Effects Of Wind Erosion And Grazing On Ecosystem Carbon Cycle In Temperate Steppe

Human activities, mainly fossil fuel combustion and land use change, have played an importantrole in influencing global environment since the industrial revolution, including the rising atmospheric CO₂concentration and average global surface temperature, atmospheric nitrogen deposition, and changingprecipitation regimes. These changes have profound impacts on terrestrial ecosystems carbon cycle.Climate warming, decreased precipitation and land use change will exacerbate the occurrence of winderosion in arid and semiarid regions. Wind erosion is one of the land degradation processes in arid,semi-arid and sub-humid areas, which is an important factor controlling soil nutrients and organic matter inthe desertified areas. However, wind erosion is the phenomenon of geographical redistribution of nutrientsrather than a complete loss of nutrients. Wind erosion makes a large number of nutritious fine particulatematters loss from the surface, and then makes large amounts of nutrient substances add to the surface viathe deposition process. Therefore, wind erosion is one of the important driving factors of surface nutrientsand carbon cycle. Grassland ecosystem is one of the most widely distributed ecosystem types in the world,storing nearly1/3of the organic carbon of terrestrial ecosystems, maintaining30%of the net primaryproductivity, providing the world with about30-50%of the livestock, and playing an important role in thecirculation of global material and energy flow. The grassland ecosystems suffer most from wind erosion asa result of less precipitation, lower plant coverage and shorter growing season. Grazing is one of the mostcommon land use patterns of the grassland ecosystems, impacting grassland plants, litter and soil carbonpools in varied degrees by feeding, trampling and excreta. However, so far, understanding of the influencesof wind erosion and grazing on grassland ecosystem carbon cycle is extremely limited. In this study, we simulated the effects of wind erosion and grazing on ecosystem carbon cycle ina temperate grassland in northern China using manipulative experiment. This experiment was designedwith six treatments: control, wind erosion, dust deposition, grazing, wind erosion+grazing, dust deposition+grazing. We draw the following conclusions by processing and analyzing data from the2010to2012growing seasons:The ability of ecosystem absorbing carbon-ecosystem net CO₂exchange （NEE） showed that thetemperate grassland in northern China was a carbon sink during the growing season. Wind erosion reducedecosystem gross primary productivity （GEP,15.16%） and ecosystem respiration （ER,17.81%）, whereasdust deposition enhanced them by0.31%and5.55%, respectively. Wind erosion and dust deposition didn’taffect NEE in spite of changing the GEP and ER. However, grazing declined NEE, GEP and ER. Winderosion didn’t change the ability of sequestrating carbon in temperate grassland ecosystem in northernChina, but grazing reduced it. Wind erosion, dust deposition and grazing altered ecosystem gas exchangeby influencing abiotic factors （soil moisture） and biotic factors （aboveground biomass）. Wind erosion anddust deposition increased soil moisture, but grazing didn’t affect it. Wind erosion and grazing reducedaboveground biomass, but dust deposition increased aboveground biomass. Grazing declined the grassesand forb aboveground biomass. Wind erosion and dust deposition only affected forb biomass. Ecosystemcarbon fluxes （NEE, GEP, ER） were negatively correlated with soil moisture, but positively correlated withaboveground biomass significantly. The results indicated that the changes of ecosystem CO₂gas exchange（NEE, GEP, ER） were mainly caused by the variations in soil moisture and grasses biomass.Wind erosion and dust deposition significantly impacted ecosystem soil respiration in temperategrassland in northern China. Wind erosion decreased soil respiration by8.57%, but dust depositionincreased it by15.36%. Results suggested that wind erosion inhibited the release of CO₂in eroded regions and promote the release of CO₂in the deposited region. The results were opposite to those in previousstudies. In addition, grazing had no effect on soil respiration. The influences of wind erosion, dustdeposition and grazing on soil respiration were caused by changing ecosystem primary productivity,aboveground biomass, vegetation coverage, litter and belowground net primary productivity. Wind erosionsignificantly reduced litter by50.12%and dust deposition decreased it by5.59%. Grazing significantlyreduced litter by24.77%. Wind erosion and dust deposition significantly impacted belowground netprimary productivity. Wind erosion declined belowground net primary productivity by11.4%, but dustdeposition increased it by10.49%. Grazing had no effect on belowground net primary productivity. Theresults indicated that the changes of substrate and root which were necessary to soil respiration processeventually lead to the change of soil respiration.Wind erosion and dust deposition did not change ecosystems’ ability in absorbing carbon, butgrazing reduced it. Wind erosion decreased soil respiration, but dust deposition increased it. Grazing has noeffect on soil respiration. The results from this study will promote the understanding of the effects of winderosion and grazing on temperate grassland ecosystem carbon cycle and providing critical data to supportthe model simulation and accurately estimating terrestrial ecosystem carbon flux.