中国森林生态系统土壤CO2释放分布规律及其影响因素

联合国气候框架公约的签署提升了人们对全球变暖、碳循环变化的关注。陆地生态系统在全球变暖格局下的地位与作用,尤其是土壤碳库对全球变暖格局的响应是全球变化研究的焦点。土壤CO₂释放作为土壤-大气CO₂交换的主要途径之一,也就成为各国生态学家研究的重点内容。在对我国森林生态系统CO₂释放通量以及相关气候、生物等因子的资料进行收集、整理和分析的基础上,探讨了我国森林生态系统土壤CO₂释放的分布规律,以及这种规律性分布的气候、生物影响因素。对于我国这样一个南北跨度大的国家,不同区域的森林生态系统土壤CO₂释放通量间存在较大的差异,在全国尺度上,森林生态系统土壤CO₂释放通量平均值为(1.79 ± 0.86) g C m^-2 d^-1,而且土壤CO₂释放通量随着纬度增加逐渐降低。作为一个复杂的生态过程,土壤CO2释放受到生物、非生物因子或独立、或综合的影响。通过分析指出,在全国尺度上,年均温、降雨量、群落净生产力及凋落物量显著地影响森林土壤CO₂释放通量。同时,也正是这些影响因子的纬度分布,导致了我国森林生态系统土壤CO₂释放通量的纬度分布规律。作为衡量土壤CO₂释放对温度敏感性的重要指标,计算了我国森林生态系统土壤CO2释放温度敏感性系数-Q₁₀值,约为1.5,该值显著低于全球平均水平,2.0。     

森林生态系统土壤CO2释放随海拔梯度的变化及其影响因子

联合国气候框架公约的签署提升了人们对全球变暖、碳循环的关注。土壤CO2释放作为土壤-大气CO2交换的主要途径之一,成为了各国生态学家研究的重点内容。通过对1800～2155m海拔梯度上森林生态系统土壤CO2释放进行研究,揭示了较小空间尺度上土壤CO2释放的变化规律及其控制机制。在研究区域内,随着海拔梯度的增加,森林土壤CO2释放由(1.94±0.06)μmolm-2s-1逐渐增加至(2.22±0.07)μmolm-2s-1。土壤温度、土壤水分、土壤有机碳(SOC)、全N、全P与土壤CO2释放呈显著正相关(n=14,P<0.05);土壤容重与土壤CO2释放速率呈显著负相关(n=14,P<0.05);土壤pH对土壤CO2释放影响不显著。作为一个复杂的生态学过程,环境因子及其交互作用对土壤CO2释放产生影响,为了减少因子共线性影响,逐步降低因子维数,采用主成分分析(PCA)揭示了土壤温度、土壤水分、SOC、全N、全P、容重6个因子的联合作用,其累积贡献率达到了57%以上;进一步运用逐步回归分析方法,探讨了影响土壤CO2释放沿海拔梯度分布的主导因子,结果表明土壤水分是研究区域森林生态系统土壤CO2释放沿海拔梯度变化的主导因子。     

森林生态系统土壤CO2释放随海拔梯度的变化及其影响因子

联合国气候框架公约的签署提升了人们对全球变暖、碳循环的关注。土壤CO₂释放作为土壤-大气CO₂交换的主要途径之一,成为了各国生态学家研究的重点内容。通过对1800~2155m海拔梯度上森林生态系统土壤CO₂释放进行研究,揭示了较小空间尺度上土壤CO₂释放的变化规律及其控制机制。在研究区域内,随着海拔梯度的增加,森林土壤CO₂释放由(1.94±006) μmol m^-2 s^-1逐渐增加至(2.22±0.07) μ mol m^-2 s^-1。土壤温度、土壤水分、土壤有机碳（SOC）、全N、全P与土壤CO₂释放呈显著正相关（n=14, P<0.05）;土壤容重与土壤CO₂释放速率呈显著负相关（n=14,P<0.05）;土壤pH对土壤CO₂释放影响不显著。作为一个复杂的生态学过程,环境因子及其交互作用对土壤CO₂释放产生影响,为了减少因子共线性影响,逐步降低因子维数,采用主成分分析（PCA）揭示了土壤温度、土壤水分、SOC、全N、全P、容重6个因子的联合作用,其累积贡献率达到了57％以上;进一步运用逐步回归分析方法,探讨了影响土壤CO₂释放沿海拔梯度分布的主导因子,结果表明土壤水分是研究区域森林生态系统土壤CO₂释放沿海拔梯度变化的主导因子。     

