Should time-lag and time-accumulation effects of climate be considered in attribution of vegetation dynamics? Case study of China's temperate grassland region.

Although the time-lag and time-accumulation effects (TLTAEs) of climatic factors on vegetation growth have been investigated extensively, the uncertainties caused by disregarding TLTAEs in the attribution analysis of long-term changes in vegetation remain unclear. This hinders our understanding of the associated changes in ecosystems and the effects of climate change. In this study, using multiple methods, we evaluate the biases of attribution analyses of vegetation dynamics caused by the non-consideration of TLTAEs in the temperate grassland region (TGR) of China from 2000 to 2019. Based on the datasets of the normalized difference vegetation index (NDVI), temperature (TMP), precipitation (PRE), and solar radiation (SR), the temporal reaction patterns of vegetation are analyzed, and the relationships among these variables under two scenarios (considering and disregarding TLTAEs) are compared. The results indicate that most areas of the TGR show a greening trend. A time-lag or time-accumulation effect of the three climatic variables is observed in most areas with significant spatial differences. The lagged times of the vegetation response to PRE are particularly prominent, with an average of 2.12 months in the TGR. When the TLTAE is considered, the areas where changes in the NDVI are affected by climatic factors expanded significantly, whereas the explanatory power of climate change on NDVI change increased by an average of 9.3% in the TGR; these improvements are more prominent in relatively arid areas. This study highlights the importance of including TLTAEs in the attribution of vegetation dynamics and the assessment of climatic effects on ecosystems.

Investigating and modeling the toxicity of arsenate on wheat root elongation: Assessing the effects of pH, sulfate and phosphate.

Excessive arsenic in soil and groundwater will not only seriously affect the growth of plants, but also endanger human health through the food chain. However, there are few studies on the effects of metalloid speciation and anion competition on the toxicity of arsenate [As(Ⅴ)]. To investigate the effects of accompanying anions and pH on the toxicity of As(Ⅴ) on wheat root elongation, wheat roots were exposed to the concentrations of As(Ⅴ) in the solution ranged from 0 to 500 mM and different levels of pH (4.5-8.0) and different accompanying anions (H2PO4-, SO42-, NO3- and Cl-) for five days. The root length of wheat was measured and the biotic ligand model (BLM) was developed to predict the potential toxicity of As(V) speciation to wheat roots. The results illustrated that EC50 of total As(V) (EC50{As(Ⅴ)T}) values increased from 6.88 to 33.9 µM with increasing pH values from 4.5 to 8.0, suggesting that increasing pH alleviated As(Ⅴ) toxicity. The EC50{AsO43-} and EC50{HAsO42-} values increased from 0.001 to 4342 µM and from 0.0214 to 27.4 µM, respectively, while the EC50{H2AsO4-} and EC50{H3AsO4} values sharply decreased from 6.62 to 2.68 µM and from 41.8 µM to 5.34 nm, respectively, when pH increased from 4.5 to 8.0. The toxicity of As(Ⅴ) decreased as the H2PO4- and SO42- activities increased but not when the activities of NO3- and Cl- increased, indicating that SO42- and H2PO4- showed competitive effects with As(Ⅴ) on the binding sites. Based on BLM theory, the stability constants were obtained: [Formula: see text] = 3.70; [Formula: see text] = 4.08; [Formula: see text] = 4.77; [Formula: see text] = 6.50; [Formula: see text] = 2.09 and [Formula: see text] = 1.86, with fAsBL50%= 0.30 and ß = 1.73. Results implied that BLM performed well in As(Ⅴ) toxicity prediction when coupling toxic species AsO43-, HAsO42-, H2AsO4-, and H3AsO4, and the competition of SO42- and H2PO4- for binding sites. The current study provides a useful tool to accurately predict As(V) toxicity to wheat roots.

Fe-CGS Effectively Inhibits the Dynamic Migration and Transformation of Cadmium and Arsenic in Soil.

