| As human activities play a more prominent role in influencing global climate change,the impact of fluctuations in global change drivers,represented by increased atmospheric nitrogen deposition and rainfall pattern variability,is increasingly significant for carbon(C)cycle of the global terrestrial ecosystem.At the same time,as the second largest flux of terrestrial ecosystems,coupled with its extreme sensitivity to environmental changes,soil respiration plays a key role in the C cycle at regional and global scales.Arid and semiarid ecosystems cover about 41%of the earth's land surface.And desert ecosystems,as an important part of these regions,are strongly constrained by nitrogen and water conditions.This determines that it will respond strongly to changes in the future global nitrogen and water patterns,and lead to a large impact on the C cycle and C balance in desert ecosystems.Therefore,an in-depth understanding of the response process and internal mechanism of soil respiration under the control of global change drivers in desert ecosystems is of great significance for predicting regional and global C cycles.This study used a field manipulative nitrogen and water addition experiment with three levels of nitrogen deposition(0,10,60 kg N ha-1 yr-1)and three levels of precipitation(ambient,+20%,+40%)in an Artemisia ordosica shrubland in the Mu Us Desert of northern China.The nitrogen and water addition treatment were applied from May to September,2015.The response of soil environment and soil respiration and its components to the changes of global nitrogen and water patterns in the desert ecosystem were explored,to describe and the response characteristics and underlying mechanisms of soil respiration and its components to short-term nitrogen and water addition.The key findings are as follows.(1)Short-term nitrogen and rainwater treatment significantly improved soil nitrogen and water availability,especially for soil nitrate nitrogen content,and high nitrogen addition treatment significantly increased its content(+360.15%),but have limited influence on soil organic carbon,pH,total nitrogen,soil microbial biomass and plant root biomass.Water addition significantly improved soil shallow water content(everage+25.07%).However,due to the absorption of water by plant roots in soil respiration pipes,the soil water content in heterotrophic respiration pipes are higher than that in soil respiration pipes.(2)Short-term nitrogen addition changed the composition of soil respiration,inhibited heterotrophic respiration(-23.71%),and promoted autotrophic respiration(+36.04%),which offset each other and the effect of nitrogen application on soil respiration was not significant.Short-term water addition significantly promoted both soil heterotrophic respiration(+26.66%)and autotrophic respiration rate(+27.42%),and the change of heterotrophic respiration rate was more sensitive to soil water content than autotrophic respiration.Nitrogen and water addition increased the temperature sensitivity of soil respiration,but had no significant effect on soil heterotrophic respiration.In addition,the higher the soil water content,the more significant the stimulating effect on heterotrophic respiration,while the autotrophic respiration rate decreased under higher water conditions(-9.1 1%).Although the main effects of nitrogen and water addition significantly changed the two components of soil respiration in the short term,but the two factors did not show significant interactions to soil respiration and its components.(3)Since short-term nitrogen and water addition treatments have no significant effect on soil microbial biomass and root biomass,the mechanism of their effects on heterotrophic and autotrophic respiration rates may be achieved through changes in soil microbes and plant root physiological activities and the biological effectiveness of organic substrates.In addition,the results of this study indicate that short-term rainfall increases mainly affect soil C emissions by increasing soil respiration rate and changing the proportion of its different components in this desert ecosystems.And in the case of future increases in rainfall,desert ecosystems may experience more soil C emissions and a greater degree of variation in soil respiration components.It is worth noting that although the short-term nitrogen application does not have a significant effect on the change of soil respiration rate,it cannot ignore the effect of increased nitrogen deposition on the different components of soil respiration in the future in desert ecosystems because it has caused the difference in the two components of soil respiration. |
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