黄土丘陵沟壑区典型人工林土壤CO2释放规律及其影响因子

为了解黄土丘陵沟壑区人工林土壤有机碳排放特征,于2007年8月、2007年10月和2008年5月对黄土丘陵沟壑区杏树、沙棘和刺槐3种人工林下土壤CO2释放速率及相关环境因子进行研究,探讨了半干旱地区侵蚀环境下不同植被土壤CO2释放速率的变化规律及影响因子.杏树、沙棘和刺槐3种人工林土壤CO2释放存在差异,日平均释放速率分别为0.83～2 61μmol·m-2·s-1、0.83～3.32μmol·m-2·s-1和0.80～3.45μmol·m-2·s-1,刺槐和沙棘人工林土壤CO2释放速率高于杏树林,3种人工林的土壤CO2释放速率日变化及季节性变化表现一致,春季和夏季的土壤CO2释放高于秋季.相关分析表明,土壤温度是影响土壤CO2释放的主要因子,但在干旱的春季和夏季,土壤水分是土壤CO2释放的主要限制因子,同时,土壤理化性质和微生物生物量也对土壤CO2释放有显著影响.     

森林生态系统细根周转规律及影响因素

根系周转是陆地生态系统碳循环的关键过程, 对研究土壤碳库变化及全球气候变化均具有重要意义。然而由于根系周转率的测量计算方法较多, 不同方法得出的结果差异较大, 且目前对全球区域尺度上森林生态系统根系周转的研究还不够充分, 使得全球森林生态系统根系周转变化规律仍不清楚。该研究通过收集文献数据并统一周转率计算方法, 对全球5种森林类型的细根周转空间格局进行整合, 同时结合土壤理化性质和气候数据, 得出影响森林生态系统细根周转的因子。结果表明, 不同森林类型细根周转率存在显著差异, 且随着纬度的升高逐渐降低; 森林生态系统细根周转率与年平均温度和年平均降水量呈正相关; 森林生态系统细根周转率与土壤有机碳含量呈正相关但与土壤pH值呈负相关。该研究为揭示森林生态系统细根周转规律及机制提供了科学依据。     

中国森林凋落量时空分布特征

通过构建全国尺度上森林叶凋落量和总凋落量与年平均温度、年平均降雨量和实际蒸散量的关系模型,应用地统计学分析方法,并结合遥感解译的森林覆盖信息,分析2001、2006和2012年中国森林叶凋落量和总凋落量的空间分布及其变异格局.结果表明: 与年平均温度和降雨量相比,区域尺度上实际蒸散量对森林叶凋落量和总凋落量有更好的解释预测关系;分布于中南地区的常绿阔叶林的年凋落量最高,为636.2 g·m^-2,分布于东北地区的温带落叶阔叶林的年凋落量范围为339～385 g·m^-2,其中,森林叶凋落量约占总凋落量的70％.2001、2006和2012年,全国森林凋落总量分别为801、865和1032 Tg,呈明显增长趋势,而基于遥感图像解译的森林年覆盖率分别为18％、20％和24％,呈增长趋势.我国人工林面积的迅速增加和林分生长,极大影响了森林凋落物量及其动态变化,进而对森林生态系统物质循环产生重要影响.     

