| As an important native tree species in the hilly areas of Sichuan,Cupressus funebris has a large area for planting.Due to unreasonable operation and management in the past,the existing pure forest of Cupressus funebris has a single structure,low productivity and ecological benefits,and urgently requires reconstruction.Toona sinensis and Koelreuteria paniculata are native deciduous broad-leaved species in the hilly area of central Sichuan,which has high economic value.Creating a coniferous and broad-leaved mixed forest is an effective way to transform low-efficiency forest.During interbreeding,the root exudates of Cupressus funebris through root system has an important influence on the soil environment and the growth of mixed tree species.In this study,the root exudates of Cupressus funebris were collected from the rhizosphere soil and set 4 levels: G1(rhizosphere soil extracts of one cypress),G2(rhizosphere soil extracts of two cypress),G4(rhizosphere soil extracts of four cypress),G8(rhizosphere soil extracts of eight cypress).The same quality non-rhizosphere soil collected soil nutrient extract,also set 4 levels: T1,T2,T4,T8,as a comparison.At the same time,set the blank processing CK.The collected extracts were divided into 12 equal parts and applied monthly to potted Toona sinensis and Koelreuteria paniculatafor soils for 1 year to simulate coniferous and broad-leaved mixing.The effects of root exudates on soil organic carbon and its active components,soil nutrients and soil enzymes are studied,which can provide some theoretical references for the improvement and sustainable management of inefficient Cupressus funebris forest.The results were found as follows:(1)The Cupressus funebris root exudates had little effect on the SOC content of Toona sinensis and Koelreuteria paniculata,which did not reach a significant level(P>0.05),and had a significant effect on soil active organic carbon(P<0.05).The soil active organic carbon content of Toona sinensis and Koelreuteria paniculata increased first and then decreased with the increase of the amount of Cupressus funebris root exudates,and reached the maximum at G4 level.G1 and G8 had no significant effect on soil active organic carbon of Toona sinensis and Koelreuteria paniculata(P>0.05).G2 and G4 significantly increased soil active organic carbon content of Toona sinensis and Koelreuteria paniculata(P<0.05).(2)The Cupressus funebris root exudates had no significant effect on soil total nitrogen,total phosphorus and total potassium of Toona sinensis and Koelreuteria paniculata(P>0.05).The soil available nutrient(alkali-hydrolyzable nitrogen,available phosphorus and available potassium)content of Toona sinensis and Koelreuteria paniculata increased first and then decreased with the increase of the amount of Cupressus funebris root exudates.Except that soil alkali-nitrogen content of Toona sinensis reached the maximum at the level of G2,other indexes reached the maximum at the level of G4.G1 had no obvious effect on the soil available nutrients of Toona sinensis and Koelreuteria paniculata or showed a promoting effect(P<0.05),G2 and G4 significantly increased soil available nutrient content of Toona sinensis and Koelreuteria paniculata(P<0.05),G8 had no obvious effect on soil available nutrient of Toona sinensis and Koelreuteria paniculata or showed a significant inhibitory effect(P<0.05).The soil pH value of Toona sinensis and Koelreuteria paniculata decreased with the increase of the amount of Cupressus funebris root exudates,and decreased significantly under G4 and G8 level(P<0.05).(3)The soil urease,neutral phosphatase,catalase and sucrase activities of Toona sinensis and Koelreuteria paniculata increased first and then decreased with the increase of the amount of Cupressus funebris root exudates.Except that soil urease activity reached the maximum value at G2 level,other soil enzymes reached the maximum value at G4 level.G1 and G2 had no significant effect on soil enzymes of Toona sinensis and Koelreuteria paniculata or showed a significant promoting effect(P<0.05).G4 significantly increased soil enzyme activity of Toona sinensis and Koelreuteria paniculata(P<0.05).G8 had no obvious effect on soil enzyme of Toona sinensis and Koelreuteria paniculata or showed a significant inhibitory effect(P<0.05).(4)The correlation analysis showed that SOC content was positively correlated with MBC,WSOC,POC and EOC content(P<0.01).There was a significant positive correlation between soil active organic carbon(P<0.01).Except that the correlation between EOC content and total potassium content was not significant(P>0.05),SOC and other active organic carbon fractions were positively(P<0.05)correlated with total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus and available potassium.The content of SOC and MBC was significantly negatively correlated with pH(P<0.05).WSOC,POC and EOC had no significant correlation with pH(P>0.05).The contents of SOC and its active components were positively correlated with urease,neutral phosphatase,catalase and sucrose enzyme activities(P<0.01).There was a significant positive correlation between soil enzymes(P<0.01).In summary,the root exudates of Cupressus funebris had little effect on the total organic carbon,total nitrogen,total phosphorus and total potassium content of soil.It had significant effects on the content of soil active organic carbon,the content of available nutrients and the activity of soil enzyme.That is,these index increased first and then decreased with the increase of the amount of Cupressus funebris root exudates.Overall,the best level of application of Cupressus funebris root exudates is G4. |
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