华北平原冬小麦农田生态系统CO_2通量特征及其影响因素

利用2014—2015年中国科学院封丘农业生态实验站涡度相关系统观测的冬小麦农田生态系统CO_2通量数据,结合试验地常规气象观测系统的气象数据,分析冬小麦4个生育期(分蘖期、越冬期、拔节期和灌浆期)内CO_2通量的日变化,研究净生态系统碳交换(NEE)的季节变化及其与气象要素的关系.结果表明:冬小麦整个生育期内NEE为-360.15g C·m^-2,总初级生产力总量为1920.01 g C·m^-2,冬小麦农田生态系统具有较强的固碳能力.冬小麦农田生态系统CO_2通量具有明显的日变化和季节变化特征,分蘖期表现为碳源,越冬期、拔节期和灌浆期表现为碳汇.表观初始光能利用率平均值为0.03 mg CO_2·μmol^-1,光饱和时的生态系统生产量平均值为1.53 mg CO_2·m^-2·s^-1,月平均生态系统呼吸为193.92g C·m^-2·month^-1.冬小麦农田生态系统4个生育期NEE与光合有效辐射的相关关系均达到极显著水平.分蘖期、拔节期和灌浆期NEE与饱和水汽压差的相关关系极显著,越冬期达显著水平.冬小麦分蘖期、越冬期和灌浆期NEE日总量与土壤温度呈正相关,拔节期呈负相关关系.     

基于植被羰基硫通量估算陆地生态系统总初级生产力研究进展

羰基硫(COS)是大气中的长周期痕量气体,其分子结构、对流层大气混合比的昼夜和季节动态类似于二氧化碳(CO₂)。植物光合作用及其水解过程中,受扩散通路导度和酶活性影响,气孔的COS与CO₂吸收紧密相关,同时,植物自养呼吸并不释放COS。最新研究中,采用植被COS通量直接指示生态系统总初级生产力(GPP)。综述了植被COS通量与光合作用中碳固定过程的关联机制,以及采用涡度相关观测、整合大气COS监测和生态系统过程模型等方法开展植被COS通量与GPP研究的最新进展,探讨了关键生态过程和参数,发现方法存在以下瓶颈：(1)生理过程、尺度效应和解析效应影响了COS与CO₂的叶片相对吸收率,(2)观测与模拟手段有待进一步耦合,(3)全球COS观测密度限制了方法验证,(4)硫循环过程影响了多区域模拟精度。方法发展的前沿领域包括：(1)开展重点地区植被COS通量观测,(2)提高COS卫星柱浓度的覆盖范围,(3)完善生态系统过程模型的COS吸收机理。展望未来研究关注的科学问题是：对于亚热带等尚待开展COS连续观测的区域,采用植被COS通量...     

三江源地区人工草地的生态系统CO2净交换、总初级生产力及其影响因子

为了揭示三江源区垂穗披碱草(Elymus nutans)人工草地生态系统(100°26′-100°41′ E, 34°17′-34°25′ N, 海拔3 980 m)的净生态系统CO₂交换(NEE), 该研究利用2006年涡度相关系统观测的数据分析了该人工草地的NEE, 总初级生产力(GPP)、生态系统呼吸(R_eco)以及R_eco/GPP的变化特征及其影响因子。CO₂日最大吸收值为6.56 g CO₂·m^-2·d^-1, 最大排放值为4.87 g CO₂·m^-2·d^-1。GPP年总量为1 761 g CO₂·m^-2, 其中约90%以上被生态系统呼吸所消耗, CO₂的年吸收量为111 g CO₂·m^-2。5月的R_eco/GPP略高于生长季的其他月份, 为90%; 6月R_eco/GPP比值最低, 为79%。生态系统的呼吸商(Q₁₀)为4.81, 显著高于其他生态系统。该研究表明: 生长季的NEE主要受光量子通量密度(PPFD)、温度和饱和水汽压差(VPD)的影响, 生态系统呼吸则主要受土壤温度的控制。     

