神农架海拔梯度上4种典型森林的土壤呼吸组分及其对温度的敏感性

量化森林土壤呼吸及其组分对温度的响应对准确评估未来气候变化背景下陆地生态系统的碳平衡极其重要。该文通过对神农架海拔梯度上常绿阔叶林、常绿落叶阔叶混交林、落叶阔叶林以及亚高山针叶林4种典型森林土壤呼吸的研究发现: 4种森林类型的年平均土壤呼吸速率和年平均异养呼吸速率分别为1.63、1.79、1.74、1.35 μmol CO₂·m^-2·s^-1和1.13、1.12、1.12、0.80 μmol CO₂·m^-2·s^-1。该地区的土壤呼吸及其组分呈现出明显的季节动态, 夏季最高, 冬季最低。4种森林类型中, 阔叶林的土壤呼吸显著高于针叶林, 但阔叶林之间的土壤呼吸差异不显著。土壤温度是影响土壤呼吸及其组分的主要因素, 二者呈显著的指数关系; 土壤含水量与土壤呼吸之间没有显著的相关关系。4种典型森林土壤呼吸的Q₁₀值分别为2.38、2.68、2.99和4.24, 随海拔的升高土壤呼吸对温度的敏感性增强, Q₁₀值随海拔的升高而增加。     

水肥一体化条件下设施菜地的N2O排放

在保证作物产量的前提下,研究减少农田土壤N_2O排放的水肥统筹管理措施对全球温室气体减排具有重要意义。以京郊典型设施菜地为例,设置了农民习惯(FP)、水肥一体化(FPD)、优化水肥一体化(OPTD)和对照(CK)4个处理,采用静态箱-气相色谱法,对果菜-叶菜(黄瓜-芹菜)轮作周期内土壤N_2O排放进行了观测,并分析了氮肥施用量、灌溉方式、土壤温度和湿度等因素对土壤N_2O排放的影响。结果表明:在黄瓜-芹菜种植模式中,各施氮处理除基肥施用后N_2O排放峰持续10—15d外,一般施肥、施肥+灌溉事件后土壤N_2O排放峰均呈现3—5d短而急促的情形。黄瓜生长季N_2O排放通量与土壤湿度(WFPS)之间呈现显著相关的关系;芹菜生长季N_2O排放通量与土壤温度之间呈现显著相关的关系。观测期内FP处理N_2O排放量为(31.00±2.15)kg N/hm~2,FPD处理与之相比N_2O排放量减少了4.2%,而OPTD处理在减少40%化肥氮量的情况下,N_2O累积排放量比FP处理减少了42.7%,且达到显著水平。说明在水肥一体化条件下,合理改变施肥体系是减少N_2O排放的前提,在此基础上进行水肥优化是设施菜地保持产量、减少N_2O排放的重要技术措施。     

中国东部亚热带森林土壤呼吸的时空格局

土壤呼吸是陆地碳循环中仅次于全球总初级生产力的第二大碳通量途径, 揭示土壤呼吸的时空格局对整个陆地碳循环具有重要意义。该文在中国东部亚热带季风气候区, 按纬度梯度由南向北选取深圳梧桐山、杨东山十二度水保护区、宁波天童山3个区域作为研究对象, 于2009年8月至2010年10月测定了不同季节各个区域内代表性植被类型的土壤呼吸速率及地下5 cm处土壤温度, 旨在初步了解中国东部亚热带森林地区土壤呼吸的时空格局及其影响因素。结果显示: 3个区域的土壤呼吸速率均存在显著的季节变化, 其变幅为2.64-6.24 μmol CO₂·m ^-2·s^-1, 总体趋势和地下5 cm处土壤温度的季节变化一致, 均为夏季最高冬季最低; 土壤温度的变化可以解释不同样地土壤呼吸季节变化的58.3%-90.2%; 各样地全年的Q₁₀值从1.56到3.27; 通过离样地最近的气象站点的日平均气温与试验样地地下5 cm处土壤温度之间的线性正相关关系推算出日土壤温度的变化, 利用土壤呼吸速率和地下5 cm处土壤温度之间的指数关系, 估算出各样地全年的土壤CO₂通量为1 077-2 058 g C·m^-2·a^-1, 在全球所有生态系统类型中处于较高水平。     

