Effects Of Magnetized Water Treatment On Growth And Physiological Charaterisitics And Soil Micro-ecological Environment Of Populus× Euramericanna 'Neva' Under Cadmium Stress

Cadmium is an important environmental pollutant with strong biological toxicity.Its toxicity not only destroys the soil ecological environment,affects plant growth and development,but also poses a threat to human health.Therefore,exploring the response of plant to cadmium stress and ecological restoration of soil cadmium pollution is of great significance.Magnetized water treatment technology is a new kind of bio-magnetic technology,which has both economic and ecological benefits.It has been widely recognized and applied in improving plant stress resistance and degraded soil ecological environment.To explore the mechanism of magnetized water irrigation treatment on plant growth and plant tolerance to heavy metals,and the potential of magnetized water irrigation for cadmium pollution in phytoremediation,we used one-year-old poplar cutting seedlings?Populus×euramericanna‘Neva'?as experimental material and designed a cadmium concentration gradient(0?mol·L^-1,50?mol·L^-1,100?mol·L^-1)under magnetized water irrigation.We researched the effects of magnetized water irrigation on photosynthetic characteristics,chlorophyll fluorescence kinetic parameters and growth characteristics,cadmium accumulation and transport in various organs of plants,absorption and distribution of nutrients,basic physical and chemical properties and nutrient contents of soil,functional enzyme activities,soil bacterial community structure and composition.The main results as follows:?1?Cadmium stress significantly inhibited plant growth and physiological activity.Plant height,stem growth and dry matter weights of roots,leaves and stems significantly dropped under cadmium stress.While root diameter and volume were enhanced under low cadmium concentration(50?mol·L^-1,P<0.05),root morphology parameters were inhibited under high concentration(100?mol·L^-1).Compared with 0?mol·L^-1 cadmium treatment,chlorophyll b and carotenoid contents decreased respectively by 12.50%and 19.27%under 50?mol·L^-1cadmium treatment,and by 43.24%and 46.37%under 100?mol·L^-1 cadmium treatment?P<0.05?.Net photosynthetic rate?P_n?,transpiration rate?T_r?and intercellular carbon dioxide concentration?C_i?respectively decreased by 13.68%,8.07%and 5.00%under 50?mol·L^-1cadmium treatment,and by 33.68%,27.81%and 14.99%?P<0.05?under 100?mol·L^-1cadmium treatment.PS?potential activity?F_v/F_m?,maximum photo-chemical rate?F_v/F_o?,photosynthetic performance index?PIabs?and quantum yield(?_Eo)also dropped to varying degrees.2)Compared with non-magnetic water treatment,magnetic water treatment enhanced the growth of plants under cadmium stress in terms of height and stem,increased dry weight of roots and leaves and also root length and surface area of the plant.The contents of chlorophyll a increased by 16.99%,6.55%and 4.02%,and carotenoid content increased by 17.32%,19.38%and 50.52%?P<0.05?,respectively,under 0,50 and 100?mol·L^-1 cadmium treatments.While P_n,G_s,C_i and WUE increased,the differences were not significant.However,T_r reduced respectively by 24.20%,23.33%and 12.06%?P<0.05?.In addition,F_v/F_m,F_v/F_o and?_Eoo remained stable whereas PIabs increased respectively by 8.01%,20.63%and 31.09%?P<0.05?.?2?Cadmium stress not only affected the absorption of mineral nutrients in Populus×euramericanna‘Neva',but also the distribution and accumulation.Cadmium stress reduced the contents of N,P,and Mg in poplar plants.At the same time,cadmium concentration gradient had different stimulation and inhibition effects on the accumulation of K,Ca,Fe,Mn Zn and Cu in roots and leaves.Magnetized water treatment significantly increased the contents of nitrogen and phosphorus by 14.42%⁴4.15%.The total nitrogen accumulation in leaves significantly increased by 7.08%,12.64%,18.76%?P<0.05?.There was no significant change in total phosphorus content,but the accumulation of total phosphorus in roots was higher than that in leaves.Moreover,magnetized water treatment significantly increased K,Ca,Mg,Zn and Cu contents in leaves,increased Fe contents in roots and decreased Mg contents?P<0.05?.?3?Analysis of cadmium content in roots and leaves of plants showed that cadmium was mainly enriched in the roots under cadmium stress;magnetized water treatment could promote cadmium enrichment in poplar roots,and cadmium content in the roots was respectively increased by 4.07%?26.68%and 66.65%compared with the non-magnetized water treatment under cadmium stress.In addition,it blocked the upward transport of cadmium in plants,and decreased the cadmium content of stem and leaf by 11.69%⁵3.64%.The enrichment coefficient of M50 and M100 were significantly increased by 22.20%,70.56%?P<0.05?,whereas the transport coefficient was respectively decreased by 16.53%and 48.82%.?4?Addition of cadmium in soil significantly inhibited the activities of soil urease,alkaline phosphatase and invertase.Catalase changed irregularly.Compared with non-magnetized water treatment,the activity of urease significantly increased by 36.10%,12.82%and 22.70%,and activity of catalase and sucrase respectively increased by 27.54%,42.89%,3.24%and 15.84%,24.34%,8.69%,however alkaline phosphatase activity decreased by 13.25%,0.84%,12.53%.?5?Magnetized water irrigation is beneficial to improve soil physical and chemical properties,stimulate soil nutrient release,and affect the soil carbon,nitrogen and phosphorus stoichiometry.The treatment of magnetized water could reduce the pH,and increase the content of exchangeable K significantly in the low concentration(50?mol·L^-1)cadmium contaminated soil?P<0.05?,also it could maintain the composition and stability of other exchangeable cations in the soil.After the magnetized water irrigation,the content of organic carbon was significantly increased and total nitrogen and total phosphorus content remained stable.In addition,the effective phosphorus content was significantly increased by 15.77%³2.56%.At the same time,the ratio of N/P,C/P and C/N were significantly increased?P<0.05?.?6?Addition of cadmium treatments leads to an increase in the diversity index of soil bacteria Chao1,ACE and so on.The magnetized water treatment increased the bacterial community diversity index of high concentration cadmium contaminated soil.The Chao1 index increased by 4.39%?P<0.05?,and the Shannon index was 1.058 times of NM100,and the difference reached a significant level?P<0.05?.At the phylum level,dominant bacteria are Proteobacteria and Acidobacteria in all treatments,but the dominant species are quite different.Magnetized water treatment changed the structure and composition of bacterial communities in cadmium-contaminated soil.Among 10 genus with relative abundance greater than 1%,magnetized water treatment increased relative abundance of six bacterial genera such as Pseudomonas and Delft.In conclusion,magnetized water treatment can enhance the tolerance of plants to cadmium,improve the physiological activity of plants under cadmium stress,regulate the absorption and distribution of nutrients,and promote plant growth.Moreover,magnetized water treatment can improve the physical and chemical properties of soil,change the structure and composition of soil bacterial community,increase the abundance of bacteria,stimulate the release of effective nutrients,and improve the soil ecological environment.