Time-dependent responses of soil CO2 efflux components to elevated atmospheric [CO2] and temperature in experimental forest mesocosms

We previously used dual stable isotope techniques to partition soil CO₂ efflux into three source components (rhizosphere respiration, litter decomposition, and soil organic matter (SOM) oxidation) using experimental chambers planted with Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings. The components responded differently to elevated CO₂ (ambient + 200 mol mol^–1) and elevated temperature (ambient + 4 °C) treatments during the first year. Rhizosphere respiration increased most under elevated CO₂, and SOM oxidation increased most under elevated temperature. However, many studies show that plants and soil processes can respond to altered climates in a transient way. Herein, we extend our analysis to 2 years to evaluate the stability of the responses of the source components. Total soil CO₂ efflux increased significantly under elevated CO₂ and elevated temperature in both years (1994 and 1995), but the enhancement was much less in 1995. Rhizosphere respiration increased less under elevated temperature in 1995 compared with 1994. Litter decomposition also tended to increase comparatively less in 1995 under elevated CO₂, but was unresponsive to elevated temperature between years. In contrast, SOM oxidation was similar under elevated CO₂ in the 2 years. Less SOM oxidation occurred under elevated temperature in 1995 compared with 1994. Our results indicate that temporal variations can occur in CO₂ production by the sources. The variations likely involve responses to antecedent physical disruption of the soil and physiological processes.     

Elevated CO(2) and elevated temperature have no effect on Douglas-fir fine-root dynamics in nitrogen-poor soil

Here, we investigate fine-root production, mortality and standing crop of Douglas-fir (Pseudotsuga menziesii) seedlings exposed to elevated atmospheric CO(2) and elevated air temperature. We hypothesized that these treatments would increase fine-root production, but that mortality would be greater under elevated temperature, leading to a smaller increase in standing crop. Seedlings were grown in outdoor, sun-lit controlled-environment chambers containing native soil. They were exposed in a factorial design to two levels of atmospheric CO(2) and two levels of air temperature. Minirhizotron methods were used to measure fine-root length production, mortality and standing crop every 4 wk for 36 months. Neither elevated atmospheric CO(2) nor elevated air temperature affected fine-root production, mortality, or standing crop. Fine roots appeared to root deeper in the soil profile under elevated CO(2) and elevated temperature. Low soil nitrogen (N) levels apparently limited root responses to the treatments. This suggests that forests on nutrient-poor soils may exhibit limited fine-root responses to elevated atmospheric CO(2) and elevated air temperature.     

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.     

Responses of dryland soil respiration and soil carbon pool size to abrupt vs. gradual and individual vs. combined changes in soil temperature, precipitation, and atmospheric [CO2]: a simulation analysis

With the large extent and great amount of soil carbon (C) storage, drylands play an important role in terrestrial C balance and feedbacks to climate change. Yet, how dryland soils respond to gradual and concomitant changes in multiple global change drivers [e.g., temperature (T_s), precipitation (Ppt), and atmospheric [CO₂] (CO₂)] has rarely been studied. We used a process‐based ecosystem model patch arid land simulator to simulate dryland soil respiration (R_s) and C pool size (C_s) changes to abrupt vs. gradual and single vs. combined alterations in T_s, Ppt and CO₂ at multiple treatment levels. Results showed that abrupt perturbations generally resulted in larger R_s and had longer differentiated impacts than did gradual perturbations. R_s was stimulated by increases in T_s, Ppt, and CO₂ in a nonlinear fashion (e.g., parabolically or asymptotically) but suppressed by Ppt reduction. Warming mainly stimulated heterotrophic R_s (i.e., R_h) whereas Ppt and CO₂ influenced autotrophic R_s (i.e., R_a). The combined effects of warming, Ppt, and CO₂ were nonadditive of primary single‐factor effects as a result of substantial interactions among these factors. Warming amplified the effects of both Ppt addition and CO₂ elevation whereas Ppt addition and CO₂ elevation counteracted with each other. Precipitation reduction either magnified or suppressed warming and CO₂ effects, depending on the magnitude of factor's alteration and the components of R_s (R_a or R_h) being examined. Overall, Ppt had dominant influence on dryland R_s and C_s over T_s and CO₂. Increasing Ppt individually or in combination with T_s and CO₂ benefited soil C sequestration. We therefore suggested that global change experimental studies for dryland ecosystems should focus more on the effects of precipitation regime changes and the combined effects of Ppt with other global change factors (e.g., T_s, CO₂, and N deposition).     