Dependence of the Q10 values on the depth of the soil temperature measuring point

The parameter Q₁₀ is commonly used to express the relationship between soil CO₂ efflux and soil temperature. One advantage of this parameter is its application in a model expression of respiration losses of different ecosystems. Correct specification of Q₁₀ in these models is indispensable. Soil surface CO₂ efflux and soil temperature at different depths were measured in a 21-year-old Norway spruce stand and a mountain grassland site located at the Experimental Ecological Study Site Bily Kriz, Beskydy Mts. (NE Czech Republic), using automated gasometric systems. A time-delay and goodness-of-fit between soil CO₂ efflux and soil temperature at different measuring depths were determined. Wide ranges of values for the time-delay of CO₂ efflux in response to temperature, Q₁₀ and the determination coefficient (R²) between CO₂ efflux and temperature were obtained at the both sites. The values of Q₁₀ and the CO₂ time-delay increased with depth, while the R² of the CO₂-temperature relationship significantly decreased. Soil temperature records obtained close to the soil surface showed the highest values of R² and the lowest value of the time-delay at both sites. Measurement of soil temperature at very shallow soil layer, preferably at the soil surface, is highly recommended to determine useable values of Q₁₀. We present a new procedure to normalize Q₁₀ values for soil temperatures measured at different depths that would facilitate comparison of different sites.     

Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO₂ concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open, gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO₂ concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material.Root respiration was strongly affected by diurnal fluctuations in temperature (Q₁₀ = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO₂ concentrations (400 to 25000 ppm CO₂; pH around 6). Soil CO₂ was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO₂ concentration to that of incoming air. Irrigation caused a temporary reduction in CO₂ diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.     

降雨对草地土壤呼吸季节变异性的影响

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

Long-Term Effects of Elevated CO2 on Woody Tissues Respiration of Norway Spruce Studied in Open-Top Chambers

In an open-top chamber experiment located in a mountain stand of 14-years-old Norway spruce (Picea abies [L.] Karst.), trees were continuously exposed to either ambient CO₂ concentration (A), or ambient + 350 µmol mol^–1 (E) over four growing seasons. Respiration rates of different woody parts (stem, branches, coarse roots) were measured during the last growing season. The calculated increase in the respiration rate related to a 10 °C temperature change (Q₁₀) was different in stem compared to branches and roots. Differences between the E and A variants were statistically significant only for roots in the autumn. Stem maintenance respiration (R_Ms) measured in April and November (periods of no growth activity) were not different. The stem respiration values (R_s) were recalculated to a standard temperature of 15 °C to estimate the seasonal course. The obtained R_s differed significantly between used variants during July and August. At the end of the season, R_s in E decreased slower than in A, indicating some prolongation of the physiological activity under the elevated CO₂ concentration. The total stem respiration carbon losses for the investigated growing season (May – September) were higher for A (2.32 kg(C) m^–2 season^–1) compared to E (2.12 kg(C) m^–2 season^–1). The respiration rates of the whorl branches (R_b) were lower compared with the stem respiration but not significantly different between the used variants. The root respiration rate was increased in E variant.     

