水热条件对锡林河流域典型草原退化群落土壤呼吸的影响

 采用碱液吸收法对锡林河流域温带典型草原一退化群落的土壤呼吸进行了测定,并分析了温度和水分对土壤呼吸的影响,结果表明：1）土壤呼吸总体趋势是夏季高,其它季节低,但季节动态呈现不规律的波动曲线;2）气温、地表温度以及5 cm、10 cm、15 cm和25 cm的土壤温度均与土壤呼吸速率呈显著的指数关系,温度对土壤呼吸的影响在低温时比高温时更显著;3）0～10 cm和10～20 cm土层的土壤含水量均与土壤呼吸速率呈显著的线性关系,消除气温的影响后则呈更为显著的乘幂关系;4）根据变量在p=0.05水平上的多元回归分析结果得到关于土壤呼吸与气温和10～20 cm土壤含水量的关系模型：y=5 911.648×e0.04216Ta×M20. 90758 (R2=0.8584,p<0.0001) ,这一模型比单变量模型能更好地解释土壤呼吸的变化情况;5）实验期间土壤呼吸的平均速率为661.35 mgC·m-2·d-1,以气温、地表温度以及5 cm、10 cm、15 cm和25 cm的土壤温度为依据得到的Q10值依次为1.63、1.47、1.52、1.70、1.90、1.97。     

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。     

塔里木河下游荒漠河岸林群落土壤呼吸及其影响因子

利用LI-8100土壤碳通量自动测定仪监测塔里木河下游荒漠河岸林群落土壤呼吸的日变化动态,分析其土壤呼吸与环境因子的关系,比较二者的差异。结果表明：（1）胡杨和柽柳群落土壤呼吸的日变化过程相同,最大值出现时间一致,呈单峰值曲线,但是不同月份最大值出现时间不同;（2）胡杨群落的土壤呼吸速率大于柽柳群落的;（3）胡杨和柽柳群落的土壤呼吸速率与距地表2cm处气温之间存在显著的指数关系,但是不同植物类型的土壤呼吸对温度的敏感性有所不同;（4）胡杨和柽柳群落的土壤呼吸速率与土壤水分都存在显著的线性关系;（5）通过多元回归分析表明,塔里木河下游76％～93％左右的荒漠河岸林群落土壤呼吸速率受温度和水分的共同控制。     

黄土高原水蚀风蚀交错带不同土地利用类型土壤呼吸季节变化及其环境驱动

以黄土高原水蚀风蚀交错区神木县六道沟小流域为研究区,采用动态密闭气室法对植物生长季节（2007年5～10月）5种土地利用方式的土壤呼吸速率进行了测定,并结合水热因子,对不同土地利用方式间土壤呼吸速率的差异性以及其和温度、含水量之间的关系进行了分析。结果表明：5种土地利用类型土壤呼吸速率季节性变化均呈现单峰型曲线,与气温变化趋势一致,其7、8月份土壤呼吸速率均显著高于其它月份（P〈0.05）;生长季节土壤CO2平均释放速率顺序为：长芒草地〉苜蓿地〉柠条地〉农地〉沙柳地,草地在生长前期和旺盛期土壤呼吸强度均显著高于农地和灌木林地;除沙柳地和苜蓿地以外,在土壤呼吸与所有温度指标的关系中,与10cm深度的土壤温度相关性最好,且除沙柳地外,其它4种土地利用类型均与之达到显著相关;农地土壤呼吸对温度的响应最敏感（Q10值为2.20）,除沙柳地（Q10值为1.48）外,其它4种土地利用类型Q10值均在2.0左右,接近于全球Q10的平均水平;通过Van’t Hoff模型估算,2007年植物整个生长季节（5～10月份）,5种土地利用类型土壤呼吸量从高到低依次为：苜蓿地259gC&#183;m^-2,长芒草地236gC&#183;m^-2,柠条地226gC&#183;m^-2,农地170gC&#183;m^-2,沙柳地94gC&#183;m^-2;水分对农地和沙柳地的土壤呼吸影响不大;长芒草地、柠条地和苜蓿地土壤呼吸的双变量模型关系显著（P〈0.05）,比相应的单变量模型更好地解释了土壤呼吸变异。     

