Soil Respiration And Its Responses To Environmental Factors In Five Vegetation Types On The Loess Hilly Region

Soils are the largest carbon reservoir in terrestrial ecosystems.The loss of soil carbon pool from soil respiration is an important loss source.To explore the characteristic of soil respiration of typical vegetation types on the loess hilly region and their responses to main environmental factors,five typical vegetation types which consist of a Black locust?Robinia pseudoacacia?plantation,a natural Oak?Quercus liaotungensis?forest,a natural Oriental arborvitae?Platycladus orientalis?forest,a natural shrub land and an abandoned land were investigated,20 m×20 m area that set in each vegetation types.Combining the data we got from field survey conducted during April 2017 and March 2018 and the earlier data from2011,2013 and 2014,the relationship between soil respiration and environmental factors was simulated and validated.The main results are as follows:?1?All the soil respiration of the five vegetation types showed obviously seasonal variation,which increased from April to August,and then decreased.There were differences among five vegetation types,ranking as Oak forest>Shrub land>Oriental arborvitae forest>Abandoned land>Black locust plantation.The CV?variable coefficient?of soil respiration of different vegetation types was smaller than that among the same vegetation types in different months,which indicated that environmental factors showed greater influence on soil respiration than the vegetation types.?2?During growing season,soil respiration fluctuated greatly,however,the soil respiration was stable and lower during dormant season.All vegetation types showed a higher soil respiration rate during growing season than dormant season except for Abandoned land.Soil respiration was significantly and positively correlated with soil temperature?P<0.01?;however,the relationship between soil respiration and soil moisture was non-significant.The sensitivity of soil respiration to temperature(Q₁₀)of different vegetation types in loess hilly region was relatively low?1.12-1.88?and the black locust plantation had the smallest Q₁₀ among the vegetation types.There was an extremely significant linear relationship between air temperature and soil temperature?P<0.01?,and therefore,soil respiration was significant influenced by air temperature?P<0.05?.?3?The stimulation effect of SWC?soil water content?to soil respiration is better than soil temperature in growing season.The equation with two parameters?both soil temperature and SWC were included?simulated better than the equation with only one parameter?either soil temperature or SWC was included?.By comparison,we found that the exponential equation of soil temperature and the power function equation of SWC showed better effect than linear equation in black locust plantation,oak forests and natural shrub.Equations with SWC had better accuracy than equations with soil temperature in all vegetation types except for black locust plantation.However,as to the predictive results,the equation with two parameters didn't work well.?4?In dormant season,soil temperature explained more of the variations in soil respiration than SWC.Among all the five kinds of equations,both exponential equation of soil temperature and equation with two parameters?SWC and soil temperature?performed better than other equations.The predictive effects of equations with SWC performed better than the equation with soil temperature.The linear function equation with SWC performed better than the exponential equation with soil temperature and the power function equation with SWC,respectively.The simulated results of the equation with two parameters?SWC and soil temperature?turned out to be better than the equation with only one parameter,however,it didn't predicted better than the latter one.?5?Both linear equation and exponential equation performed well to describe the relationship of air temperature and soil respiration?P<0.001?.Both the two equations overestimated soil respiration rate in early growing season?April to July?and underestimated the soil respiration rate in the later growing season?July to October?.However,during the dormant season?November to March?,the predicted value and the measured value showed little difference.With future meteorological data,the values of soil respiration were predicted under different RCP scenarios by 2050 and 2070.Despite the differences,the overall predictive result was RCP2.6<RCP4.5<RCP6.0<RCP8.5.The rate of soil CO₂ emission would rise in the next few decades,and the growth rate would increase as well.