) on the chlorophyll content, soluble protein content, protective enzyme activities, active oxygen generation, and ultrastructural changes in Potamogeton malaianus leaf. The results showed that with increasing concentration of Cu2+, the chlorophyll, carotenoid and soluble protein contents and superoxide dismutase (SOD) and peroxidase (POD) activities decreased, catalase (CAT) activity increased first and decreased then, while O2-*, H2O2, MDA and soluble sugar content increased. SDS-PAGE revealed that Cu2+ induced the disappearance or the decrease of the expression amount of four polypeptides with apparent molecular weights of 60.9, 18.8, 15.7, 22.3 and 30.0 kDa. Transmission electron microscopy observation indicated that the higher Cu2+, concentration, the more serious damages the leaf organelles, especially chloroplast, mitochondria and nucleus, suffered. It was concluded that the death of P. malaianus plant under Cu2+ stress was resulted from the destruction of physiological function and structural foundation, and the disorder of physiological metabolism. The lethal concentration of Cu2+ could be 2-4 mg x L(-1).

[Effects of exogenous spermidine on resistance of Nymphoides peltatum to Hg2+ stress].

Effects of different exogenous spermidine concentrations on the activities of some enzymes (SOD, CAT, POD, APX), O(-)(2) generation rate, the MDA, chlorophyll, soluble protein and polyamine contents in leaves of Nymphoides peltatum without Hg(2+) stress or under Hg(2+) stress were studied. The results showed that: (1) The spermidine (Spd) and spermine (Spm) content dropped significantly under Hg(2+) (3 mg/L) stress 4 d, while that of putrescine (Put) was increased markedly. Exogenous Spd could increase the Spd and Spm content in leaves, while that of Put lowered at first and rose later. (2) Hg(2+) 3 mg/L decreased drastically the activities of SOD, CAT and APX, increased the O(-)(2) generation rate, led to the accumulation of a large amount of MDA and loss of chlorophyll and soluble protein. Exogenous Spd could enhance the activities of SOD, CAT and APX, decrease O(-)(2) generation rate and reduce the MDA content. In addition, Spd could also decrease the loss of chlorophyll and soluble protein content induced by Hg(2+) stress, enhance the ability of Nymphoides peltatum to resist Hg(2+) stress. The most suitable concentration of Spd was in the range 0.1-0.5 mmol/L.

[Distribution and toxicity of cadmium in Hydrilla verticillata (L.f.) Royle].

Aquatic plants are known to accumulate and bioconcentrate heavy metals. In this study, aquatic vascular plant Hydrilla verticillata (L.f.) Royle was cultivated in water containing elevated concentrations of cadmium (up to 10 mg/L) for 7 d, the accumulation, subcellular distribution, ultrastructural localization, chemical form, toxic effects on mineral nutrient absorption of cadmium, photosynthesis rate and respiration rate were studied. It was found that H. verticillata fronds was able to accumulate cadmium, the bioconcentration factor was 193-307; subcellular fraction analysis revealed that cadmium major accumulated in cell wall (61.66%-52.00%) with decrease trends, the content of Cd enhanced in soluble fraction and remained stable in organelles, with the augment of pollutant concentration. The Cd levels occurred in different parts of leaf cell with the following sequence: cell wall > soluble fraction > organelles. Ultrastructural localization of cadmium with sulfide-silver method showed that Cd appeared in cell wall, chloroplast, nucleus and vacuole. Sequential extraction indicated that the ratio of different cadmium chemical form was different markedly, of which NaCl extractable Cd was predominated as compared with the other 5 forms; which could be seen in the following order: F(NaCl) > F(HAc) >F(Water) > F(Ethanol) > F(HCl) > F(Residue). The mineral nutrient absorption was also affected by cadmium stress, it increased the absorption of Ca, Mn, Cu, and Fe; but reduced that of P and K. Cd had a strong inhibitive effect on photosynthesis rate and respiration rate. The results suggested that the toxic symptoms of plant showed an evident correlation between dose and effect; the ultrastructural damage was closely related to the distribution of Cd. The conclusion could be reached that the death of plant was resulted from destruction of structure foundation of physiological function, unbalance of ion equilibrium and disorder of physiological metabolism.