西双版纳热带季节雨林与橡胶林土壤呼吸

 季节雨林和橡胶（Hevea brasiliensis）林是西双版纳热带森林生态系统中原始林和大面积种植人工林的两种代表类型。热带季节雨林层次结构复杂,多样性丰富,而橡胶林结构简单,乔木层只有橡胶树1种。应用碱吸收法,研究了这两种植被类型土壤呼吸速率 、地下5 cm土壤温度、气温和土壤含水率的季节变化规律,以及土壤呼吸速率与地下5 cm土 壤温度、气温和土壤含水率的关系。结果表明：1）季节雨林和橡胶林土壤呼吸速率、土壤温度、气温和土壤含水率都有明显的季节变化,而且两种林型的变化趋势基本一致;2 ）季节雨林和橡胶林土壤呼吸速率与地下5 cm土壤温度和气温之间具有显著的指数相关关系 ,显著水平达1%,与地下5 cm温度的相关性（r2分别为0.87和0.82）明显高于与气温 的相关性（r2分别是0.80和0.72）;3）季节雨林和橡胶林土壤呼吸速率与土壤含水率具有显著的线性相关（r2分别是0.73和0.63）,显著水平达1%;4）橡胶林的土壤呼吸速率明显高于季节雨林,这与两种林型的结构有关;5）季节雨林和橡胶林土壤呼吸的Q10分别为2.16和2.18,比文献报道的热带土壤的Q10（1.96）稍高 。     

不同土地利用方式下土壤呼吸及其温度敏感性

采用静态箱-气相色谱法对四川盆地中部紫色土丘陵区3种土地利用方式（林地、草地和轮作旱地）土壤呼吸进行测定，结果表明，林地、草地和旱地土壤呼吸速率变化范围分别为78．63～577．97、39．28～584．18和34．48～484．65mgCO2·m^-2·h^-1，年平均土壤呼吸速率分别为264．68、242．91、182．21mgCO2·m^-2h^-1。3种土地利用方式的土壤呼吸速率季节变化趋势均呈单峰曲线，林地和草地土壤呼吸速率最大值均出现在夏末（7月底与8月初之间），旱地土壤呼吸速率最大值出现的时间比林地和草地要早，在6月底与7月初之间；最小值均出现在12月底与翌年1月初之间。土壤温度和土壤湿度是影响本地区土壤呼吸的主要因子，双因素关系模型（R=αe^bTw^c）较好地拟合了土壤温度和土壤湿度对土壤呼吸的影响，二者共同解释了土壤呼吸变化的64％～90％。土壤呼吸的温度敏感性指数Q10值受土壤（5cm处）温度和土壤（0～10cm）湿度的影响。分析表明3种土地利用土壤的Q10值与土壤温度呈显著负相关关系，而与土壤湿度呈显著正相关关系。     

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.     

松嫩平原西部草甸草原典型植物群落土壤呼吸动态及影响因素

以松嫩平原西部草甸草原中典型植物虎尾草、碱茅、芦苇和羊草群落为对象,分析了4种植被群落土壤呼吸速率日动态和季节动态及其影响因素,以及土壤盐碱度与土壤呼吸碳排放量的关系.结果表明:4种植物群落的土壤呼吸速率日变化均呈明显的单峰曲线,峰值出现在11:00—15:00,而谷值大多出现在21:00—1:00或3:00—5:00;4种植被群落土壤呼吸速率的季节变化趋势一致,7、8月的土壤呼吸速率(3.21~4.84μmol CO2·m-2·s-1)最高,10月最低(0.46~1.51μmol CO2·m-2·s-1);各群落土壤呼吸速率与土壤和近地表大气温度之间呈极显著相关关系,其中,虎尾草群落的土壤呼吸速率与土壤表层含水量极显著相关,芦苇和羊草群落土壤呼吸速率与近地表的相对湿度显著相关.土壤盐分含量明显抑制了土壤CO2排放量,土壤pH、电导率和土壤交换性钠可以解释该草甸草原土壤呼吸空间变异的87%~91%.     

