The long-term changes of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in sediments can reflect the ecological risks (ER) caused by their pollution sources in different historical periods. This is of great significance to the improvement of environmental protection policies in the future. The study area is located in Taihu Lake, China. 137Cs and 210Pb were used for dating. Indicators related to local socio-economic development were introduced to optimize source identification in the absolute principal component score multiple linear regression (APCS-MLR) model. On this basis, the mean effect range median quotient (M-ERM-Q) method was used to evaluate the ER of source-oriented HMs and PAHs at different ages. The HMs content was relatively stable from 1949 to 2015, and then increased significantly. The PAH contents were on the rise during the whole historical period. The average contribution rate of traffic emission and fertilization to HMs was 50.59 % and 49.41 %. Ecological risk caused by Traffic emitted pollutants was relatively stable before 2015, then increased sharply, and finally reached a medium–high level. However, fertilization ER has always maintained an increasing trend and accelerated after 1980, ultimately reaching medium–low ER. The contribution rates of coal combustion, mixed sources (biomass and coal) and gasoline combustion to PAHs were 13.20 %, 52.45 % and 34.36 %, respectively. The ER of mixed sources and gasoline combustion showed a gradually increasing trend before 2007, and then began to decrease. However, coal combustion ER has been increasing, and the increase accelerated in 2000. Nevertheless, the ER of these three sources was still low. Overall, a certain degree of HMs pollution has been caused by traffic emissions and fertilization in recent years. Local governments should prioritize the control of these two sources to protect the Taihu Lake ecosystem.
Exploring microRNA (miRNA) expression patterns in Hemerocallis under low-temperature stress helps understanding the mechanisms of miRNA-mediated stress responses. Here, eight separate libraries were generated from the leaves and roots of two different varieties, cold-tolerant 'Jinyan 7' and cold-sensitive 'Lucretius 4', which were exposed to 20°C and −4°C for 8 h. In total, 333 cold-responsive miRNAs, including 85 putative novel and 248 conserved miRNAs, were identified during different temperature treatments. Under cold-stress conditions, two miRNAs were down-regulated and one was up-regulated in the roots, and no differentially expressed miRNAs were detected in the leaves in 'Lucretius 4'. In 'Jinyan 7', there were two novel and one conserved differentially expressed miRNAs in leaves, whereas three conserved and two novel miRNAs were differentially expressed in roots. The target genes were mainly involved in metabolic processes and cellular components. The differential expression levels of 10 miRNAs were validated using quantitative RT–PCR. Some candidate miRNAs (e.g. ath-miR165a, ath-miR166a, ath-miR395a and novel-miR67) may be involved in plant response-related processes to low-temperature.
By the method of in situ soil core-ion exchange resin bag(ISC-IERB),the characteristics of soil nitrogen mineralization in the different successive rotation stands of poplar plantation(the first rotation of four-year-old and the second rotation of four-year-old) and the effects of tillage on the soil nitrogen mineralization in the second rotation of four-year-old poplar plantation were studied in north Jiangsu province.The results showed that the seasonal changes of soil ammonification rate in two rotation stands were similar.The soil ammonification rate in the second rotation stand was not obviously decreased and even increased in April and July,compared with the first rotation stand.However,the soil nitrification rate and net mineralization rate in the second rotation stand were significantly lower than that in the first rotation stand,especially in March,April and May.Compared with the no-tillage,the annual ammonified,nitrified and mineralized nitrogen of soil in the second rotation stand treated with the tillage were increased.Meanwhile,the tillage treatment was obviously increased the soil N lose by leaching which accounted for 49.15% of the total annual mineralized N,therefore soil inorganic N content was lower in the stand treated with tillage than that in the stand with no-tillage.
