Contribution of Root Respiration to Total Soil Respiration in a Leymus chinensis （Trin.） Tzvel, Grassland of Northeast China

The loss of carbon through root respiration Is an Important component of grassland carbon budgets. However, few data are available concerning the contribution of root respiration to total soil respiration in grasslands in China. We Investigated seasonal variations of soil respiration rate, root blomaaa, microbial blomaaa C and organic C content of the soil In a semi-arid Leymus chinensis （Trin.） Tzvel. grassland of northeast China during the 2002 growing season （from May to September）. The linear regression relationship between soil respiration rate and root blomaaa was used to determine the contribution of root respiration to total soil respiration. Soil respiration rate ranged from 2.5 to 11.9 g C/m^2 per d with the maximum in late June and minimum In September. The microbial blomaaa C and organic C content of the soil ranged from 0.3 to 1.5 g C/m^2 and from 29 to 34 g C/kg respectively. Root blomaaa had two peaks, In early June （1.80 kg/m^2） and mid-August （1.73 kg/m^2）. Root respiration rate peaked In mid-August （6.26 g C/m^2 per d）, whereas microbial respiration rate peaked In late June （7.43 g C/m^2 per d）. We estimated that the contribution of root respiration to total soil respiration during the growing season ranged from 38% to 76%.     

Grazing Gradient versus Restoration Succession of Leymus chinensis (Trin.) Tzvel. Grassland in Inner Mongolia

Grazing‐induced degradation of grasslands is the primary impediment to the socioeconomic development of Inner Mongolia. It affects the entire environment of northern China. Understanding grassland dynamics is necessary for restoration and sustainable management of these degraded ecosystems. The recovery dynamics of a degraded Leymus chinensis (Trin.) Tzvel. grassland after removal of grazing was studied in comparison with its spatial variation along a grazing gradient, using its climax community as a benchmark. The species composition, diversity, and biomass of the grassland vegetation, as well as the attributes (height, density, and individual mass) of major species, were examined on the eight sites along the grazing gradient and in the recovering grassland over 11 years. The spatial pattern of grassland vegetation along the grazing gradient closely reflected its recovery trajectory over time. Both the spatial and the temporal processes exhibited the same shift in species dominance in association with grazing removal or less grazing intensity. Grassland degradation was accompanied by an increase in species density and a decrease in species size; this trend was reversed during recovery. This result suggested that the degraded grassland is highly resilient and that restoration could occur naturally by reducing or excluding grazing animals. However, some differences existed between the spatial and the temporal processes. Species richness was high on the light‐ or no‐grazing sites along the gradient, but varied little during the recovery of the degraded grassland. Species evenness was high under moderate to light grazing along the gradient and was high at the beginning of the recovery period but not at the end. Although standing biomass improved significantly during the recovery period, it did not change significantly along the grazing gradient. These observed discrepancies were related to the intrinsic difference in the spatial versus temporal processes and are discussed together with the advantage/disadvantage of the grazing gradient versus dynamic monitoring methods in grassland dynamics studies.     

锡林河流域一个羊草群落中土壤呼吸与生物量之间的相关性分析

采用根系生物量梯度上土壤呼吸变化趋势线外推法对锡林河流域一个羊草(Leymus chinensis (Trin.) Tzvel.)群落中根系呼吸占土壤总呼吸的比例进行了估计,对生物量各组分(地上、地下部分)之间以及它们与土壤呼吸间的相关性进行了分析.结果表明:在测定年度(1998年)整个生长季的不同月份,该群落中根系呼吸量占土壤呼吸总量的比例在14%～39%之间,平均为27%;地上总生物量及根系生物量与土壤呼吸间的相关性较差,但地上活生物量与土壤呼吸间存在着显著的乘幂关系.上述结果与国外同类研究结果相比,具有很好的一致性.     

锡林河流域一个羊草群落中土壤呼吸与生物量之间的相关性分析(英)

采用根系生物量梯度上土壤呼吸变化趋势线外推法对锡林河流域一个羊草 (Leymuschinensis (Trin .)Tzvel.)群落中根系呼吸占土壤总呼吸的比例进行了估计 ,对生物量各组分 (地上、地下部分 )之间以及它们与土壤呼吸间的相关性进行了分析。结果表明 :在测定年度 (1998年 )整个生长季的不同月份 ,该群落中根系呼吸量占土壤呼吸总量的比例在 14 %～ 39%之间 ,平均为 2 7% ;地上总生物量及根系生物量与土壤呼吸间的相关性较差 ,但地上活生物量与土壤呼吸间存在着显著的乘幂关系。上述结果与国外同类研究结果相比 ,具有很好的一致性。     

Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis （Trin.） Tzvel.

