Three parameters comprehensively describe the temperature response of respiratory oxygen reduction

Using an exponential model that relies on Arrhenius kinetics, we explored Type I, Type II and dynamic (e.g. declining Q ₁₀ with increasing temperature) responses of respiration to temperature. Our Arrhenius model provides three parameters: R _REF (the base of the exponential model, nmol g⁻¹ s⁻¹), E ₀ (the overall activation energy of oxygen reduction that dominates its temperature sensitivity, kJ mol⁻¹) and δ (that describes dynamic responses of E ₀ to measurement temperature, 10³ K²). Two parameters, E ₀ and δ , are tightly linked. Increases in overall activation energy at a reference temperature were inversely related to changes in δ . At an E ₀ of ca. 45 kJ mol⁻¹, δ approached zero, and respiratory temperature response was strictly Arrhenius-like. Physiologically, these observations suggest that as contributions of AOX to combined oxygen reduction increase, E ₀( REF ) decreases because of different temperature sensitivities for V _max, and δ increases because of different temperature sensitivities for K _1/2 of AOX and COX. The balance between COX and AOX activity helps regulate plant metabolism by adjusting the demand for ATP to that for reducing power and carbon skeleton intermediates. Our approach enables determination of respiratory capacity in vivo and opens a path to development of process-based models of plant respiration.     

Seasonal variation in foliar carbon exchange in Pinus radiata and Populus deltoides: respiration acclimates fully to changes in temperature but photosynthesis does not

We investigated seasonal variation in dark respiration and photosynthesis by measuring gas exchange characteristics on Pinus radiata and Populus deltoides under field conditions each month for 1 year. The field site in the South Island of New Zealand is characterized by large day-to-day and seasonal changes in air temperature. The rate of foliar respiration at a base temperature of 10 °C ( R ₁₀) in both pine and poplar was found to be greater during autumn and winter and displayed a strong downward adjustment in warmer months. The sensitivity of instantaneous leaf respiration to a 10 °C increase in temperature ( Q ₁₀) was also greater during the winter period. The net effect of this strong acclimation was that the long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures. Seasonal changes in photosynthesis were sensitive to temperature but largely independent of leaf nitrogen concentration or stomatal conductance. Over the range of day time growth temperatures (5–32 °C), we did not observe strong evidence of photosynthetic acclimation to temperature, and the long-term responses of photosynthetic parameters to ambient temperature were similar to previously published instantaneous responses. The ratio of foliar respiration to photosynthetic capacity ( R _d/ A _sat) was significantly greater in winter than in spring/summer. This indicates that there is little likelihood that respiration would be stimulated significantly in either of these species with moderate increases in temperature – in fact net carbon uptake was favoured at moderately higher temperatures. Model calculations demonstrate that failing to account for strong thermal acclimation of leaf respiration influences determinations of leaf carbon exchange significantly, especially for the evergreen conifer.     

The effect of soil warming on bulk soil vs. rhizosphere respiration

There has been considerable debate on whether root/rhizosphere respiration or bulk soil respiration is more sensitive to long-term temperature changes. We investigated the response of belowground respiration to soil warming by 3 °C above ambient in bare soil plots and plots planted with wheat and maize. Initially, belowground respiration responded more to the soil warming in bare soil plots than in planted plots. However, as the growing season progressed, a greater soil-warming response developed in the planted plots as the contribution of root/rhizosphere respiration to belowground respiration declined. A negative correlation was observed between the contribution of root/rhizosphere respiration to total belowground respiration and the magnitude of the soil-warming response indicating that bulk soil respiration is more temperature sensitive than root/rhizosphere respiration. The dependence of root/rhizosphere respiration on substrate provision from photosynthesis is the most probable explanation for the observed lower temperature sensitivity of root/rhizosphere respiration. At harvest in late September, final crop biomass did not differ between the two soil temperature treatments in either the maize or wheat plots. Postharvest, flux measurements during the winter months indicated that the response of belowground respiration to the soil-warming treatment increased in magnitude (response equated to a Q ₁₀ value of 5.7 compared with ∼2.3 during the growing season). However, it appeared that this response was partly caused by a strong indirect effect of soil warming. When measurements were made at a common temperature, belowground respiration remained higher in the warmed subplots suggesting soil warming had maintained a more active microbial community through the winter months. It is proposed that any changes in winter temperatures, resulting from global warming, could alter the sink strength of terrestrial ecosystems considerably.     