森林生态系统凋落物多样性对分解过程和土壤微生物特性影响研究进展

凋落物的分解过程是森林生态系统养分循环的关键环节, 也是林分内植被层可利用养分的重要来源。一般来说, 在自然生态系统中, 地上植被的种类越丰富, 其凋落物的多样性也越高, 多样化的凋落物在混合分解过程中存在的相互作用关系也更为复杂, 对其自身的分解过程、分解生境以及分解者群体也会产生重要影响。文章以凋落物的多样性为着眼点, 综述了凋落物的多样性对其分解过程以及对分解过程中最重要的分解者-土壤微生物特性所产生的影响, 重点阐述了凋落物多样性对分解过程中土壤微生物的生物量、群落结构、多样性以及分解活性的影响, 并对其可能的原因和潜在的机理进行了分析。综述结果表明, 较高的凋落物多样性总体上能够加速凋落物的分解, 提高分解过程中土壤微生物的生物量、多样性及分解活性。在此基础上, 对今后凋落物多样性在分解过程中的效应研究进行了展望, 为人工林可持续经营的混交林营造以及林下植被的科学管理提供理论依据。     

凋落物去除和添加处理对典型草原生态系统碳通量的影响

为揭示凋落物去除和添加处理对草原生态系统碳通量的影响, 2013和2014年连续两年在成熟群落围封样地进行凋落物去除实验、在退化群落放牧样地进行凋落物添加实验, 并运用静态箱法探讨碳通量变化规律并分析其主要影响因子。结果表明: 两种群落的净生态系统CO₂交换(NEE)有明显的季节性变化。对成熟群落而言, 去除50%凋落物显著增加了NEE, 去除100%凋落物显著降低了NEE, 而对生态系统总初级生产力(GEP)和生态系统呼吸(ER)均无显著影响; 对退化群落而言, 凋落物添加显著增加了GEP和NEE, 而对ER无显著影响。两种群落的GEP与10 cm土壤温度显著正相关, 但NEE和GEP的变化规律与土壤温度相反, 与10 cm土壤湿度相同。由此可见, 凋落物去除和添加处理对生态系统碳通量的影响主要是改变土壤湿度和地上生物量,而不是改变土壤温度。该研究为合理利用凋落物改善草地生态系统管理和促进草地恢复提供了理论依据。     

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。     

Soil CO2 efflux in a boreal pine forest under atmospheric CO2 enrichment and air warming

The response of forest soil CO₂ efflux to the elevation of two climatic factors, the atmospheric concentration of CO₂ (↑CO₂ of 700 μmol mol⁻¹) and air temperature (↑ T with average annual increase of 5°C), and their combination (↑CO₂+↑ T ) was investigated in a 4-year, full-factorial field experiment consisting of closed chambers built around 20-year-old Scots pines ( Pinus sylvestris L.) in the boreal zone of Finland. Mean soil CO₂ efflux in May–October increased with elevated CO₂ by 23–37%, with elevated temperature by 27–43%, and with the combined treatment by 35–59%. Temperature elevation was a significant factor in the combined 4-year efflux data, whereas the effect of elevated CO₂ was not as evident. Elevated temperature had the most pronounced impact early and late in the season, while the influence of elevated CO₂ alone was especially notable late in the season. Needle area was found to be a significant predictor of soil CO₂ efflux, particularly in August, a month of high root growth, thus supporting the assumption of a close link between whole-tree physiology and soil CO₂ emissions. The decrease in the temperature sensitivity of soil CO₂ efflux observed in the elevated temperature treatments in the second year nevertheless suggests the existence of soil response mechanisms that may be independent of the assimilating component of the forest ecosystem. In conclusion, elevated atmospheric CO₂ and air temperature consistently increased forest soil CO₂ efflux over the 4-year period, their combined effect being additive, with no apparent interaction.     

影响阔叶红松林土壤CO2排放的主要因素

采用静态封闭箱式技术对长白山阔叶红松林土壤CO2 的排放通量进行 1年的观测 ,并通过多元回归分析了土壤CO2 排放速率与 5个环境因子间的关系。结果表明 ,阔叶红松林土壤CO2 排放与表层无凋落物的土壤CO2 排放速率在测定年度内具有相同的季节变化趋势。在不同的月份中 ,以 7月份最高 ,2月份最低 ;在夏季 18∶0 0为土壤日CO2 排放的最高峰 ;土壤CO2 排放速率与 5个环境因子进行多元回归的结果显示 :林地土壤CO2 排放速率与地表温度和地下 2 0cm土壤湿度呈显著正相关。根据气象资料推算 ,阔叶红松林的年凋落物和土壤CO2排放通量分别为 2 80 4 gCO2 ·m-2 ·a-1和 3911gCO2 ·m-2 ·a-1。阔叶红松林凋落物排放CO2年通量占土壤林地CO2 排放总量的 2 8%。     

