Mobility and bioavailability of lead （Pb） could be affected considerably by soil physicochemical properties; however, less is known about the effect of Pb levels and aging time. This study was conducted to evaluate ...Mobility and bioavailability of lead （Pb） could be affected considerably by soil physicochemical properties; however, less is known about the effect of Pb levels and aging time. This study was conducted to evaluate the effects of Pb levels and wetting-drying （WD） cycles on distribution and bioavailability of Pb in three semi-arid zone soils treated with different levels of Pb（NO3）2. Wetting-drying cycles simulated the actual field irrigation in the semi-arid soils. A soil with a long history of Pb contamination was also taken as a reference soil. The soils were spiked with various levels of Pb and incubated under WD cycles for 160 d. Sequential extractions and batch sorption experiments were performed to assess the fractionation of Pb in the spiked soils. Redistribution index （Uts） and reduced partitioning parameter （IR） were applied to semi-quantify the distribution of Pb in the spiked soils. A small amount of Pb sorbed was desorbed by the soils, indicating a strong and irreversible binding of Pb in the studied soils. Contribution of carbonate-bound （Car） and residual （Res） Pb fl＇actions to the total Pb of the soils was more than 97%. The Car, soluble plus exchangeable （SE）, and organic matter-bound （OMB） fractions of Pb were transferred to the Res fraction under the WD cycles. The IR and Uts values were influenced by Pb loading levels and WD; therefore, the Pb lability and/or redistribution pattern could semi-quantitatively be assessed via these parameters. At the end of the experiment, the Ia and Uts values for the Pb salt-spiked soils did not show the quasi- equilibrium state. The lability of Pb in the soils decreased with increasing incubation time and showed a strong dependence on Pb levels and soil chemical composition. WD cycles significantly affected the overall lability of Pb in soils through influencing the redistribution of Pb among solid-phase components.展开更多
It has long been recognized that plant invasions may alter carbon （C） and nitrogen （N） cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effe...It has long been recognized that plant invasions may alter carbon （C） and nitrogen （N） cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effects caused by the invasion of a noxious exotic plant, Kalanchoe daigrernontiana （Crassulaceae）, on C and N mineralization and enzymatic and microbial activities in the soil of a semiarid locality in Venezuela. We compared soil parameters associated with these processes （C and N mineralization time and the cumulative values, fluorescein diacetate hydrolytic activity, and activities of dehydrogenase, β-glucosidase, glucosaminidase, and urease） between invaded and adjacent non-invaded sites. In addition, correlations among these parameters and the soil physical-chemical properties were also examined to determine if a positive feedback exists between nutrient availability and K. daigremontiana invasion. Overall, our results showed that C mineralization and transformation of organic compounds to NH4^＋ were favored at sites colonized by K. daigrernontiana. With this species, we found the highest cumulative amounts of NH4^＋-N and C and the lowest mineralization time. These results could be explained by higher activities of urease and glueosaminidase in soils under the influence of K. daigremontiana. In addition, higher amounts of organic matter and moisture content in invaded soils might favor C and N mineralization. In conclusion, invasion of Neotropical semiarid zones by K. daigrernontiana may influence the chemical and biological properties of the soils covered by this species, increasing nutrient bioavailability, which, in time, can facilitate the invasion process.展开更多
基金Supported by the National Science Foundation of Iran and Urmia University,Iran
文摘Mobility and bioavailability of lead （Pb） could be affected considerably by soil physicochemical properties; however, less is known about the effect of Pb levels and aging time. This study was conducted to evaluate the effects of Pb levels and wetting-drying （WD） cycles on distribution and bioavailability of Pb in three semi-arid zone soils treated with different levels of Pb（NO3）2. Wetting-drying cycles simulated the actual field irrigation in the semi-arid soils. A soil with a long history of Pb contamination was also taken as a reference soil. The soils were spiked with various levels of Pb and incubated under WD cycles for 160 d. Sequential extractions and batch sorption experiments were performed to assess the fractionation of Pb in the spiked soils. Redistribution index （Uts） and reduced partitioning parameter （IR） were applied to semi-quantify the distribution of Pb in the spiked soils. A small amount of Pb sorbed was desorbed by the soils, indicating a strong and irreversible binding of Pb in the studied soils. Contribution of carbonate-bound （Car） and residual （Res） Pb fl＇actions to the total Pb of the soils was more than 97%. The Car, soluble plus exchangeable （SE）, and organic matter-bound （OMB） fractions of Pb were transferred to the Res fraction under the WD cycles. The IR and Uts values were influenced by Pb loading levels and WD; therefore, the Pb lability and/or redistribution pattern could semi-quantitatively be assessed via these parameters. At the end of the experiment, the Ia and Uts values for the Pb salt-spiked soils did not show the quasi- equilibrium state. The lability of Pb in the soils decreased with increasing incubation time and showed a strong dependence on Pb levels and soil chemical composition. WD cycles significantly affected the overall lability of Pb in soils through influencing the redistribution of Pb among solid-phase components.
基金supported by the Venezuelan Institute for Scientific Research to the first author
文摘It has long been recognized that plant invasions may alter carbon （C） and nitrogen （N） cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effects caused by the invasion of a noxious exotic plant, Kalanchoe daigrernontiana （Crassulaceae）, on C and N mineralization and enzymatic and microbial activities in the soil of a semiarid locality in Venezuela. We compared soil parameters associated with these processes （C and N mineralization time and the cumulative values, fluorescein diacetate hydrolytic activity, and activities of dehydrogenase, β-glucosidase, glucosaminidase, and urease） between invaded and adjacent non-invaded sites. In addition, correlations among these parameters and the soil physical-chemical properties were also examined to determine if a positive feedback exists between nutrient availability and K. daigremontiana invasion. Overall, our results showed that C mineralization and transformation of organic compounds to NH4^＋ were favored at sites colonized by K. daigrernontiana. With this species, we found the highest cumulative amounts of NH4^＋-N and C and the lowest mineralization time. These results could be explained by higher activities of urease and glueosaminidase in soils under the influence of K. daigremontiana. In addition, higher amounts of organic matter and moisture content in invaded soils might favor C and N mineralization. In conclusion, invasion of Neotropical semiarid zones by K. daigrernontiana may influence the chemical and biological properties of the soils covered by this species, increasing nutrient bioavailability, which, in time, can facilitate the invasion process.
