Seasonal variation in CO2 efflux of stems and branches of Norway spruce trees

BACKGROUND AND AIMS: Stem and branch respiration, important components of total forest ecosystem respiration, were measured on Norway spruce (Picea abies) trees from May to October in four consecutive years in order (1) to evaluate the influence of temperature on woody tissue CO2 efflux with special focus on variation in Q10 (change in respiration rate resulting from a 10 degrees C increase in temperature) within and between seasons, and (2) to quantify the contribution of above-ground woody tissue (stem and branch) respiration to the carbon balance of the forest ecosystem. METHODS: Stem and branch CO2 efflux were measured, using an IRGA and a closed gas exchange system, 3-4 times per month on 22-year-old trees under natural conditions. Measurements of ecosystem CO2 fluxes were also determined during the whole experiment by using the eddy covariance system. Stem and branch temperatures were monitored at 10-min intervals during the whole experiment. KEY RESULTS: The temperature of the woody tissue of stems and branches explained up to 68% of their CO2 efflux. The mean annual Q10 values ranged from 2.20 to 2.32 for stems and from 2.03 to 2.25 for branches. The mean annual normalized respiration rate, R10, for stems and branches ranged from 1.71 to 2.12 micromol CO2 m(-2)s (-1) and from 0.24 to 0.31 micromol CO2 m(-2) s(-1), respectively. The annual contribution of stem and branch CO2 efflux to total ecosystem respiration were, respectively, 8.9 and 8.1% in 1999, 9.2 and 9.2% in 2000, 7.6 and 8.6% in 2001, and 8.6 and 7.9% in 2002. Standard deviation for both components ranged from 3 to 8% of the mean. CONCLUSIONS: Stem and branch CO2 efflux varied diurnally and seasonally, and were related to the temperature of the woody tissue and to growth. The proportion of CO2 efflux from stems and branches is a significant component of the total forest ecosystem respiration, approx. 8% over the 4 years, and predictive models must take their contribution into account.     

林木树干呼吸变化及其影响因素研究进展

树干呼吸是森林生态系统碳平衡的重要组成部分,它每年消耗碳同化总量(NPP)的11%~33%。受测定技术所限,过去对树干呼吸的研究未能引起足够的重视。近十几年来,由于大气CO₂温室气体浓度的持续升高,树干呼吸已成为研究的热点。测定树干呼吸的方法较多,早期一般采用气体交换法和密闭方法,最近利用便携式光合测定系统(Li-Cor6400)或土壤碳通量测量系统(Li-8100)对树干呼吸采用开路系统测定方法。大量研究结果表明: 1)树干呼吸的日变化呈双峰型曲线,即从早晨开始,树干呼吸速率随温度的上升而增加,到午间有所降低,之后逐渐增加,达到峰值后又逐渐降低。2)树干呼吸的季节动态为:生长季的树干呼吸速率明显高于非生长季,即从春季到夏季树干呼吸速率呈持续升高态势,高峰值出现在7或8月,尔后逐渐下降。树干呼吸活动是一个复杂的生物学过程,其影响因子较多。直接影响因子有气象因子(如温度、湿度和CO₂浓度)和生物因子(如树种、树龄、径阶、边材积和树干氮含量等);而纬度、海拔和地形因子通过影响气象因子或生物因子而间接影响树干呼吸。诸多因子中,树干温度对树干呼吸的贡献最大(Q₁₀可描述树干呼吸对温度升高的敏感性)。树干呼吸机理及其影响因子乃是今后研究的主要内容,一方面要采用统一的测量方法和技术,另一方面要综合考虑影响树干呼吸的内外因素,建立树干呼吸的相关模型,为构建森林生态系统碳循环模型、了解森林生态系统碳收支状况及其对大气CO₂浓度变化的贡献和对全球变化的响应提供理论依据。     

Seasonal variation in respiration of 1-year-old shoots of scots pine exposed to elevated carbon dioxide and temperature for 4 years

