Interactive effects of single, binary and trinary trace metals (lead, zinc and copper) on the physiological responses of Kandelia obovata seedlings.

Heavy metals are considered important environmental contaminants, and their mixture toxicity on plants has complex mutual interactions. The interactive effects of heavy metals on growth, photosynthetic parameters, lipid peroxidation and compatible osmolytes were studied in Kandelia obovata grown for 5 months in sediment treated with combinations of lead (Pb), zinc (Zn) and copper (Cu). The results showed no significant reduction of biomass under heavy metal stresses, except for decreased root biomass under higher Pb + Cu treatment, indicating high tolerance of K. obovata to heavy metal stress. Only the photosynthetic parameters, including net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), decreased with increasing concentration of treatments (except for Pb + Cu and Pb + Zn + Cu). Trinary treatment (Pb + Zn + Cu) increased biomass and the photosynthetic parameters when compared to the external addition of binary metals. In the roots, biomass and soluble sugar content were lower under binary than trinary treatments, indicating that the combination of Zn and Cu exhibited improved effects of alleviating toxicity than each of them alone in Pb-containing combined treatments. In the leaves, Zn-containing combined treatments significantly decreased malondialdehyde (MDA), soluble sugar and proline content in low concentration, while Pb + Cu treatments significantly increased these parameters (P < 0.05). The correlation analysis showed that leaf MDA and proline content were negatively correlated with Zn concentration (P < 0.05). Zn could alleviate the effects of combined heavy metal stress, and Pb + Cu treatment showed synergistic effects in leaves. The positive correlations between MDA content and the osmotic parameters showed that osmotic stress and lipid membranes oxidation exist simultaneously under multiple heavy metal stresses. Therefore, biomass, Tr, leaf MDA, leaf proline content and soluble sugar content could indicate metal mixture toxicity to mangrove seedlings.

Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments.

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] - [AVS])/foc, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

Discriminating growth stages of an endangered Mediterranean relict plant (Ammopiptanthus mongolicus) in the arid Northwest China using hyperspectral measurements.

Ammopiptanthus mongolicus, the only drought-resistant, leguminous, evergreen shrub in the desert region of China, is endangered due to climate change and its growth stages urgently need to be non-destructively detected. Although many spectral indexes have been proposed for characterizing vegetation, the relationships are often inconsistent, making it challenging to characterize the status of vegetation across all growth stages. This study investigated the Spectral Features of the endangered desert plant A. mongolicus at different growth stages, and extracted the identified Spectral Features for the establishment of detection and discrimination models using Partial Least Square Regression (PLSR) and Fisher Linear Discriminate Analysis (FLDA), respectively. The results showed spectral reflectance of A. mongolicus differed across different growth stages and it generally increased with the degree of senescence. Poor performance was found in the single factor model, with RMSE ranging from 20.34 to 27.39 or Overall Accuracy of 60% in the validation datasets. The multivariate PLSR model, based on Normalized Difference Vegetation Index (NDVI), Normalized Difference Red Edge Index (NDRE), Physiological Reflectance Index (PhRI) and Plant Senescence Reflectance Index (PSRI), turned out to be accurate in detecting the growth stages, with R2 of 0.89 and RMSE of 12.46, and the performance of the multivariate FLDA model based on 14 Spectral Features was acceptable, with an Overall Accuracy of 89% in the validation datasets. This research provides useful insights for timely and non-destructively discriminating different growth stages by using multivariate PLSR and FLDA analysis.

[Characteristics of Iron Plaque and Its Heavy Metal Enrichment in Typical Mangrove Plants in Shenzhen Bay, China].