Global patterns and predictors of stem CO2 efflux in forest ecosystems

Stem CO₂ efflux (E_S) plays an important role in the carbon balance of forest ecosystems. However, its primary controls at the global scale are poorly understood and observation‐based global estimates are lacking. We synthesized data from 121 published studies across global forest ecosystems and examined the relationships between annual E_S and biotic and abiotic factors at individual, biome, and global scales, and developed a global gridded estimate of annual E_S. We tested the following hypotheses: (1) Leaf area index (LAI) will be highly correlated with annual E_S at biome and global scales; (2) there will be parallel patterns in stem and root CO₂ effluxes (R_A) in all forests; (3) annual E_S will decline with forest age; and (4) LAI coupled with mean annual temperature (MAT) and mean annual precipitation (MAP) will be sufficient to predict annual E_S across forests in different regions. Positive linear relationships were found between E_S and LAI, as well as gross primary production (GPP), net primary production (NPP), wood NPP, soil CO₂ efflux (R_S), and R_A. Annual E_S was correlated with R_A in temperate forests after controlling for GPP and MAT, suggesting other additional factors contributed to the relationship. Annual E_S tended to decrease with stand age. Leaf area index, MAT and MAP, predicted 74% of variation in E_S at global scales. Our statistical model estimated a global annual E_S of 6.7 ± 1.1 Pg C yr⁻¹ over the period of 2000–2012 with little interannual variability. Modeled mean annual E_S was 71 ± 43, 270 ± 103, and 420 ± 134 g C m² yr⁻¹ for boreal, temperate, and tropical forests, respectively. We recommend that future studies report E_S at a standardized constant temperature, incorporate more manipulative treatments, such as fertilization and drought, and whenever possible, simultaneously measure both aboveground and belowground CO₂ fluxes.     

Elevated CO2 and temperature impacts on different components of soil CO2 efflux in Douglas-fir terracosms

Although numerous studies indicate that increasing atmospheric CO₂ or temperature stimulate soil CO₂ efflux, few data are available on the responses of three major components of soil respiration [i.e. rhizosphere respiration (root and root exudates), litter decomposition, and oxidation of soil organic matter] to different CO₂ and temperature conditions. In this study, we applied a dual stable isotope approach to investigate the impact of elevated CO₂ and elevated temperature on these components of soil CO₂ efflux in Douglas-fir terracosms. We measured both soil CO₂ efflux rates and the ¹³C and ¹⁸O isotopic compositions of soil CO₂ efflux in 12 sun-lit and environmentally controlled terracosms with 4-year-old Douglas fir seedlings and reconstructed forest soils under two CO₂ concentrations (ambient and 200 ppmv above ambient) and two air temperature regimes (ambient and 4 °C above ambient). The stable isotope data were used to estimate the relative contributions of different components to the overall soil CO₂ efflux. In most cases, litter decomposition was the dominant component of soil CO₂ efflux in this system, followed by rhizosphere respiration and soil organic matter oxidation. Both elevated atmospheric CO₂ concentration and elevated temperature stimulated rhizosphere respiration and litter decomposition. The oxidation of soil organic matter was stimulated only by increasing temperature. Release of newly fixed carbon as root respiration was the most responsive to elevated CO₂, while soil organic matter decomposition was most responsive to increasing temperature. Although some assumptions associated with this new method need to be further validated, application of this dual-isotope approach can provide new insights into the responses of soil carbon dynamics in forest ecosystems to future climate changes.     

