闽江河口芦苇沼泽和短叶茳芏沼泽生态系统含碳温室气体的年收支

河口感潮沼泽是全球重要的蓝碳生态系统,具有很强的固碳能力。碳收支研究是量化生态系统碳源/汇过程及固碳规模的基础。本研究运用透明箱和不同遮光率布遮盖+红外气体分析仪/气相色谱相结合的方法,模拟不同光照条件,测定闽江河口鳝鱼滩半咸水芦苇沼泽和短叶茳芏沼泽的瞬时净生态系统二氧化碳（CO₂）交换量（net ecosystem exchange,NEE）、生态系统呼吸（ecosystem respiration,ER）以及甲烷（CH₄）排放通量,并通过对总光合吸收量（gross ecosystem exchange,GEE）与光合有效辐射的拟合以及ER与气温的拟合,外推2个沼泽生态系统CO₂气体在月、年尺度上的NEE和ER,评估其年固碳量。2个沼泽生态系统的NEE和ER均具有明显的季节变化,春夏秋季为大气中CO₂的汇,而冬季则转化为大气中CO₂的源,芦苇沼泽年尺度固碳能力显著高于短叶茳芏沼泽。芦苇沼泽与短叶茳芏沼泽CH₄排放通量差异不显著。综合考虑CH₄排放,闽江河口鳝鱼滩半咸水芦苇沼泽、短叶茳芏沼泽生态系统年固碳量分别为（5371.52±336.97） g CO₂-eq/m²和（2730.32±503.67） g CO₂-eq/m²。研究表明：闽江河口半咸水沼泽湿地在年尺度上是一个较强的碳汇,在缓解全球变暖方面发挥着重要的角色。     

城市小型景观水体CO2与CH4排放特征及影响因素

淡水生态系统被认为是大气温室气体排放的重要来源,尤其在人类活动影响下,其排放强度可能进一步增强。城市小型景观水体是城市生态系统的重要组成,具有面积小、数量大以及人类干扰强的特征,其温室气体排放特征及影响因素尚不清楚。选择重庆市大学城8个景观水体和周边2个自然水体为对象,于2019年1、4、7、10月,利用漂浮箱和顶空法分析了水体CO₂与CH₄的溶存浓度及排放通量,旨在揭示城市小型景观水体CO₂与CH₄排放强度、时空变异特征以及影响因素。结果表明,10个小型水体CO₂、CH₄的溶存浓度范围分别为10.75-116.25 μmol/L和0.09-3.61 μmol/L（均值分别为（47.6±29.3）μmol/L、（1.13±0.56）μmol/L）,均为过饱和状态;漂浮箱法实测的8个景观水体CO₂和CH₄排放通量均值分别为（72.7±65.9）mmol m^-2 d^-1和（2.31±3.48）mmol m^-2 d^-1（顶空法估算值为（69.7±82.0）mmol m^-2 d^-1和（3.69±2.92）mmol m^-2 d^-1）,是2个自然水体的3.5-6.1和2.0-4.5倍,呈较强的CO₂、CH₄排放源;居民区景观水体CO₂和CH₄排放略高于校园区,均显著高于对照的自然水体;CO₂排放夏季最高,秋季次之,冬、春季最低,CH₄呈夏季>秋季≈春季>冬季的季节模式,温度和水体初级生产共同影响CO₂和CH₄排放的季节模式;水生植物分布对景观水体CO₂、CH₄排放有显著影响,有植物分布的水域比无植物水域平均高1.97和2.94倍;漂浮箱法和顶空法测得气体通量线性关系较好,但顶空法测得CO₂通量在春季明显偏低,而CH₄则普遍偏高。相关分析表明,景观水体碳、氮浓度、pH值以及DO等对CO₂排放具有较好的指示性,CH₄排放通量主要与水体中碳、磷浓度有关。城市小型景观水体CO₂、CH₄排放通量远高于大部分已有自然水体的研究结果,呈一种较强的大气温室气体排放源,在区域淡水系统温室气体排放清单中具有重要贡献,未来研究中应给以更多关注。     