Based on the five typical mangrove species in the mangrove wetland of Shenzhen Bay, the contents and distributional characteristics of iron plaques (Fe) and the Mn, Pb, Zn, Cu, As, Cr, Cd, Ni, Co, and Sb enrichment of the iron plaques on mangrove plant roots were investigated. The results show that:① There is a significant difference in the contents of iron plaques among the five mangrove species, and the contents in the species follow the order:Acanthus ilicifolius > Aeagiceras corniculatum > Bruguiera gymnorrhiza > Kandelia obovate > Heritiera littorlis; the content ranged from 0.37 g·kg-1 to 10.81 g·kg-1. ② Iron plaques have a certain enrichment effect on the heavy metals in the sediments. The contents of heavy metals in the iron plaques vary with the plant species, being the highest in A. ilicifolius and the lowest in H. littorlis. This enrichment also varies with the element species:Mn content changed from 0.11 g·kg-1 to 2.67 g·kg-1; the highest contents of Pb, Zn, Cu, As, and Cr changed from 117.44 mg·kg-1 to 189.69 mg·kg-1; and the highest contents of Cd, Ni, Co. and Sb changed from 34.84 mg·kg-1 to 63.34 mg·kg-1. The content of Zn in the iron plaque is negatively correlated with the other heavy metal contents (P<0.001), indicating that Zn might compete with the other elements. ③ Sediment pH significantly affects the content of iron plaque and the accumulation of Mn in the iron plaque (P<0.05). The water content and salinity of the sediments are positively correlated with the contents of heavy metals Cr and Co in the iron plaque (P<0.05). ④ The distribution of iron plaques and their heavy metal contents in different parts of the roots of the mangrove plants follow the order:root tip > root middle > root base.

Assessing the effect of extra nitrogen on Kandelia obovata growth under cadmium stress using high-resolution thermal infrared remote sensing and the three-temperature model.

Mangrove forests provide many ecological services and are among the most productive intertidal ecosystems on earth. Currently, these forests frequently face significant heavy metal pollution as well as eutrophication. The present study assessed the response of Kandelia obovata Sheue, H.Y. Liu & J. Yong to combined NH4+-N addition and Cd stress based on a three-temperature (3T) model using high-resolution thermal infrared remote sensing. The results show that leaf surface temperature (Tc) and the plant transpiration transfer coefficient (hat) became larger with increasing NH4+-N concentrations in the same Cd treatment, especially under high NH4+-N (50 and 100 mg·L-1) and Cd stress. The thermal bioindicators, growth responses and photosynthetic parameters changed in a consistent fashion, indicating that combined high NH4+-N addition and Cd stress led to stomatal closure, reduced the cooling effect of transpiration, and increased Tc and hat values. Furthermore, appropriate NH4+-N supply reduced stomatal conductance (gs) and the transpiration rate (Tr), which were increased by Cd stress, and then maintained Tc and hat at normal levels. The normalised hat helped to reduce the influence of environmental variation during the diagnosis of mangrove plant health. This indicated that the 3T model with high-resolution thermal infrared remote sensing provides an effective technique for determining the health status of mangrove plants under stress.

Temporal variations in physiological responses of Kandelia obovata seedlings exposed to multiple heavy metals.

A study was conducted to quantify temporal variations in physiological responses of Kandelia obovata under multiple heavy metal stress. The results showed that plant growth was not significantly affected by multiple heavy metal stress during the 120-days experiment. At the start, levels of net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) showed effects of "low-promotion, high-inhibition", but Pn and Gs reduced with increasing heavy metal stress at the end. Temporary lipid oxidation was shown by high levels of malondialdehyde (MDA) under high heavy metal stress at the start but was unaffected at the end of the experiment. MDA negatively correlated with biomass and photosynthetic parameters and acted as a sensitive indicator. Proline also shared similar trend and indicated its temporary role in osmotic adjustment. Negative correlations between osmotic adjustment matter and photosynthetic parameters further confirmed the significant role of osmotic adjustment under heavy metal stress.

Influence of introduced Sonneratia apetala on nutrients and heavy metals in intertidal sediments, South China.

To investigate the influence of Sonneratia apetala on nutrients and heavy metals in intertidal sediments, sediment cores of S. apetala marsh and mudflat in Shenzhen Bay, China were analyzed. The results showed that S. apetala improved sediment nutrient properties due to increased total carbon (TC), total nitrogen (TN), and total sulfur (TS). The levels of heavy metals were higher in S. apetala site than in mudflat, including chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg). In S. apetala site, TC, TN, and TS were not positively correlated with Cr, Ni, As, Cd, and Pb, indicating their less important roles in trapping heavy metals. There were positive correlations among Ni, Cu, Zn, and Cd in both sites, suggesting similar anthropogenic source. Levels of As were higher than the probable effect level at both sites, indicating their toxicological importance. The geo-accumulation index and potential ecological risk index revealed higher metal contaminations in S. apetala site, especially for Cd, Hg, and As. Multivariate analysis implied that S. apetala alter the biogeochemical cycle of Cd and Cr to a certain extent. These findings indicate that S. apetala may improve soil nutrient properties and facilitate heavy metal accumulation in intertidal sediments.

