Screen for low-arsenic-risk rice varieties based on environment-genotype interactions by using GGE analysis.

Arsenic (As) accumulation in rice is a global health concern that has received increased attention in recent years. In this study, 12 rice genotypes were cultivated at four As-contaminated paddy sites in Taiwan. According to the different crop seasons and As levels in the soil, the sites were further divided into 18 environmental conditions. For As in soils, results showed that 67% of the studied environments were likely to represent As contamination. For As in rice, the mean total As concentration in brown rice grains ranged from 0.17 to 0.45 mg kg-1. The analysis of variance for the environment effect indicated that grain As concentration was mainly affected by the environmental conditions, suggesting that there was a remarkable degree of variation across the trial environments. According to the combination of the GGE biplot and cumulative distribution function of order statistics (CDFOS) analysis, five genotypes-TCS17, TCS10, TT30, KH139, and TC192-were regarded as stable, low-risk genotypes because the probability of grain As concentration exceeding the maximum permissible concentration (MPC) was lower for these genotypes across all environmental conditions. Particularly, TCS17 was recommended to be the safest rice genotype. Thus, grain As levels in the selected genotypes were applied to assess the health risk to Taiwanese residents associated with As exposure through rice consumption. Results showed that the upper 75th percentile values of the hazard quotient were all less than unity. This suggested that the health risk associated with consuming the selected rice genotypes was acceptable for most of the residents. The methodology developed here would be applicable to screen for stable, low-As-risk rice genotypes across multiple field environments in other regions or countries.

Modeling Alleviative Effects of Ca, Mg, and K on Cu-Induced Oxidative Stress in Grapevine Roots Grown Hydroponically.

The aim of this study was to determine the pattern of alleviation effects of calcium (Ca), magnesium (Mg), and potassium (K) on copper (Cu)-induced oxidative toxicity in grapevine roots. Root growth, Cu and cation accumulation, reactive oxygen species (ROS) production, and antioxidant activities were examined in grapevine roots grown in nutrient solutions. The experimental setting was divided into three sets; each set contained a check (Hoagland solution only) and four treatments of simultaneous exposure to 15 µM Cu with four cation levels (i.e., Ca set: 0.5, 2.5, 5, and 10 mM Ca; Mg set: 0.2, 2, 4, and 8 mM Mg; K set: 0.6, 2.4, 4.8, and 9.6 mM K). A damage assessment model (DAM)-based approach was then developed to construct the dose-effect relationship between cation levels and the alleviation effects on Cu-induced oxidative stress. Model parameterization was performed by fitting the model to the experimental data using a nonlinear regression estimation. All data were analyzed by a one-way analysis of variance (ANOVA), followed by multiple comparisons using the least significant difference (LSD) test. The results showed that significant inhibitory effects on the elongation of roots occurred in grapevine roots treated with 15 µM Cu. The addition of Ca and Mg significantly mitigated phytotoxicity in root growth, whereas no significant effect of K treatment on root growth was found. With respect to oxidative stress, ROS and malondialdehyde (MDA) contents, as well as antioxidant (superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)) activities, were stimulated in the roots after exposure to 15 µM Cu for three days. Moreover, H2O2 levels decreased significantly as Ca, Mg, and K concentrations increased, indicating that the coexistence of these cations effectively alleviated Cu-induced oxidative stress; however, alleviative effects were not observed in the assessment of the MDA content and antioxidant enzyme activities. Based on the DAM, an exponential decay equation was developed and successfully applied to characterize the alleviative effects of Ca, Mg, and K on the H2O2 content induced by Cu in the roots. In addition, compared with Mg and K, Ca was the most effective cation in the alleviation of Cu-induced ROS. Based on the results, it could be concluded that Cu inhibited root growth and Ca and Mg absorption in grapevines, and stimulated the production of ROS, lipid peroxidation, and antioxidant enzymes. Furthermore, the alleviation effects of cations on Cu-induced ROS were well described by the DAM-based approach developed in the present study.

Cadmium in rice grains from a field trial in relation to model parameters of Cd-toxicity and -absorption in rice seedlings.

