气候过渡带锐齿栎林土壤呼吸对降雨改变的响应

作为大气与陆地生态系统之间的第二大碳通量,土壤呼吸是评价陆地生态系统碳循环及碳汇能力的不确定性来源之一。降雨格局改变及其导致的土壤水分变化是调节土壤呼吸的重要驱动。气候过渡带的水热状况受全球降雨格局改变的影响更为明显,揭示该区域森林土壤呼吸对降雨改变的响应规律有助于改善碳循环模型的预测精度。然而,气候过渡区的土壤碳排放过程如何响应降雨格局改变尚不清楚。通过在亚热带-暖温带的过渡区(宝天曼)开展降雨改变实验,以阐明锐齿栎林土壤呼吸及其温度敏感性对降雨增加(50%)和减少(50%)的响应规律。结果表明,降雨增加显著提高土壤湿度(+8.92%)而不影响土壤温度。与对照相比,降雨增加导致土壤呼吸显著提高80.5%,其土壤呼吸的温度敏感性(4.07)显著高于对照样地(2.66)。增雨处理下的土壤呼吸与土壤湿度呈负相关。降雨减少则显著降低土壤湿度(-10.25%),并对土壤呼吸有促进趋势,然而,对土壤呼吸的温度敏感性(2.64)无显著影响。减雨处理下的土壤呼吸强度与土壤湿度呈正相关。这意味着在我国亚热带—暖温带过渡区,降雨增加或减少均对土壤呼吸有不同程度的刺激作用,进而很可能减弱该区域森林生态系统土壤的固碳潜力。     

土壤异养呼吸的测定及其温度敏感性影响因子

土壤异养呼吸主要指土壤中微生物分解有机质释放CO2的过程,是陆地生态系统中土壤碳的主要净输出途径,土壤异养呼吸与净初级生产力的差值是决定生态系统碳源/汇的关键.本文介绍了土壤异养呼吸的测定方法--室内培养的去根土壤样品培养和原状土柱培养,以及野外原位测定的根排除法、环割法和同位素法等操作方法的优缺点以及适用范围.在土壤异养呼吸的研究方面,土壤异养呼吸温度敏感性(Q10)是碳循环研究的重要方面之一,温度、水分以及土壤呼吸底物是影响Q10的主要因子,一般情况下,随着温度的升高,Q10下降;土壤含水量过低或过高时,Q10降低;土壤有机碳的有效性影响着土壤异养呼吸对温度变化的响应程度,当有效性降低时Q10下降,不同周转时间的有机碳的温度敏感性也不相同,活性有机碳的温度敏感性较惰性有机碳的温度敏感性低.     

土壤呼吸温度敏感性的影响因素和不确定性

土壤呼吸是陆地生态系统碳循环的重要环节之一, 其对温度升高的敏感程度在很大程度上决定着全球气候变化与碳循环之间的反馈关系。为了深刻理解地下生态过程对气候变化的响应和适应,本文综述了土壤呼吸温度敏感性（Q10）的影响因子及其内在机制,并分析了当前研究存在的不确定性。土壤生物、底物质量和底物供应显著调控着土壤呼吸的Q10值,但研究结论仍然有很大差异。温度和水分等环境因子则通过对土壤生物和底物的影响而作用于土壤呼吸的温度敏感性,一般情况下,随着温度的升高,土壤呼吸的Q10值下降;水分过高或过低时Q10值降低。另外本文从土壤温度测定深度、时空尺度、土壤呼吸不同组分温度敏感性差异、激发效应以及采用方法的不同等几方面分析了温度敏感性研究存在的不确定性。并在此基础上, 指出了未来拟重点加强的研究方向:（1）土壤呼吸不同组分温度敏感性差异的机理;（2）底物质量和底物供应对温度敏感性的交互影响;（3）生物因子对土壤呼吸温度敏感性的影响。     