The iron-modified coal gasification slag (Fe-CGS) material has excellent performance in purifying heavy-metal-contaminated water due to its good surface properties and adsorption capacities. However, it is unclear whether it can provide long-term simultaneous stabilization of Cd and As in composite-contaminated soils in extreme environments. This study investigated the long-term stabilization of Cd and As in acidic (JLG) and alkaline (QD) soils by simulating prolonged heavy rainfall with the addition of Fe-CGS. Multiple extraction methods were used to analyze the immobilization mechanisms of Cd and As in soil and their effects on bioavailability. The results indicate that the stabilization efficiency was related to the dosage of Fe-CGS. The concentrations of Cd and As in the JLG soil leachate were reduced by 77.6% (2.0 wt%) and 87.8% (1.0 wt%), respectively. Additionally, the availability of Cd and As decreased by 46.7% (2.0 wt%) and 53.0% (1.0 wt%), respectively. In the QD soil leachate, the concentration of Cd did not significantly change, while the concentration of As decreased by 92.3% (2.0 wt%). Furthermore, the availability of Cd and As decreased by 22.1% (2.0 wt%) and 40.2% (1.0 wt%), respectively. Continuous extraction revealed that Fe-CGS facilitated the conversion of unstable, acid-soluble Cd into oxidizable Cd and acid-soluble Cd. Additionally, it promoted the transformation of both non-specifically and specifically adsorbed As into amorphous iron oxide-bound and residual As. Fe-CGS effectively improved the soil pH, reduced the bioavailability of Cd and As, and blocked the migration of Cd and As under extreme rainfall leaching conditions. It also promoted the transformation of Cd and As into more stable forms, exhibiting satisfactory long-term stabilization performance for Cd and As.

[Impacts of Climate Change and Human Activities on NDVI Change in Eastern Coastal Areas of China].

Based on the datasets of normalized difference vegetation index (NDVI), temperature, precipitation, and solar radiation and the methods of trend, partial correlation, and residual analyses, this study explored the spatiotemporal variation in NDVI and its response to climate change from 1982 to 2019 in eastern coastal areas of China. Then, the effects of climate change and non-climatic factors (e.g., human activities) on NDVI trends were analyzed. The results showed that:① the NDVI trend varied greatly in different regions, stages, and seasons. On average, the growing season NDVI increased faster during 1982-2000 (stage I) than that during 2001-2019 (stage Ⅱ) in the study area. Moreover, NDVI in spring showed a more rapid increase than that in other seasons in both stages. ② For a given stage, the relationships between NDVI and each climatic factor varied in different seasons. For a given season, the major climatic factors associated with NDVI change were different between the two stages. The relationships between NDVI and each climatic factor showed great spatial differences in the study period. In general, the increase in growing season NDVI in the study area from 1982 to 2019 was closely related to the rapid warming. The increase in precipitation and solar radiation in stage Ⅱ also played a positive role. ③ In the past 38 years, climate change played a greater role in the change in growing season NDVI than non-climatic factors, including human activities. Whereas non-climatic factors dominated the increase in growing season NDVI during stage I, climate change played a major role during stage Ⅱ. We suggest that more attention should be paid to the impacts of various factors on vegetation cover variation during different periods to promote the understanding of terrestrial ecosystem changes.

Elicitation with hydrogen peroxide promotes growth, phenolic-enrichment, antioxidant activity and nutritional values of two hydroponic lettuce genotypes.