两种农田土壤不同组分呼吸及其温度敏感性

为探讨农田土壤不同组分呼吸及其对温度变化的响应,选取山东平邑旱耕土和湖南桃江水稻土为供试土壤,设置4个温度水平(5、15、25、35 ℃),对两种土壤的轻组、重组及全土进行63 d的培养试验.结果表明: 两种土壤全土的呼吸均高于轻组和重组.旱耕土重组的呼吸高于轻组,水稻土重组和轻组的呼吸在5～25 ℃温度水平下无显著差异,但35 ℃下重组高于轻组.在不同温度水平下,旱耕土轻组、重组和全土累积呼吸量分别占其初始碳的0.3%～2.8%、0.4%～3.7%和0.6%～7.0%,水稻土分别占其初始碳的0.4%～3.0%、0.3%～3.8%和0.7%～5.3%.两种土壤全土及轻、重组呼吸的温度敏感性(Q₁₀)均随温度升高和培养时间延长而降低;水稻土重组的Q₁₀高于轻组,旱耕土重组和轻组Q₁₀的差异无明显规律.在5～25 ℃温度水平下,旱耕土全土Q₁₀显著高于水稻土,但在25～35 ℃下低于水稻土.说明平邑旱耕土有机碳矿化强度高于桃江水稻土,且对温度变化的响应总体比水稻土更敏感.     

Modelling the effect of temperature on carbon mineralization rates across a network of European forest sites (FORCAST)

Temperature is a major environmental variable influencing microbial respiration in soils. Thus, understanding how heterotrophic processes in soils may respond to potential increases in temperature is crucial for the prediction of the response of forest carbon budgets to climate change. We investigated carbon mineralization rates from eight European forest soils in relation to soil temperature. Mineral soil samples were collected from eight mature forest sites in the European network CARBOEUROFLUX and were incubated in the laboratory for ca. 270 days at four temperatures: 4, 10, 20 and 30°C. In all soils, carbon mineralization rates decreased over time when incubated at high temperatures of 20 and 30°C. In this study, we explore the different models available to analyse long-term incubation data. Carbon mineralization rates were best predicted by a first-order, two-compartment model that predicted carbon mineralization as a function of time and temperature using all of the incubation data. We found very small fractions (1–9%) of labile carbon in the upper mineral soils. Despite large differences among sites, we found higher carbon mineralization rates and larger amounts of labile carbon in the broadleaf than in the conifer forest soils. No significant differences in temperature sensitivity among the sites (average Q ₁₀ of 2.88 using the two-compartment model) were observed, as estimated with all methods used. Although not statistically significant, the sensitivities of the rate constant of the labile fractions tended to be higher than those for the rate constant of the recalcitrant fractions. Thus, the results of this modelling exercise suggest that despite large variation among sites, a single temperature sensitivity parameter can be used for a range of soils over the range of temperatures we used (4–30°C).     

武夷山不同海拔土壤呼吸对变暖和变冷的响应

由于人类活动,我国亚热带地区正面临剧烈的气候变化,这可能对土壤呼吸有潜在影响.本研究选择武夷山国家公园内针叶林(1442 m)和常绿阔叶林(645 m)为对象,通过土柱置换试验模拟变暖(针叶林置换到常绿阔叶林)和变冷(常绿阔叶林置换到针叶林),探讨模拟变暖和变冷对土壤碳过程的影响,测定两个海拔样地的原位和置换处理的微气...     

Winter soil respiration during soil-freezing process in a boreal forest in Northeast China

Aims Boreal forest is the largest and contains the most soil carbon among global terrestrial biomes. Soil respiration during the prolonged winter period may play an important role in the carbon cycles in boreal forests. This study aims to explore the characteristics of winter soil respiration in the boreal forest and to show how it is regulated by environmental factors, such as soil temperature, soil moisture and snowpack.Methods Soil respiration in an old-growth larch forest (Larix gmelinii Ruppr.) in Northeast China was intensively measured during the winter soil-freezing process in 2011 using an automated soil CO₂ flux system. The effects of soil temperature, soil moisture and thin snowpack on soil respiration and its temperature sensitivity were investigated.Important findings Total soil respiration and heterotrophic respiration both showed a declining trend during the observation period, and no significant difference was found between soil respiration and heterotrophic respiration until the snowpack exceeded 20cm. Soil respiration was exponentially correlated with soil temperature and its temperature sensitivity (Q 10 value) for the entire measurement duration was 10.5. Snow depth and soil moisture both showed positive effects on the temperature sensitivity of soil respiration. Based on the change in the Q 10 value, we proposed a 'freeze–thaw critical point' hypothesis, which states that the Q 10 value above freeze–thaw critical point is much higher than that below it (16.0 vs. 3.5), and this was probably regulated by the abrupt change in soil water availability during the soil-freezing process. Our findings suggest interactive effects of multiple environmental factors on winter soil respiration and recommend adopting the freeze–thaw critical point to model soil respiration in a changing winter climate.     