Coupling of canopy gas exchange with root and rhizosphere respiration in a semi-arid forest

The strength of coupling between canopy gas exchange and root respiration was examined in ~15-yr-old ponderosa pine (Pinus ponderosa Doug. Ex Laws.) growing under seasonally drought stressed conditions. By regularly watering part of the root system to reduce tree water stress and measuring soil CO₂ efflux on the dry, distant side of the tree, we were able to determine the strength of the relationship between soil autotrophic (root and rhizosphere) respiration and changes in canopy carbon uptake and water loss by comparison with control trees (no watering). After ~40 days the soil CO₂ efflux rate, relative to pre-treatment conditions, was twice that of the controls. This difference, attributable to root and rhizosphere respiration, was strongly correlated with differences in transpiration rates between treatments (r² = 0.73, p<0.01). By the end of the period, transpiration of the irrigated treatment was twice that of controls. Periodic measurements of photosynthesis under non-light limited conditions paralleled the patterns of transpiration and were systematically higher in the irrigated treatment. We observed no evidence for a greater sensitivity of soil autotrophic respiration to temperature compared to the response of heterotrophic respiration to temperature; the Q₁₀ for total soil respiration was 1.6 (p>0.99) for both treatments. At the ecosystem scale, daily soil CO₂ efflux rate was linearly related to gross primary productivity (GPP) as measured by eddy-covariance technique (r² = 0.55, p<0.01), suggesting patterns of soil CO₂ release appear strongly correlated to recent carbon assimilation in this young pine stand. Collectively the observed relationships suggest some consideration should be given to the inclusion of canopy processes in future models of soil respiration.     

Soil respiration in a Mediterranean oak forest at different developmental stages after coppicing

To assess the variation of soil respiration at different forest stages we measured it in a coppiced oak (Quercus cerris L.) chronosequence in central Italy during two campaigns, spanning 2 successive years, in four stands at different stages of the rotation: 1 year (S1), 5 years (S5), 10 years (S10) and 17 years (S17) after coppicing. The contribution of the different components of soil respiration flux (aboveground litter, belowground decomposition soil organic matter and root respiration) was estimated by a paired comparison of manipulative experiments between the recently coppiced stand (S1) and mature stand (S17). Ninety percent of soil respiration values were between 1.7 and 7.8 μmol m^?2 s^?1, with an overall mean (±SD) of 4.0±2.7 μmol m^?2 s^?1. Spatial variation of soil respiration was high (CV=44.9%), with a mean range (i.e. patch size) of 4.8±2.7 m, as estimated from a semivariance analysis. In the absence of limitation by soil moisture, soil respiration was related to soil temperature with the exponential Q₁₀ model (average Q₁₀=2.25). During summer, soil moisture constrained soil respiration and masked its dependence on soil temperature. Soil respiration declined over the years after coppicing. Assuming a linear decline with stand age, we estimated a reduction of 24% over a 20‐year‐rotation cycle. The response of soil respiration to temperature also changed with age of the stands: the Q₁₀ was estimated to decrease from 2.90 in S1 to 2.42 in S17, suggesting that different components or processes may be involved at different developmental stages. The contribution of heterotrophic respiration to total soil respiration flux was relatively larger in the young S1 stand than in the mature S17 stand.     

Experimental forest soil warming: response of autotrophic and heterotrophic soil respiration to a short-term 10°C temperature rise

We warmed the top soil of a mature coniferous forest stand by means of heating cables on control and trenched plots within 24 h by 10°C at 1 cm soil depth (9°C at 5 cm depth) and measured the effect on the autotrophic (R_A) and heterotrophic (R_H) component of total soil CO₂ efflux (R_S). The short time frame of warming enabled us to exclude confounding fluctuations in soil moisture and carbon (C) flow from the canopy. The results of the field study were backed up by a lab soil incubation experiment. During the first 12 h of warming, R_A strongly responded to soil warming; The Q ₁₀ values were 5.61 and 6.29 for 1 and 5 cm soil depth temperature. The Q ₁₀ values for R_A were almost twice as high as the Q ₁₀ values of R_H (3.04 and 3.53). Q ₁₀ values above 5 are above reasonable plant physiological values for root respiration. We see interactions of roots, mycorrhizae and heterotrophic microbes, combined with fast substrate supply to the rhizosphere as an explanation for the high short-term temperature response of R_A. When calculated over the whole duration (24 h) of the field soil-warming experiment, temperature sensitivities of R_A and R_H were similar (no significant difference at P < 0.05); Q ₁₀ values were 3.16 and 3.96 for R_A and 2.94 and 3.35 for R_H calculated with soil temperatures at 1 and 5 cm soil depth, respectively. Laboratory incubation showed that different soil moisture contents of trenched and control plots affected rates of R_H, but did not affect the temperature sensitivity of R_H. We conclude that a single parameter is sufficient to describe the temperature sensitivity of R_S in soil C models which operate on larger temporal and spatial scales. The strong short-term response of R_A may be of relevance in soils suspected to experience increasingly strong diurnal temperature variations.     