Sixteen 20-year-old Scots pine (Pinus sylvestris L.) trees growing in the field were enclosed for 4 years in environment-controlled chambers that maintained: (1) ambient conditions (CON); (2) elevated atmospheric CO2 concentration (ambient + 350 micro mol mol-1; EC); (3) elevated temperature (ambient +2-6 degrees C; ET); or (4) elevated CO2 and elevated temperature (ECT). The dark respiration rates of 1-year-old shoots, from which needles had been partly removed, were measured over the growing season in the fourth year. In all treatments, the temperature coefficient of respiration, Q10, changed with season, being smaller during the growing season than at other times. Respiration rate varied diurnally and seasonally with temperature, being highest around mid-summer and declining gradually thereafter. When measurements were made at the temperature of the chamber, respiration rates were reduced by the EC treatment relative to CON, but were increased by ET and ECT treatments. However, respiration rates at a reference temperature of 15 degrees C were reduced by ET and ECT treatments, reflecting a decreased capacity for respiration at warmer temperatures (negative acclimation). The interaction between season and treatment was not significant. Growth respiration did not differ between treatments, but maintenance respiration did, and the differences in mean daily respiration rate between the treatments were attributable to the maintenance component. We conclude that maintenance respiration should be considered when modelling respiratory responses to elevated CO2 and elevated temperature, and that increased atmospheric temperature is more important than increasing CO2 when assessing the carbon budget of pine forests under conditions of climate change.     

集水区尺度下东北东部森林土壤呼吸的模拟

IBIS模型是陆地碳循环模拟的有利工具,土壤呼吸是陆地碳循环的关键生态学过程,利用IBIS模型模拟估算土壤呼吸对陆地碳循环和全球变化研究具有重要意义.在地形数据、植被参数、土壤质地参数和气象数据支持下,利用改造后的IBIS模型模拟2004年张家沟集水区5种森林类型的土壤呼吸,以实测数据对模拟结果进行验证,并分析土壤呼吸时空格局及其与土壤温湿度的关系.结果表明:(1)改造后的IBIS模型模拟的土壤呼吸值与实测值相关性显著,可较好地用于集水区尺度的森林土壤呼吸模拟估算.(2)土壤呼吸年均值为571 gCm-2 a-1,年土壤呼吸空间格局与生长季土壤呼吸空间格局相似,均表现为高值区主要分布在北部、西南和东南区域,低值区主要分布在沟谷附近,该格局与集水区的地形、植被及其组合等因素有关.(3)生长季内,5种森林类型土壤呼吸的季节性变化均呈单峰曲线形式,土壤呼吸峰值均出现在7月,其中落叶松林峰值最低,为85.5gC/m2,杂木林峰值最高,为146.3 gC/m2.(4)5种森林类型的土壤呼吸值与5 cm深土壤温度存在极显著的指数关系,与土壤湿度的相关性较低,土壤温度的变化可以解释土壤呼吸约70％的季节变化.     

Productivity overshadows temperature in determining soil and ecosystem respiration across European forests

This paper presents CO₂ flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project. Overall, mean annual gross primary productivity (GPP, the total amount of carbon (C) fixed during photosynthesis) of these forests was 1380 ± 330 gC m^?2 y^?1 (mean ±SD). On average, 80% of GPP was respired by autotrophs and heterotrophs and released back into the atmosphere (total ecosystem respiration, TER = 1100 ± 260 gC m^?2 y^?1). Mean annual soil respiration (SR) was 760 ± 340 gC m^?2 y^?1 (55% of GPP and 69% of TER). Among the investigated forests, large differences were observed in annual SR and TER that were not correlated with mean annual temperature. However, a significant correlation was observed between annual SR and TER and GPP among the relatively undisturbed forests. On the assumption that (i) root respiration is constrained by the allocation of photosynthates to the roots, which is coupled to productivity, and that (ii) the largest fraction of heterotrophic soil respiration originates from decomposition of young organic matter (leaves, fine roots), whose availability also depends on primary productivity, it is hypothesized that differences in SR among forests are likely to depend more on productivity than on temperature. At sites where soil disturbance has occurred (e.g. ploughing, drainage), soil espiration was a larger component of the ecosystem C budget and deviated from the relationship between annual SR (and TER) and GPP observed among the less‐disturbed forests. At one particular forest, carbon losses from the soil were so large, that in some years the site became a net source of carbon to the atmosphere. Excluding the disturbed sites from the present analysis reduced mean SR to 660 ± 290 gC m^?2 y^?1, representing 49% of GPP and 63% of TER in the relatively undisturbed forest ecosystems.     