生物群区和林龄对森林土壤呼吸及其组分的影响

森林土壤呼吸(RS)一般分为自养呼吸(RA)和异养呼吸(RH)两个组分,各组分对环境变化具有不同的响应,对土壤和生态系统的碳平衡产生重要影响.对全球不同生物群区、林龄的森林RS及其组分RH的研究文献进行检索与分析,结果表明:林地RS沿北方森林-温带针叶林-温带落叶林-热带林次序逐步升高,非相邻区系之间差异显著(α<0.05).土壤异养呼吸组分(RH)及其贡献率(RH/RS),仅北方森林与热带林之间有显著性差异,其余区系之间无显著性差异(α>0.05).异养呼吸组分贡献率(RH/RS),随着RS的不断增加,呈现出RH/RS率降低的总体趋势.对于林地RS,幼龄林显著高于中龄林和成熟林.RH/RS率随树龄增加而略微升高,但龄组之间没有显著性差异(α>0.05).各生物群区及林龄的RH与RS之间显著性相关分析,为全球森林碳收支的估测提供有效的方法和数据基础.     

Elevated CO2, rhizosphere processes,and soil organic matter decomposition

The rhizosphere is one of the key fine-scale components of C cycles. This study was undertaken to improve understanding of the potential effects of atmospheric CO2 increase on rhizosphere processes. Using C isotope techniques, we found that elevated atmospheric CO2 significantly increased wheat plant growth, dry mass accumulation, rhizosphere respiration, and soluble C concentrations in the rhizosphere. When plants were grown under elevated CO2 concentration, soluble C concentration in the rhizosphere increased by approximately 60%. The degree of elevated CO2 enhancement on rhizosphere respiration was much higher than on root biomass. Averaged between the two nitrogen treatments and compared with the ambient CO2 treatment, wheat rhizosphere respiration rate increased 60% and root biomass only increased 26% under the elevated CO2 treatment. These results indicated that elevated atmospheric CO2 in a wheat-soil system significantly increased substrate input to the rhizosphere due to both increased root growth and increased root activities per unit of roots. Nitrogen treatments changed the effect of elevated CO2 on soil organic matter decomposition. Elevated CO2 increased soil organic matter decomposition (22%) in the nitrogen-added treatment but decreased soil organic matter decomposition (18%) without nitrogen addition. Soil nitrogen status was therefore found to be important in determining the directions of the effect of elevated CO2 on soil organic matter decomposition.     

The dependence of respiration on photosynthetic substrate supply and temperature: integrating leaf, soil and ecosystem measurements

Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO₂ concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week‐to‐week changes in temperature. All three respiration rates responded to the CO₂ concentration‐induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short‐term changes in canopy photosynthesis. The short‐term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q₁₀ was lower in leaves that developed at high CO₂, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20°C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short‐ and medium‐term changes in temperature may affect net carbon storage in terrestrial ecosystems.     

土壤温度和水分对油松林土壤呼吸的影响

用LI-COR 6400-09土壤呼吸测定系统,在太原天龙山自然保护区对油松林的土壤呼吸进行了4a测定.结果表明,土壤呼吸具有明显的季节变化特点,最大值出现在8月份,在6～10 μmol m~(-2) s~(-1) 之间,最小值出现在12月份和3月份,在0.5 μmol m~(-2) s~(-1)左右.2005、2006、2007和2008年土壤呼吸CO_2的年平均值分别为(4.71±3.74)、(3.08±2.91)、(2.96±2.58) μmol m~(-2) s~(-1)和(2.12±1.54) μmol m~(-2) s~(-1);4a的CO_2总平均值为(3.27±2.95) μmol m~(-2) s~(-1).4个测定年土壤呼吸的平均值总体差异显著.4个测定年土壤CO_2释放C量分别为1103.5、882.8、918.4 g m~(-2)和666.3 g m~(-2),总C平均值为892.8 g m~(-2),具有明显的年际差异.指数方程可以很好的表达土壤呼吸与10 cm深度土壤温度的关系,R~2值4a分别为0.39,0.60,0.68和0.71,Q_(10)值分别为3.10,4.41、4.05和5.18,用4a全部数据计算的Q_(10)值为4.31.土壤水分对土壤呼吸的作用较弱,R~2值4a分别仅为0.31、0.25、0.13和0.02,但是夏季土壤干旱对土壤呼吸的抑制作用非常明显,可使土壤呼吸下降50%以上.夏季土壤干旱是导致土壤呼吸年际变化的主要原因.4个包括土壤温度和水分的双变量模型均可以很好地模拟土壤呼吸的季节变化, 拟合方程的R~2值从0.58到0.79.     

