Study On Soil Respiration Of Dune-Meadow Cascade Ecosystems In Horqin Sandy Land

Past the study of soil respiration is mainly concentrated in humid and subhumid regions,the study of soil respiration in arid and semi-arid areas is still exist many problems to be resolved,especially serious desertification regions.This study took Horqin sandy land,a typical desertification area in China,as the research object.The study on soil respiration of dune-meadow cascade ecosystems were studied in the Eco-hydrological Experiment Research Station of Inner Mongolia Agricultural University of the dune-meadow alternating region,located in the southeastern edge of Horqin Sandy Land.The technical route is field test-variation analysis-function construction.The soil respiration and ecosystem respiration were observed synchronously using the photosynthetic active radiation meter(LI6400)and eddy covariance system in mobile sand dunes bare land,transition zone plantation and meadow reed community during growth season in 2014 and 2015(from April to October),Simultaneous continuous measurements of environmental control factors were collected,and investigated the soil properties and vegetation characteristics in the sample plot.1.The effect of litter on soil respiration in a man-made Populus L.forest in a dune-meadow transitional region was illuminated.The results showed that the difference between soil temperature with litter and soil temperature without litter was non-significant(P>0.05),that between soil moisture with litter and soil moisture without litter was significant(P<0.05).In 2014 and from July 12th to October 12th in 2015,soil respiration without litter was larger than soil respiration with litter during the growing season,with average values of 7.75,5.82 ? molm-2 s-1,and 9.75,8.75? molm-2 s-1,respectively.However,from April 12th to July 1st in 2015 soil respiration with litter was larger than soil respiration without litter,the average soil respiration values were 8.17 and 3.53?molm-2 s-1,respectively.The study showed that interactions among the quantity of litter,soil temperature,soil moisture and groundwater,which cause diurnal variations in soil respiration were diverse.Negative litter respiration may not be a measurement error,but caused by soil moisture which changes the relationship between soil respiration without litter and soil respiration with litter.Thus,this study showed that plant litter has a significant influence on soil respiration in the dune-meadow transitional region.The findings of this study will provide useful information to understand these fragile ecosystems and the terrestrial carbon cycle.2.The relationship of soil and ecosystem respiration under extreme soil moisture conditions was comparised.The results showed that the threshold of soil moisture affecting soil and ecosystem respiration in meadow was depicted by the field and capillary water holding capacity,respectively.The ecosystem respiration was larger than soil respiration in the mobile dune,with the cumulative soil respiration accounting for 72%of the cumulative ecosystem respiration.Similarly,in the meadow ecosystem respiration was larger than soil respiration before June 14th,with the cumulative soil respiration accounting for 53.5%of the cumulative ecosystem respiration.During growth season,however,the cumulative soil respiration was 1.44 times that of the cumulative ecosystem respiration.The study illustrated that considering the influences of soil moisture and different phenological phases are conducive to improving the fitting accuracy when interpolating missing soil respiration and ecosystem respiration data.The difference between soil respiration and ecosystem respiration was more pronounced under extreme soil moisture conditions.Ecosystems under extreme soil moisture conditions need to be considered in order to estimate terrestrial carbon emissions more accurately and predict future climate trends.3.The effect of different hydrological conditions on spatio-temporal distribution of soil respiration in the dune-meadow cascade ecosystem was explored;a quantitative model for soil respiration in cascade ecosystem was established.The results revealed that in sandy bare ground with soil moisture below field capacity,soil moisture had a greater impact on soil respiration than soil temperature,and rainfall could increase soil respiration.The effect of condensation on soil respiration during periods of continuous drought could not be ignored.In the meadowlands with soil moisture above field capacity,the groundwater affected soil respiration indirectly by regulating soil moisture and the relationship with soil temperature,and rainfall had an adverse effect on soil respiration.The effects of rainfall,soil moisture and soil temperature on soil respiration were minimum as soil moisture approached the saturation water content.In the transitional forest,soil moisture and soil temperature were the main factors controlling soil respiration.The most favorable soil moisture for soil respiration was close to the field capacity.The study found that the spatial variation observed in soil respiration was consistent with the local soil properties,vegetation types,and related environmental factors(groundwater,soil moisture,soil temperature);and emphasized that the field capacity and saturation water content are the demarcation points of a soil carbon emissions prediction model,and the effect of different hydrological conditions and soil temperature on soil respiration at each segment are reconsidered accordingly.Ultimately,the carbon emission patterns of the cascade ecosystems in arid and semi-arid areas are extremely complicated and have to be considered specially for estimating terrestrial carbon emissions.