Influence of Tree Species Composition and Community Structure on Carbon Density in a Subtropical Forest

We assessed the impact of species composition and stand structure on the spatial variation of forest carbon density using data collected from a 4-ha plot in a subtropical forest in southern China. We found that 1) forest biomass carbon density significantly differed among communities, reflecting a significant effect of community structure and species composition on carbon accumulation; 2) soil organic carbon density increased whereas stand biomass carbon density decreased across communities, indicating that different mechanisms might account for the accumulation of stand biomass carbon and soil organic carbon in the subtropical forest; and 3) a small number of tree individuals of the medium- and large-diameter class contributed predominantly to biomass carbon accumulation in the community, whereas a large number of seedlings and saplings were responsible for a small proportion of the total forest carbon stock. These findings demonstrate that both biomass carbon and soil carbon density in the subtropical forest are sensitive to species composition and community structure, and that heterogeneity in species composition and stand structure should be taken into account to ensure accurate forest carbon accounting.     

A substantial role of soil erosion in the land carbon sink and its future changes

Realistic representation of land carbon sink in climate models is vital for predicting carbon climate feedbacks in a changing world. Although soil erosion that removes land organic carbon has increased substantially since the onset of agriculture, it is rarely included in the current generation of climate models. Using an Earth system model (ESM) with soil erosion represented, we estimated that on average soil erosion displaces 5% of newly fixed land organic carbon downslope annually in the continental United States. In the lower Mississippi river basin and the Cascades, the fraction can be as large as 40%. About 12% of the eroded organic carbon is eventually exported to inland waters, which is equal to 14% of the simulated net carbon gain by terrestrial ecosystems. By comparing the eroded organic carbon export to rivers with the particulate organic carbon export to oceans, we demonstrated that a large fraction of the carbon export to rivers could have been mineralized in inland waters. Importantly, with a direct comparison of eroded and exported soil organic carbon and land net carbon uptake, we found that ESMs that ignore soil erosion likely offset the erosional carbon loss by increasing heterotrophic respiration implicitly. But as soil erosion and heterotrophic respiration respond differently to a warming climate, this unrealistic compensation would lead to biased predictions of future land carbon sink.     

苏南丘陵地区栓皮栎次生林与火炬松人工林土壤有效碳

采用重复熏蒸-培养法研究了苏南丘陵地区具有代表性的栓皮栎次生林和火炬松人工林土壤有效碳的变化特征。结果表明:栓皮栎次生林土壤中的有效碳和微生物量碳含量均显著高于火炬松人工林,而火炬松人工林土壤有效碳占总有机碳比率(4.7%)及土壤微生物量碳含量占土壤有效碳比率(54.3%)分别高于栓皮栎次生林(2.9%和40.9%);去除森林凋落物后,2种林分土壤有效碳含量均显著降低;土壤有效碳与土壤微生物量碳以及土壤总有效碳显著相关。重复熏蒸-培养法是估测该地区森林土壤有效碳的一种简单有效的方法。与火炬松人工林相比,天然次生栓皮栎林土壤含有较多的活性有机碳,可能对区域碳平衡产生较大的影响。     

Do grasslands act as a perpetual sink for carbon?

It is increasingly commonly suggested that grasslands are a perpetual sink for carbon, and that just maintaining grasslands will yield a net carbon sink. I examine the evidence for this from repeated soil surveys, long term grassland experiments and simple mass balance calculations. I conclude that it is untenable that grasslands act as a perpetual carbon sink, and the most likely explanation for observed grassland carbon sinks over short periods is legacy effects of land use and land management prior to the beginning of flux measurement periods. Simply having grassland does not result is a carbon sink, but judicious management or previously poorly managed grasslands can increase the sink capacity. Given that grasslands are a large store of carbon, and that it is easier and faster for soils to lose carbon that it is for them to gain carbon, it is an important management target to maintain these stocks.     