Interactive effects of global change factors on soil respiration and its components: a meta‐analysis

As the second largest carbon (C) flux between the atmosphere and terrestrial ecosystems, soil respiration (Rs) plays vital roles in regulating atmospheric CO₂ concentration ([CO₂]) and climatic dynamics in the earth system. Although numerous manipulative studies and a few meta‐analyses have been conducted to determine the responses of Rs and its two components [i.e., autotrophic (Ra) and heterotrophic (Rh) respiration] to single global change factors, the interactive effects of the multiple factors are still unclear. In this study, we performed a meta‐analysis of 150 multiple‐factor (≥2) studies to examine the main and interactive effects of global change factors on Rs and its two components. Our results showed that elevated [CO₂] (E), nitrogen addition (N), irrigation (I), and warming (W) induced significant increases in Rs by 28.6%, 8.8%, 9.7%, and 7.1%, respectively. The combined effects of the multiple factors, EN, EW, DE, IE, IN, IW, IEW, and DEW, were also significantly positive on Rs to a greater extent than those of the single‐factor ones. For all the individual studies, the additive interactions were predominant on Rs (90.6%) and its components (≈70.0%) relative to synergistic and antagonistic ones. However, the different combinations of global change factors (e.g., EN, NW, EW, IW) indicated that the three types of interactions were all important, with two combinations for synergistic effects, two for antagonistic, and five for additive when at least eight independent experiments were considered. In addition, the interactions of elevated [CO₂] and warming had opposite effects on Ra and Rh, suggesting that different processes may influence their responses to the multifactor interactions. Our study highlights the crucial importance of the interactive effects among the multiple factors on Rs and its components, which could inform regional and global models to assess the climate–biosphere feedbacks and improve predictions of the future states of the ecological and climate systems.     

全球大气CO2浓度升高对土壤微生物的影响

全球大气CO2浓度升高对土壤微生物生态系统的影响已引起广泛关注。本文从土壤微生物群落结构、微生物区系、土壤呼吸、微生物生物量以及土壤酶活性方面对大气高浓度CO2的响应进行了综述。由于提供高浓度CO2的实验系统、所选植物材料以及土壤特性等的不同,大气CO2浓度升高对土壤微生物群落结构、微生物区系、土壤呼吸、微生物生物量以及土壤酶活性的影响并未得出一致结论。但高浓度CO2对土壤微生物生态系统的影响是存在的。     

Effect of soil water stress on soil respiration and its temperature sensitivity in an 18-year-old temperate Douglas-fir stand

We analyzed 17 months (August 2005 to December 2006) of continuous measurements of soil CO₂ efflux or soil respiration (R_S) in an 18‐year‐old west‐coast temperate Douglas‐fir stand that experienced somewhat greater than normal summertime water deficit. For soil water content at the 4 cm depth (θ) > 0.11 m³ m^?3 (corresponding to a soil water matric potential of ?2 MPa), R_S was positively correlated to soil temperature at the 2 cm depth (T_S). Below this value of θ, however, R_S was largely decoupled from T_S, and evapotranspiration, ecosystem respiration and gross primary productivity (GPP) began to decrease, dropping to about half of their maximum values when θ reached 0.07 m³ m^?3. Soil water deficit substantially reduced R_S sensitivity to temperature resulting in a Q₁₀ significantly < 2. The absolute temperature sensitivity of R_S (i.e. dR_S/dT_S) increased with θ up to 0.15 m³ m^?3, above which it slowly declined. The value of dR_S/dT_S was nearly 0 for θ < 0.08 m³ m^?3, thereby confirming that R_S was largely unaffected by temperature under soil water stress conditions. Despite the possible effects of seasonality of photosynthesis, root activity and litterfall on R_S, the observed decrease in its temperature sensitivity at low θ was consistent with the reduction in substrate availability due to a decrease in (a) microbial mobility, and diffusion of substrates and extracellular enzymes, and (b) the fraction of substrate that can react at high T_S, which is associated with low θ. We found that an exponential (van't Hoff type) model with Q₁₀ and R₁₀ dependent on only θ explained 92% of the variance in half‐hourly values of R_S, including the period with soil water stress conditions. We hypothesize that relating Q₁₀ and R₁₀ to θ not only accounted for the effects of T_S on R_S and its temperature sensitivity but also accounted for the seasonality of biotic (photosynthesis, root activity, and litterfall) and abiotic (soil moisture and temperature) controls and their interactions.     

