退化草地土壤增温及其生态效应研究

Mean atmosphere temperatures have increased 0.2 °C per decade globally over the last 30 years, with faster increases in daily min. temperature than daily max. temperature,a phenomenon referred to as night-warming or asymmetric warming. Under the scenario of global warming, atmosphere temperature are increasing, In the meantime,soil temperature are increasing, but the soil temperature are increasing faster than atmosphere temperature.We define this phenomena as a novel trends of global warming,asymmetric warming of soil and atmosphere due to faster increase in soil temperature than atmosphere that.Land use changed land cover ,overgrazing reduced grassland biomass and decreased the sward cover ,making the grassland vegetation shorterness and sparserness. Lack of grassland cover changes albedo of soil surface ,which make surface soil temperature increase more and enlarge the temperature difference of soil and atmosphere for the degraded grassland. This implicates a novel perspective of global change and has high potential ecological crisis for grassland desertification.. Examinations of crop yields and natural ecosystem productivity have shown reduced productivity in response to asymmetric warming of atmosphere , presumably due to changes in the timing of the growing season or to changes in the balance of daytime photosynthesis and nighttime respiration. However, there has been no any research on the consequences of asymmetric warming for the degraded grassland..If elevated soil temperature leads to more activity of root system and microbial,soil carbon may decrease as a consequence . Additionally, plant adaptation strategies could shift between ground and above ground. It is important to identify features of ecosystems that are sensitive to changes in the novel asymmetric warming.To date, most modeling efforts and experimental manipulations investigating ecosystem responses to climate change have assumed that future warming will occur primarily during the day or uniformly over the diurnal cycle or asymmetric warming of atmosphere . This assumption clearly is not valid on a global level nor at most regional scales ,at least on regional level for degraded grassland. Furthermore, there is no a priori reason to assume that ecosystems will respond similarly to changes in atmosphere temperature and soil temperature.. The objective of the project is to investigate eco-consequences of elevated soil temperature and asymmetric warming of soil and atmosphere.The project design a series of experiments will be conducted to examine the change process of asymmetric warming of soil and atmosphere and check response of water use of soil, net primary production,soil respiration for the consequence.As a background information,we will also analyse the historic dataset of meteorological records for the soil temperature to identify spatial and temporal pattern of the asymmetric warming over the northern grassland region of China.

全球增温情景下，大气增温的同时，土壤也在增温，并且土壤温度增加速度快于大气温度增加速度，这是一种新的不对称增温模式，即土壤-大气的不对称增温，同时，土壤也存在昼夜不对称增温现象。草地退化后，土壤温度升高，扩大了土壤及土壤-大气不对称增温程度。为了理解土壤及土壤-大气不对称增温的生态作用，探索退化草地土壤增温的区域环境效应，在研究北方草地区土壤及土壤-大气增温过程和格局基础上，选择不同退化程度草地、并设置不同量枯落物和不同高矮稀疏立枯物覆盖处理，模拟研究退化草地土壤及土壤-大气温度变化过程、土壤水分动态、初级生产和土壤呼吸及后续恢复的碳截获过程，并研究退化草地水热平衡关系，揭示土壤及土壤-大气不对称增温机理及其生态效应，结合北方草地退化信息，反演退化草地土壤温度增加的区域环境效应，揭示土壤及土壤大气不对称增温的生态意义和全球变化作用，服务于退化草地恢复与健康草地管理。

项目研究了全球增温情境下，土壤增温，包括全国尺度范围内土壤增温格局及草地土壤增温变化。全国地表温度普遍上升，平均以0.38℃/10a的速度递增，高出气温（0.29℃/10a）30%。1992-2011时期的变化尤为显著，以0.89℃/10a的趋势增温。表层地温在四季呈现明显升高趋势，其中冬季升温幅度最大（0.59℃/10a），春秋次之，分别为0.37℃/10a和0.32℃/10a，夏季升温幅度最小（0.23℃/10a）。全国大部分地区增温显著，自南向北逐渐增强。全国地表日最高温以0.31℃/10a的速度增长，全国地表日最低温以0.55℃/10a速度增长，地温夜晚增高幅度大于白天增高幅度，因而导致全国地表日较差（日最高温与日最低温之差）以0.25℃/10a的速度缩小。与前30年相比，后20年日最高温与日最低温升高趋势更为显著，地表温度分别以0.58℃/10a和1.45℃/10a的速度升高，但由于日最低温的升高幅度大于日最高温的升高幅度，因此后20年的温较差呈现出更大幅度的缩小-0.87℃/10a。中国温带草原区气温和地温在过去50年均呈现增温的趋势（图1）。在1962-2011年，温带草原区气温呈现明显上升趋势，平均气温增速为0.387 C/10a，最低气温升幅 (0.489C/10a) 大于最高气温升幅 (0.303C/10a)，气温呈现不对称的增温。与气温变化相同，草原区地温（0cm）在近50年呈现明显上升趋势，最低地温升幅 (0.715C/10a) 同样大于最高地温升幅 (0.486C/10a)，表明地温变化同样存在不对称的增温。温带草原区气温增加的同时，地温也在增加，平均地温增速为0.530C/10a，地温的增速要明显快于平均气温的增速，形成另一种形式的不对称增温一 “土壤与大气的不对称增温”。