Studies On Changes Of Soil Environments Of Continuous Cropping And Allelopathy Effects Of Gerbera Jamesoni

The obstacle of continuous cropping has been the major problem in gerbera（Gerberajamesonii） production in greenhouse. Continuous cropping can decrease gerbera yield, qualityand disease resistance. Using conventional methods, an experiment was conducted toinvestigate the changes of gerbera continuous cropping on soil physical-chemical properties,soil microbial and enzyme activities. The objective of the experiment is to study the effect ofgerbera continuous cropping on soil physical-chemical and biological characters, andillustrate the soil environment effect of continuous cropping gerbera simultaneously. Theallelopathy of gerbera leaf and root extract with the gerbera was studied. Then a fewallelopathic substances were collected and identified in leaf and root exudates by GC/MS. Theresults showed as follows:1. Results showed that compared with control, soil salt content was increased by4.00%,72.80%,24.00%and88.00%, respectively, under1-7years gerbera continuous cropping,while soil pH and bulk density began to decline. With the increasing of gerbera continuouscropping years, soil organic matter content and available N content was remarkably raised,but the soil available P and available K content was decreased, illustrating soil N, P, Kproportion was imbalanced.2. The activities of soil urase and sucrase increased in1-3years gerbera continuouscropping, while those enzyme activities decreased in5-7years, the soil catalase andphosphatase activity decreased with the gerbera continuous cropping year increasing, whilethe soil protease activity increased by9.09%,50.00%,63.64%,93.18%, respectively, under1-7years continuous cropping, compared with control.3. With the time of gerbera continuous cropping increasing, soil fungi number increasedgradually, the number of7years continuous cropping increased by192.04%, the number ofsoil bacteria decreased, but the number of other soil microorganisms increased in1-3yearscontinuous cropping and decreased in5-7years. The quantities of bacteria and actinomycetesof soil decreased under5-7years continuous cropping, but soil fungi number increased, theobstacles of continuous cropping were obvious.4.19and44main allelopathic substances were identified in gerbera leaf and rootaqueous exudates, respectively, by GC/MS analysis. l,2-Benzenedicarboxylic acidramification, which many researchers have studied could be detected． 5. Gerbera leaf and root aqueous exudates have autotoxicity. It was found that gerberaleaves and roots aqueous extracts in different concentrations inhibited the root activity andfresh mass of gerbera, the sequence of material allelopathy was root> leaf. Under the0.4g·mL^-1aqueous extract, SOD, POD, CAT activities and MDA content of gerbera leaves wereraised with increasing duration of treatment. While under the0.8g·mL^-1aqueous extractsthese indicators of leaves were increased at first then decreased with increasing time oftreatment. SOD, POD, CAT activities and MDA content of gerbera roots were raised withincreasing the concentration of leaves aqueous extract, while these indicators of roots wereincreased at first then decreased with increasing the concentration of roots aqueous extract.Soluble protein and proline contents of both gerbra leaves and roots were enhanced withincreasing the concentration of leaves aqueous extract. These results indicated thatautotoxicity of high concentration (0.8g·mL^-1) gerbera leaves and roots aqueous extract wasgreater than low concentration (0.4g·mL^-1), the roots aqueous extract higher than the leavesaqueous extract.