长三角地区稻麦轮作生态系统净碳交换及其环境影响因子

采用涡度相关技术对我国长三角地区典型稻麦轮作农田生态系统(2011年11月—2012年10月)的CO2通量进行连续观测,分析了农田生态系统净碳交换(NEE)的变化特征及其环境影响因子。结果表明:长三角地区稻麦轮作生态系统NEE具有明显的日变化和季节变化特征,具有很强的固碳能力。NEE月平均日变化总体呈"U"型曲线,不同月份"U"型高度不同;NEE季节变化则呈显著的"W"型双峰特征,分别对应两季作物(小麦、水稻)的生长季节。小麦/水稻月平均最大碳吸收峰出现在4月/8月,分别达到-1.12 mg·m-2·s-1、-1.45 mg·m-2·s-1;日最大累积碳吸收量分别为-12.88 g(C)·m-2·d-1、-10.63 g(C)·m-2·d-1,长三角地区稻麦轮作生态系统年固碳量达到-769.61 g(C)·m-2·a-1。光合有效辐射是影响白天NEE的主要环境影响因子,Michaelis-Menten方程可以很好地表示作物生长季节两者之间的关系(R2=0.37~0.83);在同一光合有效辐射条件下,长三角地区稻麦轮作生态系统白天NEE随着气温的升高而增加,而当光合有效辐射大于1 800μmol·m-2·s-1时存在着一定程度的光抑制。温度是影响夜间农田生态系统呼吸特征的主要环境影响因子,长三角地区稻麦轮作生态系统夜间NEE与不同层次温度之间均存在显著的指数相关关系,但是不同作物夜间NEE的最适温度略有差异,小麦夜间NEE与土壤温度(10 cm)相关性最好(0.60),而水稻夜间NEE与气温相关系数最高(0.49)。     

基于DNDC模型的川中丘陵区不同轮作制度下稻田CO_2排放研究

利用IKONOS高分辨率（1m）卫星遥感图,选定代表川中丘陵区特征的四川省金堂县为研究区域,选取冬水田-水稻田（PF）、油菜-水稻田（RR）和小麦-水稻田（RW）3种主要轮作制度下353块稻田为研究对象,于2005年5月-2006年5月对作物田间管理、作物产出、土壤理化性状及施肥情况,以及水质与气象等基础资料进行调查、测定和统计分析,利用DNDC模型模拟川中丘陵区不同轮作制度下稻田CO2排放情况。结果表明：PF、RR和RW 3种轮作制度下CO2年总排放量分别为：4102、7512和8111kg.hm-2,且RW和RR均显著高于PF,但3种轮作制度下单季作物的CO2排放量差异不大,RR处理的单季作物的CO2排放量最小,其年总作物产量居中,RW处理产量最高。PF水稻生长期和休闲期CO2排放通量分别为25.48和3.36kg.hm-2.d-1,水稻生长期是休闲期的7.58倍;RR和RW在水稻生长期CO2排放通量平均为23.32和25.21kg.hm-2.d-1,低于PF水稻生长期CO2排放通量,但差异未达到显著水平,而RR和RW非水稻生长期的CO2排放通量分别为19.34和20.96kg.hm-2.d-1,分别为PF休闲期的5.76和6.24倍。根际呼吸是土壤呼吸的主要部分,整个生长期PF、RR、RW的根呼吸贡献率平均为59.14%～62.96%。     

淮河流域典型农田生态系统碳通量变化特征

为了准确评价农田生态系统在全球碳平衡中的作用,利用涡度相关技术对安徽省寿县冬小麦／水稻生态系统进行了碳通量的监测,并在数据校正、剔除和插补的基础上,研究生长季农田净生态系统碳交换（NEE）的变化特征。结果显示,2008年寿县农田生态系统CO2通量的日变化进程为单峰型,冬小麦和水稻最大的CO2吸收速率分别为2．45和2．48mg·m^-2·s^-1。从物候期的角度来看,冬小麦在抽穗期碳通量值最小,乳熟期最大;水稻拔节时期碳通量值最小,即固碳能力最强。冬小麦,水稻生态系统不同月份碳通量月均日变化也呈U型曲线,作物生命活动越旺盛,NEE峰值越高,夜间CO2排放则在8月份达到最高值。2008年冬小麦和水稻月平均最大日CO2吸收峰分别出现在4月和8月,分别为1．30和1．07mg·m^-2．s^-1。冬小麦生态系统NEE的日最大累积吸收量出现在4月16日．可达11．76gC·m^-2·d^-1,水稻生态系统的出现在8月3日,为10．40gC·m^-2·d^-1。冬小麦从拔节到成熟时间段内的固碳能力为326．87gC·m^-1,水稻从返青到成熟时间段内的固碳能力也达到了300．05gC·m^-2。     