Temperature and substrate availability regulate soil respiration in the tropical mountain rainforests,Hainan Island,China

Aims Tropical forest plays a key role in global C cycle; however, there are few studies on the C budget in the tropical rainforests in Asia. This study aims to (i) reveal the seasonal patterns of total soil respiration (R T), litter respiration (R L) and soil respiration without surface organic litter (R NL) in the primary and secondary Asian tropical mountain rainforests and (ii) quantify the effects of soil temperature, soil moisture and substrate availability on soil respiration.Methods The seasonal dynamics of soil CO₂ efflux was measured by an automatic chamber system (Li-8100), within the primary and secondary tropical mountain rainforests located at the Jianfengling National Reserve in Hainan Island, China. The litter removal treatment was used to assess the contribution of litter to belowground CO₂ production.Important findings The annual R T was higher in the primary forest (16.73±0.87 Mg C ha^-1) than in the secondary forest (15.10±0.26 Mg C ha^-1). The rates of R T, R NL and R L were all significantly higher in the hot and wet season (May–October) than those in the cool and dry season (November–April). Soil temperature at 5cm depth could explain 55–61% of the seasonal variation in R T, and the temperature sensitivity index (Q 10) ranked by R L (Q 10 = 3.39)> R T (2.17)> R NL (1.76) in the primary forest and by R L (4.31)> R T (1.86)> R NL (1.58) in the secondary forest. The contribution of R L to R T was 22–23%, while litter input and R T had 1 month time lag. In addition, the seasonal variation of R T was mainly determined by soil temperature and substrate availability. Our findings suggested that global warming and increased substrate availability are likely to cause considerable losses of soil C in the tropical forests.     

Responses of tree fine roots to temperature

Soil temperature can influence the functioning of roots in many ways. If soil moisture and nutrient availability are adequate, rates of root length extension and root mortality increase with increasing soil temperature, at least up to an optimal temperature for root growth, which seems to vary among taxa. Root growth and root mortality are highly seasonal in perennial plants, with a flush of growth in spring and significant mortality in the fall. At present we do not understand whether root growth phenology responds to the same temperature cues that are known to control shoot growth. We also do not understand whether the flush of root growth in the spring depends on the utilization of stored nonstructural carbohydrates, or if it is fueled by current photosynthate. Root respiration increases exponentially with temperature, but Q ₁₀ values range widely from c . 1.5 to > 3.0. Significant questions yet to be resolved are: whether rates of root respiration acclimate to soil temperature, and what mechanisms control acclimation if it occurs. Limited data suggest that fine roots depend heavily on the import of new carbon (C) from the canopy during the growing season. We hypothesize that root growth and root respiration are tightly linked to whole-canopy assimilation through complex source–sink relationships within the plant. Our understanding of how the whole plant responds to dynamic changes in soil temperature, moisture and nutrient availability is poor, even though it is well known that multiple growth-limiting resources change simultaneously through time during a typical growing season. We review the interactions between soil temperature and other growth-limiting factors to illustrate how simple generalizations about temperature and root functioning can be misleading.     

Water availability controls microbial temperature responses in frozen soil CO2 production

Soil processes in high-latitude regions during winter are important contributors to global carbon circulation, but our understanding of the mechanisms controlling these processes is poor and observed temperature response coefficients of CO₂ production in frozen soils deviate markedly from thermodynamically predicted responses (sometimes by several orders of magnitude). We investigated the temperature response of CO₂ production in 23 unfrozen and frozen surface soil samples from various types of boreal forests and peatland ecosystems and also measured changes in water content in them after freezing. We demonstrate that deviations in temperature responses at subzero temperatures primarily emanates from water deficiency caused by freezing of the soil water, and that the amount of unfrozen water is mainly determined by the quality of the soil organic matter, which is linked to the vegetation cover. Factoring out the contribution of water limitation to the CO₂ temperature responses yields response coefficients that agree well with expectations based on thermodynamic theory concerning biochemical temperature responses. This partitioning between a pure temperature response and the effect of water availability on the response of soil CO₂ production at low temperatures is crucial for a thorough understanding of low-temperature soil processes and for accurate predictions of C-balances in northern terrestrial ecosystems.     