Selecting rice varieties that absorb less Cd from soil will reduce human health risks posed by Cd through rice consumption. Nine rice cultivars that are commonly grown in Taiwan were used for investigating genotypic differences in Cd tolerance and absorption. Hydroponic testing with Cd treatments of 5, 10, and 50 µM CdCl2 for 7-day exposure was conducted for the cultivars. The reductions in plant growth by Cd treatments were fitted to a dose-response curve; the modeling parameters, that is, the effective Cd concentration resulting in 50% reduction (EC50), were obtained. The Cd concentrations in plant were expressed by a Michaelis-Menten kinetic model and the uptake rate parameters (M/k) were obtained. A field experiment was also conducted in farmland with Cd ~0.2 mg kg-1 in soil. For the rice cultivars used in hydroponics, Cd distributions and physiological traits (CAT, H2O2, and MDA) in seedlings were related to their tolerances to Cd toxicity. Modeling parameters, EC50 and M/k, correspond to the Cd concentrations in rice plant. In the field experiment, the Cd concentrations in brown rice of the indica cultivars (i.e., TCS10, TCS17, and TNGS22) were 0.6 mg kg-1; these were significantly higher than those of the japonica cultivars (i.e. TY3, TK9, TNG71, KH145, TKW1, and TKW3). By contrast, the three cultivars, KH145, TKW1, and TKW3, whose Cd concentrations in brown rice were lower than 0.3 mg kg-1 were considered safe relative to the permissible level of 0.4 mg kg-1. In addition, for the used cultivars, Cd concentrations in brown rice were well expressed (i.e., r2 = 0.95) as a function of EC50, M/k, and MDA by using multiple regression. Newly bred cultivars could be screened rapidly with hydroponic testing to predict their Cd concentrations in brown rice when grown in the field.

Effects of Copper on Root Morphology, Cations Accumulation, and Oxidative Stress of Grapevine Seedlings.

In the present study, a hydroponic experiment was conducted to investigate the oxidative stress and the copper (Cu) accumulation in grapevines exposed to three Cu levels (0, 5, and 15 µM) for 1, 2, and 3 days. The results showed that the root elongation was stunted at the highest-exposure concentration. The Cu accumulation in the grapevines increased with increasing Cu treatments, while the other nutrient elements (Ca, Mg and K) absorbed by the grapevines decreased. Most of the Cu taken up by the grapevines was accumulated in the roots. Compared to the data for 1 day after treatment, the Cu-addition significantly decreased the Mg and K concentration in the roots and leaves, yet increased the superoxide dismutase activity in the leaves after 3 days of treatment. For the reactive oxygen species, the malondialdehyde increased with increasing Cu levels in the roots and leaves; however, both the Cu-addition and exposure duration reduced the H2O2 level in the root. Additionally, the Cu-induced accumulation of ·O2- and H2O2 in the grapevine leaves can be observed by the histochemical staining of nitroblue tetrazolium and diaminobenzidine, respectively. In conclusion, the present results indicate that excess Cu results in a change of the root morphology and leads to oxidative stress for the grapevine leaves and roots.

The growth and uptake of Ga and In of rice (Oryza sative L.) seedlings as affected by Ga and In concentrations in hydroponic cultures.

