Effects Of Warming On Soil Respiration In A Coastal Wetland In The Yellow River Delta,China

Soil respiration(Rs)is the major efflux of carbon dioxide(CO2)from terrestrial ecosystem to the atmosphere.Furthermore,increasing Rs caused by increasing temperature can result in significant changes in the global carbon balance.Climate change due to greenhouse gas emissions is predicted to raise the mean global temperature by 0.3–4.8°C in next 100 years.Therefore,the response of Rs to experimental warming is one of the key challenges in global change research.The "blue carbon" of the coastal wetland is one of the most intensive carbon sinks on the earth,plays an important role in tackling climate change.The coastal wetland has shallow underground water level and is affected by the fresh water and salt water.On the one hand,elevated temperature can directly increase the rate of Rs.On the other hand,elevated temperature can also indirectly influence Rs by affecting environmental factors(e.g.,soil water,soil salt,soil physical and chemical properties)and biological factors(e.g.,photosynthesis,litter decomposition).So we used a complete random block design with 2 treatments(control,warming),and replicated 4 times in a coastal wetland in the Yellow River Delta.All the warmed plots were heated by infrared heaters.We analyzed the variation of environmental factors,biotic factors and soil respiration,discussed the mechanisms in acclimatization of soil respiration to warming,and evaluated the effect of warming on soil respiration in a coastal wetland in the Yellow River delta.The effects of warming on soil respiration was different during different periods(the drought period,the wet period and the flooding period).The soil respiration in the control was higher than that in the warming during the drought period(2.2 ? soil temperature increased,15.3% reduction in soil respiration),contrarily during the wet period(2.0 ? soil temperature increased,23.9% simulation in soil respiration).During the flooding,there were no significant differences between the two treatments.During the whole year,warming simulated the soil respiration by 11.3%.The effects of warming on soil respiration had different mechanisms during different periods(the drought period,the wet period and the flooding period).During the drought period,soil respiration was decreased in the warming plot due to the increased soil salt content on the one hand.On the other hand,the high salt content desreased the soil respiration by limiting the photosynthesis of Phragmites australis.During the wet period,soil temperature is the main factor which affected the soil respiration directly and through simulating the photosynthesis indirectly.Whereas during the flooding period,there were no differences on soil temperature,soil salt content,photosynthesis and soil respiration between warming and control.At the same time,the increased biomass could stimulate the soil respiration.The predominant factor which affected the soil respiration was soil temperature through the related analysis no matter it was warming plot or control plot.However,the relationship between soil respiration and soil temperature was different during the different periods(the drought period,the wet period and the flooding period)due to the salt restriction.Under warming plot,when soil salt content >5.0 ds·m–1,we developed the equation SR= 0.081e0.117T(r2 =0.69,p<0.001);When soil salt content <5.0 ds·m–1,equation was SR= 0.195e0.106T(r2 =0.89,p<0.001.Under the control plot,the relationship between soil respiration and soil temperature was similar during the different periods,so the equations was SR= 0.191e0.104 T(r2 =0.84,p<0.001).According to the model,we got that warming increased the soil respiration of coastal wetland of the Yellow River delta by 32.7%(warming was 2174.6 g · m-2,control was 1660.0 g · m-2)in 2015.The soil respiration was different during the different periods.During the drought period,warming decreased soil respiration by 21.6%.During the wet period,warming simulated soil respiration by 51.5%.There was no difference between warming and control during the flooding period.