稻麦轮作条件下机插水稻CH_4和N_2O的排放特征及温室效应

于2008年采用静态暗箱-气相色谱法对人工手插和机插2种水稻种植方式下CH4和N2O排放进行田间观测,研究稻麦轮作条件下机插水稻CH4和N2O的排放特征及其温室效应。结果表明,水稻生长季CH4排放通量人工手插水稻和机插水稻均呈先升高后降低的变化趋势,N2O仅在水稻搁田期间有明显排放,机插和人工手插水稻CH4平均排放通量分别为4.68、4.39 mg.m-2.h-1,N2O平均排放通量为92.80、111.33μg.m-.2h-1。与人工手插水稻相比,机插水稻增加CH4排放总量14%,减少N2O排放总量11%,使稻季排放CH4和N2O所产生的全球增温潜势（GWP）和＂单位产量的GWP＂分别提高8%和10%。在稻麦轮作条件下采用机插水稻种植方式,水稻生长期间排放的CH4和N2O所形成的温室效应有提高的趋势。     

克氏针茅草原生态系统生长季碳通量变化特征

植被和大气之间CO2通量的观测有助于理解陆地生态系统的碳循环及其控制机理。以中国北方典型草原克氏针茅草原为研究对象,以涡度相关法为主要技术手段,探讨了2008年生长季内克氏针茅草原净生态系统碳交换（NEE）的变化特征。结果表明,克氏针茅草原生态系统CO2通量的日变化进程可以依据高峰出现的时间分为两种,一种具有一个吸收高峰,出现在11：00左右,另一种则具有两个吸收高峰,在正午前后出现碳释放现象。2008年克氏针茅草原生态系统最大的CO2吸收速率为-0．4mg·m^-2·s^-1。克氏针茅草原在4月和10月的NEE昼夜变化比较平缓,在5—9月日间CO2吸收量和夜间CO2排放量都开始增大,出现了明显的CO2日吸收峰值,但各月的日动态格局差异较大。2008年生长季中7—9月白天碳吸收活动最强,6—9月夜间CO2释放量较大。克氏针茅草原碳通量日累积量在2008年出现了3个明显的碳吸收峰;NEE的日最大累积吸收量和最大累积释放量分别为-2．38和1．47gC·m^-2·d^-1,并且出现在植被生长最旺盛的7、8月份。研究表明,温度和水分是影响克氏针茅草原生态系统碳通量变化的重要因子。     

冬小麦农田尺度瞬态CO2通量与水分利用效率日变化及影响因素分析

以华北平原冬小麦农田尺度为研究对象,采用涡度相关技术,研究冬小麦灌浆期瞬态CO2通量日变化特征及其与农田热量平衡各分量的关系。结果表明,非水分胁迫下CO2通量日变化(负值表示通量指向冠层)为U型,群体净光合速率最高值为-1.2~-1.4mg/m2.s,夜间瞬态CO2通量呈非稳定变化,最高值达0.4~0.54mg/m2.s。白天时段内CO2通量与净辐射、潜热通量呈高度相关,8:00~15:30时段内CO2和水汽通量呈同步日变化趋势,水分利用效率处于稳定状态,瞬态水分利用效率基本维持在0.012~0.014g(CO2)/g(H2O)范围内;但早晨和傍晚时段内水分利用效率变化较大。     

小兴安岭天然阔叶混交林生长季CO_2通量特征分析

森林生态系统CO2通量的研究已成为全球变化研究的热点之一。本文采用开路式涡度相关系统对小兴安岭天然阔叶混交林CO2通量进行为期1a的连续观测（2008年）,分析了生长季（5-9月）CO2通量的变化特征。结果表明,在生长季,天然阔叶混交林系统的CO2通量变化范围为-0.46～0.42mg.m-2.s-1;最大吸收量出现在6月份的9：00,最大释放量出现在7月份的5：00。白天气温低于26.63℃时,碳吸收量随气温的升高而加大;但气温超过26.63℃后,则呈相反趋势。夜晚气温在13.50℃时的碳释放量最大。2008年整个生长季呈现白天碳吸收,夜晚碳释放的现象,总体表现为碳吸收,吸收总量为212.32g.m-2。     