Limited information is available on the effects of gallium (Ga) and indium (In) on the growth of paddy rice. The Ga and In are emerging contaminants and widely used in high-tech industries nowadays. Understanding the toxicity and accumulation of Ga and In by rice plants is important for reducing the effect on rice production and exposure risk to human by rice consumption. Therefore, this study investigates the effect of Ga and In on the growth of rice seedlings and examines the accumulation and distribution of those elements in plant tissues. Hydroponic cultures were conducted in phytotron glasshouse with controlled temperature and relative humidity conditions, and the rice seedlings were treated with different levels of Ga and In in the nutrient solutions. The growth index and the concentrations of Ga and In in roots and shoots of rice seedlings were measured after harvesting. A significant increase in growth index with increasing Ga concentrations in culture solutions (<10mgGaL-1) was observed. In addition, the uptake of N, K, Mg, Ca, Mn by rice plants was also enhanced by Ga. However, the growth inhibition were observed while the In concentrations higher than 0.08mgL-1, and the nutrients accumulated in rice plants were also significant decreased after In treatments. Based on the dose-response curve, we observed that the EC10 (effective concentration resulting in 10% growth inhibition) value for In treatment was 0.17mgL-1. The results of plant analysis indicated that the roots were the dominant sink of Ga and In in rice seedlings, and it was also found that the capability of translocation of Ga from roots to shoots were higher than In. In addition, it was also found that the PT10 (threshold concentration of phytotoxicity resulting in 10% growth retardation) values based on shoot height and total biomass for In were 15.4 and 10.6µgplant-1, respectively. The beneficial effects on the plant growth of rice seedlings were found by the addition of Ga in culture solutions. In contrast, the In treatments led to growth inhibition of rice seedlings. There were differences in the phytotoxicity, uptake, and translocation of the two emerging contaminants in rice seedlings.

Nonlinear biotic ligand model for assessing alleviation effects of Ca, Mg, and K on Cd toxicity to soybean roots.

Developing a nonlinear biotic ligand model (BLM) that considers the geometrical constraints for binding of different cations on biotic ligands will provide more reliable details about the hypothetical mechanism governing the alleviation of cadmium (Cd) toxicity by coexistent cations. Soybean seedlings under Cd stress produced by various activities of coexistent cations such as calcium (Ca2+), magnesium (Mg2+), and potassium (K+) were hydroponically assayed for Cd toxicity to soybean roots. The Cd2+ activity resulting in 50% reduction of root elongation (RE), EA 50, was used for assessing the Cd toxicity to the soybean seedling. Increasing Ca2+, Mg2+, and K+ activities resulted in a significant alleviation of Cd toxicity to soybean roots. This alleviation was markedly higher with increasing Ca2+ and K+ levels than with increasing Mg2+ level. In addition, EA 50 increased in nonlinear positive relationships with Ca2+ and Mg2+. The real data obtained from the soybean assay were thus used to develop the nonlinear BLM for Cd rhizotoxicity. Two parameters, competition equivalent and stability constant, indicated the profiles of the geometrical constraint and affinity of Ca2+, Mg2+, and K+ binding on the soybean root surface to alleviate Cd toxicity. Compared with the traditional linear BLM, the nonlinear BLM provided more precise predictions of relative root elongation (RRE) and EA 50. Therefore, adopting the nonlinear BLM approach will successfully improve the monitoring and assessment of heavy metal toxicity to terrestrial plants.

Influence of magnesium on copper phytotoxicity to and accumulation and translocation in grapevines.

The phytotoxic effects of excess copper (Cu) on grapevines (Vitis vinifera L. var. Kyoho) were examined, both from macroscopic and microscopic perspectives, by using a fifteen-day hydroponic experiments. The influence of magnesium (Mg) on Cu phytotoxicity to, and accumulation and translocation in grapevines was also observed. For phytotoxicity effect, results showed that a relative low median growth inhibition level of Cu was found for grapevine roots (0.809-3.671µM). Moreover, Cu toxicity was significantly alleviated by Mg treatment at Mg(2+) activity between 0.15 and 2.01mM. For accumulation and translocation effects, results indicated that competition for binding sites between Cu and Mg occurred for roots; however, Mg and Cu levels in stems and leaves were not affected by solution metals concentration. At Cu concentration less than 1µM, the translocation of Cu was decreased significantly for the highest Mg treatment; at Cu concentrations greater than 5µM, no obvious change was observed in leaf TF value between Mg treatments, while an increasing trend of stem TF value was observed with increasing Mg. These results suggest that the toxic effect resulted from metals depend not only on the competition of coexistent cations for plasma membrane surface, but also on the transport and distribution of toxic metals in physiological active sites in plants.

Alleviation effects of magnesium on copper toxicity and accumulation in grapevine roots evaluated with biotic ligand models.