苏北淤泥质海岸典型防护林地土壤呼吸及其温度敏感性

土壤呼吸及其温度敏感性研究是准确估计陆地生态系统碳平衡对未来气候变化响应的基础.我国漫长的淤泥质海岸有着大面积的防护林,其碳汇服务功能是一个非常值得研究的科学问题,因此,对淤泥质海岸防护林生态系统土壤呼吸及其温度敏感性的研究具有重要的意义.研究采用碱液吸收法对苏北淤泥质海岸杨树Populus tomentosa Carr.及水杉Metasequoia glyptostroboides Hu & Cheng两种典型海防林土壤呼吸及其温度敏感性进行了研究.结果表明:杨树和水杉林地4～11月份土壤呼吸速率变化范围分别为337～732mgCO2m-2h-1和257～821mgCO2m-2h-1,呼吸通量分别为128.57gCO2m-2和121.38gCO2m-2.杨树和水杉林地土壤呼吸速率季节变化均近似单峰曲线,最大值均出现在7月份,最小值分别出现在4月份和11月份.模型R=a×exp(b×T)能够很好地拟合林内气温及土壤温度变化对土壤呼吸的影响,温度是影响土壤呼吸的主要因子,能够解释土壤呼吸季节变化的50.5%～80.9%.土壤含水量与土壤呼吸关系不显著,不是其主要影响因子.利用林内气温及土壤2、5cm和10cm处温度得到杨树林地的Q10值分别为1.45、1.97、2.08、2.01,水杉林地的Q10值分别为1.92、3.29、2.89、3.00.研究结果表明,水杉林地土壤呼吸对全球变暖的响应比杨树林地更敏感.     

五台山臭冷杉林土壤呼吸时空变化特征

土壤呼吸是气候变化背景下森林生态系统稳定性的重要评价指标。本研究以五台山臭冷杉森林群落为对象,对不同海拔(2100、2200、2300 m)典型群落土壤理化性质及主要生长季土壤呼吸速率、土壤水热条件变化进行分析,并建立回归模型解析土壤温度、湿度与土壤呼吸速率变化的关系。结果表明:臭冷杉森林土壤为中性偏酸性,随海拔上升,土壤p H、有机碳、总氮、总磷、速效磷含量和土壤湿度增加,土壤温度和土壤呼吸速率降低; 7—10月,臭冷杉森林土壤温度和土壤呼吸速率逐渐降低,降幅分别为49.0%和64.9%,土壤湿度增加11.7%;土壤温度平均解释土壤呼吸速率变化的76.9%(P<0.001),且随海拔升高相关系数(R`2)减小、温度敏感性增加(Q₁₀),土壤湿度平均解释土壤呼吸速率变化的25.8%(P<0.001),二者共同解释土壤呼吸速率变化的71.2%(P<0.001)。本实验中,季节和海拔造成的土壤温度改变是影响土壤呼吸的主要因素,土壤湿度对土壤呼吸的影响较小。此外,土壤养分与土壤呼吸速率的RDA分析结果表明,土壤有机碳、总氮、总磷和速效磷含量是影响土壤呼...     

模拟氮沉降对长江滩地杨树林土壤呼吸温度敏感性的影响

研究氮沉降量增加对土壤呼吸温度敏感性的影响,对于研究土壤呼吸在气候变化中的作用有重要意义。以长江中下游滩地杨树人工林为对象,通过定位模拟氮沉降实验的方法,研究了滩地杨树人工林生态系统土壤呼吸的变化特征和土壤呼吸各组分的温度敏感性对几种氮沉降量浓度的短期响应。结果表明:(1)各处理土壤总呼吸、土壤微生物呼吸、根系呼吸与各层次土壤温度均呈显著正相关关系,和5cm层土壤温度相关性最大。5cm层土壤温度可以解释土壤总呼吸、土壤微生物呼吸和根系呼吸季节变化的比例分别为50.5%—71.0%、51.5%—73.9%、35.7%—63.2%;(2)对照组(CK,0g N m-2a-1)土壤总呼吸、土壤微生物呼吸与根呼吸的Q10值分别为2.54、2.72和1.94;(3)在各氮添加水平中,中氮水平(MN,10g N m-2a-1)促进了土壤总呼吸、土壤微生物呼吸和植物根呼吸的温度敏感性。高氮水平(HN,20g N m-2a-1)都降低了土壤总呼吸、土壤微生物呼吸和植物根呼吸的温度敏感性,低氮水平(LN,5g N m-2a-1)降低了土壤总呼吸和土壤微生物呼吸的温度敏感性,促进了根呼吸的敏感性。     