Stomatal response to humidity: implications for transpiration

Abstract. Transpiration rates from apple leaves are analysed in terms of the ratio of latent heat flux (λ E ) to leaf net radiation ( Q ₁) and the climatological resistance ( r_i ). Increases in stomatal resistance with increasing leaf to air vapour pressure gradient ( D ), described by an empirical model, are incorporated in the analysis. This humidity effect causes the proportion of energy dissipated as latent heat to fall as Q ₁ increases, so that leaf transpiration rates in high energy environments are likely to be similar to those in lower energy environments. Boundary layer resistance ( r _a) exerts an increasingly important effect on transpiration rates as Q ₁ increases. At constant Q ₁ stomatal closure in response to increasing D results in very small changes in leaf temperature ( T ₁) across a wide range of ambient vapour pressure deficits (δ e ); r _a is then the major factor determining T ₁. The implications of these results are discussed.     

Investigating biological control over soil carbon temperature sensitivity

Understanding the temperature sensitivity of soil respiration is critical for predicting the response of ecosystems to climate change, yet the microbial communities responsible are rarely considered explicitly in studies or models. In this study, we assessed total microbial community composition, quantified bacterial respiration temperature response, and investigated the temperature dependence of bacterial carbon substrate utilization in tropical, temperate, and taiga soils (from Puerto Rico, California, and Alaska). Microbial community composition was characterized using phospholipid fatty acid analysis. Bacterial community respiration on a standardized set of substrates was ascertained using the BiOLOG^™ substrate utilization assay incubated at four temperatures: 4, 12, 28, and 40 °C. First, we found that microbial communities from the three latitudes were compositionally distinct and that the bacterial component of the three communities had markedly different respiration temperature–response curves corresponding with their experienced temperature regimes. We use these data to highlight limitations of widely used temperature–response equations and investigate temperature-dependent patterns of substrate utilization. We found that temperature response, in terms of both respiration rates and substrate use, varied for these bacterial communities independent of substrate quality or quantity interactions such as labile depletion. In contrast to the common assumption of heterotrophic microbial ubiquity, we found that bacterial community differences from these diverse systems appeared to determine both rates of respiration and patterns of carbon substrate usage. We suggest that microbial community composition-specific responses to changing climate may be important in predicting the long-term role of ecosystems in atmospheric CO₂ dynamics.     

Quantitative aspects of heterogeneity in soil organic matter dynamics in a cool-temperate Japanese beech forest: a radiocarbon-based approach

Soil is the largest carbon reservoir in terrestrial ecosystems; it stores twice as much carbon as the atmosphere. It is well documented that global warming can lead to accelerated microbial decomposition of soil organic carbon (SOC) and enhance the release of CO₂ from the soil to the atmosphere; however, the magnitude and timing of this effect remain highly uncertain due to a lack of quantitative data concerning the heterogeneity of SOC biodegradability. Therefore, we sought to identify SOC pools with respect to their specific mean residence times (MRTs), to use those SOC pools to partition soil respiration sources, and to estimate the potential response of the pools to warming. We collected surface soil and litter samples from a cool-temperate deciduous forest in Japan, chemically separated the samples into SOC fractions, estimated their MRTs based on radiocarbon (¹⁴C) isotope measurements, and used the data to construct a model representing the soil as a complex of six SOC pools with different MRT ranges. We estimate that a minor, fast-cycling SOC pool with an MRT of less than 10 years (corresponding to the O horizon and recognizable plant leaf fragments in the A1 horizon) is responsible for 73% of annual heterotrophic respiration and 44% of total soil respiration. However, the predicted response of these pools to warming demonstrates that the rate of SOC loss from the fast-cycling SOC pool diminishes quickly (within several decades) because of limited substrate availability. In contrast, warming will continue to accelerate SOC loss from slow-cycling pools with MRTs of 20–200 years over the next century. Although using a ¹⁴C-based approach has drawbacks, these estimates provide quantitative insights into the potential importance of slow-cycling SOC dynamics for the prediction of positive feedback to climate change.     

