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Nitrogen (N) fertilization is known to have a substantial effect on heavy metal uptake in plants. However, the impact of N fertilization on plant growth and heavy metal uptake of hyperaccumulator plants remains unclear. This study examined the effect of N fertilization on growth and uptake of zinc (Zn) and cadmium (Cd) in Zn/Cd-hyperaccumulating plants species, Sedum alfredii (S. alfredii) Hance (Crassulaceae). Plants of S. alfredii were grown for 60 days in nutrient solution with 100 μmol Cd L−1 and 0–10 mmol N L−1, and in a Cd-contaminated soil receiving N fertilizer and composted pig manure amendment. Biomass production, nutrient uptake, and concentrations and accumulation of Zn and Cd in plant parts were measured. In the hydroponic experiment, both low ( 5 mmol L−1) N supply decreased the growth and Zn and Cd accumulation in the whole plants. The 2.5 mmol N L−1 is an optimal N dosage for shoot biomass production and Zn accumulation in shoots, while the 1.0 mmol N L−1 is an optimal N dosage for Cd accumulation in shoots, which was 68.1% higher than the control. The N doses of 1 to 2.5 mmol L−1 N represented optimal conditions for Zn and Cd accumulation in the shoots of S. alfredii seedlings. In the soil pot experiment, shoot dry weight decreased with increasing N fertilization rate, while composted pig manure decreased biomass production. Both Zn and Cd accumulation in the shoots of S. alfredii decreased along with the addition of higher N fertilization rate. However, the composted pig manure amendment increased the accumulation of Zn, but not Cd in the shoots. The application of N at appropriate amount enhanced the phytoremediation efficiency by S. alfredii in Zn/Cd-polluted fields, but the effectiveness of phytoextraction technology needs to be validated in the field trials.

Forest ecosystems play an important role in sequestering carbon in their biomass and soils. Moso bamboo plantations, as a special forest type, are mainly distributed in southern China. There is little information about the carbon storage in moso bamboo plantations, it is now important to better understand the moso bamboo’s carbon sequestration. The main objectives of this study were to investigate the spatial variation of aboveground biomass carbon (AGC) and soil organic carbon (SOC) in moso bamboo plantations and to compare carbon storage in moso bamboo plantations under different management options. A total of 73 moso bamboo plots were selected in Anji County, which is a famous “bamboo town” in northwest Zhejiang province, China. The diameter at breast height and the age of each moso bamboo in the selected plots were measured in order to calculate the AGC. SOC was analyzed using sulfuric acid–potassium dichromate solution. One-way ANOVA was applied to analyze the significant difference of AGC and SOC under different management options. Geostatistics and geographical information were used to study the spatial dependence characteristics of AGC and SOC. The AGC values were very variable, ranging from 9.92 to 38.70 Mg ha−1, with an average of 20.85 Mg ha−1. The SOC values were from 34.8 to 176.17 Mg ha−1. Both the AGC and SOC values were followed normal distributions. Moso bamboo plantations contributed about 16.5 % of total forest biomass carbon in Zhejiang Province, indicating its important influence on regional carbon budget. Geostatistical analysis revealed that the AGC had moderate spatial autocorrelation. A nested model (a spherical model with a Gaussian model) was chosen to describe the variogram. Spatial patterns for AGC were found in Anji County, with relatively high AGC values were found in the southwestern part of Anji County, and low values were located in the eastern and central parts of the county. While no clear spatial autocorrelation trend was observed in the semivariogram of SOC, indicating a random distribution pattern for SOC in the study area. Meanwhile, the Pearson’s correlation between AGC and SOC in bamboo plantation was weak (r = 0.064, p = 0.496), due to moso bamboo’s special growth process and different management options by human beings. In this study, moderate spatial dependency was found for AGC, while the spatial autocorrelation of SOC was poor. In moso bamboo forest ecosystem, SOC was mainly stored at the top 40 cm layer. Management options were proved to be an important factor for carbon sequestration. Extensive management is an efficient way to increase carbon stock, compared to moderate and intensive management. With the rapid increase of plantation area, moso bamboo ecosystem will continue to play an important role in regional carbon budget.

Although the bioavailability of heavy metals has been widely investigated, little information is available on the spatial correlations of heavy metals in soil–rice systems at a regional scale. A study of heavy metals in soil–rice systems at a present rice production area could provide valuable information on the safety of rice production and provide guidelines beneficial to agriculture management and strategic sustainable agriculture in China and other rapidly developing regions in the world. The overall goals of this study were to identify the characteristics of metal fractions and their bioavailability to rice plants in the paddy fields of a present rice production region. In the rice harvest season (October 2006), 96 pairs of rice grain and rooted soil samples were collected from rice production area of Wenling in southeast Zhejiang province, China, which is one of the well-known electronic and electric waste (E-waste) recycling centers. Soil samples were analyzed for total heavy metal concentrations, metal fraction concentrations, and soil properties. Soil properties analyzed in this study included soil pH, electrical conductivity, organic matter, Fe oxides, and soil particle size distribution. Rice grain samples were analyzed for heavy metal concentrations. Multivariate statistical and geostatistical methods were applied to study the spatial dependence characteristics of metal fractions and their spatial correlation with uptake by rice plants in the rice production area and to identify the bioavailability of metal fractions to rice plants. The paddy soils of the studied area showed Cd contamination and some paddy soils presented a potential Cu, Ni, and Zn risk. The elevated levels of Cd were predominantly in non-residual (extractable) fractions. The percentage of Cd in fractions decreased in the order of exchangeable > Fe–Mn oxide bound > residual > organic bound fraction. In contrast, soil Cu, Ni, Pb, and Zn were mainly in the residual (non-extractable) fractions. The fractions of Ni, Pb, and Zn followed the order of residual > Fe–Mn oxide bound > organic bound > exchangeable fraction; the fractions of Cu decreased in the order of residual > organic bound > Fe–Mn oxide bound fraction. The spatial distribution patterns of non-residual fractions exhibited similarities with the highest metal concentrations in the northwest area owing to the industries and E-waste recycling activities. Most metals in rice grain were the strongest spatially correlated with the exchangeable fraction, followed by the organic bound fraction, indicating that exchangeable and organic bound fractions had the highest bioavailability. Rice Cd and Zn were strong spatially correlated with exchangeable, Fe–Mn oxide, and organic bound fractions; rice Ni and Cu were strongly spatially correlated with the exchangeable and organic bound fractions, respectively. The principal component analysis results also confirmed that exchangeable, Fe–Mn oxide, and organic bound soil fractions can be considered as bioavailable fractions to rice for Cd and Zn, while exchangeable and organic fractions were more important sinks for Ni and Cu, respectively. Due to a comparatively high input of Cd in the paddy soils, soil Cd was predominantly associated with non-residual fractions, especially with the exchangeable fraction. The soil Cu, Ni, Pb, and Zn were largely associated with the residual fraction while little associated with the exchangeable fraction. The bioavailability of the fractions to rice varied with metal fractions. In general, the exchangeable fraction had the highest bioavailability to rice plants, followed by the organic bound fraction. The bioavailability of the fractions to rice also varied with heavy metals. The exchangeable, Fe–Mn oxide, and organic bound fractions had high bioavailability to rice for Cd and Zn; the exchangeable and organic bound fractions had highest bioavailability for Ni and Cu, respectively.