潮汐作用对黄河三角洲盐沼湿地甲烷排放的影响

盐沼湿地作为陆海交互作用的过渡带是CH₄重要的自然来源。潮汐活动通过影响CH₄的产生、氧化和传输驱动了湿地CH₄间歇性、周期性的排放。利用涡度相关和微气象监测技术,对黄河三角洲一个盐地碱蓬生态系统CH₄通量、环境因子和水文要素（潮汐）进行了长期连续监测分析了该生态系统生长季CH₄排放的季节动态及潮汐作用对CH₄排放的影响。结果表明：生长季该生态系统是CH₄的排放源,排放日均值为0.063 mg m^-2 h^-1,（范围为-0.36-0.57 mg m^-2 h^-1）。潮汐淹水阶段和落潮后湿润阶段表现为CH₄的显著源。此外我们发现,短期潮汐活动引起土壤干湿状况的变化促进了CH₄脉冲式的排放,因此未来气候变化下温度升高和降雨季节分配引起的土壤干湿变化将会对该区域CH₄排放甚至碳循环产生积极影响。     

鄱阳湖苔草湿地甲烷释放特征

2009年5月-2010年4月在鄱阳湖南矶湿地国家级自然保护区选择以灰化苔草为建群种的洲滩,设置土壤-植物系统(TC)、剪除植物地上部分 (TJ)2个试验处理,利用密闭箱-气相色谱法测定了鄱阳湖典型苔草湿地的甲烷(CH₄)释放通量。结果表明:1)TC、TJ 2个试验处理CH₄释放速率变化范围分别为-0.094-17.75 mg · m^-2 · h^-1、-0.122-19.16 mg · m^-2 · h^-1,均表现出明显的季节变化规律;2)地表未淹水期间,剪草处理CH₄释放显著高于非剪草处理(t=2.69, P<0.05);地表淹水达到15 cm后,剪草处理CH₄释放明显低于非剪草处理。3)土壤5 cm温度、土壤水分与2处理非淹水期间CH₄释放速率均呈显著正相关,是非淹水期间CH₄通量变化的主要控制因子,2因子能够共同解释非淹水期苔草湿地65%-74%的CH₄通量变异;4)试验期间,苔草湿地CH₄释放量约为12.77 gC/m²,相当于同期土壤有机质分解碳排放量的4%,甲烷释放的碳消耗不足苔草湿地年NPP的1%。     

不同恢复方式下大兴安岭重度火烧迹地林地土壤温室气体通量

为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO₂、CH₄和N₂O排放特征及其影响因素,采用静态箱/气相色谱法,在2017年生长季（6月-9月）对3种恢复方式（人工更新、天然更新和人工促进天然更新）林地土壤温室气体CO₂、CH₄、N₂O通量进行了原位观测。研究结果表明：（1）3种恢复方式林地土壤在生长季均为大气CO₂、N₂O的源,CH₄的汇;生长季林地土壤CO₂排放通量大小关系为人工促进天然更新（（634.40±246.52）mg m^-2 h^-1） > 人工更新（（603.63±213.22）mg m^-2 h^-1） > 天然更新（（575.81±244.12）mg m^-2 h^-1）,3种恢复方式间无显著差异;人工更新林地土壤CH₄吸收通量显著高于人工促进天然更新;天然更新林地土壤N₂O排放通量显著高于其他两种恢复方式。（2）土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素;土壤水分仅对人工更新林地土壤N₂O通量有极显著影响（P < 0.01）;3种恢复方式林地土壤CO₂通量与大气湿度具有极显著的响应（P < 0.01）;土壤pH仅与天然更新林地土壤CO₂通量显著相关（P < 0.05）;土壤全氮含量仅与人工促进天然更新林地土壤CH₄通量显著相关（P < 0.05）。（3）基于100年尺度,由3种温室气体计算全球增温潜势得出,人工促进天然更新（1.83×10⁴ kg CO₂/hm²） > 人工更新（1.74×10⁴ kg CO₂/hm²） > 天然更新（1.67×10⁴ kg CO₂/hm²）。（4）阿木尔地区林地土壤年生长季CO₂和N₂O排放量为8.85×10⁶ t和1.88×10² t,CH₄吸收量为1.05×10³ t。     