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。     

北京山区不同植被类型的土壤呼吸特征及其温度敏感性

土壤呼吸作为陆地生态系统碳循环的重要组成部分,是生态系统碳循环研究中的热点问题.土壤呼吸温度敏感性(Q₁₀)是估算土壤呼吸对全球变暖的反馈参数,研究不同植被类型的Q₁₀对评估森林生态系统碳收支具有重要意义.本研究以北京山区典型植被类型侧柏、油松和栓皮栎为研究对象,通过测定生长季内3种植被类型的土壤理化性质、土壤水热因素以及土壤呼吸速率(R_s)的变化,探究不同植被类型下的土壤呼吸特征及温度敏感性.结果表明:3种主要植被类型的R_s在生长季内与土壤温度、湿度的变化趋势相似,均呈现先升高后降低的单峰变化,R_s在4月初最低(0.45 μmol·m^-2·s^-1),随后逐渐增大,在7月初达到峰值(3.95 μmol·m^-2·s^-1),然后逐渐降低,3种植被类型的R_s和Q₁₀值均存在显著差异.土壤温度和湿度是土壤呼吸的重要影响因素,两者与R_s拟合的回归模型可以解析土壤呼吸速率48.1%～56.7%的变化.北京山区的Q₁₀值在2.05～3.19,在同一植被类型下,Q₁₀值与土壤有机碳含量呈显著负相关(R²>0.9),植被类型、海拔和土壤有机碳含量是造成不同植被类型Q₁₀值差异的重要原因.     

Temperature and moisture sensitivities of CO2 efflux from lowland and alpine meadow soils

Aims This study was conducted to (i) determine if soil CO₂ efflux is more sensitive to temperature changes in alpine areas than in lowland grasslands, (ii) examine the effects of temperature and moisture on soil respiration, and (iii) evaluate the potential for change in soil carbon storage in response to global warming in different grasslands in East Asia.Methods We collected soil samples from two different temperate grasslands, an alpine meadow on the Qinghai-Tibetan plateau, China, and a lowland grassland in Tsukuba, Japan. The CO₂ emission rate was then measured for these soil samples after they were incubated at 25°C and 60% of the water holding capacity for 7 days.Important findings (i)?The soil respiration rate was more sensitive to temperature change in the alpine soil than in the lowland soil. The average Q 10 was 7.6 for the alpine meadow soil but only 5.9 for the lowland soil. The increased sensitivity appears to be due, at least in part, to the soil organic carbon content and/or soil carbon to nitrogen ratio, especially in the surface layer. (ii) The relationship between the CO₂ emission rate and the soil moisture content revealed that the alpine meadow had a more clear response than the lowland soil. (iii) This study suggests that changes in soil moisture and soil temperature may have larger impacts on soil CO₂ efflux in the alpine meadow than in the lowland grassland evaluated here.     

松嫩平原西部草甸草原5种典型植物群落土壤呼吸的时空动态

土壤呼吸是陆地生态系统碳循环的重要组分, 由于受到生物因子与非生物因子的共同作用, 土壤碳排放量在时间和空间尺度上都具有一定的变异性。为弄清松嫩平原西部草甸草原植物群落土壤呼吸作用的时空动态变化及其影响因子, 以典型植被碱蓬(Suaeda glauca)、虎尾草(Chloris virgata)、碱茅(Puccinellia distans)、芦苇(Phragmites australis)、羊草(Leymus chinensis)群落为研究对象, 采用LI-6400土壤呼吸测定系统对该生态系统2011-2012年植物生长季内土壤呼吸作用进行了监测。结果表明: 土壤温度可以解释土壤呼吸作用变异的53%-82%, 是影响该生态系统土壤碳排放时间变异的主要因素。土壤水分并未对土壤呼吸作用时间变异产生明显的影响。不同植物群落的土壤呼吸的温度敏感性(Q₁₀)有所差异, Q₁₀为2.0-6.7。生长季内, 5种植物群落的土壤累积碳排放量的平均值为316.6 g C·m^-2。生长季内土壤碳累积排放量与植被地上生物量、土壤有机碳含量、平均土壤温度显著正相关, 与平均土壤含水量、pH值、土壤电导率及交换性钠百分比呈负相关关系。土壤的微气候、植被的地上生物量及土壤性质的差异是土壤碳排放空间变异的主要影响因素。     