太湖流域典型稻麦轮作农田生态系统碳交换及影响因素

利用涡度相关技术观测太湖流域典型稻麦轮作农田生态系统2a净生态系统碳交换(NEE)变化过程,分析其碳交换特征及影响机理,结果表明:太湖流域典型稻麦轮作农田年NEE为-749.49—-785.38 g C m-2a-1,考虑作物籽粒碳和秸秆还田后净吸收88.12 g C m-2a-1,为弱碳汇;稻/麦季日均NEE和白天NEE季节变化直接受作物植被生长影响;麦季夜间NEE与10 cm土壤温度呈显著指数关系,2012/2013年温度敏感系数(Q10)分别为3.03和2.67;当土壤水分低于田间持水量时,麦季夜间NEE主要受土壤温度影响,反之,夜间NEE受土壤温度和水分双重影响;降水对麦季夜间NEE有短时的激发效应;稻季淹水对土壤呼吸产生较明显的阻滞效应,降低了夜间NEE对土壤温度的敏感性,2012和2013年分别为1.88和1.39,稻季淹水与烤田交替变化对土壤呼吸产生明显的抑制或激发的短时效应。     

植物根呼吸对升温的响应

植物根呼吸碳释放量高达18Pg／a,约为全球化石燃料燃烧碳排放量（6．5Pg／a）的2．8倍。了解根呼吸对升温的响应对于构建陆地生态系统碳动态模型、评价地下碳库碳收支具有重要作用。短期升温能明显提高根呼吸速率,但在近乎恒定的温度梯度下,根呼吸速率可能逐渐恢复到温度变化前的水平。根呼吸的温度敏感性与植物种和测定的温度范围有关,其Q10值介于1．1～10之间。在野外条件下,根呼吸的温度敏感性还会受到土壤湿度、养分状况、呼吸底物有效性、太阳辐射、光合产物的地下分配模式和天气状况等影响。通常根呼吸的温度敏感性比土壤微生物呼吸的温度敏感性高,但室内控制温度下和野外环割（girdling）实验中并未观测到类似现象。根呼吸是否具有温度适应性仍是一个尚未解决的重大科学问题。有关根呼吸对升温的适应机理仍不清楚,可能是碳循环研究存在不确定性的重要来源。今后的研究方向应集中在以下几方面：（1）深入探讨根呼吸的温度适应性;（2）扩大对成年植物种的研究;（3）扩大对环境因子交互影响和模拟研究;（4）扩大对植物根呼吸测定和升温新技术的研究。     