Elevated temperature increases the accumulation of microbial necromass nitrogen in soil via increasing microbial turnover

Microbial‐derived nitrogen (N) is now recognized as an important source of soil organic N. However, the mechanisms that govern the production of microbial necromass N, its turnover, and stabilization in soil remain poorly understood. To assess the effects of elevated temperature on bacterial and fungal necromass N production, turnover, and stabilization, we incubated ¹⁵N‐labeled bacterial and fungal necromass under optimum moisture conditions at 10°C, 15°C, and 25°C. We developed a new ¹⁵N tracing model to calculate the production and mineralization rates of necromass N. Our results showed that bacterial and fungal necromass N had similar mineralization rates, despite their contrasting chemistry. Most bacterial and fungal necromass ¹⁵N was recovered in the mineral‐associated organic matter fraction through microbial anabolism, suggesting that mineral association plays an important role in stabilizing necromass N in soil, independently of necromass chemistry. Elevated temperature significantly increased the accumulation of necromass N in soil, due to the relatively higher microbial turnover and production of necromass N with increasing temperature than the increases in microbial necromass N mineralization. In conclusion, we found elevated temperature may increase the contribution of microbial necromass N to mineral‐stabilized soil organic N.     

Antecedent moisture and temperature conditions modulate the response of ecosystem respiration to elevated CO2 and warming

Terrestrial plant and soil respiration, or ecosystem respiration (R_eco), represents a major CO₂ flux in the global carbon cycle. However, there is disagreement in how R_eco will respond to future global changes, such as elevated atmosphere CO₂ and warming. To address this, we synthesized six years (2007–2012) of R_eco data from the Prairie Heating And CO₂ Enrichment (PHACE) experiment. We applied a semi‐mechanistic temperature–response model to simultaneously evaluate the response of R_eco to three treatment factors (elevated CO₂, warming, and soil water manipulation) and their interactions with antecedent soil conditions [e.g., past soil water content (SWC) and temperature (SoilT)] and aboveground factors (e.g., vapor pressure deficit, photosynthetically active radiation, vegetation greenness). The model fits the observed R_eco well (R² = 0.77). We applied the model to estimate annual (March–October) R_eco, which was stimulated under elevated CO₂ in most years, likely due to the indirect effect of elevated CO₂ on SWC. When aggregated from 2007 to 2012, total six‐year R_eco was stimulated by elevated CO₂ singly (24%) or in combination with warming (28%). Warming had little effect on annual R_eco under ambient CO₂, but stimulated it under elevated CO₂ (32% across all years) when precipitation was high (e.g., 44% in 2009, a ‘wet’ year). Treatment‐level differences in R_eco can be partly attributed to the effects of antecedent SoilT and vegetation greenness on the apparent temperature sensitivity of R_eco and to the effects of antecedent and current SWC and vegetation activity (greenness modulated by VPD) on R_eco base rates. Thus, this study indicates that the incorporation of both antecedent environmental conditions and aboveground vegetation activity are critical to predicting R_eco at multiple timescales (subdaily to annual) and under a future climate of elevated CO₂ and warming.     