Total and component carbon fluxes of a Scots pine ecosystem from chamber measurements and eddy covariance

BACKGROUND AND AIMS: Distinguishing between, and quantifying, the different components of ecosystem C fluxes is critical in predicting the responses of ecosystem C cycling to climate change. The aims of this study were to quantify the photosynthetic and respiratory fluxes of a 50-year-old Scots pine (Pinus sylvestris) ecosystem, and to distinguish respiration of branches with needles from that of stems, and that of soil. METHODS: The CO2 flux of the ecosystem was continuously measured using the eddy covariance (EC) method, and its components (respiration and photosynthesis of a branch with needles, stem and soil surface) were measured with an automated chamber system, from 2001 to 2004. KEY RESULTS: All values below are chamber based. The average temperature coefficient (Q10) of respiration was 2.7, 2.2 and 4.0, respectively, for branch (Rbran), stem (Rstem) and the soil surface (Rsoil). Respiration at a reference temperature of 15 degrees C (R15) was 1.27, 0.49 and 4.02 micromol CO2 m(-2) ground s(-1) for the three components, respectively. Over 4 years, the annual Rbran, Rstem and Rsoil ranged from 196 to 256, 56 to 83 and 439 to 598 g C m(-2) ground year(-1), respectively, with a 4-year average of 227, 72 and 507 g C m(-2) ground year(-1). Annual ecosystem respiration (Reco) was 731, 783, 909 and 751 g C m(-2) ground year(-1) in years 2001-2004, respectively, gross primary production (GPP) was 922, 1030, 1138 and 1001 g C m(-2) ground year(-1), and net ecosystem production (NEP) was 191, 247, 229 and 251 g C m(-2) ground year(-1). The average contribution of Rbran, Rstem and Rsoil to Reco was 29, 9 and 62 %, respectively. Overstorey photosynthesis accounted for 96 % of GPP. The average Reco/GPP ratio was 0.78. Net primary production (NPP) in the 4 years was 469, 581, 600 and 551 g C m(-2) year(-1), respectively, with the NPP/GPP ratio 0.54 averaged over the years. CONCLUSIONS: Respiration from the soil is the dominant component of ecosystem respiration. Differences between years in Reco were due to differences in temperature during the growing season. Rsoil was more sensitive to temperature than Rbran and Rstem, and differences in Rsoil were responsible for the differences in Reco between years.     

Measuring and simulating crown respiration of Scots pine with increased temperature and carbon dioxide enrichment

Acclimation to elevated atmospheric carbon dioxide concentration and temperature of respiration by the foliage in the crown of Scots pine (Pinus sylvestris) trees is measured and modelled. Starting in 1996, individual 20-year-old trees were enclosed in chambers and exposed to either normal ambient conditions (CON), elevated CO2 concentration (EC), elevated temperature (ET) or a combination of EC and ET (ECT). Respiration of individual leaves within the crown was measured in 2000. To extrapolate the response of respiration of individual leaves to the whole crown, a multi-layer model was developed and used to predict daily and annual crown respiration, in which the crown structure and corresponding microclimate data were used as input. Respiration measurements showed that EC led to higher Q10 values (4.6%) relative to CON, but lower basal respiration rates at 20 degrees C [R1.d(20)] (-7.1%) during the main growth season (days 120-240), whereas ET and ECT both reduced Q10 (-12.0 and -9.8%, respectively) throughout the year but increased R1.d(20) (27.2 and 21.6%, respectively) during the period of no-growth, and slightly reduced R1.d(20) (-1.7 and -2.8%, respectively) during the main growth season. Model computations showed that annual crown respiration increased: (1) by 16% in EC, with 92% of this increase attributable to the increase in foliage area; (2) by 35% in ET, with 66% related to the increase in foliage area and 17% to the rise in ambient temperature; and (3) by 27% in the case of ECT, with 43% attributable to the increase in foliage area and 29% to the rise in ambient temperature. Changed respiration parameters for individual leaves, induced by treatments, made only a small contribution to the annual crown respiration compared with the increased foliage area. The effects of changes in crown architecture and nitrogen distribution, caused by treatments, on the daily and annual course of crown respiration are discussed.     