中国伐木制品碳储量时空差异

森林生态系统碳储量是全球变化研究的热点问题之一,在国内外已经进行了深入的研究。然而,森林采伐后生产的伐木制品碳储量研究相对较少,因此基于IPCC提出的大气流动法,综合考虑伐木制品废弃情形,以2000年为基准年,估算了我国2000—2009新生产伐木制品的碳储量。结果表明,我国伐木制品是一个巨大碳库,且碳储量呈不断增加趋势。2000—2009年我国新生产的伐木制品,在2009年净碳储量为306.52 TgC,非纸木制品、纸类和竹材制品碳储量分别为114.71 TgC、4.33 TgC和199.07 TgC,而薪材燃烧累计碳释放量为11.60TgC,其他伐木制品累计碳释放量共为37.76 TgC。在2009年,终端伐木制品碳储量为318.12TgC,木材制品和竹制品碳储量分别占37.42%和62.58%;在木材制品中,非纸木制品和纸类碳储量为114.71TgC和4.33 TgC,各占96.36%和3.64%。与方精云估算的我国1999—2003年森林年碳汇量168.1 TgC/a相比,这一时期生产的伐木制品年净碳储量为25.21 Tg/a,占森林年碳汇量的15%,这说明伐木制品在维持碳平衡具有重要的作用。本文估算的竹制品碳储量约为木材制品碳储量的1.67倍,这说明竹材制品碳储量在伐木制品碳储量中占相当大的比重,是一个重要的碳库。此外,按照终端伐木制品净碳储量情况,可将我国分成高储量区、中储量区和低储量区。高储量区包括福建、浙江、湖南、云南、广西、江西6个省,这些地区终端伐木制品净碳储量占全国的67%;中储量区包括安徽、广东、湖北、四川、黑龙江、吉林和内蒙古等地区,其他地区为低储量区。我国7个地区按终端伐木制品净碳储量顺序排列为:华东、华中、华南、西南、东北、华北、西北。此外,研究还表明我国南方和北方伐木制品碳储量分别以竹材制品和木材制品储存为主。     

川西亚高山-高山土壤表层有机碳及活性组分沿海拔梯度的变化

青藏高原东缘亚高山-高山地带土壤碳被认为是我国重要的土壤碳库,作为高海拔低温生态系统,土壤碳对土壤暖化的响应可能也更加敏感。该区域亚高山森林一般分布在海拔3200 m以上,上缘接高山树线和灌丛草地,土壤有机碳含量高。海拔梯度上变化的土壤环境因子是主要土壤温度,海拔梯度上高寒土壤有机碳及活性有机碳组的分布格局,可体现海拔梯度上温度因子对土壤碳动态的影响。对沿海拔3200 m(亚高山针叶林)、3340 m(亚高山针叶林)、3540 m(亚高山针叶林)、3670 m(亚高山针叶林)、3740 m(亚高山针叶林)、3850 m(高山林线)、3940 m(高山树线)、4120 m(高山草地)的土壤表层(0-20 cm)有机碳和活性有机碳组分含量进行分析,结果表明在该海拔范围内,表层土壤总有机碳含量随着海拔的升高而增加,显示高海拔有利于土壤碳的固存;土壤活性有机碳组分中,颗粒态有机碳含量及其占总有机碳比例与海拔呈显著正相关,在海拔最高的4120 m含量和占有机碳总量比例分别达到50.81 g/kg和56.52%。在该海拔范围内海拔越高颗粒态有机碳占有机碳比例越高,显示高海拔土壤有机碳更多以土壤颗粒态碳形式贮存。微生物量碳、水溶性碳、轻组分有机碳与海拔高度没有明显的相关性,表明这些活性有机碳组分受海拔因素影响不大;易氧化有机碳含量与海拔高度显著正相关。因此,颗粒态有机碳含量及其比例可作为高海拔地带土壤活性有机碳库动态的特征指标,表征高海拔地带土壤有机碳动态与贮量受温度影响的指标。     

珊瑚共生体碳代谢特征研究进展

珊瑚礁作为一种典型的海洋生态系统,具有巨大的固碳和储碳潜力。然而,目前对于珊瑚礁的净碳能力(碳释放与碳吸收)仍存在争议,主要归因于珊瑚共生体碳代谢的多样性和复杂性。珊瑚礁在生物钙化、呼吸过程中向大气释放二氧化碳(CO₂);但在生物合成和沉积过程中却可以将碳进行固定与埋藏;为此,珊瑚礁的碳源碳汇身份还有待明确。现有部分研究表明,共生体通过碳代谢可以促进珊瑚礁吸收大气中的CO₂。此外,珊瑚礁和海岸带蓝碳生态系统通常表现出很强的连通性,珊瑚共生体碳代谢能有效提高海岸带盐沼植被、海草床、海洋浮游植物等生物的碳汇功能。为了加深对珊瑚礁碳源-碳汇功能的理解,综述了珊瑚共生体的碳代谢特征,梳理了共生体中碳的关键生态过程(有机碳的迁移、无机碳的转化、两者的赋存状态),总结了细菌-虫黄藻-病毒在共生体碳代谢中的作用,评述了珊瑚礁碳源-碳汇特征及影响因子。旨在阐明珊瑚共生体碳代谢的关键过程,并基于此寻求有效的珊瑚礁碳增汇技术,形成以碳增量为主的珊瑚保护与修复技术,提升珊瑚礁在蓝碳生态系统中的贡献。     