Copper toxicity and accumulation in plants are affected by physicochemical characteristics of soil solutions such as the concentrations of coexistent cations (e.g., Ca(2+), Mg(2+), K(+), Na(+), and H(+)). The biotic ligand model (BLM) approach has been proposed to predict metal phyto-toxicity and -accumulation by taking into account the effects of coexistent cations, given the assumption of the partition equilibrium of metal ions between soil solution and solid phase. The alleviation effects of Mg on Cu toxicity and accumulation in grapevine roots were the main concerns in this study and were investigated by using a hydroponic experiment of grapevine cuttings. The BLM approach, which incorporated competition of Mg(2+) with Cu(2+) to occupy the biotic ligands on root surfaces, was developed to predict Cu rhizotoxicity and accumulation by grapevine roots. In the results, the effective activity of Cu, {Cu (2+)}, resulting in a 50 % reduction of root elongation (EA (50)), linearly increased with increments of Mg activity, {Mg (2+)}. In addition, the Cu concentration in root, Cu ( root ), was retarded by an increase of {Mg (2+)}. The linear model was significantly fitted to the relationship between {Cu (2+)}/Cu ( root ) and {Mg (2+)}. According to the concept of BLM, the present results revealed that the amelioration effects of Mg on Cu toxicity and accumulation in roots could arise from competition between Mg(2+) and Cu(2+) on the binding sites (i.e., the biotic ligands). Then, the developed Cu-BLMs incorporating the Mg(2+) competition effectiveness were validated provide accurate predictions of Cu toxicity and accumulation in grapevine roots. To our knowledge this is the first report of the successful development of BLMs for a woody plant. This BLM approach shows promise of being widely applicable for various terrestrial plants.

Changes in soil organic carbon and nitrogen stocks in organic farming practice and abandoned tea plantation.

BACKGROUND: The restoration of conventional tea plantations and the adoption of organic farming practices could impact soil organic carbon (SOC) and nitrogen (N) stocks. This study investigated the soil properties, SOC and N contents and stocks, and their vertical distributions of a secondary forest restored from an abandoned conventional tea plantation and a converted organic tea plantation. An adjacent conventional tea plantation employing similar intermediate farming served as a comparison. RESULTS: Within a 50-cm depth, the secondary forest exhibited a higher SOC stock of 115.53 ± 7.23 Mg C ha- 1 compared to 92.1 ± 8.54 Mg C ha- 1 for the conventional tea plantation. No significant differences in N stocks were seen between the two land uses. Significantly high SOC and N contents and stocks were found in the 0-10 cm layer of the secondary forest compared to the conventional tea plantation. No significant disparities in SOC and N stocks were found between the conventional and organic tea plantations within the 50 cm depth (92.1 ± 8.54 Mg C ha- 1 and 10.06 ± 1.01 Mg N ha- 1 vs. 97.47 ± 1.53 Mg C ha- 1 and 9.70 ± 0.10 Mg N ha- 1). However, higher levels of SOC and N contents and stocks were observed at a depth of 10 cm in the conventional tea plantation and below 10 cm in the organic tea plantation. CONCLUSIONS: The C and N inputs derived from high litter production at the top soil strongly contributed to higher SOC and N contents and stocks in the secondary forest. The application of soybean amendments in the conventional tea plantation and the longer tea plantation age of the organic tea plantation influenced their distribution of SOC and N contents and stocks, respectively. Reverting a conventional tea plantation into a secondary forest contributed to C recovery and reaccumulation. The conventional tea plantation, employing similar intermediate farming practices, increased SOC and N contents and stocks in the surface soil compared to the organic tea plantation. However, adopting organic farming did not significantly increase SOC stocks compared to the conventional tea plantation.

Coupling phytotoxicity and human health risk assessment to refine the soil quality standard for As in farmlands.