西双版纳热带季节雨林优势树种树干呼吸特征

 采用红外气体分析法（IRGA）原位监测了西双版纳热带季节雨林11种优势树种树干呼吸速率、1 cm深树干温度以及林内空气变化情况。研究发 现,11种优势树种的树干呼吸具有相同的季节规律,并且雨季均大于干季时的树干呼吸。树种间树干呼吸速率差异显著,在0. 823～2.727 μmol&;#8226;m^-2&;#8226;s^-1。树干1.3 m处所测南北方向树干呼吸无显著性差异。树干呼吸与树干温度显著相关(0.552<0.92),呈良好的自然指数回归关 系,Q₁₀值为1.90～3.03。20 ℃时各树种的RT（总树干呼吸）速率为0.771～2.570μmol&;#8226;m^-2&;#8226;s^-1。     

古尔班通古特沙漠白梭梭枝干光合及其影响因素

植物枝干光合（P_g）固定其自身呼吸所释放的CO₂，有效减少植物向大气的CO₂排放量。以古尔班通古特沙漠优势木本植物白梭梭（Haloxylon persicum）为研究对象，利用LI-COR 6400便携式光合仪与特制光合叶室（P-Chamber）相结合，观测白梭梭叶片、不同径级枝干的光响应及光合日变化特征；同时监测环境因子（大气温湿度、光合有效辐射、土壤温度及含水量等）与叶片/枝干性状指标（叶绿素含量、含水量、干物质含量、碳/氮含量等），揭示叶片/枝干光合的主要影响因子；采用破坏性取样，量化个体水平上叶片与枝干的总表面积，阐明枝干光合对植株个体碳平衡的贡献。研究结果显示：（1）白梭梭叶片叶绿素含量是枝干叶绿素含量的12-16倍，各径级枝干叶绿素含量差异不显著；（2）枝干光饱和点低于叶片，枝干不同径级（由粗至细），暗呼吸速率和枝干光合逐渐减小；（3）光合有效辐射、土壤含水量和空气温湿度是影响叶片光合的主要因子，对枝干光合无显著影响；（4）枝干光合可以固定其自身呼吸产生CO₂的73%，最高可达90%，枝干光合固定CO₂约占个体水平固碳量的15.4%。研究结果表明，忽视枝干光合的贡献来预测未来气候变化背景下荒漠生态系统碳过程，可能存在根本性缺陷，并且在估算枝干呼吸时，需要考虑枝干是否存在光合作用，以提高枝干呼吸的准确性。     

Night temperature has a minimal effect on respiration and growth in rapidly growing plants

BACKGROUND AND AIMS: Carbon gain depends on efficient photosynthesis and adequate respiration. The effect of temperature on photosynthetic efficiency is well understood. In contrast, the temperature response of respiration is based almost entirely on short-term (hours) measurements in mature organisms to develop Q(10) values for maintenance and whole-plant respiration. These Q(10) values are then used to extrapolate across whole life cycles to predict the influence of temperature on plant growth. METHODS: In this study, night temperature in young, rapidly growing plant communities was altered from 17 to 34 degrees C for up to 20 d. Day temperature was maintained at 25 degrees C. CO(2) gas-exchange was continuously monitored in ten separate chambers to quantify the effect of night-temperature on respiration, photosynthesis and the efficiency of carbon gain (carbon use efficiency). KEY RESULTS: Respiration increased only 20-46 % for each 10 degrees C rise in temperature (total respiratory Q(10) of between 1.2 to about 1.5). This change resulted in only a 2-12 % change in carbon use efficiency, and there was no effect on cumulative carbon gain or dry mass. No acclimation of respiration was observed after 20 d of treatment. CONCLUSIONS: These findings indicate that whole-plant respiration of rapidly growing plants has a small sensitivity to temperature, and that the sensitivity does not change among the species tested, even after 20 d of treatment. Finally, the results support respiration models that separate respiration into growth and maintenance components.     