降雨量改变对黄河三角洲滨海湿地土壤呼吸的影响

全球变化背景下,降雨模式变化造成土壤水分波动是引起土壤呼吸动态变化的重要驱动力。但滨海湿地如何响应降雨模式变化,进而引起生态系统蓝碳功能改变的机制尚不清楚。依托黄河三角洲滨海湿地增减雨野外控制试验平台,采用土壤碳通量观测系统(LI—8100)对湿地土壤呼吸速率进行监测,探究了2017年黄河三角洲滨海湿地土壤呼吸及环境、生物因子对减雨60%、减雨40%、对照60%、对照40%、增雨40%、增雨60%等变化的响应及机制。结果表明:1)随着降雨量增加,湿地土壤温度逐渐降低;同时增雨和减雨处理均显著提高了湿地土壤湿度(P0.05)。(2)降雨量变化显著影响湿地植被物种组成、地上和地下生物量分配以及植被根冠比(P0.05)。增雨40%和增雨60%均显著提高了湿地植物种类和植被根冠比,但同时显著降低了湿地植被地上生物量。此外,增雨40%和减雨60%处理均显著提高了湿地植被地下生物量。(3)降雨量变化对2017年湿地季节土壤呼吸无显著影响,但在湿地非淹水期,增雨60%和增雨40%均显著提高了湿地土壤呼吸速率(P0.05)。(4)2017年湿地不同降雨处理的土壤呼吸与土壤湿度均呈二次曲线关系(P0.05),相关系数随降雨量增加而降低;同时在非淹水期不同降雨处理的土壤呼吸与土壤温度均指数相关(P0.05),土壤呼吸温度敏感性(Q_(10))随降雨量增加而增大。在淹水期不同降雨处理土壤呼吸与土壤温度无显著相关关系。(5)淹水期土壤呼吸速率与地表水位呈指数负相关(P0.001)。     

辽西樟子松人工林净生态系统碳交换

樟子松是三北地区造林的主要树种之一,研究樟子松人工林净生态系统碳交换(NEE)及其影响要素对理解我国人工林碳平衡有重要意义。本研究以辽西樟子松人工林为对象,采用涡度相关系统及其配套设备于2020年对樟子松人工林NEE和环境要素进行了原位连续观测。结果表明: 在0.5 h尺度上,1—12月夜间为碳源,白天为碳汇,且受干旱影响5—8月下午碳吸收受到明显抑制。在日尺度上,受干旱影响,控制夜间NEE季节动态的主要要素为土壤温度和土壤湿度,控制白天NEE季节动态的主要要素为土壤湿度和饱和水汽压差;土壤干旱时降水可促进夜间和白天NEE,并导致光合呼吸参数升高。在月尺度上,白天NEE与表观量子利用效率和最大光合速率均呈显著负相关,当空气温度小于5 ℃时,10 ℃生态系统呼吸和生态系统呼吸温度敏感性随空气温度降低而呈线性增加。2020年辽西樟子松人工林NEE积累量为-145.17 g C·m^-2,表现为弱碳汇。     

降雨对草地土壤呼吸季节变异性的影响

利用土壤碳通量自动观测系统(LI-8150)对呼伦贝尔草原在自然降雨条件下的土壤呼吸作用进行了野外定位连续观测,研究结果表明:降雨对土壤呼吸作用存在激发效应和抑制效应,降雨发生后1-2 h内土壤呼吸速率可增加约1倍,当单次或者连续降雨累积量大于7-8 mm,或土壤含水量大于29%-30%时,降雨对土壤呼吸会产生明显的抑制作用。土壤呼吸的激发效应往往体现在次日,表现为次日平均土壤呼吸速率的显著升高;而抑制效应则在当日即可体现出来,表现为观测当日平均土壤呼吸速率的明显下降。土壤呼吸季节变异性与降雨频率和降雨强度密切相关,在降雨量一定的情况下,较低的降雨频率和较高的降雨强度会增加土壤呼吸的变异性。呼伦贝尔草甸草原而言,在生长季土壤平均含水量为16.5%时,土壤呼吸的温度敏感性值(Q₁₀)为2.12;而平均土壤含水量为26%时,Q₁₀值为2.82,明显高于前者,土壤含水量与Q₁₀之间存在正相关关系。降雨导致土壤呼吸的激发效应和抑制效应交替发生,使草地土壤呼吸的季节变异性增加,降雨格局变化必然会对草地碳循环和碳通量特征产生深刻影响。     

Temperature Sensitivity of Microbial Respiration of Fine Root Litter in a Temperate Broad-Leaved Forest

