Effects Of Soil Moisture, PH And Straw On Soil Microbial Diversity And PLAF Composition In A Coastal Saline Soil

To assess the response of the microbial community to salinity, soil moisture and organic matterusing denaturing gradient gel electrophoresis (DGGE) and phospholipid fatty acids (PLFAs)analysis, we carried out incubation experiments along soil salinity, pH, moisture and organic mattergradients by adding varying amounts of salt, KOH, water and straws to a coastal saline soil.Treatments included four salinity levels (1.90,9.41,19.76and26.92g NaCl g-1soil, correspondingto an electrical conductivity of0.68,3.55,7.49and10.22dS m-1), three soil moisture contents (20%、30%and40%), three pH values:(7.8、8.8and9.8) and four organic matter contents (0、1、3and5g kg-1soil). The results showed:(1) Changes in soil moisture had no significant effect on soil bacterial diversity index, butsignificant effect on soil fungi diversity index and PLFA concentration. Soil moisture did notsignificantly affect soil bacterial diversity index, but soil fungi diversity index decreased withincreasing soil salinity at the high moisture (40%); in addition, the interaction of soil moisture andsalinity did not significantly affect the bacterial diversity index. By PLFAs analysis of soil microbialcommunity, under the high soil moisture content (40%) the bacterial PLFA concentration was lowerat high soil salinity than at low soil salinity. Soil moisture had no significant effect on soil bacteriaPLFA concentration, but reduced the fungi PLFA concentration.Soil moisture and salinityinteraction also significantly affected the bacterial PLFA concentrations.(2) The diversity indices of bacteria and fungi decreased as soil pH value increased. At the samevalue of soil pH, the bacteria diversity index and fungi PLFA concentration decreased withincreasing soil salinity. The diversity indices and PLFA concentrations of soil bacteria and fungi atpH8.8was higher than those at pH7.8and9.8. The interaction of soil salinity and pH significantlyaffected the diversity indices and PLFA concentrations of soil bacteria and fungi.The total PLFAsand fungi PLFAs were much higher at pH8.8than at pH values of7.8and10.0. The total PLFAsand fungal PLFAs decreased with increasing soil salinity at pH9.8, but fungal PLFAs increased assoil salinity rose at pH7.8.(3) The bacteria and fungal diversity indices increased at the start of adding straws and thendecreased after adding organic matters. At the same soil salinity, soil bacteria, fungi, Gram-positivebacteria and Gram-negative bacteria PLFA concentrations increased with the amount of soil strawaddition. Total PLFA concentrations significantly reduced with increasing soil salinity. The bacteriadiversity indices were the least at19.76g NaCl kg-1soil and26.92g NaCl kg-1soil. Under the samestraw addition, the fungal diversity indices were higher at1.88g NaCl kg-1soil and9.41g NaClkg-1soil than at19.76g NaCl kg-1soil and26.92g NaCl kg-1soil. Under the same soil salinity, the bacteria, fungi, Gram-positive bacteria and Gram-negative bacteria PLFA concentrations increasedwith the addition of straws. Total PLFA concentrations were significantly higher without straw andwith adding1%straws than with adding3%and5%straws.