Exploring the characteristics of vegetation change and its influencing factors is essential to construct an ecological environment. Based on the NDVI dataset from 2000 to 2020, this study analyzed the spatial temporal attributes of NDVI changes in Shandong Province using the Sen trend analysis and the gravity center migration model. Furthermore, the spatial heterogeneity of NDVI and its influencing factors within the whole study area and different soil and water conservation zones were investigated using a Geo-detector model, considering population, hydrological, topographic, soil types, and vegetation types. The results were as follows： ① The NDVI in Shandong Province from 2000 to 2020 showed a fluctuating upward trend with significant seasonal characteristics that varied from different zones. The annual NDVI change showed a trend of single-peak in the Ⅲ-4-2t, Ⅲ-4-1xt, and Ⅲ-5-2w but showed a trend of double-peak in the Ⅲ-5-3fn. ② Regarding the spatial distribution, the NDVI was higher in the west-north and west-south areas and lower in the north and coastal areas. During the 21 years, the primary type of NDVI change was "medium-high coverage → high coverage," especially in the northeastern part of the soil conservation area of the Ⅲ-4-2t, the western part of the Ⅲ-4-1xt, and the ecological maintenance area of the Ⅲ-5-2w. Overall, 61.47% of the area had a positive trend of NDVI change with the gravity center of high coverage mitigating to the northeast, and the ecological environment was improved. ③ Soil types and population density were the dominant factors affecting NDVI in Shandong Province, with
Effects of rhizosphere acidification on P efficiency in different poplar clones were conducted by the method of soil culture in greenhouse. Potassium dihydrogen phosphate was applied to furnish 0, 40, 80, and 120 mg P2O5 kg-1. The experiment consisted of three replicates of each treatment, with a pot of 40 kg soil in a randomized block. The results showed that high P efficiency clones, such as S17, S19, and 105, could decrease their pH values in rhizosphere under P deficiency stress much stronger than clones 106, 797, I-69, 1388, and 3,244, which were low P efficiency clones. The most decrement of pH for the former even accounted to 1.32 pH units and the ratios of the decrements were over 10% in comparison with the pH values in bulk soil. Whereas for the latter less than 0.21 pH units and 2.5% of the decreasing ratio respectively. In contrast to low P efficiency clones, high P efficiency clones could acidify their rhizosphere through a kind of specific mechanism because the pH values in rhizosphere of high P efficiency clones were gradually decreased corresponding with the intensity of P deficiency stress and vice versa. The amounts of available P in rhizosphere of clone S17, S19, and 105 reached 2.64, 3.27, and 3.28 mg.kg-1, respectively, obviously higher than those of the other five low P efficiency clones, which all were below 2.00 mg.kg-1 under P deficiency stress, and the summation percentages of available P in rhizosphere were over 60% for all high P efficiency clones, but less than 10% for low P efficiency clones. The amounts of P taken up by high P efficiency clones were statistically greater than by low P efficiency clones. Regression analysis also indicated that the increment of available P in rhizosphere was closely correlated with the decrement of pH values in rhizosphere under P deficiency stress. This demonstrated the impact of rhizosphere acidification on availability of rhizosphere P, and identified that high P efficiency clones could enhance their contents of available P in rhizosphere, absorb more P and thus grow better through rhizosphere acidification depended on deficiency stress.
The adsorption and desorption of organic and inorganic phosphorus in the three types of paddy soils were studied in the lab experiments. The results showed that the maximum adsorption capacity both to monopotassium phosphate and inositol hexaphosphate from big to small were: red loam soil, stagnic anthrosols, loamy sand soil, and adsorption capacity of organic phosphorus was larger than that of inorganic phosphorus. The adsorption of organic and inorganic phosphorus could be fitted well by equations of Langmuir, Freundlich and Temkin. The Langmuir equation was the best for the fit of inorganic phosphorus adsorption. The Temkin equation was the best for the fit of organic phosphorus adsorption. The desorption of organic and inorganic phosphorus correlate exponentially with the adsorpted phosphorus. The desorbed phosphorus from big to small was loamy sand soil, stagnic anthrosols, red loam soil. The adsorption was affected by the ionic strength of the sorption solutions.
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