林下植被和凋落物对寒温带森林生长季土壤CH4通量的影响

为进一步探究林下植被和凋落物管理对我国寒温带森林生长季土壤CH₄通量的影响,采用静态箱-气相色谱法对大兴安岭北部4种林型（白桦林、山杨林、樟子松林和兴安落叶松林）4种处理（自然状态、去除凋落物、去除林下植被以及去除林下植被和凋落物）的土壤CH₄通量排放特征进行观测研究。结果表明：该地区森林生长季土壤均表现为CH₄的汇,4种林型不同处理后土壤CH₄通量表现为单峰变化趋势,吸收峰值出现在7月或8月。自然状态4种林型土壤CH₄平均吸收通量表现为白桦林（-79.23±14.92）μg m^-2 h^-1>山杨林（-64.27±9.60）μg m^-2 h^-1>樟子松林（-62.54±15.48）μg m^-2 h^-1>兴安落叶松林（-48.73±12.26）μg m^-2 h^-1,兴安落叶松土壤CH₄平均吸收通量显著小于其他三种林型（P<0.05）。相比于自然状态,4种林型在去除凋落物后土壤CH₄吸收通量提高了2.12%-12.15%,但变化幅度均没有达到显著水平（P>0.05）。去除林下植被后4种林型CH₄吸收通量提高了0.84%-20.55%,且只有山杨林吸收增加达到显著水平（P<0.05）。同时去除林下植被和凋落物后,对白桦林和樟子松土壤CH₄通量影响不显著（P>0.05）,但对山杨林和兴安落叶松林影响显著（P<0.05）。总之,去除凋落物或林下植被均会提高土壤对CH₄吸收,去除林下植被对土壤CH₄通量的影响要大于去除凋落物的影响,但不同林型不同处理之间还存在差异。     

太湖流域农田稻季CH4通量特征及影响因子

开展太湖流域农田稻季CH₄排放研究,深入了解稻田CH₄排放规律,为稻田CH₄减排、制定合理稻田管理措施提供科学依据。以太湖流域稻麦轮作农田为研究区域,运用涡度相关法观测其稻季CH₄通量变化,分析其通量变化特征及影响因子。结果表明：太湖流域典型稻麦轮作区稻季为CH₄的源,CH₄排放总量为28.95 g/m²,稻季CH₄通量日变化表现为无规则型与单峰型两种模式;稻季CH₄排放整体集中在水稻生长前期（81.61%）及中期（16.16%）、后期排放相对较弱（2.23%）,返青期排放量较低（日均0.102 μmol m^-2 s^-1）,分蘖期较强（日均0.451 μmol m^-2 s^-1）,成熟期最低（日均0.006 μmol m^-2 s^-1）;模型所模拟的累计CH₄排放通量比累计测量CH₄通量低6.69%,较好地模拟了太湖流域稻田CH₄的排放,土壤温度、土壤水分、土壤电导率、摩擦风速可确认为太湖流域农田稻季CH₄排放的主要驱动因子。     

湿地生态系统土壤温度对气温的响应特征及对CO2排放的影响

通过2年的野外定位观测,研究了沼泽湿地土壤温度对气温变化的响应特征,以及土壤温度对沼泽湿地植物 土壤系统CO₂排放的影响,并对CO₂排放的季节性变化进行模拟计算.结果表明,随融冻作用开始,沼泽湿地土壤温度对气温变化的响应强度不断增大,根层土壤温度与气温间呈显著指数关系（R²=0.94,P<0.01）,但不同深度土壤温度对气温变化的响应强度存在一定的差异,表现为随土壤深度的增加,二者之间的相关系数变小,土壤温度对气温的响应强度减弱.沼泽湿地植物 土壤系统CO₂排放与根层土壤温度有关,二者呈显著指数相关关系（R²=0.84,P<0.01）,利用模型模拟计算出沼泽湿地2003年生长季植物 土壤系统CO₂排放通量平均值为664.5±213.9 mg·m^-2·h^-1,野外定位观测值为634.0±227.7 mg·m^-2·h^-1,二者之间差值不大,表明利用此方法可以对沼泽湿地生长季CO₂排放进行估算.     