The microbial decomposition respiration of plant litter generates a major CO₂ efflux from terrestrial ecosystems that plays a critical role in the regulation of carbon cycling on regional and global scales. However, the respiration from root litter decomposition and its sensitivity to temperature changes are unclear in current models of carbon turnover in forest soils. Thus, we examined seasonal changes in the temperature sensitivity and decomposition rates of fine root litter of two diameter classes (0–0.5 and 0.5–2.0 mm) of Quercus serrata and Ilex pedunculosa in a deciduous broad-leaved forest. During the study period, fine root litter of both diameter classes and species decreased approximately exponentially over time. The Q₁₀ values of microbial respiration rates of root litter for the two classes were 1.59–3.31 and 1.28–6.27 for Q. serrata and 1.36–6.31 and 1.65–5.86 for I. pedunculosa. A significant difference in Q₁₀ was observed between the diameter classes, indicating that root diameter represents the initial substrate quality, which may determine the magnitude of Q₁₀ value of microbial respiration. Changes in these Q₁₀ values were related to seasonal soil temperature patterns; the values were higher in winter than in summer. Moreover, seasonal variations in Q₁₀ were larger during the 2-year decomposition period than the 1-year period. These results showed that the Q₁₀ values of fine root litter of 0–0.5 and 0.5–2.0 mm have been shown to increase with lower temperatures and with the higher recalcitrance pool of the decomposed substrate during 2 years of decomposition. Thus, the temperature sensitivity of microbial respiration in root litter showed distinct patterns according to the decay period and season because of the temperature acclimation and adaptation of the microbial decomposer communities in root litter.     

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.     

降雨量改变对常绿阔叶林干旱和湿润季节土壤呼吸的影响

通过野外原位试验,研究降雨量改变对华西雨屏区常绿阔叶林干旱和湿润季节土壤呼吸速率的影响。采用LI-8100土壤碳通量分析系统(LI-COR Inc.,USA)测定干旱和湿润季节对照(CK)、增雨10%(LA)、增雨5%(TA)、减雨10%(LR)、减雨20%(MR)、减雨50%(HR)6个处理水平的土壤呼吸速率,并通过回归方程分析温度和湿度与土壤呼吸速率间的关系。结果表明:湿润季节土壤呼吸速率高于干旱季节,HR处理对干旱季节土壤呼吸速率影响较大,而LA处理对湿润季节土壤呼吸速率的影响较大。TA和LR处理使土壤呼吸的温度敏感性增加,而HR、LA和MR处理使土壤呼吸的温度敏感性降低,干旱季节Q10值高于湿润季节。各处理湿润季节土壤微生物量碳氮含量显著高于干旱季节,HR、MR和LA处理减少土壤微生物生物量碳、氮的含量,而TA和LR处理增加土壤微生物生物量碳、氮的含量。与湿润季节相比,干旱季节土壤水分对土壤呼吸速率的影响较大;而与土壤温度相比,土壤水分对土壤呼吸速率的影响较小。在降雨量改变的背景下,华西雨屏区常绿阔叶林无论是干旱还是湿润季节,适当增雨和减雨都会促进土壤呼吸速率,而较高量的增雨和减雨会抑制土壤呼吸速率。     

Annual variation in soil respiration and its components in a coppice oak forest in Central Italy

