Study On Soil Nutrients And Microbial Characteristics Of Juglans Sigillata Forests In Karst Mountainous Area

The soil texture of Juglans sigillata forest is the key factor to determine the yield and quality of J.sigillata.The study on soil fertility and soil microbial characteristics of J.sigillata forest in Karst mountain area not only helps to guide the rational fertilization of J.sigillata forest,but also provides scientific basis for land restoration and rocky desertification control in Karst mountain area.For researching soil fertility status,soil nutrient and microbiological characteristics to different planting years and phenological periods of J.sigillata in Karst mountainous area,this paper studied the changes of soil physicochemical properties and microbiological characteristics and their relationships in J.sigillata forests of different ages(4,6,7,11 years)and phenological periods(flowering stage,fruit expansion stage,fruit maturity stage).The main results are as follows:(1)According to the classification standard of soil nutrients,the soil organic matter content(SOM),total nitrogen(TN),exchangeable calcium(ECa),available iron(AFe),available zinc(AZn)and available boron(AB)in the J.sigillata forests were all in the medium and high-level state.The soil total phosphorus(TP)and available phosphorus(AP)contents of the studied plots were deficient,but the soil total potassium content(TK)and available potassium(AK)were deficient only in the 4-and 11-years old J.sigillata forests.The soil AK,ECa,AFe and AZn in the 6-and 7-years old J.sigillata forests were significantly higher than those of 4 and 11 years(P<0.01).The contents of the soil SOM,TN,TP,TK,AP and AB in the 6-and 7-years plantations were significantly higher than the 4-and 11-years old plantations.The soil SOM、ECa、AZn in fruit expanding stage of J.sigillata was significantly higher than that in flowering stage and fruit maturity stage(P<0.01).The content of the soil TN,TP,TK,AP,AK,AB in fruit expanding stage of J.sigillata was higher than that in flowering stage and fruit maturity stage,but the difference was not completely significant.(2)The contents of the soil microbial biomass carbon and nitrogen(MBC、MBN)in J.sigillata forests forested for 6 and 7 years were significantly higher than those of 4 and 11 years(P<0.01).The MBC/MBN ratio ranged from 6.303 to 7.967,the results showed that actinomycetes were the dominant fungi in soil microorganism pool of J.sigillata forest.From the perspective of phenology,the content of soil microbial biomass carbon in fruit expansion stage was significantly higher than that in flowering stage and fruit maturity stage(P<0.01).The soil microbial biomass nitrogen content in J.sigillata forests forested for 4 years at fruit expansion stage was significantly higher than that at flowering stage and fruit maturity stage(P<0.01).There was no significant difference in soil microbial biomass nitrogen content in J.sigillata forests forested for 6,7 and 11 years during different phenological periods(P>0.05).(3)The activities of soil phenoloxidase(PO)and peroxidase(PER)in the 4years old J.sigillata plantations were significantly higher than those of 7 and 11years(P<0.01),The activities of PO and PER decreased with increasing stand age.The activities of soil hydrolytic enzyme in the 6-and 7-years old J.sigillata forest were stronger than those of 4 and 11 years.The activities of soil cellobiohydrolase(CB)in the 6 years old J.sigillata forest were significantly stronger than those of 4,7 or 11 years(P<0.01).The activities of soil leucine aminopeptidase(LAP),urease(UR)in the 6-and 7-years old stands were significantly stronger than those of 4 years(P<0.01).The activities of soil CB and N-acetylglucosidase(NAG)in 11 years old plantations were significantly lower than those of other ages(P<0.01).From the perspective of phenology,the soil oxidase activities – PO and PER – at fruit expansion stage were higher than those at flowering stage and fruit maturity stage;the activities of β-glucosidase(BG)and CB at fruit maturity stage were higher than those in flowering stage and fruit expansion stage.The LAP and UR activities in flowering stage were higher than those at fruit expanding stage and fruit maturity stage.(4)The carbon metabolism function of soil microbial community in the6-year-old J.sigillata stands was similar to that in the 7-year-old stands but were different from the soil below the 4 or 11 years old forests.There was no obvious change in the soil microbial community metabolism Mc Intosh index,Shannon-Wiener index and Simpson index in different forest age and different phenology period.In conclusion,the soil fertility of 6 and 7-year-old J.sigillata forest was higher than that of 4 and 11 years old.The soil fertility was highest at the fruit expansion stage.This study represents a scientific reference for fertilization management to improve the soil quality of J.sigillata forest in Karst mountain area,especially at 4 and 11 years old.Reasonable application of phosphorus and potassium fertilizer,and correspondingly increase the amount and frequency of fertilization in spring and autumn is advised.