Changes In Environmental Behaviors Of Trace Metals Involved In Poplar-Based Phytomanagement On Low-Phosphorus Calcareous Soil

Phytomanagement,a new paradigm of phytoremediation in the last decade,is the use of soil–plant systems to mitigate the environmental risk posed by contaminated sites.Meanwhile,the remediation of the calcareous soil comtaminated with trace metals is quite urgent in rescent years.Thus,as a sustainable strategy,phytomanage is becoming the promising option for remediating and managing the calcareous soil comtaminated with trace metals.However,most researches were conducted under the short-term phytomanagement,changes in environmental behaviors are unclear in low-phosphorus calcareous soils afforested with a long duration by fast-growing tree species.A multi-metal contaminated sites phytomanaged by poplar?Populus hopeiensis Hu et Chow?with a long-term chronosequence?i.e.,10,15,20,and 25 years?was selected to study the regulation mechanism of metal bioavailability,uptake of metal by poplar and impacts of metal bioavailability on physiologic index of soils and plants.The results as follows:?1?Due to the limilation of low total phpsphorus did not provide enough available P,persisit uptake of popla resulted in that Olsen P in rhizospheric soils under 10,15,20-year-old stand separately dcreased as 23.3%,21.0%and 28.1%.Nevertheless,the Olsen P increased as 27.4%in rhizospheric soil of 25-year-old stand compared with the bulk soil.Phosphorus mobilization during the phytomanagement associated with SOM depletion induced soil acidification and then CaCO₃ dissolution.In this paper,pH in rhizospheric soil decreased at least as 0.2,meanwhile,CaCO3 declined as 38.9%in rhizospheric soil of 25-year-old stand.The SOM depletion and CaCO₃ collectively resulted in an increase in bioavailability of Cd,Pb and Zn.The soil acidification induced the desorption of Ni from soil solid phase,causing the mobilization of Ni.?2?The increase of metal bioavailability in soils promoted the uptake of metal by poplar,resulting in that concentrations of metals in poplar tissues,especially in leaves,remained at high levels during the process of phytomanagement.The enhanced uptake of Ni in leaves was noted in the 25-year-old stand relative to other stands.The Pb concentration in leaveswas generally higher than 30 mg kg^–1.?3?The extensive accumulation of metal in leaves induced by the metal mobilization enhanced the metal stress to leaves,resulting in the decrease of chlorophyll content and the increase of malondialdehyde content in leaves.Under this situation,poplar would promote the synthesis of proline and sulfhydryl compound for allieviating the metal stress.?4?Besides,mobilization of metals remarkably inhibited the enzymatic activities.The activity of soil urease was significantly and negatively influenced by the mobilization of Ni and Zn,and alkaline phosphatase was signicifantly inhibited by the increasing in bioavailability of Cd and Pb.In addition,soil ALP activity was also regulated by soil nutrient?i.e.,C,N,and P?pool as well as their ecological stoichiometry.This is largely because P acquisition needs a high N investment in the production of ALP.In general,metal would be mobilized in low-P calcareous soils afforested with a long duration,which would increase the environmental risks posed by metals and negatively influence the plants and soil organisms.Therefore,it is essential to meet the need of poplar for nutrients for avoiding the mobilization of metals during the phytomanagement.