In the present study, a field experiment was conducted to investigate arsenic (As) concentrations in soils and in grains of 15 rice varieties in a contaminated site in Taiwan. The studied site was divided into two experimental units, namely plot A and plot B. The results showed that mean total As concentrations were 70.94 and 61.80 mg kg-1 in plot A and plot B, respectively, and thus greater than or approximate to the soil quality standard for total As in Taiwan (60 mg kg-1). The As levels in rhizosphere soil in plot A (19.71-32.33 mg kg-1) were much higher than in plot B (6.41-8.60 mg kg-1); however, As accumulation in brown rice did not significantly differ between the plots. These results implied that a significant variation in the bioconcentration factor (BCF) value of As existed among different rice genotypes, and a negative correlation was observed between BCF value and rhizosphere As level in the soil. In phytotoxicity, the median values of the ecological risk indicator were 104.85 and 103.89 in plot A and plot B, respectively, indicating considerable risk. In human health risk assessment, the median and 97.5%-tile values for cancer risk for both male and female residents were markedly higher than the acceptable risk (1 × 10-4). Furthermore, non-cancer and cancer risks were higher for males than females, mainly due to the greater rice ingestion rate of males. Sensitivity analysis showed that total As concentration in soil was the main factor affecting health risks, suggesting that priority should be given to the reduction of soil As levels. To better manage the phytotoxicity of As on rice, as well as the health risk to residents resulting from exposure to As-contaminated soils, the soil quality standard for As in farmland soils should be set between 5 and 10 mg kg-1. The methodology developed in this study could also be applied to provide the basis for refining and revising the soil quality standard for heavy metals in farmland in other regions and countries.

Model evaluation of plant metal content and biomass yield for the phytoextraction of heavy metals by switchgrass.

To better understand the ability of switchgrass (Panicum virgatum L.), a perennial grass often relegated to marginal agricultural areas with minimal inputs, to remove cadmium, chromium, and zinc by phytoextraction from contaminated sites, the relationship between plant metal content and biomass yield is expressed in different models to predict the amount of metals switchgrass can extract. These models are reliable in assessing the use of switchgrass for phytoremediation of heavy-metal-contaminated sites. In the present study, linear and exponential decay models are more suitable for presenting the relationship between plant cadmium and dry weight. The maximum extractions of cadmium using switchgrass, as predicted by the linear and exponential decay models, approached 40 and 34 µg pot(-1), respectively. The log normal model was superior in predicting the relationship between plant chromium and dry weight. The predicted maximum extraction of chromium by switchgrass was about 56 µg pot(-1). In addition, the exponential decay and log normal models were better than the linear model in predicting the relationship between plant zinc and dry weight. The maximum extractions of zinc by switchgrass, as predicted by the exponential decay and log normal models, were about 358 and 254 µg pot(-1), respectively. To meet the maximum removal of Cd, Cr, and Zn, one can adopt the optimal timing of harvest as plant Cd, Cr, and Zn approach 450 and 526 mg kg(-1), 266 mg kg(-1), and 3022 and 5000 mg kg(-1), respectively. Due to the well-known agronomic characteristics of cultivation and the high biomass production of switchgrass, it is practicable to use switchgrass for the phytoextraction of heavy metals in situ.

Coupling bioaccumulation and phytotoxicity to predict copper removal by switchgrass grown hydroponically.

A major challenge in phytoextraction is to increase plants' removal rates of metals from contaminated soils. In this study, we developed a phytoextraction model, by coupling a saturable Michaelis-Menten type accumulation model and an energy-based toxicity model, to predict copper (Cu) removal by switchgrass (Panicum virgatum L.) grown hydroponically under various exposure concentrations. Results of the present study indicated that the phytotoxicity of Cu to switchgrass is relatively low, whereas a certain accumulation capacity exists in the plant for Cu. In addition, the simulation results suggested that, under a lower dissolved concentration, Cu removal is increased more efficiently as the exposure duration increases. Although it is difficult to extrapolate the results from greenhouse-based hydroponic experiments to field conditions, we believe that the current methodology can offer a first approximation in predicting the phytoextraction duration needed for plant species to remove a specific metal from contaminated sites, which is crucial in evaluating the economic costs for remediation purposes.

Using chemical fractionation to evaluate the phytoextraction of cadmium by switchgrass from Cd-contaminated soils.