Changes in leaf nitrogen and carbohydrates underlie temperature and CO2 acclimation of dark respiration in five boreal tree species

We tested the hypothesis that acclimation of foliar dark respiration to CO₂ concentration and temperature is associated with adjustments in leaf structure and chemistry. Populus tremuloides Michx. , Betula papyrifera Marsh. , Larix laricina (Du Roi) K. Koch , Pinus banksiana Lamb., and Picea mariana (Mill.) B.S.P. were grown from seed in combined CO₂ (370 or 580 μ mol mol^–1) and temperature treatments (18/12, 24/18, or 30/24 °C). Temperature and CO₂ effects were predominately independent. Specific respiration rates partially acclimated to warmer thermal environments through downward adjustment in the intercept, but not Q ₁₀ of the temperature–response functions. Temperature acclimation of respiration was larger for conifers than broad-leaved species and was associated with pronounced reductions in leaf nitrogen concentrations in conifers at higher growth temperatures. Short-term increases in CO₂ concentration did not inhibit respiration. Growth in the elevated CO₂ concentration reduced leaf nitrogen and increased non-structural carbohydrate concentrations. However, for a given nitrogen concentration, respiration was higher in leaves grown in the elevated CO₂ concentration, as rates increased with increasing carbohydrates. Across species and treatments, respiration rates were a function of both leaf nitrogen and carbohydrate concentrations ( R ² = 0·71, P < 0·0001). Long-term acclimation of foliar dark respiration to temperature and CO₂ concentration is largely associated with changes in nitrogen and carbohydrate concentrations.     

Temperature responses are a window to the physiology of dark respiration: differences between CO2 release and O2 reduction shed light on energy conservation

We showed that temperature responses of dark respiration for foliage of Pinus radiata could be approximated by Arrhenius kinetics, whereby E ₀ determines shape of the exponential response and denotes overall activation energy of respiratory metabolism. Reproducible and predictable deviation from strict Arrhenius kinetics depended on foliage age, and differed between R _CO2 and R _O2. Inhibition of oxygen reduction ( R _O2) by cyanide (inhibiting COX) or SHAM (inhibiting AOX) resulted in reproducible changes of the temperature sensitivity for R _O2, but did not affect R _CO2. Enthalpic growth – preservation of electrons in anabolic products – could be approximated with knowledge of four variables: activation energies ( E ₀) for both R _CO2 and R _O2, and basal rates of respiration at a low reference temperature ( R _REF). Rates of enthalpic growth by P. radiata needles were large in spring due to differences between R _REF of oxidative decarboxylation and that of oxygen reduction, while overall activation energies for the two processes were similar. Later during needle development, enthalpic growth was dependent on differences between E ₀ for R _CO2 as compared with R _O2, and increased E ₀( R _O2) indicated greater contributions of cytochrome oxidase to accompany the switch from carbohydrate sink to source. Temperature-dependent increments in stored energy can be calculated as the difference between R _CO2▵ H _CO2 and R _O2▵ H _O2.     

鄱阳湖苔草湿地非淹水期CO2释放特征

2009年9月至2010年4月非淹水期,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湿地,设置土壤-植物系统(TC)、剪除植物地上部分(TJ)2个试验处理（分别代表生态系统和土壤呼吸）,利用密闭箱-气相色谱法测定了非淹水期鄱阳湖苔草湿地CO₂释放通量.结果表明：苔草湿地生态系统呼吸与土壤呼吸均具有明显的季节变化模式,释放速率变化范围分别为89.57～1243.99和75.30～960.94mg CO₂·m^-2·h^-1,土壤呼吸占生态系统呼吸的比例为64%(39%～84%);土壤温度是苔草湿地CO₂通量的主要控制因子,可以解释呼吸速率80%以上的变异;生态系统呼吸与土壤呼吸的温度敏感性指数(Q₁₀)分别为3.31和2.75,且冬季的Q₁₀值明显高于春秋季节;土壤水分与CO₂释放速率之间未达到显著相关;非淹水期,鄱阳湖苔草湿地是大气CO₂的汇,其强度为1717.72 g C·m^-2.