枯落物输入变化对云南松林地CO2释放的影响

为研究枯落物输入变化对云南松（Pinus yunnanensis）林地CO₂释放的影响。本研究于2018年3月至2020年2月,应用枯落物添加和去除实验（DIRT）,设置对照（CK）、双倍枯落物（DL）、去除枯落物（NL）、去除有机层和A层（O/A-Less）、去除根系（NR）和无输入（NI）6个处理水平,采用Li-6400便携式光合作用测量仪及TRIME-PICO 64/32土壤温度水分测定仪对不同处理样地每月的CO₂通量（R_s）、土壤温度和土壤水分（15cm）进行了测定。结果表明：（1）不同处理样地CO₂通量均呈现出明显的月变化,7至8月最高,1至4月最低,平均值表现为R_{s （DL）}=8.10 μmol m^-2 s^-1 > R_{s （CK）}=6.27 μmol m^-2 s^-1 > R_{s （NL）}=5.44 μmol m^-2 s^-1 > R_{s （NR）}=4.46 μmol m^-2 s^-1 > R_{s （O/A-Less）}=3.86 μmol m^-2 s^-1 > R_{s （NI）}=2.94 μmol m^-2 s^-1。（2）与CK相比,DL样地CO₂通量升高了29.12%,而去除地上枯落物和地下根系样地CO₂通量显著降低,CO₂通量平均变幅分别为α（NR）=-28.85%,α（NI）=-53.14%,α（O/A-Less）=-38.46%,α（NL）=-13.29%。（3）不同处理土壤水分和土壤温度均存在显著的月变化（P<0.01）,NL和O/A-Less的土壤水分显著低于CK,而其余处理与CK间无显著差异（P>0.05）;不同处理间土壤温度表现为NR和NI均显著高于CK,其余处理与CK间无显著差异（P>0.05）。（4）不同处理样地CO₂通量与土壤温度呈显著指数相关（P<0.01）,与土壤水分在NI和O/A-Less处理中无显著相关（P>0.05）;与CK相比,NI、O/A-Less和NL处理的Q₁₀增加,而NR和DL处理的Q₁₀则降低;不同处理林地CO₂通量与土壤水热因子双因素模型能更好的解释林地CO₂通量的变化。本研究表明枯落物不同处理通过改变土壤碳输入和土壤环境因子从而影响生态系统碳排放,研究结果可为未来气候变化和人为干扰下云南松林的碳循环提供基础数据。     

城市化地区典型水体的N2O排放通量特征——以南京市为例

内陆淡水水体是大气中N₂O的重要排放源,然而目前对于内陆典型城市水体N₂O排放通量的监测数据依然匮乏,典型城市水体的N₂O排放特征及驱动因素尚不清楚。本研究选取了南京市江北新区的典型水体,包括湖库、河流、养殖池塘和景观池塘,在2020年5月-2021年4月利用漂浮箱法连续监测了不同水体类型的水-气界面N₂O排放特征,并通过测定水环境特征,探究驱动水体N₂O排放通量的关键因素。研究结果表明,典型城市水体整体均表现为N₂O排放源,河流和养殖池塘的日平均排放通量最大,分别为（503±1236）μg m^-2 d^-1和（508±797）μg m^-2 d^-1,其次为景观池塘（（179±989）μg m^-2 d^-1）,而湖库的N₂O排放通量最小,仅表现为微弱的N₂O排放源（（54±212）μg m^-2 d^-1）。水体的N₂O排放呈现季节性差异,河流和养殖池塘夏季的N₂O排放通量显著高于其他季节（P<0.01）。水体全年N₂O排放数据与水体温度和溶解氧含量（DO）呈显著相关。而在温度较高的5月份-9月份（>20℃）,氮输入成为影响N₂O排放通量的关键因素（P<0.01）,因此控制城市水体的氮输入尤其是在水温较高的夏季是减少N₂O排放的有利措施。此外,由于水文化学条件差异等因素,小型封闭水体包括养殖池塘和景观池塘的N₂O排放通量差异较大,未来应加强监测不同水体的水文化学特征和N₂O的时空排放特征,探讨影响小型封闭水体水-气界面N₂O排放通量的具体驱动因素。此研究为城市区域N₂O排放的精准核算提供了数据支撑,为N₂O排放模型的修正提供了科学依据。     