Metabolism of haloforms to carbon monoxide. IV. Studies on the reaction mechanism in vivo

In vivo studies have been carried out in order to understand more fully the mechanism of haloform oxidation to carbon monoxide. A deuterium isotope effect on carbon monoxide production from chloroform was observed in both control and phenobarbital-treated rats. Diethyl maleate treatment decreased blood carbon monoxide concentrations produced from bromoform and chloroform and attenuated the effect of deuterium substitution on the metabolism of both compounds to carbon monoxide. Cysteine also decreased blood carbon monoxide concentrations seen after giving chloroform. A reaction mechanism similar to that proposed on the basis of in vitro data, which included a central role for dihalocarbonyl compounds in the formation of 2-oxothiazolidine-4-carboxylic acid, carbon monoxide, and carbon dioxide, is suggested for the in vivo metabolism of haloforms to carbon monoxide. These data indicate that carbon monoxide production may be a detoxification pathway for haloforms and that both the inhibition of carbon monoxide production from haloforms and the potentiation of haloform-hepatotoxicity by diethyl maleate are due to the depletion of glutathione.     

海岛碳排放核算与时空特征——以东山岛为例

把握地区碳信息发展动态是开展区域碳平衡规划的科学基础。以统计年鉴数据为基础,对东山岛2012—2021年整体及各产业的直接碳排放量进行核算,同时,将产业与土地利用结合,分析其空间表现形态,运用核密度分析和克里金法分析碳排放源的空间影响,采用高斯烟羽模型对工业点源的碳排放扩散进行空间模拟,通过渔网和人口修正的方法分析海岛碳排放的空间分异,以此探讨海岛碳排放的空间分布和空间影响特征。结果显示,工业是东山岛的首要碳排放源,2021年工业碳排放量的大幅下降表明能源种类的转换对于工业碳减排具有重要作用;渔业碳排放量总体占比25%左右,是海岛地区不容忽视的碳排放源之一。在空间分布方面,东山岛综合碳排放的空间分布呈“点状聚集,面状扩散”的基本特征,工业碳排放对周围地区的影响最大,往往形成以工业碳排放源点为中心的碳排放热点核心区,其次碳排放量较高的地区为人口聚集区,丘陵区的碳排放量最低,不同土地利用类型之间形成碳排放的交叉过渡区。最后,本文从碳排放空间影响的视角出发,根据不同形态的碳排放源提出“包围”、“伴随”和“介入”的碳汇空间规划策略,这对区域的低碳规划具有一定参考意义。     

Dynamics of Maize Carbon Contribution to Soil Organic Carbon in Association with Soil Type and Fertility Level

Soil type and fertility level influence straw carbon dynamics in the agroecosystems. However, there is a limited understanding of the dynamic processes of straw-derived and soil-derived carbon and the influence of the addition of straw carbon on soil-derived organic carbon in different soils associated with different fertility levels. In this study, we applied the in-situ carborundum tube method and ¹³C-labeled maize straw (with and without maize straw) at two cropland (Phaeozem and Luvisol soils) experimental sites in northeast China to quantify the dynamics of maize-derived and soil-derived carbon in soils associated with high and low fertility, and to examine how the addition of maize carbon influences soil-derived organic carbon and the interactions of soil type and fertility level with maize-derived and soil-derived carbon. We found that, on average, the contributions of maize-derived carbon to total organic carbon in maize-soil systems during the experimental period were differentiated among low fertility Luvisol (from 62.82% to 42.90), high fertility Luvisol (from 53.15% to 30.00%), low fertility Phaeozem (from 58.69% to 36.29%) and high fertility Phaeozem (from 41.06% to 16.60%). Furthermore, the addition of maize carbon significantly decreased the remaining soil-derived organic carbon in low and high fertility Luvisols and low fertility Phaeozem before two months. However, the increasing differences in soil-derived organic carbon between both soils with and without maize straw after two months suggested that maize-derived carbon was incorporated into soil-derived organic carbon, thereby potentially offsetting the loss of soil-derived organic carbon. These results suggested that Phaeozem and high fertility level soils would fix more maize carbon over time and thus were more beneficial for protecting soil-derived organic carbon from maize carbon decomposition.     