Randomly amplified polymorphic DNA （RAPD） analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis （Trin.） Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% （P 〈 0.04）, and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% （P 〈 0.002）. A 21.06% RAPD variation among all 16 populations among two regions was found （P 〈 0.001）, as well as 72.59% variation within populations （P 〈 0.001）. Molecular variation within populations was significantly different among 16 populations.     

Molecular Genetic Variation in a Clonal Plant Population of Leymus chinensis (Trin.) Tzvel.

Randomly amplified polymorphic DNA (RAPD) analysis was used to investigate the genetic variation among populations, between populations, and within populations, relationships between genetic distance and geographic distance, and the molecular variation and population size. The effects of geographic and genetic distances, as well as of genetic differentiation and population size, on genetic variations of Leymus chinensis (Trin.) Tzvel. are discussed. The present study showed that there was significant RAPD variation between the Baicheng region population and the Daqing region population, with a molecular variance of 6.35% (P ＜ 0.04), and for differentiation among area populations of the Daqing region, with a molecular variance of 8.78% (P ＜ 0.002). A 21.06% RAPD variation among all 16 populations among two regions was found (P ＜ 0.001), as well as 72.59% variation within populations (P ＜ 0.001). Molecular variation within populations was significantly different among 16 populations.     

锡林河流域两类植物群落土壤呼吸特征的比较

采用碱液吸收法对锡林河流域一个半干旱典型草原群落的土壤呼吸进行了5个月的野外测定,并对其与气候因子和生物量之间的关系进行了分析.另选择了锡林河岸边的一个沼泽化草甸群落作为对比来研究土壤湿度和植被类型对土壤呼吸的影响.主要结果包括:1)两个群落土壤呼吸的季节动态基本一致,均出现了两个峰值,其中草原群落和草甸群落土壤呼吸速率的变化范围分别为312.8～1 738.9mgC@m-2@d-1和354.6～2 235.6 mg C@m -2@d-1.草甸群落的土壤呼吸速率明显高于草原群落,它们的日平均土壤呼吸速率分别为1 349.6 mg C@m-2@d-1和785.9mg C@m-2@d1;2)在草原群落中,土壤呼吸速率与土壤湿度的相关性比其与温度的关系更加显著,而在草甸群落正好相反,反映出这两种气候因子在不同生境中起着不同的作用.根据土壤呼吸与气温之间的同归关系外推出2001年生长季草原群落和草甸群落的土壤呼吸量分别为142.4 g C/m2和236.1 g C/m2;3)在草甸群落中,地上总生物量与土壤呼吸速率之间没有显著的相关关系,而地上部活体生物量与土壤呼吸速率之间则存有很显著的幂函数关系.在草原群落中,土壤呼吸速率与地上活体生物量或地上总生物量的相关性均很弱.     

东北松嫩平原羊草群落的土壤呼吸与枯枝落叶分解释放CO2贡献量

根据静态气室法的测量结果 ,分析了羊草群落土壤呼吸量和枯枝落叶分解释放 CO2 量的季节动态 ,及其与地上生物量 ,枯枝落叶分解量及环境因子的关系。结果表明 :( 1 )在整个观测期内 ,羊草群落土壤呼吸的季节动态呈现单峰曲线 ,8月中旬达到最大值 1 3.2 7g C/( m2 · d)。 ( 2 )羊草群落土壤呼吸的季节变化规律与地上绿色体生物量的季节动态同步。( 3)羊草群落土壤呼吸的季节动态与枯枝落叶分解量的季节动态同步。 ( 4 )羊草群落土壤呼吸量与土壤 0～ 1 0 cm土壤含水量显著正相关。( 5 )地表枯枝落叶层直接排放 CO2 量的季节动态呈现逐渐递减的趋势 ,释放量平均为 -0 .87g C/( m2·d)。有减缓土壤向大气排放 CO2 的作用。 ( 6 )枯枝落叶分解释放 CO2 量同地表枯枝落叶量显著正相关。     