西南喀斯特地区轮作旱地土壤CO2通量

中国已承诺大幅降低单位GDP碳排放,农业正面临固碳减排的重任.西南喀斯特地区环境独特,旱地面积占据优势比例,土壤碳循环认识亟待加强.以贵州省开阳县玉米-油菜轮作旱地为研究对象,采用密闭箱-气相色谱法对整个轮作期土壤CO2释放通量进行了观测研究,结果表明:(1)整个轮作期旱地均表现为CO2的释放源.其中油菜生长季土壤CO2通量为(178.8±104.8)mg CO2·m-2·h-1,玉米生长季为(403.0±178.8) mg CO2·m-2·h-1,全年平均通量为(271.1±176.4) mg CO2·m-2·h-1,高于纬度较高地区的农田以及同纬度的次生林和松林;(2)CO2通量日变化同温度呈现显著正相关关系,季节变化与温度呈现显著指数正相关关系,并受土壤湿度的影响,基于大气温度计算得出的Q10为2.02,高于同纬度松林以及低纬度的常绿阔叶林;(3)CO2通量与土壤pH存在显著线性正相关关系,显示出土壤pH是研究区旱地土壤呼吸影响因子之一.     

Process-level controls on CO<Subscript>2</Subscript> fluxes from a seasonally snow-covered subalpine meadow soil,Niwot Ridge,Colorado

Fluxes of CO₂ during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow on Niwot Ridge, Colorado, soil CO₂ fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements during summer 2007. The CO₂ fluxes of 0.71 μmol m⁻² s⁻¹ in 2006 and 0.86 μmol m⁻² s⁻¹ in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m⁻² emitted over the winter, ~30% of the annual soil CO₂ efflux at this site. In general, the CO₂ flux increased during the winter as soil moisture increased. A conceptual model was developed with distinct snow cover zones to describe this as well as the three other reported temporal patterns in CO₂ flux from seasonally snow-covered soils. As snow depth and duration increase, the factor controlling the CO₂ flux shifts from freeze–thaw cycles (zone I) to soil temperature (zone II) to soil moisture (zone III) to carbon availability (zone IV). The temporal pattern in CO₂ flux in each zone changes from periodic pulses of CO₂ during thaw events (zone I), to CO₂ fluxes reaching a minimum when soil temperatures are lowest in mid-winter (zone II), to CO₂ fluxes increasing gradually as soil moisture increases (zone III), to CO₂ fluxes decreasing as available carbon is consumed. This model predicts that interannual variability in snow cover or directional shifts in climate may result in dramatically different seasonal patterns of CO₂ flux from seasonally snow-covered soils.     

Carbon Dioxide Dynamics and Controls in a Deep-water Wetland on the Qinghai-Tibetan Plateau

To initially characterize the dynamics and environmental controls of CO₂, ecosystem CO₂ fluxes were measured for different vegetation zones in a deep-water wetland on the Qinghai-Tibetan Plateau during the growing season of 2002. Four zones of vegetation along a gradient from shallow to deep water were dominated, respectively by the emergent species Carex allivescens V. Krez., Scirpus distigmaticus L., Hippuris vulgaris L., and the submerged species Potamogeton pectinatus L. Gross primary production (GPP), ecosystem respiration (Re), and net ecosystem production (NEP) were markedly different among the vegetation zones, with lower Re and GPP in deeper water. NEP was highest in the Scirpus-dominated zone with moderate water depth, but lowest in the Potamogeton-zone that occupied approximately 75% of the total wetland area. Diurnal variation in CO₂ flux was highly correlated with variation in light intensity and soil temperature. The relationship between CO₂ flux and these environmental variables varied among the vegetation zones. Seasonal CO₂ fluxes, including GPP, Re, and NEP, were strongly correlated with aboveground biomass, which was in turn determined by water depth. In the early growing season, temperature sensitivity (Q₁₀) for Re varied from 6.0 to 8.9 depending on vegetation zone. Q₁₀ decreased in the late growing season. Estimated NEP for the whole deep-water wetland over the growing season was 24 g C m⁻². Our results suggest that water depth is the major environmental control of seasonal variation in CO₂ flux, whereas photosynthetic photon flux density (PPFD) controls diurnal dynamics.     