Dietary vegetables rich in bioactive compounds are major responsible for promoting human health. Herein, the effect of hydrogen peroxide (H2O2), an important signaling compound, on growth and quality of two hydroponic lettuce genotypes was investigated. The maximum enhancement of growth traits was shown in lettuce elicited with 10 mmol/L H2O2, while 40 mmol/L H2O2 significantly reduced above growth traits. H2O2 elicitation increased pigment contents and photosynthetic process, which consequently caused enhancements of phenolic compounds, ascorbic acid, glutathione, carotenoids, soluble sugars, free amino acids, soluble protein, minerals, and antioxidant capacity, while above alterations appeared in a genotype-dependent manner. The phenolic accumulation was correlated with improved activity of phenylalanine ammonia lyase (PAL) and expression levels of genes related to phenolic biosynthesis, including PAL, chalcone synthase, flavanone 3-hydroxylase, dihydroflavonol-4 reductase, and UDP-glucose: flavonoid 3-O-glucosyltransferase. Therefore, elicitation with H2O2 is a promising strategy to develop lettuce with high bioactive compounds and biomass.

Spatiotemporal differences in climate change impacts on vegetation cover in China from 1982 to 2015.

The impacts of climate change on vegetation cover in different regions in China are not entirely clear because of the interference of non-climatic factors, such as human activity. This study aims to analyze the spatiotemporal differences in climate impacts qualitatively and quantitatively by applying trend, correlation, and multiple linear regression (MLR) analyses to the data of Normalized Difference Vegetation Index (NDVI) and two climatic factors (air temperature and precipitation) during 1982-2015 in China. The MLR equation linking two climatic variables with NDVI was used to identify the NDVI trend caused by climate change. We demonstrated that the central and eastern regions of China, dominated by deciduous and evergreen broadleaf forests, experienced a rapid increase in NDVI from 1982 to 2015. The response of NDVI to variations in temperature and precipitation exhibited large spatiotemporal differences across China, which was closely related to climatic conditions and vegetation types. Overall, warming, particularly the sharp rise in spring, was the main climatic driving force behind China's NDVI increase, and precipitation also influenced the NDVI increase in temperate grassland and desert regions due to the relatively arid climate, particularly in summer. The contributions of climate change to the total NDVI trend (CC) showed a large spatiotemporal heterogeneity across China. Overall, only 45% of the pixels (with a resolution of 8 km) in the study area showed that the MLR equations between NDVI and two climatic factors were significant at the 0.05 significance level during the growing season (April-October), and the average CC of these pixels was 38%. Among the eight vegetation sub-regions of China, the temperate desert and Qinghai-Tibet Plateau alpine meadow regions generally exhibited relatively larger CCs than other vegetation sub-regions in different seasons. At a national scale, the regional average CC reached 64% during the growing season. These results at multiple scales can help to deeply understand the mechanisms of regional environmental variation and sustainability.

Impact of variations in vegetation on surface air temperature change over the Chinese Loess Plateau.

Studying the drivers and combating the effects of climate change is more urgent than ever, particularly in regions with limited water and sensitive ecosystems. This study evaluated the effect of vegetation variation on surface air temperature (SAT) change in the Chinese Loess Plateau over 1982-2015 based on the 'observation minus reanalysis' (OMR) method. Observed temperature, ERA-Interim reanalysis temperature, and Global Inventory Modeling and Mapping Studies normalized difference vegetation index (NDVI) 3rd generation were used to analyze the relationship between OMR temperature (representing vegetation impact on SAT) and NDVI. Results showed that the Loess Plateau, especially its central-east areas, has undergone a rapid increase in NDVI and rapid decrease in OMR temperature during 1982-2015. This implies a strong cooling effect of vegetation restoration on SAT change. The mean annual NDVI (MNDVI) and NDVI trend (SlopeNDVI) were negatively correlated with OMR temperature trend (SlopeOMR) on the Loess Plateau (P < 0.001). However, the relationships between MNDVI (SlopeNDVI) and SlopeOMR varied among the arid, semi-arid, and semi-humid regions. As a result, the impacts of restoration of vegetation condition on SAT change during 1982-2015 were estimated to be 0.04, -0.01, and -0.07 °C decade-1 in the arid, semi-arid, and semi-humid regions, respectively. For the entire Loess Plateau, the restoration of its vegetation condition led to a cooling effect of -0.02 °C decade-1 during 1982-2015 and a cooling effect of -0.05 °C in the period following the implementation of the Grain for Green Project (GGP). Moreover, among the three major land use types of the Loess Plateau (i.e., grassland, farmland, and forest), vegetation restoration of forest demonstrated the most obvious cooling effect (-0.06 °C decade-1 during 1982-2015). These results are the first quantitative estimation of the impact of vegetation variation on SAT across the entire Loess Plateau, and demonstrate the ecological effect of afforestation efforts in the southeastern areas in terms of climate warming alleviation.