Distribution and accumulation of mercury and copper in mangrove sediments in Shenzhen, the world's most rapid urbanized city.

To investigate the influence of mangrove forest on heavy metal accumulation and storage in intertidal sediments, core sediments from natural mangrove, restored mangrove, and adjacent mud flat spanning the intertidal zone along the south coastline of the most heavily urbanized Deep bay, Guangdong province, China were analyzed. The average concentrations of mercury (Hg) in surface sediments of natural mangrove and restored mangrove were 172 and 151 ng g(-1), whereas those of copper (Cu) were 75 and 50 µg g(-1), respectively. Compared to those from other typical mangrove wetlands of the world, the metal levels in Shenzhen were at median to high levels, which is consistent with the fact that Shenzhen is in high exploitation and its mangrove suffer intensive impact from human activities. Hg and Cu concentration profiles indicated a higher metal accumulation in surface layers of sediments, in agreement with enrichment of organic matter contents. Maximum concentration, enrichment factors, and excess (background-deducted) concentration inventories of metals (Hg and Cu) were substantially different between environments, decreasing from natural mangrove sediments to restored mangrove sediments to mud flat. Furthermore, metal inputs to Futian mangrove decreased in the order natural mangrove > restored mangrove > mud flat, indicating that mangrove facilitated the accumulation and storage of Hg and Cu in sediment layers.

Distribution, Fraction, and Ecological Assessment of Heavy Metals in Sediment-Plant System in Mangrove Forest, South China Sea.

Overlying water, sediment, rhizosphere sediment and mangrove seedlings in the Futian mangrove forest were analyzed for heavy metals. The results showed that mangrove plant acidified sediment and increased organic matter contents. Except for chromium (Cr), nickel (Ni) and copper (Cu) in Aegiceras corniculatum sediment, heavy metals in all sediments were higher than in overlying water, rhizosphere sediment and mangrove root. Heavy metals in Avicennia marina sediments were higher than other sediments. The lower heavy metal biological concentration factors (BCFs) and translocation factors (TFs) indicated that mangrove plant adopted exclusion strategy. The geo-accumulation index, potential ecological risk index and risk assessment code (RAC) demonstrated that heavy metals have posed a considerable ecological risk, especially for cadmium (Cd). Heavy metals (Cr, Ni, Cu and Cd) mainly existed in the reducible fractions. These findings provide actual heavy metal accumulations in sediment-plant ecosystems in mangrove forest, being important in designing the long-term management and conservation policies for managers of mangrove forest.

[Comparing Cell Toxicity of Schizosaccharomyces pombe Exposure to Airborne PM2.5 from Beijing and Inert Particle SiO2].

To figure out the main factor of PM2.5 toxicity to cell, this study compared the cell toxicity of Schizosaccharomyces pombe (S. pombe), a model organism, exposed to inert ultrafine SiO2 particles, a model particle, and airborne PM2.5 collected from campus of Peking University Beijing China. Using ultraviolet spectrophotometry to measure cell proliferation ratio, and environmental scanning microscope to observe the particle adhesion on the cell surface, and detecting cellular ROS generation with DHE fluorescent dye chromogenic method, and using single cell gel electrophoresis to test cell DNA damage, the experiment results indicated that the ultrafine SiO2 particles (< 60 nm) could inhibit the cell proliferation of S. pombe, mainly through adsorbing onto the cell surface to change the permeability of the cell wall; but it could not induce cells to generate ROS to cause the oxidative damage. PM2.5, the average particle size of which was larger than that of SiO2 particles, could cause oxidative damages to cells mainly by inducing cells to generate ROS, and damage DNA simultaneously. It might illustrate that there was no direct relationship between the toxicity of PM2.5 and its physical properties such as the particle size.

[Profile nutrient distribution and sedimentary characteristics in typical marshes of Sanjiang Plain].