毛白杨树干呼吸及其温度敏感性季节变化特征

树干呼吸(E_s)是森林生态系统碳循环过程的重要组成部分,深入理解树干呼吸过程对未来气候变暖的响应及反馈机制有助于更加精确地估算森林生态系统碳储量。为揭示毛白杨树干呼吸及其温度敏感性的昼夜变化和季节动态规律,利用Li-Cor6400便携式光合作用测定系统及其配套使用的土壤呼吸测量气室(LI-6400-09)对冀南平原区毛白杨的树干呼吸和树干温度实施为期1年的连续监测。结果表明:(1)在生长季,毛白杨树干呼吸与树干温度之间在晚上呈现正相关的关系(R~2=0.88);相反,两者在白天为负相关的关系(R~2=0.96)。(2)整个观测期内,毛白杨树干呼吸和树干温度均呈现"钟形"的变化曲线,树干呼吸与树干温度之间存在着较好的指数函数关系(R~2=0.93),且树干呼吸的温度敏感性系数(Q_(10))为2.62;不同季节毛白杨树干呼吸的Q_(10)存在差异,生长季的Q_(10)(1.95)明显低于非生长季(3.00),表明生长呼吸和维持呼吸对温度的响应也并不相同。(3)温度矫正后的毛白杨树干呼吸(R_(15))在昼夜和季节尺度上均存在明显的变异,即夜晚的R_(15)显著高于白天(P0.01),生长季的R_(15)明显高于非生长季(P0.05);树干可溶性糖含量与生长季的R_(15)存在较好的相关性(R~2=0.52),而非生长季的R_(15)却主要受到树干淀粉含量的影响。研究结果表明,在生长季,毛白杨树干呼吸的在日变化主要受到温度的影响,而在季节尺度上Q_(10)的变异则与树干呼吸中维持呼吸所占比例及树干中非结构性碳水化合物(可溶性糖和淀粉)的含量及类型紧密相关。     

西双版纳地区稻田CO2排放通量

采用静态暗箱-气相色谱法对云南西双版纳地区单季稻田CO2排放及氮肥、水热因子对CO2排放的影响进行田间原位观测研究.试验设3个氮肥水平处理:N0(0 kg N hm-2)、N150(150 kg N hm-2)和N300(300 kg N hm-2).结果表明,受一天温度变化的影响,西双版纳地区稻田生态系统呼吸日变化为单峰型,其最大值出现在11:00～13:00之间,最小值出现在凌晨.稻田土壤呼吸呈明显的季节变化趋势,土壤呼吸平均速率为水稻收获后休闲季节>种植前休闲季节>水稻生长季节,差异达到1%显著水平.不同季节影响土壤呼吸的环境因子不同.土壤水分含量低于34%时,土壤呼吸速率与土壤含水量呈正相关,达5%显著水平;地面淹水时,土壤呼吸速率与淹水深度呈1%极显著负相关;水分含量高于38%时,土壤呼吸速率与温度呈极显著指数相关.长期考虑(整个生长季节),氮肥的施用对稻田土壤呼吸和生态系统呼吸无影响;N300处理抑制植株呼吸作用,单位生物量呼吸速率下降.氮肥的施用对土壤呼吸有短期影响,氮肥用量增加,土壤呼吸速率增加.计算得出N0、N150和N300处理年土壤呼吸量分别为6.27、6.31 t C hm-2 a-1和5.89 t C hm-2 a-1;年净固定大气中CO2-C分别为1.41、2.22 t C hm-2 a-1和1 11 t C hm-2 a-1,表明西双版纳稻田生态系统是碳汇.     

Temporal and spatial variations of stem CO2 efflux of three species in subtropical China

Aims Although stem CO₂ efflux is critical to ecosystem carbon and energy balance and its feedback to future climate change, little information is available on stem CO₂ efflux and its responses to temperature, especially in subtropical China. This study aims to (i) evaluate the temporal and spatial variations of stem CO₂ efflux of three species, including oak (Quercus acutissima Carr.), masson pine (Pinus massoniana Lamb.) and loblolly pine (Pinus taeda Linn.) in subtropical China and (ii) analyze the temperature sensitivity of stem CO₂ efflux in the three species based on 2-year field measurements.Methods We measured stem CO₂ efflux and stem temperature (at 3 cm depth) of the three species using the horizontally oriented soil chamber technique from September 2008 to August 2010. We also conducted a 24-h measurement to examine the diurnal variation of stem CO₂ efflux in three consecutive days in April 2009.Important findings The temporal dynamics of stem CO₂ efflux followed the change of the stem temperature in a 3-cm depth with a bell-shaped curve in the three species. Stem temperature explained 77–85% of the seasonal variations of stem CO₂ efflux over the entire study period in the three species. The temperature sensitivity (Q 10) of stem CO₂ efflux was obviously different among the three species with higher Q 10 value found in oak (2.24) and lower values in the coniferous species (1.76 and 1.63). Our results also showed that the Q 10 values of stem CO₂ efflux in all the three species were lower in the growing season than that in the non-growing season, indicating that the growth and maintenance respiration had different temperature responses. Moreover, we found that the temperature-normalized stem CO₂ efflux (R 10) changed greatly between the growing and non-growing seasons in oak and masson pine, but not in loblolly pine. Additionally, we also found that in the non-growing season, the principal factor responsible for the spatial variation of stem CO₂ efflux among the 15 sampling trees was sapwood volume, whereas in the growing season, stem CO₂ efflux was closely related to annual dry-matter production in the three subtropical species.     