Effects of Surface Area and Flow Rate on Marine Bacterial Growth in Activated Carbon Columns

The colonization of granular activated carbon columns by bacteria can have both beneficial and potentially detrimental consequences. Bacterial growth on the carbon surface can remove adsorbed organics and thus partially regenerate the carbon bed. However, growth can also increase the levels of bacteria in the column effluents, which can adversely affect downstream uses of the treated water. This study of a sand column and several activated carbon columns demonstrated that considerable marine bacterial growth occurred in both sand and carbon columns and that this growth increased the number of bacteria in column effluents. Activated carbon supported approximately 50% more bacteria than did sand. Bacterial growth on activated carbon was reduced by increasing the flow rate through a carbon column and increasing the carbon particle size. Scanning electron micrographs showed that bacteria preferred to attach in the protected crevices on both the sand and carbon surface. The results of this study indicated that the colonization of activated carbon by marine bacteria was enhanced because of carbon's high surface area, its rough surface texture, and its ability to absorb organic materials.     

能源对北京市城市碳循环的影响

研究城市碳循环过程并阐明能源对碳循环的影响,可为城市节能减排政策的制定和实施提供参考依据。基于城市碳循环模型核算了2005—2014年北京市的碳储量和碳通量,并通过能源碳效应指数来探讨能源对城市碳循环的影响。结果表明人为碳储量是北京市总碳储量增加的主要驱动力。北京市的碳输入主要来自水平方向,表明北京市的发展在很大程度上依赖于外部环境的物质供给;北京市的碳输出主要是能源消耗产生的垂直碳输出。能源活动相关的碳通量占北京市总碳通量的比重,即能源碳效应,在2006年高达79.46%,而后开始呈波动下降的趋势。能源对北京市碳循环影响最大的是垂直输出方向,其次是水平输入方向,因此低碳城市建设需要加强对垂直碳通量和水平碳通量的调节和管理,尤其是与能源活动相关的碳通量,与此同时,保护自然植被和增加生态用地对提高城市碳减排能力也至关重要。     

黄土高原小流域不同地形下土壤有机碳分布特征

研究了黄土高原小流域尺度塬面、坡地、沟道和梯田4种地形条件下土壤有机碳总量和活性组分的分布、储量及碳库管理指数的差异.结果表明,小流域土壤有机碳和不同活性有机碳的变异系数介于32％-70％之间,表现出中到高度的变异特征.4种地形下各组分有机碳含量和储量以塬面土壤最高,沟道土壤最低,并随土层深度的增加而降低,降低程度随有机碳活性增强而增加.以塬面土壤为对照所获得的碳库管理指数可灵敏指示有机碳对地形条件的响应特征,中活性有机碳库管理指数的指示效果最好.研究结果可部分解释黄土高原土壤有机碳地带性分布特征.     

广东土壤有机碳储量及空间分布特征

根据广东省第2次土壤普查资料,采用GIS技术估算广东省土壤有机碳储量及空问分布规律,结果表明,广东省陆地土壤有机碳储量约为17．52×10^8t．砖红壤、红壤和赤红壤的土壤有机碳密度分别为8．83、10．31和9．15kg·m^-2,略低于全国的平均水平,三者占广东省土壤面积的67．91％;广东省黄壤和水稻土的有机碳密度分别为12．08和12．17kg·m^-2,高于全国平均水平;广东省平均土壤碳密度为10．44kg·m^-2．土壤有机碳密度总的分布规律是东南沿海地区高于粤北山区,其中粤北和粤中土壤有机碳密度为5～10kg·m^-2,粤东的沿海地区土壤有机碳密度为10～15kg·m^-2,二者合计占全省土壤面积的89．24％;土壤有机碳密度主要在5～15kg·m^-2范围内变动．     

Simulation of terrestrial carbon equilibrium state by using a detachable carbon cycle scheme