Soil CO2 efflux and its spatial variation in a Florida slash pine plantation

The efflux of CO2 from the soil surface can vary markedly in magnitude both in time and space and its correct determination is crucial in many ecological studies. In this paper, we report results of field measurements, using an open-top dynamic chamber, of soil CO2 efflux in a mature Florida slash pine (Pinus elliottii Engelm. var.elliottii) plantation. The daily average efflux was 0.217 mg CO2 m-2s-1 in the autumn and 0.087 mg CO2 m-2s-1 in the winter. Soil temperature, which accounts for most of the temporal variability in CO2 efflux, is by far the most influential factor controlling soil respiration rate and its temporal variation. The CO2 efflux in the slash pine plantation is highly spatially variable and effluxes from the soil under palmetto is significantly higher than that from the open floor. The CO2 efflux generally increases with increase in soil fine root biomass, litter and humus amount on the forest floor but is inversely related to the amount of organic matter in the mineral soil. The spatial variation in CO2 efflux can be well characterised by a simple multiple regression model incorporating live and dead biomass and soil total porosity as predictor variables. Understorey plants, mostly Serenoa repens, are an important component of the C cycle and the major contributor to the spatial heterogeneity of soil CO2 efflux. The influence of understorey plants on soil respiration is probably via two approaches: increasing litterfall and root metabolism, both consequently stimulating microbial activity in the mineral soil.     

Separating the effects of moisture and temperature on soil CO2 efflux in a coniferous forest in the Sierra Nevada mountains

Separating the effects of soil temperature and moisture on soil CO₂ efflux is critical to modeling and understanding the belowground carbon dynamics of forest ecosystems. We developed two analytical procedures to separate the effects of soil temperature and moisture, based on continuous measurements of the CO₂ efflux, temperature and moisture of the soil at a ponderosa pine plantation in the Sierra Nevada Mountains in California, from May 1998 to August 1999. We found that the combined effects of temperature and moisture on the seasonal variation of soil CO₂ efflux could be effectively separated and represented with the product of a temperature term and a moisture term. The relationship between soil CO₂ efflux and temperature could be well described using a power function. This relationship was modified by soil moisture which affects only the coefficient, but not the exponent, of the power function. We also found that when soil moisture was held constant, the temperature effect explained 82% of the temporal variation in CO₂ efflux of the soil. Similarly, when temperature was held constant, the moisture effects explained 84% of the variation. Temperature and moisture together explained 89% of the total temporal variations in soil CO₂ efflux. A multiplicative formulation with power functions representing both temperature and moisture dependences was recommended for modeling soil CO₂ efflux. This formulation can be used to model the seasonal trend of soil CO₂ efflux of the forest based on temperature and moisture, two key variables influenced by climate change and management practices.     

Soil CO2 efflux in a beech forest: comparison of two closed dynamic systems

The aim of this study was to understand why two closed dynamic systems with a very similar design gave large differences in soil CO₂ efflux measurements (PP systems and LI-COR). Both in the field (forest beech stand) and in the laboratory, the PPsystems gave higher estimations of soil CO₂ efflux than the LI-COR system (ranging from 30% to 50%). The difference in wind speed occurring within the soil respiration chambers (0.9 m s⁻¹ within the SRC-1 and 0.4 m s⁻¹ within the LI-6000-09 chambers) may account for the discrepancy between the two systems. An excessive air movement inside the respiration chamber is thought to disrupt the high laminar boundary layer over the forest floor. This would promote an exhaust of the CO₂ accumulated into the upper soil layers into the chamber and a lateral diffusion of CO₂ in the soil towards the respiration chamber. The discrepancy between the two systems was reduced (i) by decreasing fan speed within the SRC-1, (ii) by increasing wind speed over the soil surface outside the respiration chamber, or (iii) by using an artificial soil design without high CO₂ concentration in soil pores. We show that wind speed is an important component of soil CO₂ diffusion which must be taken into account when measuring soil CO₂ efflux, even on very fine textured soil like silt-loam soil. Proper measurement can be achieved by maintaining wind speed inside the chamber below 0.4 m s⁻¹ since low wind speed conditions predominate under forest canopies. However, more accurate measurements will be obtained by regulating wind speeds within the chamber at a velocity representative of the wind speed recorded simultaneously at the floor surface. This revised version was published online in June 2006 with corrections to the Cover Date.