Seasonal respiration of foliage, fine roots, and woody tissues in relation to growth, tissue N, and photosynthesis

Autotrophic respiration may regulate how ecosystem productivity responds to changes in temperature, atmospheric [CO₂] and N deposition. Estimates of autotrophic respiration are difficult for forest ecosystems, because of the large amount of biomass, different metabolic rates among tissues, and seasonal variation in respiration rates. We examined spatial and seasonal patterns in autotrophic respiration in a Pinus strobus ecosystem, and hypothesized that seasonal patterns in respiration rates at a common temperature would vary with [N] for fully expanded foliage and fine roots, with photosynthesis for foliage, and with growth for woody tissues (stems, branches, and coarse roots). We also hypothesized that differences in [N] would largely explain differences in maintenance or dormant‐season respiration among tissues. For April–November, mean respiration at 15 °C varied from 1.5 to 2.8 μmol kg^?1 s^?1 for fully expanded foliage, 1.7–3.0 for growing foliage, 0.8–1.6 for fine roots, 0.6–1.1 (sapwood) for stems, 0.5–1.8 (sapwood) for branches, and 0.2–1.5 (sapwood) for coarse roots. Growing season variation in respiration for foliage produced the prior year was strongly related to [N] (r² = 0.94), but fine root respiration was not related to [N]. For current‐year needles, respiration did not covary with [N]. Night‐time foliar respiration did not vary in concert with previous‐day photosynthesis for either growing or fully expanded needles. Stem growth explained about one‐third of the seasonal variation in stem respiration (r² = 0.38), and also variation among trees (r² = 0.43). We did not determine the cause of seasonal variation in branch and coarse root respiration, but it is unlikely to be directly related to growth, as the pattern of respiration in coarse roots and branches was not synchronized with stem growth. Seasonal variations in temperature‐corrected respiration rates were not synchronized among tissues, except foliage and branches. Spatial variability in dormant‐season respiration rates was significantly related to tissue N content in foliage (r² = 0.67), stems (r² = 0.45), coarse roots (r² = 0.36), and all tissues combined (r² = 0.83), but not for fine roots and branches. Per unit N, rates for P. strobus varied from 0.22 to 3.4 μmol molN^?1 s^?1 at 15 °C, comparable to those found for other conifers. Accurate estimates of annual autotrophic respiration should reflect seasonal and spatial variation in respiration rates of individual tissues.     

Photosynthesis and carbon balance of a Sahelian fallow savanna

Eddy-covariance measurements of CO₂ exchange above a Sahelian savanna consisting of small shrubs over a near-continuous herb layer were made during the HAPEX-Sahel experiment in Niger, West Africa. The measurements were made near-continuously during an 8-week period, covering the main part of the rainy season and three weeks at the beginning of the dry season. The measurements were corrected for in-canopy storage of CO₂ and the night-time measurements used to derive respiration functions for the soil, roots and above-ground plant material. Photosynthetic CO₂ uptake was estimated and compared to simulations using a biochemical photosynthesis model in a simple, ‘big-leaf’, implementation. The model satisfactorily reproduced the measurements (coefficient of determination 0.80) using parameters defined from the literature and based on soil nutrient concentrations. When the quantum yield (α) and rubisco capacity (V_mr) were fitted to the data with allowance for physiological changes through the season, an excellent agreement between model and measurements was obtained (coefficient of determination 0.93, RMS error 1.46 μmol m^–2 s^–1). The fitted photosynthesis and respiration model was used to estimate the carbon balance of the savanna site during the growing season of 1992 and for the complete calendar year. Harvest estimates of net plant biomass accumulation during the growing season and annual wood accumulation agreed well with modelled net photosynthesis and annual net carbon accumulation, respectively. Peak instantaneous ecosystem CO₂ uptake was comparable to peak values observed in other biomes, but annual photosynthesis and carbon sequestration were considerably lower than observed elsewhere.     

