The Effects Of Erosion Environment On Soil Nitrogen And Microbial Community Diversity On The Hilly-gully Area Of Loess Plateau

The Loess Plateau is the biggest loess deposition region in the world with the frailecological environment. In this area, slope soil erosion is extremely common and serious.Since the implementation of the “Grain for Green” project, the ecological environment andsoil quality were improved. Different vegetation zones, including arbor-brush-grassvegetation zone, brush-grass vegetation zone and grass vegetation zone, were choosen as theresearch area in the Gully region of Loess Plateau. We determined soil physiochemicalproperties, nitrogen contents, microbial biomass, soil respiration, metabolic quotient andPLFA characteristics during different erosion environment, to unearth the effect of thevegetation zones and erosion environment on soil nitrogen and microbial community diversity.The results showed that:Arbor-brush-grass vegetation zone overall manifested that Shady lower slope wasoptimal, followed by Sunny lower slope, Shady middle slope, Sunny middle slope and Hilltop. While soil C/N was relatively stable. Soil pH and bulk density showed that Sunny slope>Hill top> Shady slope. While in brush-grass vegetation zone, soil organic matte content, totalnitrogen and C/N showed little change. Total P showed that Shady slope> Sunny slope> Hilltop, whereas total K did that Sunny slope> Shady slope. In grass zone, soil pH, bulk density,total P and C/N were relatively stable, while organic matter and total N represented Hill topand Sunny middle slope were higher than Sunny lower, whereas total K did Hill top> Middleslope> Lower slope. Overall, soil physiochemical property of arbor-brush-grass zone wassuperior than brush-grass and grass zones, while the latter two had little difference.With the expection of ammonium nitrogen, soil various forms of nitrogen fractionsin arbor-brush-grass community overall manifested that Shady lower slope> Sunny lowerslope> Shady middle slope> Sunny middle slope and Hill top. Brush-grass and grass communities showed little change as a whole in0-10cm depth, while10-20cm depth soils hadthe stronger change. At brush-grass community, different nitrogen fractions presenteddifferent change on the erosion environment in10-20cm depth soils. At grass community,total nitrogen, organic nitrogen and mineralizable nitrogen manifested Sunny middle slope>Hill top> Shady lower slope and Sunny lower slope> Shady middle slope. Nitrate nitrogenand ammonium nitrogen were higher in Sunny middle slope and Shady middle slope. NitrateN changed more quickly than the other N fractions. Soil nitrogen contents ofarbor-brush-grass zone were higher than brush-grass and grass zones, while the latter two hadlittle difference. There were significant positive correlations between soil total carbon,nitrogen, phosphorous, potassium and soil different N fractions, while negative correlationbetween soil bulk density, pH and N contents. There were significant positive correlationsamong the various N fractions. The ratio of mineralizable N to total soil N increased as thetotal soil N concentration increased, whereas the ratio of ammonium N to total N decreased.Soil metabolic quotient had no significant difference among different erosionenvironment in arbor-brush-grass zone, whereas soil microbial biomass and basal respirationshowed that Shady lower slope> Shady middle slope> Hill top. In brush-grass zone, basalrespiration did not change significantly, while microbial biomass and metabolic quotientshowed Hill top and Shady lower slope were better than Shady middle. In grass zone, basalrespiration changed little similarly, microbial biomass and metabolic quotient showed Shadylower slope and Shady middle slope were better. Soil microbial properties manifested thatarbor-brush-grass zone> brush-grass zone> grass zone. Soil microbial properties were moresensitive to environmental conditions than physiochemical properties and nitrogen. Therewere significant positive correlations between soil basal respiration, microbial biomass andsoil nitrogen. Similarly，there were significant positive correlations among microbial biomasscarbon, nitrogen and phosphorous.Total nineteen PLFA (phospholipid) profiles were detected among the threevegetation zones. Total PLFAs, individual PLFA and various kinds of microbes inarbor-brush-grass zone showed that Shady lower slope> Shady middle slope> Hill top.While in brush-grass zone and grass zone, total PLFAs had no significant difference amongdifferent erosion environment. As for individual PLFA and various microbes, Shady middleslope was slightly above Hill top and Shady lower slope in brush-grass zone, while Hill topwas above Shady lower slope and Shady middle slope in grass zone. Soil PLFAs and variousmicrobes showed that arbor-brush-grass zone> brush-grass zone> grass zone.Soil PLFAcomposition were similar in study area. The PLFA of16:0,18:1ω9c,18:1ω9t and19:0weredominance in microbial community. Soil PLFAs and microbes significantly positive correlated with soil nitrogen and microbial biomass, while their change trend was different.