Adjustment of Forest Ecosystem Root Respiration as Temperature Warms

Adjustment of ecosystem root respiration to warmer climatic conditions can alter the autotrophic portion of soil respiration and influence the amount of carbon available for biomass production. We examined 44 published values of annual forest root respiration and found an increase in ecosystem root respiration with increasing mean annual temperature (MAT),but the rate of this cross-ecosystem increase (Q10 = 1.6) is less than published values for short-term responses of root respiration to temperature within ecosystems (Q10 = 2-3). When specific root respiration rates and root biomass values were examined, there was a clear trend for decreasing root metabolic capacity (respiration rate at a standard temperature) with increasing MAT. There also were tradeoffs between root metabolic capacity and root system biomass, such that there were no instances of high growing season respiration rates and high root biomass occurring together. We also examined specific root respiration rates at three soil warming experiments at Harvard Forest, USA, and found decreases in metabolic capacity for roots from the heated plots. This decline could be due to either physiological acclimation or to the effects of co-occurring drier soils on the measurement date. Regardless of the cause, these findings clearly suggest that modeling efforts that allow root respiration to increase exponentially with temperature, with Qt0 values of 2 or more, may over-predict root contributions to ecosystem CO2 efflux for future climates and underestimate the amount of C available for other uses,including net primary productivity.     

小麦与羊草体细胞杂种的细胞核和细胞质基因组分析

通过原生质体融合与培养获得小麦与羊草的体细胞杂种,其核基因组成以羊草(供体)为主,用线粒体特异探针atp6与叶绿体特异探针rbcL进行的RFLP分析结果表明,胞质基因组成偏向羊草并发生了重组.讨论了受体核基因组消减对杂种再生及对受体胞质基因组消减的影响.     

Soil respiration associated with plant succession at the meadow steppes in Songnen Plain,Northeast China

Aims Soil CO₂ emission from steppes is affected by soil properties and vegetation in different successional stages. Primary and secondary succession of plants frequently occurred at the meadow steppe in Songnen Plain, Northeast China, which indicates the large uncertainty associated with CO₂ emission in this environment. This study aims to investigate the temporal variations of soil respiration (Rs) and the effect of plant succession on cumulative soil CO₂ emission during the growing season.Methods Using a LI-6400 soil CO₂ flux system, Rs of five vegetation types which represented different stages of plant succession in meadow steppes of Songnen Plain, China, was investigated during the growing seasons of 2011 and 2012.Important findings Soil temperature (Ts) was the dominant controlling factor of Rs, which could explain ~64% of the change in CO₂ fluxes. The Q 10 values of Rs were ranged from 2.0 to 6.7, showing a decreasing trend with the plant successional stages. The cumulative CO₂ emission increased with the degree of vegetation succession and it averaged to 316±6g C m ?2 (ranges: 74.8±6.7 to 516.5±11.4g C m ?2) during the growing season. The magnitude of soil CO₂ emission during the growing season was positively correlated with aboveground plant biomass, soil organic carbon content and mean soil water content, while negatively linked to mean Ts, pH, electrical conductivity and exchangeable sodium percentages. The results implied that soil CO₂ emission increased with the development of plant communities toward more advanced stages. Our findings provided valuable information for understanding the variations of CO₂ emission in the process of vegetation succession.     

Seasonal Changes in Soil Respiration with An Elevation Gradient in <i>Abies nephrolepis</i> (Trautv.) Maxim. Forests in North China