中国东北地区兴安落叶松林树干呼吸的研究

树干呼吸是森林碳平衡估计中的一个重要项目同时还能够显示树木的活力。对于如何准确估计森林树干呼吸释放CO2总量还存在争论。在本项研究中,2001、2002连续两年在一个33年生的兴安落叶松(Larix gmelini Rupr.)人工林内对树干呼吸进行了测定,同时测定了不同高度树干呼吸、呼吸的日变化、同龄落叶松林内不同个体的树干呼吸以及相关生长状态因子、水分因子和温度因子。结果显示：1)树干上部的呼吸速率在不同季节都高于下部呼吸速率,树下温度的差异能够一定程度上解释这种差异;2)树干呼吸有午间降低的现象,上午的测定结果树干温度与树干呼吸速率紧密相关,而下午则温度依赖性很小,土壤、空气、小枝木质部水势、叶片蒸腾速率和气孔导度都显示下午植物水分亏缺下午较上午严重,呼吸的这种上下午温度相关性的差异可能受这种水分亏缺的影响;3)在同龄林内,树木个体生长状念包括平均生长速率和树冠投影面积与树干呼吸速率有显著相关关系,而树干温度与之相关性很小。幂指数模型和S曲线模型能够产生较好的拟合效果;4)树干呼吸季节变化明显,7月份出现最大值,但同一月份的年间差异较大。自然指数模型能够较好地拟合温度与树干呼吸的季节变化规律。Q10值在2．22(2001年)和3．53(2002年)之间,与以往研究的结果相当。从以上结果可以看出,通过单一的Q10值估计森林树干呼吸总量会产牛偏差,要想得到准确的估计,至少应该考虑生长状态的差异和水分状态的差异。     

呼伦贝尔地区贝加尔针茅草甸草原土壤CO2排放特征

采用Li-8150多通道土壤碳通量自动观测系统,于2009年6月—2010年6月对呼伦贝尔地区贝加尔针茅草甸草原土壤呼吸进行连续野外观测,分析该地区土壤CO₂通量排放特征.结果表明: 生长季内贝加尔针茅草甸草原土壤呼吸日动态呈单峰曲线,最高值出现在13:00—15:00,最低值出现在5:00—6:00,土壤呼吸呈明显的季节变化,与土壤温度和土壤含水量季节动态相吻合.土壤呼吸与各层土壤温度和土壤含水量关系可以用线性模型和指数-乘幂模型来表示;土壤呼吸与各层土壤温度呈显著的指数回归关系,Q₁₀变化范围分别为1.68～2.14和3.03～3.60,非生长季土壤温度对土壤呼吸的影响更为显著;生长季内土壤呼吸与10 cm土壤含水量呈显著正相关.2009和2010年土壤CO₂年排放量分别为488.47和507.20 g C·m^-2·a^-1,生长季排放量约占年排放量的90%.     

Significance of cold-season respiration and photosynthesis in a subarctic heath ecosystem in Northern Sweden

While substantial cold-season respiration has been documented in most arctic and alpine ecosystems in recent years, the significance of cold-season photosynthesis in these biomes is still believed to be small. In a mesic, subartic heath during both the cold and warm season, we measured in situ ecosystem respiration and photosynthesis with a chamber technique at ambient conditions and at artificially increased frequency of freeze–thaw (FT) cycles during fall and spring. We fitted the measured ecosystem exchange rates to respiration and photosynthesis models with R²-values ranging from 0.81 to 0.85. As expected, estimated cold-season (October, November, April and May) respiration was significant and accounted for at least 22% of the annual respiratory CO₂ flux. More surprisingly, estimated photosynthesis during this period accounted for up to 19% of the annual gross CO₂ uptake, suggesting that cold-season photosynthesis partly balanced the cold-season respiratory carbon losses and can be significant for the annual cycle of carbon. Still, during the full year the ecosystem was a significant net source of 120 ± 12 g C m⁻² to the atmosphere. Neither respiration nor photosynthetic rates were much affected by the extra FT cycles, although the mean rate of net ecosystem loss decreased slightly, but significantly, in May. The results suggest only a small response of net carbon fluxes to increased frequency of FT cycles in this ecosystem.     

