[Effects of exogenous plant hormones on physiological characteristics and yield of sweet potato under drought stress]. / å¹²æ—±èƒè¿«ä¸‹å–·æ–½å¤–æºæ¤ç‰©æ¿€ç´ å¯¹ç”˜è–¯ç”Ÿç†ç‰¹æ€§å’Œäº§é‡çš„å½±å“.

To explore the alleviation effect of spraying phytohormone on physiological characteristics and yield of sweet potato under drought stress in different periods, and to determine the best period of spraying external plant hormones, the effects on endogenous hormone content, photosynthetic fluorescence characteristics and yield of sweet potato were examined by spraying 6-benzylaminopurine (6-BA), α-naphthylacetic acid (NAA) and abscisic acid (ABA) respectively under drought stress after transplanting for 20 days (early stage), 60 days (middle stage) and 100 days (later stage) under artificial water control. The results showed that compared with spraying water, exogenous phytohormones significantly increased the yield of sweet potato under drought stress, among which 6-BA had the highest effect, followed by NAA and ABA. The effect of spraying in early stage was better than that in middle and late stages. Exogenous phytohormones significantly increased photosynthetic and chlorophyll fluorescence parameters of sweet potato leaves under drought stress at different stages, alleviated the decrease in eatin ribonucleoside (ZR) and auxin (IAA) caused by drought. Stepwise regression analysis showed that endogenous hormones and photosynthetic characteristics were key factors affecting yield of sweet potato. Results of path analysis showed that spraying exogenous plant hormone affected sweet potato yield by changing net photosynthetic rate (Pn), IAA, ZR, maximal photochemical efficiency and photochemical performance index under drought stress at early stage. Therefore, spraying 6-BA could regulate the content of endogenous hormones and improve photosynthetic characteristics of sweet potato at the early growth stage, and thus effectively alleviate the loss of yield caused by drought stress.

[Pollution Characteristics and Source Analysis of Polycyclic Aromatic Hydrocarbons in Agricultural Soils from Shandong].

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that originate mainly from anthropogenic sources. PAHs have elicited much concern because they exhibit strong toxic, carcinogenic, and mutagenic properties. Agricultural soil is at risk of PAH contamination mainly caused by atmospheric depositions, wastewater irrigation, or organic substances and biowaste applied as fertilizers. The surface agricultural soils were collected from Shandong in July 2015, and measured for 16 US EPA priority PAHs using high performance liquid chromatography with UV and fluorescence detector. The content and composition of PAHs were analyzed. The differences of PAHs between soils from the field for growing crops and from vegetable greenhouses, and between soils from point sources and from non-point sources were compared. The sources of PAHs were determined with methods of ratio between PAHs and positive matrix factorization (PMF), and the risks of PAHs were assessed. The results showed that the total content of 16 PAHs (∑16PAHs) ranged from 111.5 ng·g-1 to 2744.1 ng·g-1, with the mean of 556.3 ng·g-1. The content of 3-ring PAHs was relatively high, with the mean of 201.5 ng·g-1; while the contents of 2-ring and 6-ring PAHs were relatively low, with the mean of 39.3 ng·g-1 and 43.4 ng·g-1, respectively. According to the contamination classification in Poland, 71% of the samples in Shangdong were weakly contaminated. Compared with other areas in China, the content of PAHs in the agricultural soils in Shandong was in the middle range. Acenaphthene, fluorine, and fluoranthene were the major PAH compounds, accounting for more than 10% of the total PAHs; while the contribution of indeno (1,2,3-cd) pyrene was low. The content of ∑16PAHs and contribution of 7 carcinogenic PAHs were significantly higher in soils polluted by point sources than those in soils from non-point sources. Moreover, the contribution of PAHs with 2-3 rings was significantly higher in soils from non-point sources, while the contribution of PAHs with 4-6 rings was significantly higher in soils polluted by point sources. There was no significant difference in soils from vegetable greenhouses and from adjacent field soils, and the contribution of PAHs with 3-4 rings was high. The PAH isomer pair ratios of Ant/(Ant+Phe), Flu/(Flu+Pyr), BaA/(BaA+Chr), and InP/(InP+BP) were utilized as molecular indices to elucidate the possible PAH sources, and the results suggested that the PAHs in the soils were mainly from combustion. To quantitatively assess the contribution of various sources to PAH contamination, PMF was used to analyze the sources. The sources of PAHs were combustion of coal biomass, oil combustion from traffic, coking, and petroleum pollution, with contribution of 42.7%, 19.3%, 22.8% and 15.2%, respectively. Toxic equivalency factors were used to evaluate PAH contamination in the soils, and the carcinogenicity of other PAHs relative to BaP was quantified to estimate the BaP-equivalent concentration (TEQBaP). The TEQBaPof 16 PAHs (∑16TEQBap) in soils from non-point sources and vegetable greenhouses was 31.69 and 44.47 ng·g-1, respectively, which were below the safe value in Canadian soil quality guidelines. However, the ∑16TEQBap in some field soils from point sources exceeded the safe value, indicating that there were potential risks in the soils from point sources in Shandong.

