| Microbes play a decisive role in the quality of the grapes as well as the wine.Conditions for the growth of grapevines,including soil,topography,weather,and climate,affect microbial communities,and colonized microbes may potentially alter wine composition.How the microbial communities associated with grapes/ wines interact with microclimate or wine biochemical characteristics and shape wine quality needs further clarification.Based on the widespread application of rain-shelter cultivation in continental monsoon climate wine regions,this study used a typical red grape variety,Cabernet Sauvignon,as an example,and open-field cultivation as a control to assess the effects of rain-shelter patterns on the diversity and succession of microbial communities in four tissue habitats during the grape growing stage and in spontaneous wine fermentation.Meanwhile,the interaction patterns of meteorological factors and the distribution of microbial community under rain-shelter cultivation were elucidated.In addition,the evolution patterns of 10 basic biochemical characteristics and 13 monomeric phenols in spontaneous wine fermentation under two types of cultivation were also explored.Finally,the sensory profiles and aroma-flavor differences of wines produced under the two cultivation modes were investigated.The main contents of this study are summarized as follows:(1)Microbial communities were characterized in four habitats(berry surface,leaves,branches and soil)of Cabernet Sauvignon grapes from the setting stage,the beginning of véraison,the end of véraison and ripening stage in two cultivation modes,and the dynamics of six meteorological factors were monitored in real time under two microclimates during grape development.The average temperature under rain-shelter conditions was 2-3 °C higher than under open conditions,while the maximum reduction in air humidity was 5.79%(P<0.05).After the véraison stage,soil temperature was significantly higher under rain-shelter conditions than the control,while soil humidity was significantly lower than the control(P<0.05).Compared to the control,UV intensity and precipitation were reduced by72% and 96%,respectively,in the rain shelter treatment(P<0.05).The rain-shelter condition presented lower fungal and bacterial OTUs.Under both cultivation patterns,the principal fungal genera identified mostly Alternaria,Aspergillus,Mycosphaerella,Aureobasidium,Penicillium,Hanseniaspora,Cladosporium,Starmerella and Trichothecium,and the core bacterial OTUs comprised principally Tatumella,Methylobacterium,Stenotrophomonas,Acinetobacter,Pantoea,Sphingomonas and Gluconobacter.Rain-shelter cultivation reduced the abundance of Alternaria and Colletotrichum,which adversely affected grape health.Multivariate statistical analysis showed that the effect of vineyard microclimate on microbiota distribution and succession was influenced by cultivation pattern and grape growth stage.(2)The microbial communities of Cabernet Sauvignon harvested under both cultivation patterns during spontaneous fermentation were characterized.From the juice to the end of alcoholic fermentation,the fungal taxa were mainly composed by Saccharomyces,Schwanniomyces,Starmerella,Mycosphaerella and Cladosporium;the bacterial community was mainly enriched by Tatumella,Acinetobacter,Gluconobacter and Acetobacter were enriched.Under both treatments,32.5% of the fungal and 5.2% of the bacterial OTUs were shared throughout the fermentation process.Fungal diversity decreased as fermentation advanced(P<0.05),and bacterial community diversity decreased and then increased during fermentation,independent of cultivation mode.In addition,rain-shelter treatment increased the abundance of several species,including Acetobacter,Pseudonocardia,Pantoea and Limnothrix.Cooccurrence network analysis between core microbial genera during fermentation revealed a significant interactions between microbiota.Finally,the microbial community of the fermentation process was predicted based on KEGG metabolic pathways,which showed that the fungal community functions were more abundant in glycolytic pathway and coenzyme A biosynthesis pathway as well as fatty acid elongation pathway;the functions of bacterial genes were indicated to be concentrated largely in the pathways of carbohydrate metabolism as well as amino acid metabolism.(3)The dynamics of 10 basic biochemical characteristics and 13 monomeric phenols during the spontaneous fermentation of wine under both cultivations were analyzed.Rain-sheltered cultivation altered the levels of alcohol,glycerol,malic acid and catechins in the final wine,which were significantly higher than the control by 2.6%,6.8%,10.3% and20.3%,respectively(P<0.05).During alcoholic fermentation,ethanol,acetic acid,lactic acid,glycerol,epicatechin,catechin,morin,butyric acid and rutin concentrations continued to increase significantly(P<0.05).Based on RDA and Spearman correlation analysis,Providencia,Acetobacter,Pseudonocardia,Leuconostoc,Mycosphaerella,Cladosporium,Starmerella,Aspergillus and Saccharomyces were significantly correlated with changes in biochemical characteristics and monomeric phenols.(4)Fifty-two volatile aromas and sensory profiles were evaluated in wines spontaneously fermented with Cabernet Sauvignon under both cultivations and correlated with the core microorganisms involved in the fermentation process.Compared to the control,rain-shlter cultivation significantly reduced the content of(E)-3-hexen-1-ol,linalool and higher alcohols(e.g.,isobutanol,isovalerol,1-octen-3-ol);and increased the concentration of2-ethyl methylbutyrate,octanoic acid and isovaleric acid.In terms of fermentation aromas,a total of 14 fermentation aromas with OAV > 0.1 were significantly different between the two types of wine.The rain-shelter mode enhances the aromas of drupes(e.g.apples),greens(e.g.peppers,mushrooms,truffles),toasts(e.g.caramel)and nuts(e.g.dried prunes)in the wine,and reduces the odor of nail polish.Spearman analysis revealed that Hanseniaspora vineae and Candida apicola showed significant positive correlations with esters(hexyl acetate,diethyl succinate)and higher alcohols(3-methyl-1-pentanol,3-methylthiopropanol).Starmerella bacillaris and Pichia terricola were positively correlated with ethyl butyrate,isoamyl acetate and ethyl lactate(ρ≥0.7;P<0.05).Gluconobacter oxydans and Lactococcus lactis were positively correlated with higher alcohols(e.g.1-heptanol,isobutanol). |
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