巢湖沉积物-水界面磷酸盐释放通量研究

采用现场采样与室内测试方法,对调水后巢湖沉积物-水界面磷酸盐释放通量进行了研究。结果表明,夏季巢湖表层水、底层水、间隙水磷酸盐浓度变化范围分别为0.02～0.16、0.02～0.17、0.01～0.08mg.L-1,均值分别为（0.03±0.04）、（0.04±0.04）mg.L-1和（0.03±0.02）mg.L-1。秋季6个取样点表层水、底层水磷酸盐含量的变化范围均为0.03～0.06mg.L-1,均值为（0.04±0.04）mg.L-1,显著高于夏季对应样点浓度。而秋季间隙水磷酸盐浓度平均值为（0.015±0.003）mg.L-（1变化范围0.01～0.02mg.L-1）,与夏季对应样点相比差异不显著。夏季沉积物-水界面磷酸盐释放通量的变化范围为-27.46～6.27μgP.m-.2d-1,平均值为-1.54μgP.m-.2d-1。秋季磷酸盐释放通量变化范围为-10.61～-3.77μgP.m-.2d-1,均值为-6.19μgP.m-.2d-1,与夏季对应样点释放通量差异显著（α=0.05,P=0.002）。情景模拟表明,排除外源污染的影响,当引入长江水磷酸盐浓度介于0.003～0.009mg.L-1时,巢湖调水后替换水体可在7.2a左右达二次富营养化。     

冬季淹水稻田CH4排放通量及其δ13C的时间变化特征

通过田间试验研究了持续淹水稻田冬季休闲期和水稻生长期CH4排放通量及其稳定性碳同位组成的时间变化。结果表明:CH4排放在冬季休闲期从4月份呈逐渐上升趋势,至6月份出现排放峰,为CH46.4 mg m-2h-1;水稻移栽后则迅速增加,于7月和8月出现两个排放峰,分别为CH423.1 mg m-2h-1和CH429.8 mg m-2h-1,此后急剧下降,末期稻田排水落干期间出现一个排放峰。冬季休闲期CH4排放总量为CH43.3 g m-2,占全年排放总量的8.9%。稻田排放的δ13CH4在冬季休闲期后期逐渐从-51‰上升至-44‰,然后下降至-56‰。水稻移栽后,δ13C值从-62‰迅速降至-68‰,然后慢慢上升至-60‰,并在较长一段时间内保持不变,后期再次富集13C。末期排水落干对排放δ13CH4影响显著。排放δ13CH4在水稻生长期较冬季休闲期低得多,原因在于冬季休闲期的CH4氧化率很高(60%～90%),而水稻生长期的CH4氧化率相对较低(10%～80%)。全观测期内,CH4排放通量的季节变化均与土壤温度显著正相关(p<0.01),与土壤Eh显著负相关(p<0.01),与δ13CH4呈显著负相关(p<0.05)。     

华北平原典型农田CO2和N2O排放通量及其与土壤养分动态和施肥的关系

对华北平原小麦-棉花(麦棉)、小麦-大豆(麦豆)、小麦-玉米(麦玉)轮作田的CO2和N2O排放通量进行了测定,分析了温室气体排放通量与土壤中碳、氮元素、气温以及施肥等之间的关系。主要结论:1)麦棉、麦豆、麦玉田的土壤CO2平均排放通量分别为CO2-C 141.7、109.8、128.2 mg.m-2.h-1,其中夏播作物的排放通量高于小麦季;2)麦棉、麦豆及麦玉田作物生长季的土壤N2O平均排放通量分别为N2O-N 98.8、38.9、44.7μg.m-2.h-1,也表现为麦后季作物的排放量高于小麦季;3)同一生育期中不同处理的N2O排放主要与土壤中无机氮含量相关,不同生育期的N2O排放通量主要受不同生育期的土壤温度及水分状况的影响;4)在施肥灌溉后的9 d内土壤N2O排放通量较高,之后逐渐降低,至施肥后22～27 d即与不施肥处理的排放持平。     

通量及其不确定性对农业区高塔CO_2浓度模拟的影响

利用WRF-STILT模型模拟玉米种植区生长季(6-9月)小时CO_2浓度,并基于美国最大农业种植区‘玉米带’100m高塔CO_2浓度观测数据,对WRF-STILT模型的模拟能力及CO_2通量的不确定性对模拟结果的影响进行分析。结果表明:(1)WRF-STILT能够模拟高塔观测的CO_2浓度日变化特征,模拟值与观测值的均方根误差为13.70mmol×mol~(-1),模拟结果偏高7.26mmol×mol~(-1)。(2)EDGAR和Carbon Tracker两种典型化石燃料的CO_2通量,其区域平均值相差6%,但两者对CO_2浓度增加值的模拟结果相差约10%;(3)CO_2通量空间分辨率的差异会导致模拟结果产生偏差,使用区域边长为1o的EDGAR化石燃料CO_2通量模拟的浓度贡献值仅为0.1o的0.4倍,且空间分辨率越低,模拟误差越大;(4)白天和夜晚Carbon Tracker模拟的植被生态系统净交换数据是高塔涡度相关方法观测结果的2.26和1.56倍,下垫面分类的误差以及相应的通量模拟误差使模拟的CO_2浓度贡献出现12mmol×mol~(-1)的差异,这是模拟结果偏高7.26mmol×mol~(-1)的潜在误差来源。研究认为,WRF-STILT模型和高空间及时间分辨率的CO_2通量能够较好模拟出农业区生长季的CO_2强日变化特征,CO_2通量的误差是模拟结果误差的主要来源,研究结果表明该方法具有评估和优化通量的巨大潜力。     