Determining the equilibrium state of terrestrial carbon is a prerequisite for scientific analysis on the carbon cycle. However, the mechanism through which the carbon cycle reaches the equilibrium state remains unclear. Moreover, the carbon cycle in most of the short–term field experiments rarely reaches the equilibrium state. In this study, a detachable carbon cycle (DCC) model was proposed to simulate the equilibrium state of each carbon pool. The model was established based on a pool–and–flux scheme and contained 14 carbon pools, or carbon flow processes, each process could be detached from the main model and evaluated as an independent component. The environmental scalar algorithms of the Integrated Terrestrial Ecosystem Carbon budget model (InTEC) and Community Atmosphere Biosphere Land Exchange (CABLE) were incorporated in the DCC model. Four situations were compared using the two environmental scalar algorithms and model structure (9 vs. 14 carbon pools). Furthermore, the size and turnover time of each carbon pool were analyzed at the equilibrium state. A sensitivity analysis was then conducted to investigate the responses of carbon density and equilibrium time to 12 key parameters of the model. Results indicated that the combination of the CABLE environmental scalar algorithm and 14 pools exhibited improved performance on carbon storage simulation than that of the other combinations, and the effect of the environmental scalar algorithm was considerably larger than that of the carbon pool number. Sensitivity analysis indicated that the carbon density of grassland and cropland was more vulnerable and sensitive to key parameters of the model than that of the other biomes. This study elucidates influencing factors and underlying control mechanisms in the carbon accumulation, and provides a framework for quantitative analysis of each component of the carbon cycle.     

Soil carbon storage and its determinants in the forests of Shaanxi Province,China

Aims The bank of soil carbon of forests plays an important role in the global carbon cycle. Our aim is to understand the characteristics of soil carbon storage and its determinants in the forests in Shaanxi Province.Methods The data of forest inventory in 2009 and resampling in 2011 were used to analyze the characteristics of soil carbon storage and its determinants in the forest soil in Shaanxi Province.Important findings The soil carbon storage in the forests in Shaanxi Province was 579.68 Tg. Soil carbon storage of Softwood and Hardwood forests were the highest among all forest types, accounting for 36.35% of the whole province forest soil carbon storage. The forest soil carbon storage was 4.15 times greater in the natural forest (467.17 Tg) than that in the plantations. The young and middle-aged forests were the main contributors to the total carbon storage across all age groups, accounting for about 57.30% of the total forest soil carbon storage. The average soil carbon density of forests in Shaanxi Province was 90.68 t∙hm^-2, in which the soil carbon density of Betula forests was the highest (141.74 t∙hm^-2). Soil carbon density of different forest types were gradually decreased with soil depth. In addition, it was highest in middle-aged forest. Soil carbon density was higher in the natural forest ecosystems than that in the plantations within the each age group, indicating natural forest ecosystems have higher capacity of carbon sequestration. Differences in the spatial patterns between carbon storage and density indicated that carbon storage was related to forest coverage. The soil carbon density and storage of forests in Yulin were the lowest across the province. This suggests that, in order to enhance the regional carbon sequestration capacity in this region, we need to appropriately strengthen artificial afforestation activities and manage them scientifically and rationally. The soil carbon density of forests in Shaanxi Province decreased with the increase of longitude, latitude, and annual temperature, but increased with the increase of altitude and annual rainfall. This study provides data basis for provincial estimation of forest soil carbon bank in China.     

低碳导向下土地覆被演变模拟——以深圳市为例

全球碳排放水平的不断增加引起的全球变暖越发严重,导致了严重的自然灾害和经济损失,这种失衡发展的态势促使着各个国家开始探索低碳环保的发展模式。为了探究何种土地利用组成可以更好的为低碳城市服务,以深圳市为研究区,结合2020年土地利用现状结构和2020年土地利用规划结构分别估算出碳汇最大化情景和碳排放量最小化情景下2020年各土地利用类型的数量结构,并运用FLUS模型模拟出深圳市土地利用类型在这两种情景下的空间分布特征。最后,从碳密度和碳排放视角对比这两种情景的低碳效益。研究结果如下：①碳汇最大化和碳排放最小化情景下土地利用总碳盈余均比2020年少,且碳汇最大化情景下土地利用总碳盈余最小。碳汇最大化情景下耕地、园地和林地面积增加而水域和建设用地减少,碳排放最小化情景下园地和林地面积增加来源于草地、水域和建设用地的减少,这两种低碳情景的碳汇能力增强而碳排放量减少;②碳汇最大化和碳排放最小化情景下林地明显增加故而土地利用总碳盈余均比实际情景小,而园地和草地的缩减和扩张是引起两种低碳情景碳密度和碳排放量有差异的主要原因。碳汇最大化和碳排放最小化情景下,西部和东南部主要是碳密度增加和碳排放减少的区域,而中部是碳密度减少和碳排放增加的区域。因此对中部区域进行重点调控,有利于深圳市碳中和和碳达峰的实现。研究可以为深圳的低碳发展提供规划建议,同时给其他区域的低碳规划提供参考意见。     