Short term effect of ploughing a permanent pasture on N2O production from nitrification and denitrification

Soils are an important source of N₂O, which can be produced both in the nitrification and the denitrification processes. Grassland soils in particular have a high potential for mineralization and subsequent nitrification and denitrification. When ploughing long term grassland soils, the resulting high supply of mineral N may provide a high potential for N₂O losses. In this work, the short-term effect of ploughing a permanent grassland soil on gaseous N production was studied at different soil depths. Fertiliser and irrigation were applied in order to observe the effect of ploughing under a range of conditions. The relative proportions of N₂O produced from nitrification and denitrification and the proportion of N₂ gas produced from denitrification were determined using the methyl fluoride and acetylene specific inhibitors. Irrespectively to ploughing, fertiliser application increased the rates of N₂O production, N₂O production from nitrification, N₂O production from denitrification and total denitrification (N₂O + N₂). Application of fertiliser also increased the denitrification N₂O/N₂ ratio both in the denitrification potential and in the gaseous N productions by denitrification. Ploughing promoted soil organic N mineralization which led to an increase in the rates of N₂O production, N₂O production from nitrification, N₂O production from denitrification and total denitrification (N₂O + N₂). In both the ploughed and unploughed treatments the 0–10 cm soil layer was the major contributing layer to gaseous N production by all the above processes. However, the contribution of this layer decreased by ploughing, gaseous N productions from the 10 to 30 cm layer being significantly increased with respect to the unploughed treatment. Ploughing promoted both nitrification and denitrification derived N₂O production, although a higher proportion of N₂O lost by denitrification was observed as WFPS increased. Recently ploughed plots showed lower denitrification derived N₂O percentages than those ploughed before as a result of the lower soil water content in the former plots. Similarly, a lower mean nitrification derived N₂O percentage was found in the 10–30 cm layer compared with the 0–10 cm.     

高寒矮嵩草草甸冬季CO2释放特征

冬季碳排放在高寒草地年内碳平衡中占有重要位置。为探讨高寒草地冬季碳排放特征及温度敏感性,于2003-2005年在中国科学院海北高寒草甸生态系统研究站,利用密闭箱-气相色谱法连续观测了高寒矮嵩草草甸2个冬季的生态系统、土壤呼吸通量特征。结果表明:1)高寒矮嵩草草甸冬季生态系统呼吸、土壤呼吸均具有明显的日变化和季节变化规律,温度是其主要的控制因子,能够解释44%以上的呼吸速率变异。2)冬季生态系统呼吸与土壤呼吸速率在统计上没有显著差异,土壤呼吸占生态系统呼吸的比例高达85%以上。3)2003-2004年冬季生态系统呼吸、土壤呼吸的Q₁₀值分别为1.53,1.38;2004-2005年冬季生态系统呼吸与土壤呼吸的Q₁₀值为1.86,1.68,2个冬季生态系统呼吸的Q₁₀值均高于土壤呼吸。4)未发现高寒矮嵩草草甸冷冬年份的Q₁₀值高于暖冬年份以及冬季的Q₁₀值高于生长季。     

Emissions of nitrous oxide from three tropical forests in Southern China in response to simulated nitrogen deposition