岩溶区不同土地利用方式下土壤CO2排放模拟研究

土地利用变化作为全球气候变化研究的重要内容之一，对土壤CO₂的排放具有重要影响。岩溶区石漠化治理过程中植被恢复伴随着土地利用方式的转变，其对土壤CO₂排放的影响有待进一步研究。基于控制性实验，以土壤、岩溶含水介质初始条件相同，仅土地利用方式不同的贵州普定沙湾模拟试验场为研究对象，通过1年的土壤CO₂浓度和通量数据，研究岩溶区不同土地利用方式下土壤CO₂的排放规律及其影响因素。结果表明：(1)土壤CO₂的浓度和通量具有明显的季节变化规律，不同季节下的土壤CO₂通量呈现昼夜变化规律，温度和降雨影响着土壤CO₂的排放，前者可促进排放量，后者可抑制排放量，且不同土地利用方式受影响的程度不同；(2)耕作活动也会影响土壤CO₂的排放，耕作使得土壤变得松散，加上岩溶区下伏基岩的溶蚀作用，增加了土壤CO₂向含水层的扩散，导致春季耕地表现为负通量；(3)不同土地利用方式下土壤CO₂的年排...     

青藏高原高寒草甸土壤CO2排放对模拟氮沉降的早期响应

研究大气氮沉降输入对青藏高原高寒草甸土壤-大气界面CO₂交换通量的影响,对于准确评价全球变化背景下区域碳平衡至关重要。通过构建多形态、低剂量的增氮控制试验,利用静态箱-气相色谱法测定土壤CO₂排放通量,同时测定相关土壤变量和地上生物量,分析高寒草甸土壤CO₂排放特征及其主要驱动因子。研究结果表明:低、高剂量氮输入倾向于消耗土壤水分,而中剂量氮输入有利于土壤水分的保持;施氮初期总体上增加了土壤无机氮含量,铵态氮累积效应更为显著;施氮显著增加地上生物量和土壤CO₂排放通量,铵态氮的促进效应显著高于硝态氮。另外,土壤CO₂排放通量主要受土壤温度驱动,其次为地上生物量和铵态氮储量。上述结果反映了氮沉降输入短期内可能刺激了植物生长和土壤微生物活性,加剧了土壤-大气界面CO₂排放。     

Seasonal patterns in soil surface CO<Subscript>2</Subscript> flux under snow cover in 50 and 300 year old subalpine forests

Soil CO₂ flux can contribute as much as 60–80% of total ecosystem respiration in forests. Although considerable research has focused on quantifying this flux during the growing season, comparatively little effort has focused on non-growing season fluxes. We measured soil CO₂ efflux through snow in 50 and ~300 year old subalpine forest stands near Fraser CO. Our objectives were to quantify seasonal patterns in wintertime soil CO₂ flux; determine if differences in soil CO₂ flux between the two forest ages during the growing season persist during winter; and to quantify the sample size necessary to discern treatment differences. Soil CO₂ flux during the 2002–2003 and 2003–2004 snow season averaged 0.31 and 0.35 μmols m⁻² s⁻¹ for the young and old forests respectively; similar to the relative difference observed during summer. There was a significant seasonal pattern of soil CO₂ flux during the winter with fluxes averaging 0.22 μmols m⁻² s⁻¹ in December and January and increasing to an average of 0.61 μmols m⁻² s⁻¹ in May. Within-plot variability for measurements used in calculating flux was low. The coefficients of variation (CV) for CO₂ concentration, snowpack density, and snow depth were 17, 8 and 14%, respectively, yielding a CV for flux measurements within-plot of 29%. A within plot CV of 29% requires 8 sub-samples per plot to estimate the mean flux with a standard error of ±10% of the mean. Variability in CO₂ flux estimates among plots (size = 400 m²) was similar to that within plot and was also low (CV = ~28%). With a CV of 28% among plots, ten plots per treatment would have a 50% probability of detecting a 25% difference in treatment means for α = 0.05.     