Soil respiration (Rs) plays an important role in regulating carbon cycle of terrestrial ecosystems and presents temporal and spatial heterogeneity. Abies nephrolepis is a tree species that prefers the cold and wet environment and is mainly distributed in Northeast Asia and East Asia. The Rs variations of Abies nephrolepis forests communities are generally environmental-sensitive and can effectively reflect the adaptive responses of forest ecosystems to climate change. In this study, the growing-seasonal variations of Rs, soil temperature, soil water content and soil properties of Abies nephrolepis forests were analyzed along an altitude gradient (2000, 2100, 2200 and 2300 m) over two years on Wutai Mountain in North China. As the main results showed, soil respiration keeps the same change trend as soil temperature and reached peaks in July at 2000 m in 2019 and 2020. During 26^th July to 25^th October in 2019 and 27^th May to 23^rd October in 2020, on the whole, the soil temperature independently explained 76.2% of Rs variations while the soil water content independently explained 26.8%. Soil temperature and soil water content jointly explained 81.8% of Rs variations. Soil properties explained 61.8% and 69.6% of Rs variation in 2019 and 2020, respectively. Soil organic carbon content and soil enzyme activity had the signifi- cant (P < 0.01) negative and positive relationships, respectively, with Rs variation. With altitudes evaluated from 2000 to 2300 m, soil respiration temperature sensitivity (Q₁0) and the soil organic carbon content increased by 12.4% and 10.4%, respectively, while invertase activity, cellulase activity and urease activity dropped by 41.2%, 29.45% and 38.19%, respectively. The results demonstrate that (1) soil temperature is the major factor affecting Rs variations in Abies nephrolepis forests; (2) weakened microbial carbon metabolism in high-altitude areas results in the accumulation of soil organic carbon; (3) with a higher Q₁, forest ecosystems in high-altitude areas might be more easily affected by climate change; (4) climate warming might accelerate the consumption of soil organic carbon sink in forest ecosystems, especially in high-altitude areas.     

中国东北羊草草原生长季内产量生态模拟及信息参数应用

通过对中国北方羊草草原生物量动态、生物量垂直空间格局及其与环境因子相互关系等主要产量生态数量特征的模拟与内在相关性的研究 ,结果表明 ,草地地上生物量的生长规律呈“单峰”型 ,最大地上生物量出现在 8月 5日 ,其值为1 97.3g· m- 2 干物质 ,而后下降 ;在达到峰值前 ,符合 logistic模型 ,进一步分析模型有关特征值获得了草地有效管理期为返青后的第 73天到第 1 1 9天等十分重要的产量生态信息参数。生长季内地上生物量动态与前一个月的平均气温 ( R=0 .82 87)和积累降雨量 ( R=0 .8932 )均呈极显著正相关 ,这是实施科学水肥管理的重要参数 ;而地上部生物量最大绝对增长速率 ( AGR)出现在 6月 2 0日至 7月 5日 ,平均为 3.35 33g· m- 2 · d- 1干物质 ;而地上部生物量最大相对增长速率( RGR)出现在 5月 2 0日至 6月 5日 ,平均为 0 .0 6 6 2 g· g- 1· d- 1干物质 ;在生长后期绝对增长速率和相对增长速率均出现负值 ,这表明地上部生物量的生长效率在生长初期最高。地上生物量垂直空间格局由下向上呈幂函数变化 ,其模型为 :Bn=a Xb,其中 93%的产量集中在 4 0 cm以下 ,这对不同的家畜的选择利用与刈割利用提供了依据 ;不同种群对草原牧草产量形成的作用是不同的 ,羊草种群对草原牧草产量形成的正向     

松嫩平原羊草草地盐碱化过程

通过野外调查及定位研究,探讨了松嫩平原羊草草地盐碱化发生原因和过程,论证了羊草草地盐碱化过程的土壤“干扰-裸露”假说.松嫩平原羊草草地表层土壤(0～30 cm)盐分含量低,表层以下土壤层盐分含量高, 定义此为土壤盐渍化草地;土壤表层盐分含量增多的过程称为羊草草地盐碱化过程,盐碱化后形成的草地为盐碱化草地或盐生植物群落.羊草草地表层土壤盐分增多的主导原因是原初含盐量低的土壤表层被干扰消失,表层以下富含盐分的土层直接裸露成新地表,深层盐分在新的表层积累,这种积累也表现在其他各层.次生盐生植物群落形成于羊草草地土壤表层被干扰后的裸地上,各盐生植物群落间没有演替序列关系.松嫩平原羊草草地的退化进程为土壤退化在先、植被退化在后,盐生植物侵入并形成群落及后续的演变近于始自原生状态.     