基于通量观测数据的玉米水碳交换量及水分利用效率分析

揭示玉米生长期内水分、二氧化碳交换量及水分利用效率的变化规律,对于认识玉米生长规律,指导农业灌溉具有重要意义。该文采用美洲通量网(Ameri Flux)3个农田通量站的数据,计算玉米生育期内的水分消耗量ET(evapotranspiration)、总初级生产力GPP(gross primary productivity)和生态系统净交换量NEE(net ecosystem exchange)及水分利用效率,并采用统计分析方法分析饱和水汽压差和光合有效辐射对水分利用效率的影响。结果表明,该区域玉米整个生育周期约为156~180 d,ET为440~520 mm,GPP为1 320~1 640 g/m2,以C计,NEE为-560~-620 g/m2,以C计;水分利用效率,NEE/ET为1.2~1.4 g/kg,GPP/ET为3.0~3.5 g/kg。水分利用效率与饱和水汽压差(VPD)成负指数关系,存在常数k使得GPP/ET正比于VPD-k,最优k值为0.42~0.63。水分利用效率与光合有效辐射无显著相关性。     

小麦-玉米-大豆轮作下黑土农田土壤呼吸与碳平衡

农田生态系统是陆地生态系统的重要组成部分,探讨农田生态系统的土壤呼吸与碳平衡对于科学评价陆地生态系统在全球变化下的源汇效应具有重要意义。基于中国科学院海伦农业生态实验站的长期定位试验,对不同施肥处理下黑土小麦-玉米-大豆轮作体系2005—2007年的作物固碳量与土壤CO2排放通量进行了观测,并对该轮作体系下黑土农田生态系统的碳平衡状况进行了估算。结果表明:在小麦-玉米-大豆轮作体系中,作物固碳量的高低表现为:玉米>大豆>小麦,平均值分别为6 513 kg(C).hm-2、4 025 kg(C).hm-2和3 655kg(C).hm-2。从作物生长季土壤CO2排放总量来看,3种作物以大豆农田生态系统的土壤CO2排放总量最高,平均值达4 062 kg(C).hm-2;其次为玉米,为3 813 kg(C).hm-2;而小麦最低,为2 326 kg(C).hm-2。3种作物轮作下NEP(净生态系统生产力)均为正值,表明黑土农田土壤-作物系统为大气CO2的"汇",不同作物系统的碳汇强度表现为玉米>小麦>大豆,三者的平均值分别为3 215 kg(C).hm-2、1 643 kg(C).hm-2和512 kg(C).hm-2。长期均衡施用氮、磷、钾化肥或氮、磷、钾化肥配施有机肥后,小麦、玉米和大豆农田生态系统的固碳量和土壤CO2排放总量均明显增加,并在氮、磷、钾配施有机肥处理下达到最高。不同的施肥管理措施将改变土壤-植物系统作为大气CO2"汇"的程度,总体表现为化肥均衡施用下NEP值较高,而化肥与有机肥配施下农田生态系统的NEP值较低。     

Evaluation of carbon exchange in a boreal coniferous stand over a 10-year period: An integrated analysis based on ecosystem model simulations and eddy covariance measurements

