【作者】 赵明明；

【导师】 孙伟； 史宝库；

【作者基本信息】 东北师范大学 ， 草地生态学， 2019， 硕士

【摘要】 N₂O因单位分子量增温效应强、间接破坏臭氧层以及在大气中滞留时间长等特点备受重视。为了更准确地估算区域尺度N₂O通量,需要量化小空间尺度N₂O通量空间变异及其控制因子。大气氮沉降和放牧强烈影响生态系统的结构和功能。分析理解氮沉降和放牧干扰对土壤N₂O通量空间异质性的影响,设计适合的取样策略是准确估算氮沉降和放牧干扰对土壤温室气体总通量影响的前提条件。本研究对松嫩草甸草原进行模拟氮沉降、放牧以及二者互作处理,量化不同处理条件下N₂O通量、植物生物量、土壤微气候以及土壤性质空间异质性,构建N₂O通量空间变异回归模型。探讨生物和环境因子变化对N₂O通量空间异质性的影响,最终揭示氮沉降、放牧以及二者互作对N₂O通量空间异质性的影响及驱动机制。研究结果如下:（1）不同季节（春、夏和秋季）对照样地N₂O空间异质性存在明显变化,具体表现在N₂O通量强度、空间变异强度。其中,2017年夏季N₂O通量显著高于春、秋两季。土壤温度、含水量、硝态氮含量变化及这几个因素的共同作用,是影响松嫩草甸草原N₂O通量空间格局季节动态变化的关键因素。（2）不同处理之间N₂O通量均值存在显著差异,氮添加、放牧交互处理N₂O通量均值最大,对照和放牧处理N₂O通量均值最小。对照、放牧、氮添加以及二者交互处理空间结构比C/（Co+C）分别为0.822、0.940、0.844和0.998,均具有较强的空间异质性强度。（3）对照处理下土壤有机碳、土壤温度、含水量、pH、土壤容重异质性强度较高,表明松嫩草甸草原土壤异质性较强。放牧显著降低了植物地上生物量（P<0.05）,并对土壤物理性质产生直接影响,具体表现为土壤温度升高、含水量下降。氮添加条件下,植物生物量、凋落物异质性强度均显著高于其他处理。（4）不同处理条件下,植物因子、土壤养分、土壤理化因子均作用于N₂O通量空间异质性。N₂O通量的控制因子及其相对贡献随处理不同而变化。对照和放牧处理条件下,地上生物量相对贡献率最高,而在氮添加和氮添加、放牧交互处理下,土壤含水量是最重要的控制因子。研究结果有助于减少测试点到样地、生态系统和区域尺度对土壤N₂O通量估算产生的误差,理解N₂O通量空间变异的控制机制,获取N₂O通量最优取样策略。准确评估样地尺度上土壤N₂O通量对大气氮沉降和放牧干扰的响应。更多还原

【Abstract】 N₂O has attracted more attention due to its strong warming effects per unit molecular weight,indirect damaging to the ozone layer and long existing time in the atmosphere.In order to accurately estimate N₂O flux at the plot scale,it is necessary to quantify spatial variation in N₂O flux and identify key factors that regulate the spatial variation in N₂O flux at small scales.Atmospheric nitrogen deposition and grazing have strongly affected the structure and function of ecosystem.The analyzing and understanding of the effects of increased nitrogen deposition and grazing disturbance on the spatial heterogeneity of soil N₂O flux and the design of optimal sampling strategies are the preconditions for accurately estimating their effects on the total soil greenhouse gas flux.We proposed a manipulative experiment with treatments of control,nitrogen addition,grazing and nitrogen addition plus grazing in Songnen meadow steppe,northeastern China.We quantify spatial variability in N₂O flux,plant biomass,soil microclimate and soil properties and identify key factors that regulate the spatial variability in N₂O flux under different treatments.Our objectives are to explore the effects of global change factors and land-use types induced grassland ecosystem composition and structure changes on the spatial variability of N₂O flux and unravel the underlying ecological mechanisms.The research results are as follows:（1）The spatial patterns and rates of N₂O flux remarkably varied across the three measurement campaigns（spring,summer and autumn）.The mean N₂O flux in the summer was significantly higher than in the spring and autumn.The changes in patterns of soil temperature,soil water content and soil NO₃^--N,all of which may have altered the spatial heterogeneity of N₂O flux.（2）There were significant differences in N2O flux between the treatments.The N₂O flux in the grazing plus nitrogen addition was the highest,and it was the lowest in the control and grazing plot.Spatial dependence[C/（Co+C）]of N₂O flux in control,grazing,N addition and NG treatments was 0.822,0.940,0.844 and 0.998,respectively.N₂O flux exhibited strong spatial dependence in all treatments.（3）Soil organic carbon,soil temperature,soil water content,pH,soil bulk density in control treatment exhibited strong spatial dependence,which imply that soil properties of Songnen meadow grassland have a strong spatial heterogeneity.Grazing decreased plant aboveground biomass and soil water content,and increased soil temperature.Spatial dependence of above ground biomass and litter biomass in N addition treatment were larger than other treatments.（4）The spatial variation in N₂O flux under four treatments was controlled by plant factors,soil nutrients,and soil physicochemical properties.The controlling factors for regulating N₂O flux depend on treatments.N₂O flux was mostly controlled by aboveground biomass under control and grazing treatments.Soil water content was the most significant predictor of N₂O flux in the N treatment and grazing plus N addition treatment.Our results enable us reduce errors in the estimates of N₂O flux when scaling up from plot-scale measurements to stand,landscape,and regional scales,to understand the mechanisms underlying N₂O flux,to design an optimal sampling approach and to accurately estimate how N₂O flux at the plot scale may respond to grazing,N addition and their interaction in grassland ecosystems.更多还原