Emissions of nitrous oxide (N₂O) from the soil following simulated nitrogen (N) deposition in a disturbed (pine), a rehabilitated (pine and broadleaf mixed) and a mature (monsoon evergreen broadleaf) tropical forest in southern China were studied. The following hypotheses were tested: (1) addition of N will increase soil N₂O emission in tropical forests; and (2) any observed increase will be more pronounced in the mature forest than in the disturbed or rehabilitated forest due to the relatively high initial soil N concentration in the mature forest. The experiment was designed with four N treatment levels (three replicates; 0, 50, 100, 150 kg N ha⁻¹ year⁻¹ for C (Control), LN (Low-N), MN (Medium-N), and HN (High-N) treatment, respectively) in the mature forest, but only three levels in the disturbed and rehabilitated forests (C, LN and MN). Between October 2005 to September 2006, soil N₂O flux was measured using static chamber and gas chromatography methodology. Nitrogen had been applied previously to the plots since July 2003 and continued during soil N₂O flux measurement period. The annual mean rates of soil N₂O emission in the C plots were 24.1 ± 1.5, 26.2 ± 1.4, and 29.3 ± 1.6 μg N₂O–N m⁻² h⁻¹ in the disturbed, rehabilitated and mature forest, respectively. There was a significant increase in soil N₂O emission following N additions in the mature forest (38%, 41%, and 58% when compared to the C plots for the LN, MN, and HN plots, respectively). In the disturbed forest a significant increase (35%) was observed in the MN plots, but not in the LN plots. The rehabilitated forest showed no significant response to N additions. Increases in soil N₂O emission occurred primarily in the cool-dry season (November, December and January). Our results suggest that the response of soil N₂O emission to N deposition in tropical forests in southern China may vary depending on the soil N status and land-use history of the forest.     

封育对羊草草地土壤碳矿化激发效应和温度敏感性的影响

土壤碳矿化(或土壤异养呼吸)的温度敏感性和激发效应是深入揭示土壤呼吸控制机理及其对未来气候变化响应与适应的重要研究方向。该文以自由放牧(FG0)、封育11年(FG11)、封育31年(FG31)的羊草(Leymus chinensis)草地为研究对象, 通过0、5、10、15、20、25 ℃培养, 探讨了封育对羊草草地土壤碳矿化激发效应和温度敏感性的影响。结果表明: 封育年限、添加葡萄糖、培养温度和培养时间对土壤碳矿化速率均具有显著的影响, 不同因素间存在显著的交互效应(p < 0.000 1)。FG0的羊草草地土壤碳矿化累积量显著高于FG11和FG31的, 在添加葡萄糖处理下也呈现相同的趋势。长期封育降低了羊草草地土壤碳矿化的激发效应。在添加葡萄糖后, 培养前7天的土壤碳矿化的激发效应随温度增加而增加, 增加2.28-9.01倍; 在整个56天培养期间, 激发效应介于2.21-5.10倍, 最高值出现在10或15 ℃。土壤碳矿化速率可用经典的指数方程来表示, FG0草地的土壤碳矿化的温度敏感性指数(Q₁₀)大于长期封育草地(FG11和FG31); 与未添加处理相比, 添加葡萄糖显著增加了土壤碳矿化速率的温度敏感性, 即在添加葡萄糖后土壤微生物呼吸受温度的影响更大。长期封育会降低羊草草地土壤的碳矿化速率、温度敏感性和激发效应, 从而降低土壤碳周转速率和释放速率, 使内蒙古地区长期封育草地仍然具有碳固持能力。     