温带荒漠中温度和土壤水分对土壤呼吸的影响

 荒漠对气候变化具有高度敏感性, 深刻认识和量化非生物因子对荒漠生态系统土壤呼吸的影响具有重要意义。采用自动CO₂通量系统(Li-8100)监测了梭梭(Haloxylon ammodendron)、假木贼(Anabasis aphylla)和盐穗木(Halostachys caspica)群落生长季土壤呼吸及温度、土壤含水量等, 深入分析了水热因子对土壤呼吸的影响。土壤呼吸具有不对称的日格局, 最小值出现在8:00, 最大值在12:00~14:00。土壤呼吸的季节格局与气温变化基本同步, 最小值在生长季末期(10月), 最大值在生长季中期(6~7月)。梭梭、假木贼和盐穗木群落生长季平均土壤呼吸速率分别为0.76、0.52和0.46 μmol CO₂·m^–2·s^–1。气温对假木贼(51%)和盐穗木群落(65%)土壤呼吸季节变化的解释率高于梭梭(35%)。梭梭、假木贼和盐穗木群落土壤呼吸温度敏感性(Q₁₀)逐渐增大, 基础呼吸速率(R₁₀)逐渐减小。剔除温度影响后, 梭梭、假木贼群落土壤呼吸与土壤含水量呈显著的幂二次方函数关系, 盐穗木群落两者关系却明显减弱, 未达到显著水平。气温、土壤含水量的二元方程均能解释群落土壤呼吸大部分的时间变异: 梭梭群落71%~93%、假木贼群落79%~82%、盐穗木群落70%~80%。人工模拟降水后土壤呼吸速率表现出降水后10 min减小、180 min时明显增加、达到最大值后再次衰减的现象。5和2.5 mm降水处理下的土壤呼吸速率最大值和其后的递减值高于对照处理, 土壤呼吸增加、达到峰值和其后递减过程与5 cm土壤温度变化基本同步。     

次生栎林与火炬松人工林土壤呼吸的季节变异及其主要影响因子

土壤呼吸是陆地生态系统碳循环的重要组成部分.随着全球气候变暖趋势逐渐明显,土壤呼吸的时空变异及其对温度变化的响应已成为生态学研究的重要内容之一.利用LI-6400-09土壤碳通量观测仪,在江苏省南京林业大学下蜀实验基地,采用随机区组实验设计方法,连续两年测定了北亚热带次生栎林和火炬松人工林土壤呼吸的季节动态变化,结果表明:(1)两种林分内土壤呼吸速率均具有明显的季节波动,表现为:在最冷的1月份,土壤呼吸速率最低,随着土壤温度的升高,土壤呼吸速率也逐渐上升,在7、8月份达到最大值,随后又逐渐下降;(2)次生栎林月平均土壤呼吸速率在0.271～3.22μmolCO2 · m-2 · s-1之间,年变异幅度为11.88;火炬松人工林月平均土壤呼吸速率在0.336～3.06μmolCO2 · m-2 · s-1 ,年变异幅度为9.11;(3)次生栎林土壤呼吸的 Q10值在2.19至2.27之间,火炬松人工林土壤呼吸的Q10值在2.02至2.15之间,次生栎林土壤呼吸对温度的敏感性大于火炬松人工林;(4)土壤呼吸速率与不同深度层次土壤温度之间均呈显著性正相关,与土壤微生物生物量之间呈显著性负相关,而与土壤含水率、凋落物输入量之间相关不显著.研究结果初步阐明了江淮流域北亚热带典型森林植被土壤呼吸的季节动态特征及主要影响因子,为进一步揭示该区域森林土壤碳循环特点提供了理论基础.     

