Effect Of Biological Soil Crust On Soil CO₂Flux In Different Erosion Region On The Loess Plateau

Biological soil crust （biocrust） as a compact and photosynthetic complex layer of soil,exert profound influences on the process of carbon exchange between soil-atmosphere. Inrecent years, the ecological function of biocrust received considerable attention in arid andsemiarid region. In this study, the influence of biocrust on soil CO₂flux and its effectedfactors were studied, the differences between water erosion, water-wind erosion crisscross andwind erosion regions on the Loess Plateau were analyzed, the biocrust soil carbon balancewas estimated. The main results were as follows:（1） Biocrust affected carbon exchange between soil and atmosphere. Soil CO₂flux wasdecreased by162%under the effects of actived biocrusts as compared with those of thedormant state. Soil CO₂flux of cyanobacteria crust and moss crust was decreased by92%and305%under light condition, respectively, as compared with the fluxes without biocrusts. Thedecrements of soil CO₂flux by the biocrusts were related to the biocrusts components andtheir biomass. Soil CO₂flux of the dark cyanobacteria crust and moss crust was decreased by141%and484%as compared with that in bare land.（2） The diurnal curve of soil CO₂flux of biocrusts presented as a trend ofdrop-rise-drop, with the maximum carbon uptake of cyanobacteria crust and moss crust being0.13and^-1.02μmolCO₂·m^-2·s^-1and occurred at about8:00and9:00am, respectively. On theseasonal scale, the daily CO₂flux with biocrust before rainy season was2.01times of therainy season, while the flux during rainy season was3.97times of the flux after rainy season.CO₂flux under of biocrust soil was increased by28%and8%before rainy season and afterrainy season, respectively, while that under effects of biocrust during rainy season wasdecreased by5%, as compared with the CO₂flux in bare land.（3） Soil CO₂flux with activated biocrust was decreased compared with the flux withoutbiocrust in the three regions. The daily average CO₂flux of biocrust soil was reducedrespectively by5.0%,8.9%and20.5%in the water erosion region, water-wind alternatederosion region and wind erosion region. The soil CO₂flux in the day time showed a simplepeak curves, with the peak fluxes under effect of biocrust being1.64,1.64and1.37μmolCO₂·m^-2·s^-1and occurred at about12:00^-14:00pm in the water erosion region, the water-wind alternated erosion region and the wind erosion region, respectively.（4） Temperature and water condition were the main influence factors on soil respiration.Other factors such as soil texture, organic carbon content, microbial biomass carbon and so onwere also exert impact on soil respiration. Soil respiration rate increased along withtemperature rising. Range of temperature sensitivity quotients （Q10） changed between1.93and2.43in the water erosion region and in the water-wind alternated erosion region, while therange of Q10values was4.80-5.56in the wind erosion region. The results indicated that theeffect of temperature on biocrust soil respiration in the wind erosion region was moresensitive than that in the water erosion region and the water-wind alternated erosion region.Response of biocrust soil CO₂flux to water content showed a single peak curve. Soil CO₂fluxes of water erosion region, water-wind erosion region and wind erosion region showedtheir peak vealue under60%,40%and30%field water holding capacity, respectively.（5） Biocrust has greater contribution to soil organic carbon accumulation. We estimatedthat moss crust reduce about13.24t·ha^-1carbon emissions in a year. The results suggestedthat biocrust had significant effects on reducing soil carbon emissions.