全球陆地生态系统光合作用与呼吸作用的温度敏感性

基于全球647套通量数据,定量分析了全球尺度下生态系统光合作用和呼吸作用的温度敏感性(Q10)随纬度、气候和植被的分布规律。结果表明:在全球尺度下,光合作用和呼吸过程的温度敏感性(Q10,G和Q10,R)都随纬度的升高而增加,其中Q10,G和Q10,R的均值分别为3.99±0.21和2.28±0.074。除热带多树草原、常绿落叶林外,Q10,G均大于Q10,R值。不同植被类型的温度敏感性存在显著性差异,表现为:针叶林阔叶林;落叶林常绿林,其中生态系统的季节性变异是造成差异的主要原因。当植被类型和纬度区域共同影响Q10值时,植被类型对Q10值的总变异贡献更大。气候类型对Q10,G和Q10,R都有显著影响。在气候带上,干旱带的Q10,G最小,而冷温带的Q10,G最高。不同气候类型下(除温带草原气候外)的Q10,G都大于Q10,R。在极端条件下,温度可能不在是主导因素,而水分对温度敏感性的影响不可忽略,今后的研究需要更多的关注生态系统温度敏感性对水分变化的响应。     

川西北高寒草甸不同放牧模式对土壤呼吸的影响

采用土壤二氧化碳(CO_2)通量自动测量系统,对不同放牧模式(全年禁牧、夏季放牧、冬季放牧和自由放牧)下川西北高寒草甸的土壤呼吸进行监测,比较了不同放牧模式下土壤呼吸的季节动态和温度敏感性。研究发现:1)放牧模式可以改变高寒草甸土壤呼吸的季节动态变化。禁牧、夏季放牧以及自由放牧样地的土壤呼吸在季节上的变化趋势基本相似,而冬季放牧样地的土壤呼吸最大值与前者相比明显向后推迟;2)放牧模式并不改变高寒草甸年平均土壤呼吸速率,但对不同季节土壤呼吸速率的影响不同;3)不同放牧模式可以改变土壤呼吸对温度的敏感性(Q_(10))。不同放牧模式下土壤呼吸Q_(10)值大小依次为:禁牧1a(8.13)冬季放牧(7.49)禁牧3a(5.46)夏季放牧(5.20)自由放牧(4.53)。该地区土壤呼吸的Q_(10)值均明显高于热带和其它温带草地土壤呼吸的Q_(10)值。结果表明,放牧模式是影响高寒草甸土壤碳排放的一个重要因素。此外,在未来全球气候变暖背景下,在生长季节无放牧干扰的高寒草甸可能比放牧干扰的高寒草甸释放出更多的CO_2到大气中。     

Contribution of root respiration to total soil respiration in a Japanese cedar (Cryptomeria japonica D. Don) artificial forest

Soil respiration was measured for 2 years in an artificial gap and in an undisturbed area in a Japanese cedar (Cryptomeria japonica D. Don) forest to estimate the contribution of root respiration to total soil respiration. Measurement plots were set up at the center of the gap, the edge of the gap, the edge of the surrounding stand and within the stand. Using a small gap (2.5 m × 2.5 m) enabled us to maintain the same soil temperature and soil moisture as found in the stand. Seasonal fluctuations in soil respiration, increasing in summer and decreasing in winter, corresponded to changes in the soil surface temperature. Soil respiration in the gap site did not differ significantly from those in the stand in the first year of gap formation. However, in the second year, the minimum CO₂ flux was observed at the center of the gap and the maximum at the edge of the surrounding stand. Assuming that the differences between soil respiration in the center of the gap and that in the stand were equal to the root respiration, the root respiration rate was calculated from the relationship between the root respiration rates (Rr) and the soil surface temperature (Ts) by Ln(Rr) = 0.07Ts + 3.48. The average contribution of root respiration to total soil respiration, as estimated from the soil surface temperature in the stand by using the above equation, was 49%. After taking root decomposition into consideration, the contribution of root respiration to soil respiration increased from 49 to 57%.     

温带针阔混交林土壤碳氮气体通量的主控因子与耦合关系

中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。     

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

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

太湖流域典型稻麦轮作农田生态系统碳交换及影响因素

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