Effects of climate warming on carbon fluxes in grasslands— A global meta‐analysis

Climate warming will affect terrestrial ecosystems in many ways, and warming‐induced changes in terrestrial carbon (C) cycling could accelerate or slow future warming. So far, warming experiments have shown a wide range of C flux responses, across and within biome types. However, past meta‐analyses of C flux responses have lacked sufficient sample size to discern relative responses for a given biome type. For instance grasslands contribute greatly to global terrestrial C fluxes, and to date grassland warming experiments provide the opportunity to evaluate concurrent responses of both plant and soil C fluxes. Here, we compiled data from 70 sites (in total 622 observations) to evaluate the response of C fluxes to experimental warming across three grassland types (cold, temperate, and semi‐arid), warming methods, and short (≤3 years) and longer‐term (>3 years) experiment lengths. Overall, our meta‐analysis revealed that experimental warming stimulated C fluxes in grassland ecosystems with regard to both plant production (e.g., net primary productivity (NPP) 15.4%; aboveground NPP (ANPP) by 7.6%, belowground NPP (BNPP) by 11.6%) and soil respiration (Rs) (9.5%). However, the magnitude of C flux stimulation varied significantly across cold, temperate and semi‐arid grasslands, in that responses for most C fluxes were larger in cold than temperate or semi‐arid ecosystems. In semi‐arid and temperate grasslands, ecosystem respiration (Reco) was more sensitive to warming than gross primary productivity (GPP), while the opposite was observed for cold grasslands, where warming produced a net increase in whole‐ecosystem C storage. However, the stimulatory effect of warming on ANPP and Rs observed in short‐term studies (≤3 years) in both cold and temperate grasslands disappeared in longer‐term experiments (>3 years). These results highlight the importance of conducting long‐term warming experiments, and in examining responses across a wide range of climate.     

锡林河流域一个放牧羊草群落中碳素平衡的初步估计

 野外调查与历史资料相结合,对内蒙古锡林河流域一个放牧羊草（Leymus chinensis）草原群落的碳素贮量、主要流量和周转速度等进行了估计,在此基础上对放牧情况下该群落的碳素收支进行了概算。结果表明：1）该群落中地上部净初级生产固碳量的两年平均值为78.2 gC·m－2·a－1, 根系碳素输入量的平均值为322.5 gC·m－2·a－1, 碳素输入总量为400.7 gC·m－2·a－1; 2）土壤净呼吸量为343.7 gC·m－2·a－1,家畜采食量为49.7 gC·m－2·a－1,动物（昆虫）采食量为14.7 gC·m－2·a－1,地上立枯阶段的淋溶与光化学分解损失为3.2 gC·m－2·a－1,碳素输出总量为411.3 gC·m－2·a－1; 3）该群落中碳素输出略大于输入,净释放速率为10.6 gC·m－2·a－1,0～30 cm土壤中的碳素周转速率为6.2%,周转时间为16年。     

农牧交错区不同植物群落土壤呼吸的日动态观测与测定方法比较

 采用动态密闭气室法（IRGA）对农牧交错区10种植物群落最大生物量时期的土壤呼吸日动态进行了测定,并将该方法得到的土壤日呼吸速率与碱液吸收法（AA）进行了比较。结果表明：1）10个群落土壤呼吸的昼夜变化比较明显,均为单峰型曲线,主要受土壤温度的驱动,但同时也受到当日降水情况和云量、风速等气象因子的较大影响。因此,这些群落土壤呼吸日动态的一致性较差,规律性并不明显。2）用碱液吸收法和动态密闭气室法测定的10个群落的土壤呼吸速率变化范围分别为394～894 mg C·m-2·d-1和313～2043 mg C·m-2·d-1,其中碱液吸收法测定结果平均为动态气室法的67.5%,明显低于动态密闭气室法。3）两种测定方法具有很好的相关性,R2为0.873 9。本研究中发现,在土壤呼吸速率低的情况下,两种方法的测定结果十分接近甚至碱液吸收法测定结果稍大于动态密闭气室法,而在土壤呼吸速率较高的情况下,动态密闭气室法测定结果则显著高于碱液吸收法。上述结果与国内外同类研究的结果高度一致,从而为校正以往采用碱液吸收法在该区域的测定结果提供了可靠依据。     

Alpine grassland ecosystem respiration variation under irrigation in Northern Tibet