CO2浓度增加对长白山森林土壤甲烷氧化影响

大气CO2浓度升高可能对森林土壤的甲烷(CH4)氧化速率产生影响.本文采用开顶箱技术,对连续6年高浓度CO2(500 μmol·mol-1)处理的长白山森林典型树种蒙古栎树下土壤CH4氧化速率进行研究,并利用CH4氧化菌的16S rRNA特异性引物以及CH4单加氧酶功能基因引物分析了土壤中CH4氧化菌的群落结构与数量.结果表明:CO2浓度增高后,生长季土壤甲烷氧化量与对照和裸地相比分别降低了4％和22％;基于16S rRNA特异性引物的DGGE分析表明,CO2浓度增高导致两类甲烷氧化菌的多样性指数降低;CO2浓度增高对土壤中Ⅰ类甲烷氧化菌数量无显著影响,而使土壤中Ⅱ类甲烷氧化菌数量显著减少,功能基因pmoA拷贝数与对照和裸地相比分别降低了15％和46％.CO2浓度增高导致森林土壤甲烷氧化菌数量与活性降低,土壤含水量的增加可能是导致这一现象的主要原因.     

Rhizospheric and heterotrophic components of soil respiration in six Chinese temperate forests

Partitioning soil respiration (R_S) into heterotrophic (R_H) and rhizospheric (R_R) components is an important step for understanding and modeling carbon cycling in forest ecosystems, but few studies on R_R and R_H exist in Chinese temperate forests. In this study, we used a trenching plot approach to partition R_S in six temperate forests in northeastern China. Our specific objectives were to (1) examine seasonal patterns of soil surface CO₂ fluxes from trenched (R_T) and untrenched plots (R_UT) of these forests; (2) quantify annual fluxes of R_S components and their relative contributions in the forest ecosystems; and (3) examine effects of plot trenching on measurements of R_S and related environmental factors. The R_T maximized in early growing season, but the difference between R_UT and R_T peaked in later summer. The annual fluxes of R_H and R_R varied with forest types. The estimated values of R_H for the Korean pine (Pinus koraiensis Sieb. et Zucc.), Dahurian larch (Larix gmelinii Rupr.), aspen‐birch (Populous davidiana Dode and Betula platyphylla Suk.), hardwood (Fraxinus mandshurica Rupr., Juglans mandshurica Maxim. and Phellodendron amurense Rupr.), Mongolian oak (Quercus mongolica Fisch.) and mixed deciduous (no dominant tree species) forests averaged 89, 196, 187, 245, 261 and 301 g C m⁻² yr⁻¹, respectively; those of R_R averaged 424, 209, 628, 538, 524 and 483 g C m⁻² yr⁻¹, correspondingly; calculated contribution of R_R to R_S (RC) varied from 52% in the larch forest to 83% in the pine forest. The annual flux of R_R was strongly correlated to biomass of roots <0.5 cm in diameter, while that of R_H was weakly correlated to soil organic carbon concentration at A horizon. We concluded that vegetation type and associated carbon metabolisms of temperate forests should be considered in assessing and modeling R_S components. The significant impacts of changed soil physical environments and substrate availability by plot trenching should be appropriately tackled in analyzing and interpreting measurements of R_S components.     

The impacts of rising CO2 concentrations on Australian terrestrial species and ecosystems

The increasing atmospheric concentration of carbon dioxide ([CO₂]) contributes to global warming and the accompanying shifts in climate. However, [CO₂] itself has the potential to impact on Australia's terrestrial biodiversity, due to its importance in the photosynthetic process, which underlies all terrestrial food webs. Here, we review our knowledge regarding the impacts of elevated [CO₂] on native terrestrial species and ecosystems, and suggest key areas in which we have little information on this topic. Experimental information exists for 70 (or less than 0.05%) of Australia's native terrestrial plant and animal species. Of these, 68 are vascular plants. The growth of Australian woody species is more reliably increased by elevated [CO₂] than it is in grasses. At the species level, the most overwhelming responses to increased [CO₂] are a reduction in plant nitrogen concentration and an increase in the production of secondary metabolites. This is of particular concern for Australia's unique herbivorous and granivorous marsupials, for which no information is available. While many plant species also displayed increased growth rates at higher [CO₂], this was far from universal, indicating that changes in community structure and function are likely, leading to alterations of habitat quality. Future research should be directed to key knowledge gaps including the relationship between [CO₂], fire frequency and fire tolerance and the impacts of increasing [CO₂] for Australia's iconic browsing mammals. We also know virtually nothing of the impacts of the increasing [CO₂] on Australia's unique shrublands and semi‐arid/arid rangelands. In conclusion, there is sufficient information available to be certain that the increasing [CO₂] will affect Australia's native biodiversity. However, the information required to formulate predictions concerning the long‐term future of almost all organisms is far in excess of that currently available.     