Efflux of carbon dioxide from snow-covered forest floors

The release of CO₂ from the snow surface in winter and the soil surface in summer was directly or indirectly measured in four cool-temperate deciduous broadleaved and evergreen needle forests. The closed chamber method (CC-method) and Fick's diffusion model (DM-method) were used for the direct and indirect measurements, respectively. The winter soil temperatures from the soil surface to 10 cm depth were between 0 and 2°C. The concentration of CO₂ within snowpack increased linearly with increasing snow depth. The average effluxes of CO₂ calculated from the gradients of CO₂ concentration in the snow using the DM-method ranged from 20 to 75 mg CO₂ m⁻² h⁻¹, while the CC-method showed the average effluxes of 20 to 50 mg CO₂m⁻²h⁻¹. These results reveal that the snow thermally insulates the soil, allowing CO₂ production to continue at soil temperatures a little above freezing throughout the winter. Carbon dioxide formed in the soil can move across snowpack up to the atmosphere. The winter/summer ratio of CO₂ emission was estimated to be higher than 7%. Therefore, the snow-covered soil served as a source of CO₂ in the winter and the effluxes represent an important part of the annual CO₂ budget in snowy regions.     

鼎湖山针阔叶混交林凋落物CO2释放对模拟酸雨的响应

该研究2011年1月开始在鼎湖山针阔叶混交林(混交林)进行模拟酸雨实验,设置4个不同处理水平,即对照(CK)(pH为4.5左右的天然湖水)、T_1(pH=4.0)、T_2(pH=3.25)和T_3(pH=2.5)。2013年1—12月对不同酸雨强度处理下的森林凋落物CO_2释放速率进行为期1 a的连续观测,探讨酸雨对混交林凋落物C排放的影响。结果表明:凋落物CO2释放通量在对照样方为(1 507.41±155.19) g CO_2·m~(-2)·a~(-1),其中湿季和旱季分别占年通量的68.7%和31.3%。模拟酸雨抑制了森林凋落物CO_2释放,与CK相比,T_2和T_3处理下的CO_2释放通量分别显著降低15.4%和42.7%(P0.05);且这种抑制作用具有季节差异性,处理间的显著差异只出现在湿季。凋落物CO_2释放速率与土壤温度和土壤湿度分别呈显著指数相关和显著直线相关,同时,酸雨处理降低了凋落物CO_2释放的温度敏感性。混交林凋落物CO_2释放在模拟酸雨下的抑制效应与土壤累积酸化而导致的土壤微生物活性变化有关,表现为模拟酸雨作用下土壤pH值和微生物量碳显著下降。上述结果说明酸雨是影响混交林土壤碳循环的重要因子之一。     

The effects of elevated atmospheric CO<Subscript>2</Subscript> and nitrogen amendments on subsurface CO<Subscript>2</Subscript> production and concentration dynamics in a maturing pine forest

Profiles of subsurface soil CO₂ concentration, soil temperature, and soil moisture, and throughfall were measured continuously during the years 2005 and 2006 in 16 locations at the free air CO₂ enrichment facility situated within a temperate loblolly pine (Pinus taeda L.) stand. Sampling at these locations followed a 4 by 4 replicated experimental design comprised of two atmospheric CO₂ concentration levels (ambient [CO₂]^a, ambient + 200 ppmv, [CO₂]^e) and two soil nitrogen (N) deposition levels (ambient, ambient + fertilization at 11.2 g_N m⁻² year⁻¹). The combination of these measurements permitted indirect estimation of belowground CO₂ production and flux profiles in the mineral soil. Adjacent to the soil CO₂ profiles, direct (chamber-based) measurements of CO₂ fluxes from the soil–litter complex were simultaneously conducted using the automated carbon efflux system. Based on the measured soil CO₂ profiles, neither [CO₂]^e nor N fertilization had a statistically significant effect on seasonal soil CO₂, CO₂ production, and effluxes from the mineral soil over the study period. Soil moisture and temperature had different effects on CO₂ concentration depending on the depth. Variations in CO₂ were mostly explained by soil temperature at deeper soil layers, while water content was an important driver at the surface (within the first 10 cm), where CO₂ pulses were induced by rainfall events. The soil effluxes were equal to the CO₂ production for most of the time, suggesting that the site reached near steady-state conditions. The fluxes estimated from the CO₂ profiles were highly correlated to the direct measurements when the soil was neither very dry nor very wet. This suggests that a better parameterization of the soil CO₂ diffusivity is required for these soil moisture extremes.