Grassland ecosystems are important parts of terrestrial ecosystems and play an important role in the global carbon cycle. In recent years, the grasslands in Northern Tibet have experienced warming, and its precipitation has also increased. Alpine grassland irrigation measures could be a reasonable pathway to redistribute and make full use of the increased precipitation. In this study, we measured the soil respiration in alpine grassland in Northern Tibet under sprinkler head irrigation in the growing season to determine the relationships between soil temperature /water and ecosystem/soil respiration, soil moisture and Q₁₀, and soil temperature and Q₁₀. The results showed that after 2 years irrigation, alpine grassland aboveground biomass increased significantly, with 2010 higher than 2009. There was significant annual, seasonal and daily variation of soil respiration. Under irrigation, ecosystem respiration and soil respiration increased 75% and 64% respectively; soil water increase can promote the respiration of ecosystem and its components. In our results, the Q₁₀ value was 2.23–2.81, over the global average. The irrigation can promote ecosystem respiration temperature sensitivity. There was a positive linear correlation between ecosystem respiration and grassland aboveground biomass. The aboveground biomass accounted for 32.8% of ecosystem respiration variation. Soil respiration accounted for more than 70% of ecosystem respiration, indicating that the contribution to carbon emissions of soil respiration is very high. In short, we can project that in grasslands biomass and ecosystem respiration will increase under future precipitation change, which will significantly affect the function of alpine grassland carbon storage.     

Transplantation of organic surface horizons of boreal soils into warmer regions alters microbiology but not the temperature sensitivity of decomposition

Changes in soil carbon, the largest terrestrial carbon pool, are critical for the global carbon cycle, atmospheric CO₂ levels and climate. Climate warming is predicted to be most pronounced in the northern regions and therefore the large soil carbon pool residing in boreal forests will be subject to larger global warming impact than soil carbon pools in the temperate or the tropical forest. A major uncertainty in current estimates of the terrestrial carbon balance is related to decomposition of soil organic matter (SOM). We hypothesized that when soils are exposed to warmer climate the structure of the ground vegetation will change much more rapidly than the dominant tree species. This change will alter the quality and amount of litter input to the soil and induce changes in microbial communities, thus possibly altering the temperature sensitivity of SOM decomposition. We transferred organic surface soil sections from the northern borders of the boreal forest zone to corresponding forest sites in the southern borders of the boreal forest zone and studied the effects of warmer climate after an adaptation period of 2 years. The results showed that initially ground vegetation and soil microbial community structure and community functions were different in northern and southern forest sites and that 2 years of exposure to warmer climate was long enough to cause changes in these ecological indicators. The rate of SOM decomposition was approximately equally sensitive to temperature irrespective of changes in vegetation or microbial communities in the studied forest sites. However, as temperature sensitivity of the decomposition increases with decreasing temperature regime, the proportional increase in the decomposition rate in northern latitudes could lead to significant carbon losses from the soils.     

The effects of warming and nitrogen addition on soil nitrogen cycling in a temperate grassland, northeastern China

Background

Both climate warming and atmospheric nitrogen (N) deposition are predicted to affect soil N cycling in terrestrial biomes over the next century. However, the interactive effects of warming and N deposition on soil N mineralization in temperate grasslands are poorly understood.

Methodology/Principal Findings

A field manipulation experiment was conducted to examine the effects of warming and N addition on soil N cycling in a temperate grassland of northeastern China from 2007 to 2009. Soil samples were incubated at a constant temperature and moisture, from samples collected in the field. The results showed that both warming and N addition significantly stimulated soil net N mineralization rate and net nitrification rate. Combined warming and N addition caused an interactive effect on N mineralization, which could be explained by the relative shift of soil microbial community structure because of fungal biomass increase and strong plant uptake of added N due to warming. Irrespective of strong intra- and inter-annual variations in soil N mineralization, the responses of N mineralization to warming and N addition did not change during the three growing seasons, suggesting independence of warming and N responses of N mineralization from precipitation variations in the temperate grassland.

Conclusions/Significance

Interactions between climate warming and N deposition on soil N cycling were significant. These findings will improve our understanding on the response of soil N cycling to the simultaneous climate change drivers in temperate grassland ecosystem.     