Influence of lead acetate on soil microbial biomass and community structure in two different soils with the growth of Chinese cabbage (Brassica chinensis).

A greenhouse pot experiment was conducted to evaluate the impact of different concentrations of lead acetate on soil microbial biomass and community structure during growth of Chinese cabbage (Brassica chinensis) in two different soils. The field soils were used for a small pot, short-term 60-day growth chamber study. The soils were amended with different Pb concentrations, ranging from 0 to 900mgkg(-1) soil. The experimental design was a 2 soilx2 vegetation/non-vegetationx6 treatments (Pb)x3 replicate factorial experiment. At 60 days the study was terminated and soils were analyzed for microbial parameters, namely, microbial biomass, basal respiration and PLFAs. The results indicated that the application of Pb at lower concentrations (100 and 300mgkg(-1)) as lead acetate resulted in a slight increase in soil microbial biomass, whereas Pb concentrations >500mgkg(-1) caused an immediate gradual significant decline in biomass. However, the degree of impact on soil microbial biomass and basal respiration by Pb was related to management (plant vegetation) or the contents of clay and organic matter in soils. The profiles of 21 phospholipid fatty acids (PLFAs) were used to assess whether observed changes in functional microbial parameters were accompanied by changes in the composition of the microbial communities after Pb application at 0, 300 and 900mg Pbkg(-1) soil. The results of principal component analyses (PCA) indicated that there were significant increases in fungi biomarkers of 18:3omega6c, 18:1omega9c and a decrease in cy17:0, which is an indicator of gram-negative bacteria for the high levels of Pb treatments In a word, soil microbial biomass and community structure, therefore, may be sensitive indicators reflecting environmental stress in soil-Pb-plant system. However, further studies will be needed to better understand how these changes in microbial community structure might actually impact soil microbial community function.

Effects of lead contamination on soil microbial activity and rice physiological indices in soil-Pb-rice (Oryza sativa L.) system.

The effect of lead (Pb) treatment on the soil microbial activities (soil microbial biomass and soil basal respiration) and rice physiological indices were studied by greenhouse pot experiment. Pb was applied as lead acetate at six different levels in two different paddy soils, namely 0 (control), 100, 300, 500, 700, 900 mg kg-1 soil. The results showed that the application of Pb at lower level (<300 mg kg-1) as lead acetate resulted in a slight increase in soil microbial activities compared with the control, and had an inhibitory influence at high concentration (>500 mg Pb kg-1 soil), which might be the critical concentration of Pb causing a significant decline in the soil microbial activities. However, the degree of influence on soil microbial activities by Pb was related to the clay and organic matter contents of the soils. On the other hand, when the level of Pb treatments increased to 500 mg kg-1, there was ecological risk for both soil microbial activities and plants. The results also revealed that there was a consistent trend that the chlorophyll contents increased initially, and then decreased gradually with increase in Pb concentration. Pb was effective in inducing proline accumulation and its toxicity causes oxidative stress in rice plants. In a word, soil microbial activities and rice physiological indices, therefore, may be sensitive indicators reflecting environmental stress in soil-Pb-rice system.