Responses Of Soil And Heterotrophic Respiration And Sensitivity To Climate Warming And Changing Precipitation Regime In Three Temperate Grasslands

Since the Industrial Revolution,human activities including land-use change and fossil fuel combustion have resulted in climate change,with subsequent effects on ecosystem structure and function.Climate change including climate warning and changing precipitation regimes can affect carbon dioxide(CO2)fluxes between terrestrial biosphere and the atmosphere,with consequent feedback to climate change.Soil respiration is the component of carbon cycling.A field manipulative experiment with nocturnal warning and changing precipitation was conducted by excavating soil monoliths from three temperate steppes(desert steppe,typical steppe,and meadow steppe)along a natural precipitation gradient in the arid and semiarid region of northern China.Across the three temperate grassland ecosystems and three growing seasons(May-October)from 2014 to 2016,nocturnal warning significantly increased soil temperature(ST)by 0.5°C,but reduced soil moisture(SM)by 1.1%(absolute change).Increased precipitation decreased ST by 0.4°C,whereas elevated SM by 1.4%.Decreased precipitation suppressed SM by 1.8%,but did not affect ST.When analyzed by grassland type,nocturnal warning increased ST by 0.4,0.6,and 0.5°C in desert steppe,typical steppe,and meadow steppe,respectively.Increased precipitation improved SM by 2.0 and 2.5%in desert steppe and typical steppe,respectively.Decreased precipitation reduced SM by 2.5 and 3.3%in desert steppe and meadow steppe,respectively.Across the three temperate grassland ecosystems and three growing seasons from 2014 to 2016,nocturnal warning had no influence on SR or heterotrophic respiration(HR).Increased precipitation notably stimulated SR and HR by 38.8 and 29.5%(relative change),respectively,whereas decreased precipitation declined SR and HR by 20.9 and 9.7%,respectively.When analyzed by grassland type,nocturnal warning did not affect SR or HR in any of the three temperate grasslands.Increased precipitation enhanced SR by 57.3,31.0,and 35.8%in desert steppe,typical steppe,and meadow steppe,respectively.In addition,increased precipitation improved HR by 49.6,21.1,and 26.5%in desert steppe,typical steppe,and meadow steppe,respectively.Decreased precipitation suppressed SR and HR by 21.7 and 15.4%in typical steppe.The response of soil carbon efflux to increased precipitation was stronger than decreased precipitation in temperate grasslands.Different ecosystems have the diverse sensitivity to increased versus decreased precipitation.In the unwarmed plots,SR and HR had greater sensitivity to increased precipitation than decreased precipitation in desert steppe.In the nocturnal warmed plots,SR and HR also had greater sensitivity to increased precipitation than decreased precipitation in desert steppe.Xeric grasslands were more sensitive to increased precipitation than mesic grasslands,and mesic grasslands were more sensitive to decreased precipitation than xeric grasslands.The above observations suggest that increased and decreased precipitation treatments have an asymmetric effect on the C cycling of the temperate grasslands.The findings indicate that intensified precipitation variability may have profound impacts on grassland C cycling and its response to climate warning under future climate change scenarios.Increased precipitation may be more important in mediating the C cycling of the temperate grasslands than decreased precipitation.