Annual soil respiration in broadleaf forests of northern Wisconsin: influence of moisture and site biological,chemical, and physical characteristics

Soil temperature and moisture influence soil respiration at a range of temporal and spatial scales. Although soil temperature and moisture may be seasonally correlated, intra and inter-annual variations in soil moisture do occur. There are few direct observations of the influence of local variation in species composition or other stand/site characteristics on seasonal and annual variations in soil moisture, and on cumulative annual soil carbon release. Soil climate and soil respiration from twelve sites in five different forest types were monitored over a 2-year period (1998–1999). Also measured were stand age, species composition, basal area, litter inputs, total above-ground wood production, leaf area index, forest floor mass, coarse and fine root mass, forest floor carbon and nitrogen concentration, root carbon and nitrogen concentration, soil carbon and nitrogen concentration, coarse fraction mass and volume, and soil texture. General soil respiration models were developed using soil temperature, daily soil moisture, and various site/soil characteristics. Of the site/soil characteristics, above-ground production, soil texture, roots + forest floor mass, roots + forest floor carbon:nitrogen, and soil carbon:nitrogen were significant predictors of soil respiration when used alone in respiration models; all of these site variables were weakly to moderately correlated with mean site soil moisture. Daily soil climate data were used to estimate the annual release of carbon (C) from soil respiration for the period 1998–1999. Mean annual soil temperature did not differ between the 2 years but mean annual soil moisture was approximately 9% lower in 1998 due to a summer drought. Soil C respired during 1998 ranged from 8.57 to 11.43 Mg C ha⁻¹ yr⁻¹ while the same sites released 10.13 and 13.57 Mg C ha⁻¹ yr⁻¹ in 1999; inter-annual differences of 15.41 and 15.73%, respectively. Among the 12 sites studied, we calculated that the depression of soil respiration linked to the drought caused annual differences of soil respiration from 11.00 to 15.78%. Annual estimates of respired soil C decreased with increasing site mean soil moisture. Similarly, the difference of respired carbon between the drought and the non-drought years generally decreased with increasing site mean soil moisture.     

Carbon sequestration and ecosystem respiration for 4 years in a Scots pine forest

The net exchange of CO₂ (NEE) between a Scots pine (Pinus sylvestris L.) forest ecosystem in eastern Finland and the atmosphere was measured continuously by the eddy covariance (EC) technique over 4 years (1999–2002). The annual temperature coefficient (Q₁₀) of ecosystem respiration (R) for these years, respectively, was 2.32, 2.66, 2.73 and 2.69. The light‐saturated rate of photosynthesis (A_max) was highest in July or August, with an annual average A_max of 10.9, 14.6, 15.3 and 17.1 μmol m^?2 s^?1 in the 4 years, respectively. There was obvious seasonality in NEE, R and gross primary production (GPP), exhibiting a similar pattern to photosynthetically active radiation (PAR) and air temperature. The integrated daily NEE ranged from 2.59 to ?4.97 g C m^?2 day^?1 in 1999, from 2.70 to ?4.72 in 2000, from 2.61 to ?4.71 in 2001 and from 5.27 to ?4.88 in 2002. The maximum net C uptake occurred in July, with the exception of 2000, when it was in June. The interannual variation in ecosystem C flux was pronounced. The length of the growing season, based on net C uptake, was 179, 170, 175 and 176 days in 1999–2002, respectively, and annual net C sequestration was 152, 101, 172 and 205 g C m^?2 yr^?1. It is estimated that ecosystem respiration contributed 615, 591, 752 and 879 g C m^?2 yr^?1 to the NEE in these years, leading to an annual GPP of ?768, ?692, ?924 and ?1084 g C m^?2 yr^?1. It is concluded that temperature and PAR were the main determinants of the ecosystem CO₂ flux. Interannual variations in net C sequestration are predominantly controlled by average air temperature and integrated radiation in spring and summer. Four years of EC data indicate that boreal Scots pine forest ecosystem in eastern Finland acts as a relatively powerful carbon sink. Carbon sequestration may benefit from warmer climatic conditions.