Backwashing performance of self-cleaning screen filters in drip irrigation systems.

The self-cleaning screen filter is one of the most common types used in drip irrigation systems. Backwashing pressure difference and backwashing time for two screen filters with one geometry and two different screens (178 µm and 124 µm) using two water qualities (tap water and sand-water mixture) were studied in a total of 88 runs (42 runs for tap water, 22 and 24 filtration cycles for sand-water mixture and backwashing, respectively). The backwashing pressure difference and backwashing time were calculated using the experimental data, and the results were largely in the range of measured values. Three constraint conditions (flowrate, sand condition and filtration time) of backwashing pressure difference were analysed, and the optimal values of backwashing pressure difference were given as 60.0 and 70.0 kPa for 178 µm and 124 µm filters, respectively. The backwashing time of the screen filter should be an optimal value that ensures that the pressure difference between the internal and external surfaces of the screen decreased to the initial value, and the sand concentration of the backwashed outlet decreased to a small, stable value. Based on the results of the backwashing experiment and prototype observation, the optimal backwashing time was given as 30 to 45 s for both screen filters.

Analytical equation for outflow along the flow in a perforated fluid distribution pipe.

Perforated fluid distribution pipes have been widely used in agriculture, water supply and drainage, ventilation, the chemical industry, and other sectors. The momentum equation for variable mass flow with a variable exchange coefficient and variable friction coefficient was developed by using the momentum conservation method under the condition of a certain slope. The change laws of the variable momentum exchange coefficient and the variable resistance coefficient along the flow were analyzed, and the function of the momentum exchange coefficient was given. According to the velocity distribution of the power function, the momentum equation of variable mass flow was solved for different Reynolds numbers. The analytical solution contains components of pressure, gravity, friction and momentum and reflects the influence of various factors on the pressure distribution along the perforated pipe. The calculated results of the analytical solution were compared with the experimental values of the study by Jin et al. 1984 and Wang et al. 2001 with the mean errors 8.2%, 3.8% and 2.7%, and showed that the analytical solution of the variable mass momentum equation was qualitatively and quantitatively consistent with the experimental results.

Dynamic channel adjustments in the Jingjiang Reach of the Middle Yangtze River.

Significant channel adjustments have occurred in the Jingjiang Reach of the Middle Yangtze River, because of the operation of the Three Gorges Project (TGP). The Jingjiang Reach is selected as the study area, covering the Upper Jingjiang Reach (UJR) and Lower Jingjiang Reach (LJR). The reach-scale bankfull channel dimensions in the study reach were calculated annually from 2002 to 2013 by means of a reach-averaged approach and surveyed post-flood profiles at 171 sections. We find from the calculated results that: the reach-scale bankfull widths changed slightly in the UJR and LJR, with the corresponding depths increasing by 1.6 m and 1.0 m; the channel adjustments occurred mainly with respect to bankfull depth because of the construction of large-scale bank revetment works, although there were significant bank erosion processes in local regions without the bank protection engineering. The reach-scale bankfull dimensions in the UJR and LJR generally responded to the previous five-year average fluvial erosion intensity during flood seasons, with higher correlations being obtained for the depth and cross-sectional area. It is concluded that these dynamic adjustments of the channel geometry are a direct result of recent human activities such as the TGP operation.