The purpose of this study is to evaluate the phytoextraction of cadmium (Cd) from contaminated soils by switchgrass (Panicum virgatum L.), which is a promising energy crop with high biomass. Two ecotypes of switchgrass cultivars, Alamo and Blackwell, were investigated in a pot experiment. Dry weight and plant Cd concentration of the switchgrass plants growing on Cd-spiked soils (0, 20, and 60 mg Cd kg(-1) soil) with chelating agent amendments (1 g kg(-1) citric acid [CA] and 0.1 g kg(-1) ethylene diaminetetraacetic acid [EDTA]) were measured to examine the phytotoxicity and accumulation of Cd in the switchgrass. Fractions of Cd (F1, exchangeable; F2, carbonate; F3, Fe-Mn oxide; F4, organic matter; F5, residual) for the soils sampled at the time of harvesting were also determined using chemically sequential extractions. In the results, the dry weight of the switchgrass decreased with increasing Cd, with a significant dry weight reduction when Cd exceeded 20 mg kg(-1). However, the high Cd spike of 60 mg kg(-1) was not lethal to Alamo and Blackwell, which suggests that switchgrass plants can tolerate Cd and grow in contaminated soils. Compared with the control, the CA and EDTA amendments had no adverse effect on the growth of switchgrass plants. With regard to Cd accumulation, higher plant Cd concentrations were frequently found after CA amendment in Alamo; however, the Cd concentrations of Blackwell plants may increase when amended with EDTA. On the basis of the fractionation of soil Cd, dry weight and plant Cd concentration could be expressed as a function of Cd fractionation to predict the phytoextraction of Cd. Thus, the fractionation of Cd is a useful approach for evaluating the phytoextraction of Cd by switchgrass in contaminated soils. According to the comparison of phytoextractions of Cd between Alamo and Blackwell, Alamo plants removed substantially more Cd from Cd-spiked soils than Blackwell. Therefore, Alamo is better suited for the phytoextraction of Cd from contaminated soils.

Assessing human health risk of arsenic for rice consumption by an iron plaque based partition ratio model.

A field experiment was conducted to study the transport and uptake of arsenic (As) from soil to rice roots and the subsequent translocation from roots to shoots and grains. Twelve rice cultivars were used in the field experiment. The amount of As accumulated in rice grains and sequestered by root iron plaque and rhizosphere soil, were determined to establish the relationship between As concentrations in brown rice and As sequestration by iron oxides. Human health risk was then assessed for Taiwan's population exposed to As through rice consumption. The result of this study showed that the mean total As concentrations in the experimental site and in brown rice were 93.02 mg/kg and 0.158 mg/kg, respectively. The As sequestration by iron oxides on root plaque (3.48-9.51) was higher than that of the rhizosphere soil (1.86-4.09) for all tested rice cultivars. Therefore, the partition ratio (PR) representing the relative tendency of As sequestration by rhizosphere soil to that in root iron plaque was all less than 1. In addition, there was a significant negative linear relationship between inorganic As concentration (iAs) in brown rice and PR value (r2 = 0.38, p < 0.05). Based on the iAs in brown rice, the median value of hazard quotient (HQ) and target cancer risk (TR) was 1.13 and 5.10 × 10-4, respectively, indicating potential cancer and non-cancer risk for Taiwan residents exposed to As through the consumption of rice grown on the studied site. Various PR values were then successfully used for estimating risk, implying that screening the PR of the rice plant before harvest could serve as an early warning signal for protecting consumers' health. However, more experiments with different rice cultivars for the paddy soils were suggested in the future to establish a comprehensive relationship between iAs in brown rice and PR value.

Aspects of cultivar variation in physiological traits related to Cd distribution in rice plants with a short-term stress.