In order to assess the capacity of the boreal forest ecosystem to intercept atmospheric carbon over a period of years, a climate-driven growth model (FinnFor, process-based) was applied to calculate the seasonal and inter-annual variability of net ecosystem CO₂ exchange (NEE) and component carbon fluxes (gross primary production - GPP and total ecosystem respiration - TER) against a 10-year (1999-2008) period of eddy covariance (EC) measurements in a Scots pine (Pinus sylvestris L.) stand in Eastern Finland. Furthermore, the role of climatic factors, leaf area index (LAI) and physiological responses of trees regarding the ecosystem carbon fixation processes were evaluated. An hourly time-step was used to simulate the carbon exchange based on measured tree/stand characteristics and meteorological input for the experimental site, and the dynamic LAI was used throughout the 10-year simulations. The model predicted well the annual course of NEE compared to the measured values for most of the years, with the development of LAI (2.4-3.3 m² m⁻², as simulated). The simulated NEE over the study period shows that, on average, 62% of the variation refers to daily and 88% to monthly measured NEE. Both modeled and measured daily NEE showed similar responses to the temperature, photosynthetically active radiation and vapor pressure deficit during the growing seasons. In the simulation, the annual amount of GPP varied from 720.8 to 910.4 g C m⁻² with a mean value of 825.3 g C m⁻², and the annual mean TER/GPP ratio was 0.79, close to the measured value. Carbon efflux from the forest floor was the dominant contributor to the forest ecosystem respiration. The inter-annual variation of GPP mostly corresponded to the development of LAI, temperature sum and total incoming radiation over the 10-year simulation period. It was suggested that the process-based model could be applied to study the carbon processes for natural and management-induced dynamics of Scots pine forest ecosystem over longer periods across a wider climate gradient in the boreal zone.     

Increasing net CO2 uptake by a Danish beech forest during the period from 1996 to 2009

The exchange of CO₂ between the atmosphere and a beech forest near Sorø, Denmark, was measured continuously over 14 years (1996-2009). The simultaneous measurement of many parameters that influence CO₂ uptake makes it possible to relate the CO₂ exchange to recent changes in e.g. temperature and atmospheric CO₂ concentration. The net CO₂ exchange (NEE) was measured by the eddy covariance method. Ecosystem respiration (RE) was estimated from nighttime values and gross ecosystem exchange (GEE) was calculated as the sum of RE and NEE. Over the years the beech forest acted as a sink of on average of 157 g C m⁻² yr⁻¹. In one of the years only, the forest acted as a small source. During 1996-2009 a significant increase in annual NEE was observed. A significant increase in GEE and a smaller and not significant increase in RE was also found. Thus the increased NEE was mainly attributed to an increase in GEE. The overall trend in NEE was significant with an average increase in uptake of 23 g C m⁻² yr⁻². The carbon uptake period (i.e. the period with daily net CO₂ gain) increased by 1.9 days per year, whereas there was a non significant tendency of increase of the leafed period. This means that the leaves stayed active longer. The analysis of CO₂ uptake by the forest by use of light response curves, revealed that the maximum rate of photosynthetic assimilation increased by 15% during the 14-year period. We conclude that the increase in the overall CO₂ uptake of the forest is due to a combination of increased growing season length and increased uptake capacity. We also conclude that long time series of flux measurements are necessary to reveal trends in the data because of the substantial inter-annual variation in the flux.     

CO2/heat fluxes in rice fields: Comparative assessment of flooded and non-flooded fields in the Philippines

The seasonal fluxes of heat, moisture and CO₂ were investigated under two different rice environments: flooded and aerobic soil conditions, using the eddy covariance technique during 2008 dry season. The fluxes were correlated with the microclimate prevalent in each location. This study was intended to monitor the environmental impact, in terms of C budget and heat exchange, of shifting from lowland rice production to aerobic rice cultivation as an alternative to maintain crop productivity under water scarcity.The aerobic rice fields had higher sensible heat flux (H) and lower latent heat flux (LE) compared to flooded fields. On seasonal average, aerobic rice fields had 48% more sensible heat flux while flooded rice fields had 20% more latent heat flux. Consequently, the aerobic rice fields had significantly higher Bowen ratio (0.25) than flooded fields (0.14), indicating that a larger proportion of the available net radiation was used for sensible heat transfer or for warming the surrounding air.The total C budget integrated over the cropping period showed that the net ecosystem exchange (NEE) in flooded rice fields was about three times higher than in aerobic fields while gross primary production (GPP) and ecosystem respiration (R_e) were 1.5 and 1.2 times higher, respectively. The high GPP of flooded rice ecosystem was evident because the photosynthetic capacity of lowland rice is naturally large. The R_e of flooded rice fields was also relatively high because it was enhanced by the high photosynthetic activities of lowland rice as manifested by larger above-ground plant biomass. The NEE, GPP, and R_e values for flooded rice fields were −258, 778, and 521 g C m⁻², respectively. For aerobic rice fields, values were −85, 515, and 430 g C m⁻² for NEE, GPP, and R_e, respectively. The ratio of R_e/GPP in flooded fields was 0.67 while it was 0.83 for aerobic rice fields.This short-term data showed significant differences in C budget and heat exchange between flooded and aerobic rice ecosystems. Further investigation is needed to clarify seasonal and inter-annual variations in microclimate, carbon and water budget of different rice production systems.