锡林河流域两类植物群落土壤呼吸特征的比较

采用碱液吸收法对锡林河流域一个半干旱典型草原群落的土壤呼吸进行了5个月的野外测定,并对其与气候因子和生物量之间的关系进行了分析。另选择了锡林河岸边的一个沼泽化草甸群落作为对比来研究土壤湿度和植被类型对土壤呼吸的影响。主要结果包括:1)两个群落土壤呼吸的季节动态基本一致,均出现了两个峰值,其中草原群落和草甸群落土壤呼吸速率的变化范围分别为312.8～1 738.9 mg C·m-2·d-1 和354.6～2 235.6 mg C·m-2·d-1。草甸群落的土壤呼吸速率明显高于草原群落,它们的日平均土壤呼吸速率分别为1 349.6 mg C·m-2·d-1和785.9mg C·m-2·d-1; 2)在草原群落中,土壤呼吸速率与土壤湿度的相关性比其与温度的关系更加显著,而在草甸群落正好相反,反映出这两种气候因子在不同生境中起着不同的作用。根据土壤呼吸与气温之间的回归关系外推出2001年生长季草原群落和草甸群落的土壤呼吸量分别为142.4 g C/m2 和 236.1 g C/m2;3)在草甸群落中,地上总生物量与土壤呼吸速率之间没有显著的相关关系,而地上部活体生物量与土壤呼吸速率之间则存有很显著的幂函数关系。在草原群落中,土壤呼吸速率与地上活体生物量或地上总生物量的相关性均很弱。     

三江平原4种典型湿地土壤碳氮分布差异和微生物特征

选择三江平原洪河湿地保护区4种典型湿地类型：小叶章+沼柳湿地、小叶章湿地、毛苔草湿地和芦苇湿地作为研究对象,分析了不同湿地土壤有机碳(SOC)、全氮(TN)含量和微生物活性指标(土壤蔗糖酶、纤维素酶、过氧化氢酶、微生物生物量碳MBC、微生物生物量氮MBN、微生物呼吸速率MBR、微生物商q_MB和代谢商q CO₂)的变化及其相互关系.结果表明： SOC和TN含量均随土层深度增加而减少,不同湿地类型之间具有极显著性差异(P<0.01).各湿地土壤酶活性(除过氧化氢酶)、MBC、MBN含量和MBR均以表层(0～10 cm)最高,并随着土层深度的增加而降低.在0～30 cm土层内,小叶章+沼柳湿地和小叶章湿地SOC、TN含量、土壤酶活性、MBC、MBN含量、MBR、q_MB和qCO₂均高于淹水区的毛苔草湿地和芦苇湿地.统计分析表明,SOC、TN与微生物活性指标(qCO₂除外)均存在极显著正相关关系(P<0.01).表明研究区土壤微生物特征对SOC、TN的变化具有重要的影响和指示作用.     

黄土旱塬区冬小麦不同施肥处理的土壤呼吸及土壤碳动态

依据黄土旱塬区黑垆土上中国科学院长武站长期定位试验 (始于1984年),于2008年3月到6月,测定了冬小麦连作系统中返青期、拔节期、抽穗期、灌浆期和收获期土壤呼吸日变化、生育期变化以及土壤可溶性有机碳(Dissolved organic C, DOC)和微生物量碳(Soil microbial biomass C, MBC),研究了施肥措施对土壤呼吸、DOC和MBC的影响以及土壤呼吸与碳组分之间的关系.研究涉及6个处理:休闲地(F)、不施肥(CK)、有机肥(M)、氮肥(N)、氮磷肥(NP)和氮磷有机肥(NPM).结果表明,冬小麦连作系统中土壤呼吸的日变化格局呈单峰曲线,最高值出现在12:00左右(拔节期)和14:30左右(成熟期),最小值出现在0:00～3:00之间或6:00左右;冬小麦土壤呼吸速率拔节期最高,其次是灌浆后期,抽穗期最低;不同施肥条件下,各生育期土壤呼吸速率大小顺序:NPM＞M＞NP＞N＞CK＞F.土壤水分亏缺是导致抽穗期和灌浆期土壤呼吸速率降低的重要原因.各施肥处理DOC含量高低顺序为灌浆期＞抽穗期＞成熟期＞返青期＞拔节期;除M,NPM处理MBC含量拔节期＞灌浆期外,各施肥处理MBC含量高低顺序为成熟期＞抽穗期＞灌浆期＞拔节期＞返青期.同一处理不同生育期土壤呼吸速率与DOC,MBC的相关性较低,但同生育期不同施肥处理土壤呼吸与土壤有机碳组分间存在显著的相关性.以F处理土壤呼吸为基础,估算CK、N和NP处理生育期根系对土壤呼吸的平均贡献率依次为36%、45%和54%.     