Profile distribution characteristics of organic carbon (C), total nitrogen (N), total phosphorus (P) and total sulfur (S) were studied in two typical marshes including Carex lasiocarpa marsh and Phragmites australis marsh in the Sanjiang Plain. Sedimentary characteristics of typical mashes were analyzed. The results showed that vertically these soil chemical elements also varied, showing obvious stratification and enrichment. In a soil profile, soil organic C under both vegetation communities gradually decreased; soil total N first increased and then decreased under both; total P under Carex lasiocarpa first decreased and then increased, whereas it decreased with the increasing depth under Carex lasiocarpa; total S was reduced with increasing depth under both marshes. Total N, total P and total S were all strongly correlated with soil organic C (P < 0.01); soil organic C was strongly correlated with bulk density (P < 0.01). Our study also illustrated that the vegetation types had different influences for organic C, total N, total P and total S of the marsh profiles. Environmental 137Cs and 210Pb dating techniques were applied to determine recent sedimentation rates, and the constant rate of supply (CRS) was applied to deduce the age of sediment core, and the results showed that the mean sedimentation rate was 0.33 cm x a(-1), and the sedimentation fluxes ranged 0.03-0.48 g x (cm2 x a)(-1) [Mean = 0.29 g x (cm2 x a) -1].

[Mercury and copper accumulation during last fifty years and their potential ecological risk assessment in sediment of mangrove wetland of Shenzhen, China].

The processes of sediment transport and deposition can record some relative anthropogenic information in gulf region. Chronological analysis of the sediment core collected from mangrove wetland in Shenzhen Bay showed that the sedimentation rate was about 1.38 cm x a(-1). Soil buck density, pH, electrical conductivity (EC) and total organic carbon (TOC) changed in range of 0.36-0.71 g x cm(-3), 6-7, 2.93 x 10(3) -4.97 x 10(3) microS x cm(-1), and 1.5% - 3.8%, respectively. With the increase of soil depth, the soil buck density and EC increased gradually. However, the TOC decreased, with no significant change of pH. Contents of Hg and Cu in the whole depth of core ranged between 92-196 ng x g(-1) and 29-83 microg x g(-1), respectively. And both of them in sediment increased firstly and then decreased with the increasing soil depth. At 14 cm depth, contents of Hg and Cu reached up to the highest levels. Correspondingly, the ecological risk of Hg and Cu changed similarly with the contents of Hg and Cu. At 14 cm depth, the ecological risk indexes of Hg and Cu were at the highest levels of 39.10 and 13.85, respectively. The potential ecological risks of both Hg and Cu in sediments were mild. The rapid economical development of Hong Kong in 1960-1985 and Shenzhen in 1985-2000 contributed much to the Hg and Cu accumulation in mangrove wetland of Shenzhen Bay, China. Since the year of 2000, the reduction in contents of Hg and Cu has been expected as a consequence of the adoption of contamination control policies, improving the environment for growth of mangrove. In conclusion, the variations of core sediment heavy metal contents and its ecological risk assessment along the vertical profile reveal the interaction processes and extent of anthropogenic influences from the areas around the Shenzhen Bay and the catchments.

Effects of the "Conversion of Cropland to Forest and Grassland Program" on the water budget of the Jinghe River catchment in China.

In 1999 China adopted the "Conversion of Cropland to Forest and Grassland Program" (CCFGP), a nationwide ecological recovery program, to minimize wide-scale soil erosion and vegetation degradation in China, as well as to improve water budgeting results. In the 10 yr since implementation, the CCFGP has resulted in the recovery and reforestation of >100,000 km of cropland and bare land, though the quantitative effect of this program on catchment water budget is not entirely clear. Therefore, we used the Soil and Water Assessment Tool to evaluate and quantify the effects of the CCFGP on the water budget of the Jinghe River catchment, a tributary of the Yellow River covering the central region of the Loess Plateau. Our results indicated that precipitation had dropped by 12.0% from the 1970s (611.6 mm) to the 2000s (538 mm) and that there was a corresponding 25.2% decrease in humidity index from 0.48 to 0.36. Before the CCFGP's implementation, forest and grassland had been decreasing, while bare land, cropland, and shrub land had been increasing. After the implementation of the CCFGP, the opposite trend was observed. Moreover, streamflow increased by about 15 and 20% for the upstream and middle stream subbasins, respectively, while soil water content also showed an obvious increase. Over the same period, evapotranspiration decreased by 5.2 and 13.5 mm and runoff decreased by 37.5 and 38.6% in the two subbasins. The same trends were obtained in the downstream subbasin, where changes were even greater. As a result of the reduced runoff and evapotranspiration, utilization of water resources was more efficient and ecological environment was improved under the CCFGP policy. Our results indicate the CCFGP resulted in a favorable ecological impact and should therefore be maintained.