模拟大气CO2浓度和温度升高对亚高山冷杉(Abies faxoniana)林土壤酶活性的影响

采用控制环境生长室研究了川西亚高山森林生态系统中与C、N、P循环有关的土壤转化酶、脲酶、硝酸还原酶和酸性磷酸酶活性的月动态及其对模拟大气CO2浓度增加、温度升高以及交互作用的动态响应。在一个生长季节内,土壤有机层和矿质土壤层的转化酶、脲酶、硝酸还原酶和酸性磷酸酶的活性高峰均出现在温度较高的夏季。其中,土壤有机层的转化酶活性高峰出现在6月份,但土壤矿质层的转化酶活性高峰出现在7月份,土壤有机层和矿质土壤层的脲酶和酸性磷酸酶的活性高峰均出现在7月份,而硝酸还原酶的活性高峰均出现在8月份。升高大气CO2浓度处理(EC)对土壤有机层和矿质土壤层的转化酶、脲酶、硝酸还原酶和酸性磷酸酶活性没有显著影响。升高温度处理(ET)显著增加了土壤有机层和矿质土壤层的酶活性,并且土壤有机层的转化酶、硝酸还原酶和脲酶活性增加更显著。大气CO2浓度增加和温度升高之间的交互作用(ECT)对土壤有机层和矿质土壤层酶活性的影响主要是温度升高引起的。     

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）gCm^-2d^-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。     

The turnover of carbon pools contributing to soil CO2 and soil respiration in a temperate forest exposed to elevated CO2 concentration

Soil carbon is returned to the atmosphere through the process of soil respiration, which represents one of the largest fluxes in the terrestrial C cycle. The effects of climate change on the components of soil respiration can affect the sink or source capacity of ecosystems for atmospheric carbon, but no current techniques can unambiguously separate soil respiration into its components. Long‐term free air CO₂ enrichment (FACE) experiments provide a unique opportunity to study soil C dynamics because the CO₂ used for fumigation has a distinct isotopic signature and serves as a continuous label at the ecosystem level. We used the ¹³C tracer at the Duke Forest FACE site to follow the disappearance of C fixed before fumigation began in 1996 (pretreatment C) from soil CO₂ and soil‐respired CO₂, as an index of belowground C dynamics during the first 8 years of the experiment. The decay of pretreatment C as detected in the isotopic composition of soil‐respired CO₂ and soil CO₂ at 15, 30, 70, and 200 cm soil depth was best described by a model having one to three exponential pools within the soil system. The majority of soil‐respired CO₂ (71%) originated in soil C pools with a turnover time of about 35 days. About 55%, 50%, and 68% of soil CO₂ at 15, 30, and 70 cm, respectively, originated in soil pools with turnover times of less than 1 year. The rest of soil CO₂ and soil‐respired CO₂ originated in soil pools that turn over at decadal time scales. Our results suggest that a large fraction of the C returned to the atmosphere through soil respiration results from dynamic soil C pools that cannot be easily detected in traditionally defined soil organic matter standing stocks. Fast oxidation of labile C substrates may prevent increases in soil C accumulation in forests exposed to elevated [CO₂] and may consequently result in shorter ecosystem C residence times.     

Elevated CO2 and temperature effects on soil carbon and nitrogen cycling in ryegrass/white clover turves of an Endoaquept soil

Effects of elevated CO₂ (700 L L^–1) and a control (350 L L^–1 CO₂) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 L L^–1 CO₂ and a temperature 6°C higher throughout than in the other treatments, was included.Under the same temperature conditions, overall herbage yields in the 700 L L^–1 CO₂ treatment were ca. 7% greater than in the control at the end of the summer period. Root mass (to ca 25 cm depth) in the 700 L L^–1 CO₂ treatment was then about 50% greater than in the control, but in the 700 L L^–1 CO₂+6°C treatment it was 6% lower than in the control. Based on decomposition results, herbage from the 700 L L^–1+6°C treatment probably contained the highest proportion of readily decomposable components.Elevated CO₂ had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO₂-C production) and invertase activity. The effects of elevated CO₂ on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO₂, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials.Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO₂ enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO₂ on the soil C balance.