玉米农田土壤呼吸作用的空间异质性及其根系呼吸作用的贡献

基于4月底到9月底东北地区玉米农田土壤呼吸作用全生长季的观测,阐明了土壤呼吸作用的空间异质性特征,综合分析了水热因子、土壤性质、根系生物量及其测定位置对土壤呼吸作用空间异质性的影响,并对生长季中根系呼吸作用占土壤呼吸作用的比例进行了估算。结果表明,在植株尺度上,土壤呼吸作用存在着明显的空间异质性,较高的土壤呼吸速率通常出现在靠近玉米植株的地方。根系生物量的分布格局是影响土壤呼吸作用空间异质性的关键因素。在空间尺度上,土壤呼吸作用与根系生物量呈显著的线性关系,而土壤湿度、土壤有机质、全氮和碳氮比对土壤呼吸作用空间异质性的影响并不显著。通过建立土壤呼吸作用与玉米根系生物量的回归方程,对根系呼吸作用占土壤呼吸作用的比例进行了间接估算。玉米生长季中,根系呼吸作用占土壤呼吸作用的比例在43．1％～63．6％之间波动,均值为54．5％。     

藏北高寒草甸根系生物量与碳氮分布格局及关联特征

根系生物量的分布格局及其与土壤环境因子的关系对草地保护与退化草地恢复研究有重要意义。以藏北当雄县的高寒草甸为研究对象,在三个海拔上（4300、4500、4700 m）对2011年0-50 cm的群落根系生物量、根碳氮含量、土壤碳含量（SOC、DOC、MBC）、氮含量（DTN、MBN、TN）、碳氮比（MBC/MBN、SOC/TN）、pH、电导率进行了测定,以期探讨藏北高寒草甸根系生物量与碳氮的分布格局及其关联特征。结果表明：（1）土壤中所测量的各种形式的碳氮含量均随着土壤深度的增大呈下降趋势,0-50 cm的DOC和SOC都随海拔的升高呈上升趋势。（2）随土壤深度的增加,根系生物量呈指数下降。随海拔的增加,根系生物量越集中分布于上层土壤,下层土壤根系生物量分布越少且变化趋于平缓。（3）根系生物量与所测的碳氮指标、电导率呈正相关关系,与pH呈负相关关系。根系氮库是影响根系生物量分布格局的主要因素,而pH值、电导率及土壤碳氮指标是影响根系生物量分布格局的重要因素。     

干旱胁迫降低了内蒙古羊草草原的碳累积

采用涡度相关法, 分析了2004年(平水年)和2005-2006年(干旱年)生长季内蒙古锡林河流域羊草(Leymus chinensis)草原的净生态系统碳交换(net ecosystem exchange, NEE)、总初级生产力(gross primary productivity, GPP)和生态系统呼吸(ecosystem respiration, R_e)的季节和年度变化。结果表明: 平水年羊草草原的日最大GPP和R_e分别为4.89和1.99 g C·m^-2·d^-1, 而干旱年GPP和R_e分别为1.53-3.01和1.38-1.77 g C·m^-2·d^-1。与平水年相比, 干旱年日最大GPP、R_e分别下降了38%-68%和11%-12%。平水年羊草草原累积的GPP、R_e分别为294和180 g C·m^-2, 而在干旱年分别为102-123 g C·m^-2和132-158 g C·m^-2。和平水年相比, 干旱年的GPP、R_e分别下降了58%-65%和12%-27%。用Van’t Hoff模型模拟的8个窄土壤含水量(θ)跨度生态系统呼吸(R_e)对土壤温度(T_s)的敏感程度表明: 曲线斜率在θ = 0.16-0.17 m³·m^-3范围内达到最大, 高于或者低于这个阈值, R_e对T_s的敏感度降低。干旱胁迫降低了生态系统生产力和生态系统呼吸量。与平水年相比, 干旱年的GPP比R_e下降的幅度更大, 干旱胁迫降低了内蒙古羊草草原的碳累积, 使生态系统由碳汇变为碳源。