BACKGROUND: Genotypic variations are seen in cadmium (Cd) tolerance and accumulation in rice plants. Cultivars that show low Cd translocation from the root into shoot can be selected to reduce Cd contamination in rice grains. This study aims to clarify the physiological regulation related to Cd absorption by rice plants for screening out the cultivars, which have relatively low Cd accumulation in grains. Eight Taiwan mega cultivars of paddy rice: japonica (TY3, TK9, TNG71, and KH145 cultivars), indica (TCS10 and TCS17 cultivars), and glutinous (TKW1 and TKW3 cultivars), which are qualified with the criteria for rice grain quality by the Council of Agriculture, Taiwan, were used for illustration. An experiment in hydroponics was conducted for the rice seedlings with a treatment of 50 µM CdCl2 for 7 days. RESULTS AND DISCUSSION: After the Cd treatment, the reductions in shoot growth were more significant than those in root growth; however, Cd absorbed in the rice plant was sequestered much more in the root. The malondialdehyde (MDA) was preferentially accumulated in rice root but the hydrogen peroxide (H2O2) was increased more significantly in the shoot; the antioxidative enzymes, superoxide dismutase (SOD) and ascorbate peroxidase (APX), were pronounced more in rice shoot. CONCLUSIONS: The rice cultivars preferentially accumulated Cd in the root rather than the shoot with the Cd treatment, which resulted in significant enhancements of MDA and growth reductions in the root. However, H2O2 accumulation was toward the shoot to retard shoot growth suddenly and then the root could keep a gradual growth. Also, the rice cultivars, which preferentially accumulate Cd in the root, would have the regulation tendency of SOD toward the shoot. Due to that SOD is responsible for H2O2 production, H2O2 accumulation would be thus toward the shoot. Moreover, the cultivars, which have a less regulation tendency of APX toward the shoot, would present higher translocation of Cd into the shoot.

The effectiveness of four organic matter amendments for decreasing resin-extractable Cr(VI) in Cr(VI)-contaminated soils.

This paper compared the effectiveness of four organic materials for decreasing the amounts of soil extractable Cr(VI) in Cr(VI)-contaminated soils using the DOWEX M4195 resin-extraction method. Organic matters were added into Cr(VI)-spiked soils [500 mg Cr(VI)(kgsoil)(-1)] in the form of sugarcane dregs compost (SCDC), cattle-dung compost (CDC), soybean meal (SBM) and rice bran (RB), in the amounts of 0, 1%, and 2% by dry weight, respectively. The results indicated that adding only 1% organic matter to the studied soils could effectively decrease the amount of soil resin-extractable Cr(VI) after 12 days of incubation. The decrease of resin-extractable Cr(VI) by organic materials was mainly the result from the reduction of Cr(VI) to Cr(III) supported by the XANES spectroscopy. Among the four tested organic materials, SBM and RB had higher effectiveness in decreasing soil resin-extractable Cr(VI) than CDC and SCDC. This result may be due to the fact that SBM and RB have more dissolved organic carbon (DOC) and protein than CDC and SCDC. Therefore, it was concluded that the contents of DOC and protein are the main factors that determine the effectiveness of organic materials for decreasing the amounts of soil available Cr(VI) in Cr(VI)-contaminated soils.

Additional sampling based on regulation threshold and kriging variance to reduce the probability of false delineation in a contaminated site.

Kriging-based delineation when used to determine a cost-effective remediation plan should be based on the spatial distribution of the pollutant. This study proposed an adaptive cluster sampling (ACS) approach based on the regulation threshold and kriging variance for additional sampling to improve the reliability of delineating a heavy-metal contaminated site. A reliability index for reducing the probability of false delineation was used to determine the size and configuration of additional samples. A data set of Ni concentrations in soil was used for illustration. The results showed that the additional sampled observations during ACS were clustered where the Ni concentrations were close to the regulation threshold of 200 mg kg(-1), and were located where the first-phased sampling density was low. Compared with a simple random sampling (SRS), the relative frequency of misclassification over the whole study area (RFMW) using ACS in a 100 replicates simulation was lower when the same sample number of pooled data was used. In addition, the spatial distribution of the local misclassification rate (LMR) showed that the area with a high-valued LMR could be reduced and that the LMR gradients in the region could be lowered by using ACS instead of SRS. The above results suggest that the proposed ACS approach could improve the reliability of kriging-based delineation of heavy-metal contaminated soils.

Field experiment for determining lead accumulation in rice grains of different genotypes and correlation with iron oxides deposited on rhizosphere soil.