Net carbon flux from agriculture: Carbon emissions, carbon sequestration, crop yield, and land-use change

There is a potential to sequester carbon in soil by changing agricultural management practices. These changes in agricultural management can also result in changes in fossil-fuel use, agricultural inputs, and the carbon emissions associated with fossil fuels and other inputs. Management practices that alter crop yields and land productivity can affect the amount of land used for crop production with further significant implications for both emissions and sequestration potential. Data from a 20-year agricultural experiment were used to analyze carbon sequestration, carbon emissions, crop yield, and land-use change and to estimate the impact that carbon sequestration strategies might have on the net flux of carbon to the atmosphere. Results indicate that if changes in management result in decreased crop yields, the net carbon flux can be greater under the new system, assuming that crop demand remains the same and additional lands are brought into production. Conversely, if increasing crop yields lead to land abandonment, the overall carbon savings from changes in management will be greater than when soil carbon sequestration alone is considered.     

Exogenous carbon turnover within the soil food web strengthens soil carbon sequestration through microbial necromass accumulation

Exogenous carbon turnover within soil food web is important in determining the trade-offs between soil organic carbon (SOC) storage and carbon emission. However, it remains largely unknown how soil food web influences carbon sequestration through mediating the dual roles of microbes as decomposers and contributors, hindering our ability to develop policies for soil carbon management. Here, we conducted a ¹³C-labeled straw experiment to demonstrate how soil food web regulated the residing microbes to influence the soil carbon transformation and stabilization process after 11 years of no-tillage. Our work demonstrated that soil fauna, as a “temporary storage container,” indirectly influenced the SOC transformation processes and mediated the SOC sequestration through feeding on soil microbes. Soil biota communities acted as both drivers of and contributors to SOC cycling, with 32.0% of exogenous carbon being stabilizing in the form of microbial necromass as “new” carbon. Additionally, the proportion of mineral-associated organic carbon and particulate organic carbon showed that the “renewal effect” driven by the soil food web promoted the SOC to be more stable. Our study clearly illustrated that soil food web regulated the turnover of exogenous carbon inputs by and mediated soil carbon sequestration through microbial necromass accumulation.     

The carbon-quality temperature hypothesis: Fact or artefact?

Climate warming can reduce global soil carbon stocks by enhancing microbial decomposition. However, the magnitude of this loss remains uncertain because the temperature sensitivity of the decomposition of the major fraction of soil carbon, namely resistant carbon, is not fully known. It is now believed that the resistance of soil carbon mostly depends on microbial accessibility of soil carbon with physical protection being the primary control of the decomposition of protected carbon, which is insensitive to temperature changes. However, it is still unclear whether the temperature sensitivity of the decomposition of unprotected carbon, for example, carbon that is not protected by the soil mineral matrix, may depend on the chemical recalcitrance of carbon compounds. In particular, the carbon-quality temperature (CQT) hypothesis asserts that recalcitrant low-quality carbon is more temperature-sensitive to decomposition than labile high-quality carbon. If the hypothesis is correct, climate warming could amplify the loss of unprotected, but chemically recalcitrant, carbon and the resultant CO₂ release from soils to the atmosphere. Previous research has supported this hypothesis based on reported negative relationships between temperature sensitivity and carbon quality, defined as the decomposition rate at a reference temperature. Here we show that negative relationships can arise simply from the arbitrary choice of reference temperature, inherently invalidating those tests. To avoid this artefact, we defined the carbon quality of different compounds as their uncatalysed reaction rates in the absence of enzymes. Taking the uncatalysed rate as the carbon quality index, we found that the CQT hypothesis is not supported for enzyme-catalysed reactions, which showed no relationship between carbon quality and temperature sensitivity. The lack of correlation in enzyme-catalysed reactions implies similar temperature sensitivity for microbial decomposition of soil carbon, regardless of its quality, thereby allaying concerns of acceleration of warming-induced decomposition of recalcitrant carbon.