Effects Of Phenolic Acids On Soil Nutrient Availability And Bacteria Diversity Of Continuous Cropping Poplar Plantation

Poplar is one of the most appropriate tree species of industrial plantation directionallycultivating in China. But because of the limited land resources, poplar plantation is onlycarried out in limited long-term continuous cropping management on forest land in China. Itlead to the declination of forest land productivity gradually. In the study of the declination offorest land productivity on continuous cropping plantation, the changes of soil nutrientsenvironment and microbial community structure diversity has been the focus of scholar’sattention.It’s lack of the system futher research of the fertility decline in the continuous poplarplantation,which is caused by the soil nutrient availability and bacterial diversity of allelopathy mechanism in the past research.This study took the many generations of continuous cropping poplar in shandongningyang as the research object, and adopted the methods of exogenous add to simulate thephenolic acid environment, and set up different phenolic acids concentration to study theinfluence of soil nutrients （NH₄-N, NO₃-N, PO₄, K, Fe, Mn, Zn, Cu） validity changes andbacterial diversity by benzoic acid, ferulic acid, p-hydroxy benzoic acid, vanillin andcinnamic acid, in order to reveal the mechanism further of soil fertility decline on continuouscropping plantation.The results showed that:（1） In the same piece of forestland of poplar, the nutrient availability in rhizosphere soilis higher significantly than bulk soil. After three generations of continuous cropping, nutrientefficiency dropped rapidly. The soil microbial diversity is also different different generation,and it was smaller after the first increase, and the soil microbial diversity index of the thirdgeneration forest was the lowest, and was3.902.（2） After adding exogenous phenolic acids in the bulk soil of the first generation poplarforest, soil nutrient （NH₄-N, NO₃-N, PO₄, K, Fe, Mn, Zn, Cu） validity appeared significantchange. Phenolic acids suppressed the validity of NH₄-N, K and Fe, and promoted the validityof NO₃-N, Mn. In the first week of training, NH₄-N content was4.67μg in control treatment.With the increase of phenolic acids concentration, its content decreased significantly, and thetreatment of2.0X content down to2.85μg. With the increase of the number of days, soilnutrient availability had different content in different phenol acid treatment, and the content ofNH₄-N and Mn changed little. The content of Cu had the most obvious change, and it reachedto very low level after the third week of training. The content of K and Fe also had a differentdegree of reduced while the time increasing. （3） Used the Shannon-Wiener diversity index to calculate the bacterial diversity. Theresults showed that it could promote bacterial diversity in a certain scope of phenolic acidsconcentration, while bacterial diversity index of0X phenolic acid treatment is2.835, and0.5X treatment bacterial diversity index increased to2.835. High concentration of phenolicacids could reduce bacterial diversity, and with the time increasing, bacterial diversitydecreased more obviously. The soil sample diversity index of2.0X phenolic acid treatment inthe first week is2.845, and decreased to2.647in the second week. The bacterial diversity oflow concentration phenol acid treatment had a tendency to increase, and the bacterial diversityof0.5X sample is2.835in the first week, then become2.970after two weeks.（4） It shows relationship between every nutrient index （NH₄-N, NO₃-N, PO₄, K, Fe, Mn,Zn, Cu） and through analysis relationship between poplar soil nutrient availability andbacterial diversity. In the first week of training phenolic acids, there was a significant negativecorrelation between the NO₃-N, Fe and bacterial diversity. And the correlation coefficientswere-0.824and-0.812. There was a positive correlation between K and bacterial diversity.And the correlation coefficient was0.728. In the second week of training phenolic acids,there was a positive correlation between NH₄-N, K and bacterial diversity, and the correlationcoefficients were0.866and0.856. There was a significant negative correlation between Mn,Zn, Cu and bacterial diversity, and the correlation coefficients were0.795，-0.982and-0.722.That is to say different relationships between the same nutrient availability and bacterialdiversity in different time.