The Fate Of Biological Soil Crusts Fixed Nitrogen In The Loess Plateau Region, China

Soil nutrient is low in the hilly-gully Loess Plateau region, especially of the nitrogen.Biological soil crusts (biocrusts) that composed of pioneer organisms such as algae,cyanobacteria, mosses and lichens were extensively developed in the Loess Plateau region, China,which covers up70%soil surface in rehabilitated grasslands after the “Grain for Green”eco-project was implemented in the region.Aimed to determine biocrusts’ contributions to thesoil nitrogen, the study investigated content changes of nitrogen with different ages’ revegetatedgrassland. Besides, The way about where nitrogen-fixing going were studied by the method ofpot and nitrogen transport experiment. The paper was aimed at understanding the role of nitrogenfixation by biocrusts in nitrogen cycles.1.Soil nitrogen content was significantly improved for the formation of biocrusts.Content of total nitrogen, soil alkali-hydrolyzable nitrogen, and nitrate and ammoniumnitrogen were both relevant to biocrusts and showed obviously temporal-spatialdistribution characteristics.1) Influence of biocrust on soil nitrogen content was mainly reflected onthe biocrustslayers. The contents of soil total nitrogen, alkali-hydrolyzable nitrogen, nitrate and ammoniumnitrogenin biocrusts layers was significantly higher than that in the0-10cm layers.2)Content of soil organic matter and total nitrogen in BSCs were obviously higher thanthose in the fresh revegetated grassland, and increased gradually along with the extending age ofrehabilitation, and tended to be stable after13years rehabilitated.3)Activity of nitrogen in the soil was increased in the process of biocrust on soil nitrogenaccumulation2. Effects of biocrusts nitrogen fixation on subsoil were changed with the change ofcrust type and culture time.1) Effects of moss crusts on subsoil nitrogen lower than algal crust and mixed crust.2) Biological crusts increased the content of subsoil available nitrogen significantly, thenitrate nitrogen content increased significantly, while ammonium nitrogen content decreasedslightly.3) Effects of biocrusts on subsoil available nitrogen had difference with the change ofculture time, as the culture time prolonged, the soil available nitrogen in each soillayer increased.3.Biocrust had an effect on the plant growth and development, and this effect varies depending on the type of plant. Effect on oilseed rape (nitrogen plant) impressed moreobviously than that of tarragon grows in poor soil areas.4.Without considering the volatile gases, the nitrogen that fixated by biological crusthas an important influence on surrounding environment. The fate of fixation nitrogenincludes plant uptake, biological crust fixation and migrating downward into deep soil layeror surface runoff.Nitrogen fixation potential of biological crust is close to10.4kg ha-1a-1in loess hillyregion, and29.9%of these fixed nitrogen were absorbed by plants. Without the plants, thenitrogen fixed by biological crusts were largely concentrated in crusts, and58.9%and3.5%nitrogen fixed by algal crusts and mixed crust, respectively, were all concentrated in relevantcrusts.