Soil Respiration and Belowground Carbon Allocation in Mangrove Forests

Mangrove forests cover large areas of tropical and subtropical coastlines. They provide a wide range of ecosystem services that includes carbon storage in above- and below ground biomass and in soils. Carbon dioxide (CO₂) emissions from soil, or soil respiration is important in the global carbon budget and is sensitive to increasing global temperature. To understand the magnitude of mangrove soil respiration and the influence of forest structure and temperature on the variation in mangrove soil respiration I assessed soil respiration at eleven mangrove sites, ranging from latitude 27°N to 37°S. Mangrove soil respiration was similar to those observed for terrestrial forest soils. Soil respiration was correlated with leaf area index (LAI) and aboveground net primary production (litterfall), which should aid scaling up to regional and global estimates of soil respiration. Using a carbon balance model, total belowground carbon allocation (TBCA) per unit litterfall was similar in tall mangrove forests as observed in terrestrial forests, but in scrub mangrove forests TBCA per unit litter fall was greater than in terrestrial forests, suggesting mangroves allocate a large proportion of their fixed carbon below ground under unfavorable environmental conditions. The response of soil respiration to soil temperature was not a linear function of temperature. At temperatures below 26°C Q10 of mangrove soil respiration was 2.6, similar to that reported for terrestrial forest soils. However in scrub forests soil respiration declined with increasing soil temperature, largely because of reduced canopy cover and enhanced activity of photosynthetic benthic microbial communities.     

Different responses of ecosystem carbon exchange to warming in three types of alpine grassland on the central Qinghai–Tibetan Plateau

Climate is a driver of terrestrial ecosystem carbon exchange, which is an important product of ecosystem function. The Qinghai–Tibetan Plateau has recently been subjected to a marked increase in temperature as a consequence of global warming. To explore the effects of warming on carbon exchange in grassland ecosystems, we conducted a whole‐year warming experiment between 2012 and 2014 using open‐top chambers placed in an alpine meadow, an alpine steppe, and a cultivated grassland on the central Qinghai–Tibetan Plateau. We measured the gross primary productivity, net ecosystem CO₂ exchange (NEE), ecosystem respiration, and soil respiration using a chamber‐based method during the growing season. The results show that after 3 years of warming, there was significant stimulation of carbon assimilation and emission in the alpine meadow, but both these processes declined in the alpine steppe and the cultivated grassland. Under warming conditions, the soil water content was more important in stimulating ecosystem carbon exchange in the meadow and cultivated grassland than was soil temperature. In the steppe, the soil temperature was negatively correlated with ecosystem carbon exchange. We found that the ambient soil water content was significantly correlated with the magnitude of warming‐induced change in NEE. Under high soil moisture condition, warming has a significant positive effect on NEE, while it has a negative effect under low soil moisture condition. Our results highlight that the NEE in steppe and cultivated grassland have negative responses to warming; after reclamation, the natural meadow would subject to loose more C in warmer condition. Therefore, under future warmer condition, the overextension of cultivated grassland should be avoided and scientific planning of cultivated grassland should be achieved.     

Plant community structure regulates responses of prairie soil respiration to decadal experimental warming

Soil respiration is recognized to be influenced by temperature, moisture, and ecosystem production. However, little is known about how plant community structure regulates responses of soil respiration to climate change. Here, we used a 13‐year field warming experiment to explore the mechanisms underlying plant community regulation on feedbacks of soil respiration to climate change in a tallgrass prairie in Oklahoma, USA. Infrared heaters were used to elevate temperature about 2 °C since November 1999. Annual clipping was used to mimic hay harvest. Our results showed that experimental warming significantly increased soil respiration approximately from 10% in the first 7 years (2000–2006) to 30% in the next 6 years (2007–2012). The two‐stage warming stimulation of soil respiration was closely related to warming‐induced increases in ecosystem production over the years. Moreover, we found that across the 13 years, warming‐induced increases in soil respiration were positively affected by the proportion of aboveground net primary production (ANPP) contributed by C₃ forbs. Functional composition of the plant community regulated warming‐induced increases in soil respiration through the quantity and quality of organic matter inputs to soil and the amount of photosynthetic carbon (C) allocated belowground. Clipping, the interaction of clipping with warming, and warming‐induced changes in soil temperature and moisture all had little effect on soil respiration over the years (all P > 0.05). Our results suggest that climate warming may drive an increase in soil respiration through altering composition of plant communities in grassland ecosystems.