Remotely monitoring evaporation rate and soil water status using thermal imaging and "three-temperatures model (3T Model)" under field-scale conditions.

Remote monitoring of soil evaporation and soil water status is necessary for water resource and environment management. Ground based remote sensing can be the bridge between satellite remote sensing and ground-based point measurement. The primary object of this study is to provide an algorithm to estimate evaporation and soil water status by remote sensing and to verify its accuracy. Observations were carried out in a flat field with varied soil water content. High-resolution thermal images were taken with a thermal camera; soil evaporation was measured with a weighing lysimeter; weather data were recorded at a nearby meteorological station. Based on the thermal imaging and the three-temperatures model (3T model), we developed an algorithm to estimate soil evaporation and soil water status. The required parameters of the proposed method were soil surface temperature, air temperature, and solar radiation. By using the proposed method, daily variation in soil evaporation was estimated. Meanwhile, soil water status was remotely monitored by using the soil evaporation transfer coefficient. Results showed that the daily variation trends of measured and estimated evaporation agreed with each other, with a regression line of y = 0.92x and coefficient of determination R(2) = 0.69. The simplicity of the proposed method makes the 3T model a potentially valuable tool for remote sensing.

An infrared-based coefficient to screen plant environmental stress: concept, test and applications.

By introducing a reference dry leaf (a leaf without transpiration), a formerly proposed plant transpiration transfer coefficient (hat) was applied to detect environmental stress caused by water shortage and high temperature on melon, tomato and lettuce plants under various conditions. Results showed that there were obvious differences between leaf temperature, dry reference leaf temperature and air temperature. The proposed coefficient hat could integrate the three temperatures and quantitatively evaluate the environmental stress of plants. Experimental results showed that the water stress of melon plants under two irrigation treatments was clearly distinguished by using the coefficient. The water stress of a tomato plant as the soil dried under a controlled environmental condition was sensitively detected by using hat. A linear relationship between hat and conventional crop water stress index was revealed with a regression determination coefficient R2 = 0.97. Further, hat was used to detect the heat stress of lettuce plants under high air temperature conditions (28.7°C) with three root temperature treatments (21.5, 25.9 and 29.5°C). The canopy temperature under these treatments was respectively 26.44, 27.15 and 27.46°C and the corresponding hat value was -1.11, -0.74 and -0.59. Heat stress was also sensitively detected using hat. The main advantage of hat is its simplicity for use in infrared applications.

Accurate estimation of forest carbon stocks by 3-D remote sensing of individual trees.

Forests are one of the most important carbon sinks on Earth. However, owing to the complex structure, variable geography, and large area of forests, accurate estimation of forest carbon stocks is still a challenge for both site surveying and remote sensing. For these reasons, the Kyoto Protocol requires the establishment of methodologies for estimating the carbon stocks of forests (Kyoto Protocol, Article 5). A possible solution to this challenge is to remotely measure the carbon stocks of every tree in an entire forest. Here, we present a methodology for estimating carbon stocks of a Japanese cedar forest by using a high-resolution, helicopter-borne 3-dimensional (3-D) scanning lidar system that measures the 3-D canopy structure of every tree in a forest. Results show that a digital image (10-cm mesh) of woody canopy can be acquired. The treetop can be detected automatically with a reasonable accuracy. The absolute error ranges for tree height measurements are within 42 cm. Allometric relationships of height to carbon stocks then permit estimation of total carbon storage by measurement of carbon stocks of every tree. Thus, we suggest that our methodology can be used to accurately estimate the carbon stocks of Japanese cedar forests at a stand scale. Periodic measurements will reveal changes in forest carbon stocks.