Differences In Rhizospheric Microbial Community Between Rice Cultivars With High/Low-DEHP Accumulation And The Uptake Of DEHP By Their Roots

Due to the widely use of phthalic acid esters(PAEs)in industrial and agricultural production and daily living,especially the plastic film mulching and plastic greenhouses,agricultural soil has been generally polluted by PAEs.Plants can take up and accumulate PAEs from soil,which affects the safety of agricultural products.At present,the interspecific and intraspecific differences and influencing factors of plant uptake and accumulation of PAEs have been studied at home and abroad,but there are few reports on the mechanism of accumulation difference by various cultivars of rice(Oryza sativa L.)and their influencing factors.Here,a rhizobox experiment was conducted to investigate the variations in uptake and accumulation of DEHP as well as antioxidant system between low(Fengyousimiao)and high(Peizataifeng)PAE-accumulating cultivars of rice grown in DEHP(0,20,100 mg/kg)contaminated soil.Moreover,the variation of microbial diversity in rhizosphere soil of two rice cultivars was investigated by high-throughput sequencing technology.In addition,the uptake kinetics of PAE compounds including DEP,DBP and DEHP by rice root and its effect factors were studied through a hydroponic experiment.These results will preliminarily clarify the different mechanism of PAE accumulation by low and high PAE-accumulating cultivars of rice and provide scientific basis for selecting low accumulative rice cultivars and ensuring the quality and safety of agricultural products.The main results are shown as follows:(1)Low concentration of DEHP stress could activate superoxide dismutase activity in the two rice cultivars,but high DEHP concentration decreased the activities of catalase and peroxidase in rice roots.The activity of polyphenol oxidase in shoots of two rice cultivars increased with increasing DEHP concentrations.Peizataifeng showed higher tolerance to DEHP stress than Fengyousimiao.The roots of two rice cultivars have greater abilities to accumulate DEHP than the shoots.In two DEHP concentrations,DEHP dissipation in the rhizospheric soils of the two cultivars decreased generally in the order of adjacent rhizosphere>central root compartment>bulk soil.The DEHP dissipation rates in the rhizospheric soils of Peizataifeng were significantly higher than those of Fengyousimiao.(2)High-throughput sequencing revealed that there were significant differences in the diversity and community structure of bacteria and fungi in different rhizospheric soils of the two rice varieties.The DEHP dissipation rates were positively correlated with microbial community diversities in some rhizospheric compartments.Furthermore,the relative abundance of some specific bacterial genera like Acinetobacter,Pseudomonas,and Bacillus as well as fungal genera like Purpureocillium capable of degrading DEHP were positively correlated with DEHP dissipation rates,especially in the adjacent rhizosphere of Peizataifeng.At low and high DEHP concentrations,the relative abundances of the three bacterial genera(Acinetobacter,Pseudomonas,and Bacillus)were relatively higher than that of Purpureocillium.The relative abundances of Acinetobacter,Pseudomonas,and Bacillus in the rhizospheric soil of Peizataifeng were generally higher than those of Fengyousimiao.Changes in the microbial community,especially DEHP-degrading genera,may play an important role in DEHP dissipation variationof rhizospheric soils between the two rice cultivars.(3)The hydroponic experiment on uptake kinetics DEP,DBP and DEHP indicated that PAE uptake by roots of the two rice cultivars increased with growth time.The whole uptake process consisted of a fast accumulation process followed by a slow one.The absorption capacity and uptake rate constant(k)of PAEs by Peizataifeng were greater than those of Fengyousimiao.Concentration-dependent uptake of PAEs by roots of two rice cultivars can be described with Michaelis-Menten equation.Moreover,the K_m value of Peizataifeng was smaller than that of Fengyousimiao.That means the affinity of Peizataifeng root carrier to the PAE compounds was greater than that of Fengyousimiao.These may be one of the reasons for the difference in PAE accumulation between the two rice cultivars.