[Seasonal Variations of Soil Microbial PLFAs and Soil Enzyme Activity Under the Citrus Plantation in Mt. Jinyun, Chongqing].

The soil microbial community and soil enzyme activity are important parts of soil ecosystem,and they are sensitive to the ecological environment.In this study,citrus plantation in Mt.Jinyun was chosen as the research object.The phospholipid fatty acid (PLFAs) combined with principal component analysis method was used to study the effect of season changes on soil microbial quantity,community structure characteristics and soil enzyme activity at 0-20 cm soil layer under citrus forest.The results obtained from this study were as follows:① The season changes had a significant impact on soil microbes (P<0.05).Moreover,16:0,i17:0,16:1 2OH,18:0,cy19:0ω8c,i17:1ω9c or 16:0 10-methyl were found to be common in all four seasons,and the proportion of each phospholipid fatty acid was 49.57%,41.63%,35.41% and 38.05%,respectively.In various microbial species,the PLFAs content of bacteria was the highest,followed by fungi,and that of actinomycetes was the lowest.Our results revealed that all kinds of micro-organisms showed obvious seasonal variation characteristics.The total PLFAs quantity of citrus forest ranged from 6.868 to 24.085 nmol·g-1,which had a content order of spring >autumn >winter >summer.The PLFAs content of bacteria,G-,G+ and actinomycetes also showed the same variation trend.However,the PLFAs content of fungi showed a different variation trend,i.e.,autumn was the highest,followed by winter and summer,and spring was the lowest.The results suggested that season change also had a significant impact on microbial community functional diversity index.The variation trend of richness index (R) followed the order of spring >winter >autumn >summer.Moreover,the variation trend of diversity index (H') was winter >autumn >spring >summer.Furthermore,the variation trend of evenness index (J) was summer >autumn >winter >spring.The dominance index (D) increased with the change of season.2 Urease showed a change with the seasons following summer >spring >autumn >winter;Soil invertase,soil catalase and acid phosphatase activity changed obviously in autumn,followed by spring,summer,and winter.3 The principal component analysis demonstrated that the PLFAs content of bacteria,G-,G+,actinomycetes and total PLFAs made the greatest contribution to soil fertility followed by that of invertase,catalase,acid phosphatase and fungi.Moreover,our studies showed that the PLFAs content of urease made a minimum contribution to the soil fertility.