Soil Microbial Diversity In Organic Versus Conventional Vegetable Management Systems

Soil microbe plays a significant role in agro-ecosystem. They arepresent in almost every process of interaction between soil and crop. Forexample: nutrient cycling, growth regulation of crop, microbial control,optimization of soil texture. On the other hand, soil microbe is liable tochange the community structure and diversity under differentmanagement, cultivation environment, and different season. In this study,we researched shifts of activities of enzymes and soil microbial diversityunder different management and cultivation type in a vegetable system.The results show us that:1) The EC of organic management were less than it of conventionalmanagement by12%and16%in greenhouse and open field respectively;The level of Microbial C and Microbial N under organic managements ishigher than it under conventional management; There has significanteffect to activities of Proteinase and Urease by different managementpractices; The activities of Proteinase, Urease, Dehydrogenase andβ-glucosidase under organic management at a high level comparatively; Environment conditions of cultivation have significant effect to activitiesof Proteinase, Urease, β-glucosidase, Nitrate reductase; Enzymeactivities displayed a higher level in organic management of greenhousethan it in other treatments; Correlation analysis showed that Proteinase,Urease, Dehydrogenase, β-glucosidase have close correlation whichreached significance level partly with total dissolved nitrogen, microbialmass C, microbial mass N. In sum, organic system significantly improvedsoil microbial characteristics and increased soil organic C, thus improvingsoil enzymes activities. Moreover, Proteinase, Urease, Dehydrogenase,β-glucosidase were suitable indicators of soil fertility.2) Soil bacterial diversity has a significant change under differentmanagements and sample period by analyzing DGGE gels. Moreover, theabundance of each dominant band varied among each treatment duringthree sample periods. On the other hand, by observing16S rRNA DGGEfingerprint, we found that there has less variability than that in16S rDNAfingerprints, and16S rRNA DGGE fingerprint can be grouped separatelyin terms of organic and conventional management by UPGMA.Additionally,16S rDNA DGGE fingerprint indicated that a seasonal shiftof bacterial community. From26different bands which were excisedfrom DGGE gel, the result showed us that there were9bands belong toPseudomonas and the rest of bands belong to uncultured bacterium clones.Shannon-Wiener index showed that organic management promoted bacterial diversity in soil more intensively than conventional managementdid. According to the figure drew by CCA, it points out that soil pH is thestrongest environmental factor which can influence soil bacterial diversity.Meantime, the level of microbial mass C, and N and organic matter has asignificant increase under organic management. On the other hand,results indicated that soil of greenhouse has a higher humidity than soilfrom open field. During the same period, pH value was higher in organicmanagement soil than it under conventional management virtually. Insum, organic management can diversify active bacterial community andhave beneficial ecological effects.3) Soil DNA fingerprints discriminated the fungal community by themanagement and cultivation types, while cDNA fingerprints indicated agreater seasonal effect. Soil organic matter content, electricalconductivity and ammonium concentration could significantly explainmost of the variation observed in the fingerprints. Sequencing of theDGGE bands revealed a greater presence of fungi affiliated to Pythiumultimum, Alternaria spp., Fusarium oxysporum, Sporisorium reilianumand Chaetomium globosum in conventional soils and Cordyceps gunnii inorganic soils, with only partial overlapping of the sequenced18S rDNAand18S rRNA bands observed. The far-reaching influence of organicmanagement is evidenced by the changes produced in both the total andtheoretically active fungal populations. Changes in the fungal community due to greenhouse cultivation were associated with an increased salinity,producing a decrease in fungal biomass and increased bacterial activity.This suggests that the benefits derived from fungi in organically managedsoils may be reduced by greenhouse cultivation practices. ThecDNA-DGGE fingerprints could more sensitively detect changes in thepatterns of the fungal community and were the only means to observeseasonal effects.In sum, organic management can optimized soil texture and enlargethe diversity of soil microbe. To joint analysis of soil DNA and RNA inthe same study achieves a higher resolution than DNA based studiesalone, and allows the observation of otherwise unnoticed importantchanges in the microbial community.