In order to investigate the annual variation of soil respiration and its components in relation to seasonal changes in soil temperature and soil moisture in a Mediterranean mixed oak forest ecosystem, we set up a series of experimental treatments in May 1999 where litter (no litter), roots (no roots, by trenching) or both were excluded from plots of 4 m². Subsequently, we measured soil respiration, soil temperature and soil moisture in each plot over a year after the forest was coppiced. The treatments did not significantly affect soil temperature or soil moisture measured over 0–10 cm depth. Soil respiration varied markedly during the year with high rates in spring and autumn and low rates in summer, coinciding with summer drought, and in winter, with the lowest temperatures. Very high respiration rates, however, were observed during the summer immediately after rainfall events. The mean annual rate of soil respiration was 2.9 µ mol m^?2 s^?1, ranging from 1.35 to 7.03 µmol m^?2 s^?1. Soil respiration was highly correlated with temperature during winter and during spring and autumn whenever volumetric soil water content was above 20%. Below this threshold value, there was no correlation between soil respiration and soil temperature, but soil moisture was a good predictor of soil respiration. A simple empirical model that predicted soil respiration during the year, using both soil temperature and soil moisture accounted for more than 91% of the observed annual variation in soil respiration. All the components of soil respiration followed a similar seasonal trend and were affected by summer drought. The Q₁₀ value for soil respiration was 2.32, which is in agreement with other studies in forest ecosystems. However, we found a Q₁₀ value for root respiration of 2.20, which is lower than recent values reported for forest sites. The fact that the seasonal variation in root growth with temperature in Mediterranean ecosystems differs from that in temperate regions may explain this difference. In temperate regions, increases in size of root populations during the growing season, coinciding with high temperatures, may yield higher apparent Q₁₀ values than in Mediterranean regions where root growth is suppressed by summer drought. The decomposition of organic matter and belowground litter were the major components of soil respiration, accounting for almost 55% of the total soil respiration flux. This proportion is higher than has been reported for mature boreal and temperate forest and is probably the result of a short‐term C loss following recent logging at the site. The relationship proposed for soil respiration with soil temperature and soil moisture is useful for understanding and predicting potential changes in Mediterranean forest ecosystems in response to forest management and climate change.     

Responses of switchgrass soil respiration and its components to precipitation gradient in a mesocosm study

Aims

The objective of this study was to investigate the effects of the precipitation changes on soil, microbial and root respirations of switchgrass soils, and the relationships between soil respiration and plant growth, soil moisture and temperature.

Methods

A mesocosm experiment was conducted with five precipitation treatments over two years in a greenhouse in Nashville, Tennessee. The treatments included ambient precipitation, ?50%, ?33%, +33% and +50% of ambient precipitation. Soil, microbial, and root respirations were quantified during the growing seasons.

Results

Mean soil and root respirations in the +50% treatment were the highest (2.48 and 0.93 μmol CO₂ m^?2 s^?1, respectively) among all treatments. Soil microbial respiration contributed more to soil respiration, and had higher precipitation sensitivity mostly than root respiration. Increases in precipitation mostly enhanced microbial respiration while decreases in precipitation reduced both microbial and root respirations. Across precipitation treatments, soil respiration was significantly influenced by soil moisture, soil temperature, and aboveground biomass.

Conclusions

Our results showed that microbial respiration was more sensitive to precipitation changes, and precipitation regulated the response of soil respiration to soil temperature. The information generated in this study will be useful for model simulation of soil respiration in switchgrass fields under precipitation changes.

     

施肥方式对紫色土土壤异养呼吸的影响

采用静态暗箱-气相色谱法于2010年12月至2011年10月对不同施肥方式下的紫色土土壤呼吸进行了研究,以揭示施肥方式对紫色土异养呼吸的影响。结果表明:施肥可对土壤异养呼吸产生激发效应。施肥后第5天出现峰值,猪厩肥处理的异养呼吸峰值为2356.8 mg CO2m-2h-1,显著高于秸秆配施氮磷钾(970.1 mgCO2m-2h-1)和常规氮磷钾处理(406.8 mgCO2m-2h-1)(P0.01);小麦季常规氮磷钾、猪厩肥和秸秆配施氮磷钾处理的平均土壤异养呼吸速率为212.9、285.8和305.8mgCO2m-2h-1,CO2排放量为255.1、342.3和369.5 gC/m2,玉米季为408.2、642.8和446.4 mgCO2m-2h-1,CO2排放量为344.7、542.8和376.9 gC/m2,玉米季土壤异养呼吸平均速率及CO2排放量均高于小麦季。全年平均土壤异养呼吸速率分别为310.6、446.3和377.4 mg CO2m-2h-1,CO2排放总量分别为599.8、885.1和746.4 gC/m2。猪厩肥对土壤异养呼吸速率和CO2排放量的影响最大,秸秆配施氮磷钾肥次之,氮磷钾肥最小,说明有机物料的投入是紫色土土壤异养呼吸速率的主要调控措施,低碳氮比的有机物料能促进土壤异养呼吸和CO2的排放。猪厩肥和秸秆配施氮磷钾肥处理相应地表和地下5 cm温度的Q10值分别为2.64、1.88和2.77、1.99,表明低碳氮比的有机物料还能增加土壤异养呼吸Q10值,使土壤异养呼吸速率对温度的敏感性加强。     