Paddy rice (Oryza sativa L.) is a major staple crop in Asia. However, heavy metal accumulation in paddy soil poses a health risk for rice consumption. Although plant uptake of Pb is usually low, Pb concentrations in rice plants have been increasing with Pb contamination in paddy fields. It is known that iron oxide deposits in the rhizosphere influence the absorption of soil Pb by rice plants. In this study, 14 rice cultivars bred in Taiwan, including ten japonica cultivars (HL21, KH145, TC192, TK9, TK14, TK16, TN11, TNG71, TNG84, and TY3) and four indica cultivars (TCS10, TCS17, TCSW2, and TNGS22), were used in a field experiment. We investigated the genotypic variation in rice plant Pb in relation to iron oxides deposited in the rhizosphere, as seen in a suspiciously contaminated site in central Taiwan. The results showed that the cultivars TCSW2, TN11, TNG71, and TNG84 accumulated brown rice Pb exceeding the tolerable level of 0.2mgkg-1. In contrast, the cultivars TNGS22, TK9, TK14, and TY3 accumulated much lower brown rice Pb (<0.1mgkg-1); therefore, they should be prioritized as safe cultivars for sites with potential contamination. Moreover, the iron oxides deposited on the rhizosphere soil show stronger affinity to soil-available Pb than those on the root surface to form iron plaque. The relative tendency of Pb sequestration toward rhizosphere soil was negatively correlated with the Pb concentrations in brown rice. The iron oxides deposited on the rhizosphere soil but not on the root surface to form iron plaque dominate Pb sequestration in the rhizosphere. Therefore, the enhancement of iron oxide deposits on the rhizosphere soil could serve as a barrier preventing soil Pb on the root surface and result in reduced Pb accumulation in brown rice.

Effects of adjacent land-use types on the distribution of soil organic carbon stocks in the montane area of central Taiwan.

BACKGROUND: Soil organic carbon (SOC) stocks can be altered through reforestation and cropping. We estimated the effects of land use on SOC stocks after natural deciduous forests replaced by crops and coniferous plantations by examining the vertical distribution of SOC stocks at different depth intervals in an adjacent Oolong tea (Camellia sinensis L.) plantation, Moso bamboo (Phyllostachys pubescens) forest, Japanese cedar (Cryptomeria japonica) forest, and Taiwania (Taiwania cryptomerioides) forest in central Taiwan. The main soil characteristics, soil nitrogen (N) content, and soil carbon to nitrogen (C/N) ratio were also determined. RESULTS: Different land uses resulted in significantly higher bulk density, lower cation exchange capacity, SOC, soil N, soil C/N ratio, and SOC stocks in croplands compared to forestlands. Due to the long-term application of chemical fertilizers, a significantly lower soil pH was found in the tea plantation. Croplands had a lower soil C/N ratio because of less C input into the soil and a higher mineralization rate of organic carbon during cultivation. Similar SOC stocks were found in Taiwania and Japanese cedar forests (148.5 and 151.8 Mg C ha-1, respectively), while the tea plantation had comparable SOC stocks to the bamboo forest (101.8 and 100.5 Mg C ha-1, respectively). Over 40% of SOC stocks was stored in croplands and over 56% was stored in forestland within the upper 10 cm of soil. CONCLUSIONS: Coniferous plantations can contribute to a higher SOC stock than croplands, and a significant difference can be found in the top 0-5 cm of soil.

Adaptive sampling based on the cumulative distribution function of order statistics to delineate heavy-metal contaminated soils using kriging.

Correctly classifying "contaminated" areas in soils, based on the threshold for a contaminated site, is important for determining effective clean-up actions. Pollutant mapping by means of kriging is increasingly being used for the delineation of contaminated soils. However, those areas where the kriged pollutant concentrations are close to the threshold have a high possibility for being misclassified. In order to reduce the misclassification due to the over- or under-estimation from kriging, an adaptive sampling using the cumulative distribution function of order statistics (CDFOS) was developed to draw additional samples for delineating contaminated soils, while kriging. A heavy-metal contaminated site in Hsinchu, Taiwan was used to illustrate this approach. The results showed that compared with random sampling, adaptive sampling using CDFOS reduced the kriging estimation errors and misclassification rates, and thus would appear to be a better choice than random sampling, as additional sampling is required for delineating the "contaminated" areas.