| In natural environment,soil microorganisms usually exist in the form of microbial aggregates rather than the free single microbial cell by secreting extracellular polymeric substances on the surface of soil particles.These microbial aggregates are widely known as soil microbial films.Soil microbial films are an important adaptive approach for soil microbial self-protection and efficient growth.In addition,more and more people are realizing that soil microbial films potentially contribute to the anti-erodibility and water retention improvement of aeolian soils due to the strong cohesiveness of the extracellular polymeric substances.Therefore,as an emerging research approach,soil microbial films are at the forefront for desertification combating.However,the mechanism of this improved process remains unclear,these knowledge gaps have been hindering soil microbial films to be an alternative to the traditional techniques for desertification combating.In this study,the controlled experiment was conducted in a greenhouse using the common aeolian soils and soil bacteria(Bacillus subtilis and B.pumilus).6 microbial agents(0,1,3,5,7 and 10 g/kg)were involved to test various soil properties and to identify the ecological function of soil microbial films.The results indicated that:(1)Proteobacteria,Acidobacteria and Actinobacteria had high relative abundance in the soil of Horqin Sandy Land,which relative abundance were 41.47%,19.80%and 9.72%,respectively.Soil organic matter content was significantly correlated with soil bacterial Shannon diversity index(P<0.05).Firmicutes has high relative abundance in aeolian sandy soil,and Bacillus is a common genus.B.subtilis and B.cereus were obtained by strain screening with higher polysaccharide content.(2)Soil microbial films were successfully and largely induced by the microbial agents and clearly detected by the scanning electron microscope at multiple scales.In details,soil microbial cells first gathered,and then filled the space and cement aeolian soil particles using extracellular polymeric substances.In this process,soil microbial biomass carbon and nitrogen as well as soil polysaccharide were all increased,which were 2.41%-8.82%,0.79%-8.60%,and 8.92%-11.97% higher than the control group,respectively.(3)On the 49th day of the experiment,most of the soil properties were increasing affected by soil microbial films as follow soil porosity(0.39%-3.91%),soil moisture(0.11%-0.25%,P<0.05),soil aggregates(5.59%-25.01%),soil organic matter(26.92%?88.46%),and soil pH value(from 7.16 to8.32-9.23,P<0.05).Soil bulk density was the only index which was in a deceasing tendency(0.54%-8.88%).According to the redundancy analysis,soil polysaccharide was the most critical factor affecting aeolian soils with the highest interpretation rate(47%),followed by soil microbial biomass nitrogen and carbon.(4)Soil microbial films could promoted soil infiltration,inhibited soil evaporation,reduced soil saturated hydraulic conductivity,and effectively retained soil moisture.At the end of the experiment,infiltration rate of the treatment group increased by 14.15% ? 36.12% compared with the control group.The daily soil evaporation of 1?10 g/kg treatment group was 0.26?0.35 mm,which was26.39%?53.85% lower than that of the control group.Compared with the control group,soil cumulative evaporation decreased by 18.78%?24.37%.Inhibition efficiency of soil cumulative evaporation in 3g/kg treatment group was the highest,which was 19.60%In conclusion,soil microbial films effectively improve aeolian soils involving anti-erodibility and water retention.However,what is worth noting is that the microbial agents in a high concentration significantly increased soil pH resulting in soil salinization.Therefore,we highly recommended that the suitable microbial agents were 1-5 g/kg.Moreover,the recipe of adsorbent is also can be optimized to alleviate and curb soil salinization.This improved information is expected to provide a better understanding of the mechanism of soil microbial films affecting sand fixation and soil moisture,eventually and substantially contribute to a firm theoretical basis and scientific & technological support for the new technology exploration of desertification combating in a soil microbial approach. |
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