Soil water content and temperature as independent or confounded factors controlling soil respiration in a temperate mixed hardwood forest

Variation in soil temperature can account for most of the seasonal and diel variation in soil CO₂ efflux, but the temperature effect is not always consistent, and other factors such as soil water content are known to influence soil respiration. The objectives of this research were to study the spatial and temporal variation in soil respiration in a temperate forested landscape and to evaluate temperature and soil water functions as predictors of soil respiration. Soil CO₂ fluxes were measured with chambers throughout an annual cycle in six study areas at the Harvard Forest in central Massachusetts that include soil drainage classes from well drained to very poorly drained. The mean annual estimate of soil CO₂ efflux was 7.2 Mg ha^–1, but ranged from 5.3 in the swamp site to 8.5 in a well-drained site, indicating that landscape heterogeneity is related to soil drainage class. An exponential function relating CO₂ fluxes to soil temperature accounted for 80% of the seasonal variation in fluxes across all sites (Q₁₀ = 3.9), but the Q₁₀ ranged from 3.4 to 5.6 for the individual study sites. A significant drought in 1995 caused rapid declines in soil respiration rates in August and September in five of the six sites (a swamp site was the exception). This decline in CO₂ fluxes correlated exponentially with decreasing soil matric potential, indicating a mechanistic effect of drought stress. At moderate to high water contents, however, soil water content was negatively correlated with soil temperature, which precluded distinguishing between the effects of these two confounded factors on CO₂ flux. Occurrence of high Q₁₀ values and variation in Q₁₀ values among sites may be related to: (i) confounding effects of high soil water content; (ii) seasonal and diel patterns in root respiration and turnover of fine roots that are linked to above ground phenology and metabolism; and (iii) variation in the depth where CO₂ is produced. The Q₁₀ function can yield reasonably good predictions of annual fluxes of CO₂, but it is a simplification that masks responses of root and microbial processes to variation in temperature and water content throughout the soil.     

模拟氮沉降和降雨对华西雨屏区常绿阔叶林土壤呼吸的影响

从2013年12月至2014年11月,通过野外原位试验,对华西雨屏区常绿阔叶林进行了模拟氮沉降和降雨试验,采用LI-8100土壤碳通量分析系统(LI-COR Inc.,USA)测定了对照(CK)、氮沉降(N)、减雨(R)、增雨(W)、氮沉降+减雨(NR)、氮沉降+增雨(NW)6个处理水平的土壤呼吸速率,并通过回归方程分析了温度和湿度与土壤呼吸速率间的关系。结果表明:(1)氮沉降和增雨抑制了常绿阔叶林土壤呼吸速率,减雨促进了常绿阔叶林土壤呼吸速率。(2)减雨使华西雨屏区常绿阔叶林土壤呼吸年通量增加了258 g/m~2,而模拟氮沉降和增雨使华西雨屏区常绿阔叶林土壤呼吸年通量分别减少了321g/m~2和406g/m~2。(3)减雨增加了土壤呼吸的温度敏感性,模拟氮沉降和增雨降低了土壤呼吸的温度敏感性。(4)模拟温度和湿度与土壤呼吸速率间回归方程分析表明,土壤水分对土壤呼吸速率的影响较小。(5)模拟氮沉降和增雨处理减少土壤微生物生物量碳、氮的含量,减雨处理增加了土壤微生物生物量碳、氮的含量。(6)模拟氮沉降和降雨对华西雨屏区土壤CO_2释放的影响未表现出明显的交互作用。