【作者】 王晶；

【导师】 张宇清；

【作者基本信息】 北京林业大学 ， 林业硕士（专业学位）， 2019， 硕士

【摘要】 随着人类活动(例如化石燃料燃烧、过度放牧)的加剧,其对全球气候变化的影响也日益显著,以大气氮沉降增加和降雨格局变异为代表的全球变化驱动因子的波动,对全球陆地生态系统碳(C)循环的影响也日益显著。与此同时,作为陆地生态系统的第二大通量,加之其对环境变化的极端敏感性,土壤呼吸在区域及全球尺度上的C循环过程中发挥着关键作用。全球陆地面积的41%为干旱半干旱地区,荒漠生态系统作为该地区的重要组成部分,由于受到氮素和水分条件的严重制约,决定了其对未来全球氮、水格局的改变势必会产生强烈的响应,进而对荒漠生态系统的C循环和C平衡产生巨大的影响。因此,深入探究荒漠生态系统土壤呼吸在全球变化驱动因子控制下的响应过程和内在机理,对于预测区域及全球C循环具有重要意义。本研究以毛乌素沙地典型的灌木群落——油蒿(Artemisia ordosica)群落为研究对象,通过一个生长季(2015年5月～9月)的短期氮素和水分添加野外控制试验(包括3个氮素添加处理:0、10、60kgNha-1 yr.1;3种增雨情形:自然降雨、增雨20%、增雨40%),对荒漠生态系统的土壤环境和土壤呼吸及其组分的响应规律进行了初步探索,阐述了土壤呼吸及其组分对短期氮素和水分添加的响应特征及其潜在机制,主要结果及结论如下:(1)短期的施氮和增雨处理显著地改善了土壤中的氮素和水分有效性,尤其是对土壤中的硝态氮含量,高氮添加处理使其含量显著提高(+360.15%),而对土壤有机碳、pH、全氮、土壤微生物量和植物根系生物量的影响微弱;水分添加显著提高了表层土壤呼吸的土壤含水量(平均增幅25.07%),但是由于测定土壤呼吸的土壤环内存在植物根系对水分的吸收,使得测定异养呼吸的土壤环内的土壤含水量高于土壤呼吸环。(2)短期的氮素添加改变了土壤呼吸的组分,抑制了异养呼吸(-23.71%),促进了自养呼吸(+36.04%),二者相互抵消使得施氮处理对土壤呼吸的影响并不显著。短期的水分添加对土壤异养呼吸(+26.66%)和自养呼吸(+27.42%)速率均产生了显著的促进作用,并且相比于自养呼吸,异养呼吸速率对土壤水分有效性的变化更为敏感。施氮和增雨均增加了土壤呼吸的温度敏感性(Q10),但是对土壤异养呼吸的温度敏感性无显著影响。另外,土壤含水量越高,对异养呼吸速率的激发效应越显著,而自养呼吸速率则在较高的水分条件下有所下降(-9.1 1%)。虽然氮素和水分添加各自的主效应均显著改变了土壤呼吸的两个组分,但是在短期内这两个因素对土壤呼吸及其组分的影响,并没有表现出明显的交互作用。(3)由于短期的氮素和水分添加处理对土壤微生物量和根系生物量均无显著影响,因此其对异养和自养呼吸速率的影响机制,可能改变了土壤微生物和植物根系的生理活性以及有机底物的生物有效性。另外,本研究结果表明,在荒漠生态系统中,短期降雨增加主要通过提高土壤呼吸速率和改变不同组分所占的比重,从而对土壤的C排放产生影响。在未来降雨可能增多的情况下,荒漠生态系统可能发生更多的土壤C排放和产生更大程度的土壤呼吸组分的变异。值得注意的是,尽管短期内施氮处理并未对土壤呼吸速率产生显著的影响,但由于其已经引起土壤呼吸两个组分发生增加和减少的差异性变化,所以也不能忽视未来大气氮沉降增加对土壤呼吸不同组分的改变作用。更多还原

【Abstract】 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.更多还原