Effects Of Increased Precipitation And Nitrogen Enrichment On Soil Respiration In A Typical Temperate Steppe

Soil respiration?SR?and its impact on environmental change plays an essential role in evaluating terrestrial ecosystem carbon emission and terrestrial-climatic feedback.Precipitation regime change and nitrogen?N?enrichment are two critical factors that lead to global environmental change.these factors can significantly affect soil water availability and nitrogen content,and thus result in a profound impact on SR.Manipulative experiments and modelling studies have been carried out worldwide to investigate the effects of precipitation change and N enrichment on SR.However,most studies only consider either changing precipitation or N enrichment via the two treatment levels approach?control vs.N enrichment or changing precipitation?.Therefore,our knowledge and understanding of SR variability are limited when precipitation change and N enrichment occur simultaneously with a gradually increased rate.In this study,two long-term manipulative experiments were conducted in a typical temperate steppe in Inner Mongolia to examine the interaction between increased precipitation and N enrichment,as well as,the effects of multi-level N enrichment on SR.The main results included:?1?Effects of increased precipitation and nitrogen enrichment on SRFrom 2015 to 2017 across three consecutive growing seasons,the obtained mean SR form the control,N addition(10.0 g N m^-2 yr^-1),water addition?120 mm water addition?,N and water simultaneous addition treatments(10.0 g N m^-2 yr^-1 and 120 mm water addition)were 4.35,4.11,5.33,and 5.02 ?mol m^-2 s^-1,respectively.SR was increased by 22.3% with water addition,but decreased by 5.6% with N addition.It was found that there is no interaction effect within water and N addition on SR in the typical temperate steppe.Further,N addition directly reduced SR by decreasing soil temperature,whereas water addition enhanced SR through increasing soil moisture.?2?SR in response to multi-level N additionAcross two consecutive growing seasons in 2015 and 2016,the calculated mean SR were 3.30,3.02,2.84,2.92,2.68,2.88,2.76,and 2.55 ?mol m^-2 s^-1 at the N addition rates of 0.0,1.0,2.0,4.0,8.0,16.0,32.0,64.0 g N m^-2 yr^-1,respectively.Compared with the control(0 g N m^-2 yr^-1),N addition gradient reduced SR by 8.6,14.1,11.5,18.7,12.6,16.4,and 22.7%,respectively.There is an inverse and non-linearly relationship between SR and the rates of N addition in the temperate steppe.Besides,soil moisture,aboveground biomass of forb and total belowground biomass contributed to a total of 57.1% of SR variability under N addition,and soil moisture played a leading role in regulating the responses of SR to the rates of N addition.The results demonstrate that changes in N and water supply during the growing season can significantly affect the SR of the typical temperate grassland via different paths.Increased precipitation will enhance soil carbon emission from the temperate steppe,resulting in an accelerated loss of soil carbon.On the other hand,N enrichment can suppress soil carbon emission.Furthermore,the negative impact of multi-level N enrichment on soil carbon emission depends on soil water availability in the temperate steppe.These findings not only provide theoretic support for management and protection of the temperate steppe ecosystem,but also enhance the understanding of global climate change impact on terrestrial carbon cycles.