科尔沁草甸生态系统水分利用效率及影响因素

生态系统水分利用效率(WUE)是衡量碳水循环耦合程度的重要指标。利用科尔沁温带草甸草地碳水通量观测数据,对该生态系统总初级生产力水分利用效率(WUEGPP)的日季变化规律及对环境和生理因子的响应进行分析。结果表明:(1)WUEGPP日变化呈下降-稳定-上升的变化趋势,最大值出现在日出后1—2 h,阴天条件下WUEGPP高于晴天,生长中期WUEGPP高于生长初期和末期;(2)总初级生产力、总蒸散和WUEGPP季节变化均呈夏季高、春秋低的形式,生长季平均值分别为0.57 mg m-2s-1、0.08 g m-2s-1和5.97 mg/g,最大值分别为1.49 mg m-2s-1、0.16 g m-2s1和13.62 mg/g;(3)总初级生产力与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系;总蒸散与气温呈二次曲线关系,与饱和差、叶面积指数和冠层导度相关性均不显著;(4)WUEGPP与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系,饱和差、冠层导度和叶面积指数分别为2.0 k Pa、0.0015 m/s和4.2是控制WUEGPP增加的阈值;(5)净生态系统生产力水分利用效率(WUENEP)和净初级生产力水分利用效率(WUENPP)季节变化规律与WUEGPP一致,均值分别为3.47和5.47 mg/g。     

华北平原冬小麦农田生态系统CO2通量特征及其影响因素

利用2014—2015年中国科学院封丘农业生态实验站涡度相关系统观测的冬小麦农田生态系统CO₂通量数据,结合试验地常规气象观测系统的气象数据,分析冬小麦4个生育期(分蘖期、越冬期、拔节期和灌浆期)内CO₂通量的日变化,研究净生态系统碳交换(NEE)的季节变化及其与气象要素的关系.结果表明: 冬小麦整个生育期内NEE为-360.15 g C·m^-2,总初级生产力总量为1920.01 g C·m^-2,冬小麦农田生态系统具有较强的固碳能力.冬小麦农田生态系统CO₂通量具有明显的日变化和季节变化特征,分蘖期表现为碳源,越冬期、拔节期和灌浆期表现为碳汇.表观初始光能利用率平均值为0.03 mg CO₂·μmol^-1,光饱和时的生态系统生产量平均值为1.53 mg CO₂·m^-2·s^-1,月平均生态系统呼吸为193.92 g C·m^-2·month^-1.冬小麦农田生态系统4个生育期NEE与光合有效辐射的相关关系均达到极显著水平.分蘖期、拔节期和灌浆期NEE与饱和水汽压差的相关关系极显著,越冬期达显著水平.冬小麦分蘖期、越冬期和灌浆期NEE日总量与土壤温度呈正相关,拔节期呈负相关关系.     

遥感GPP模型在中亚干旱区4个典型生态系统的适用性评价

总初级生产力(GPP)是全球生态系统碳循环的重要组成部分,对全球气候变化有重要影响。目前有多种遥感模型可以模拟总初级生产力,比较不同遥感模型在中亚干旱区上的适用性对推进全球干旱区碳收支估算具有重要意义。基于涡度协相关技术观测的四个地面站数据验证MOD17、VODCA2、VPM、TG、SANIRv五种模型的模拟精度。结果表明：(1)基于光能利用率理论的MOD17、VPM模型模拟咸海荒漠植被和阜康荒漠植被GPP的精度最高(R²分别为0.52和0.80),但在模拟草地、农田生态系统生产力时存在较明显的低估(RE>20%);基于植被指数的遥感模型TG模型、SANIRv模型模拟巴尔喀什湖草地生态系统和乌兰乌苏农田生态系统GPP的精度最高(R²分别为0.91和0.81),同时模拟值与实测值的相对误差也较低;基于微波的VODCA2模型模拟各生态系统生产力的效果最差。(2)水分亏缺是限制植被GPP的主要因素,因此是否合理考虑水分胁迫是影响GPP模型在中亚干旱区适用性的重要因素。研究揭示了遥感GPP模型在中亚干旱区的应用潜力,为推进全球植被碳通量的准确估...     

2020-2050年CO2施肥效应促进全球陆地生态系统碳吸收

CO₂施肥效应是全球变绿的主要原因,随着大气中CO₂浓度的持续增加,预估未来气候变化条件下,CO₂施肥效应对陆地生态系统的影响对减缓全球气候变化具有重大意义。基于未来气候情景数据和Farquhar模型,并结合生态过程模型BEPS(Boreal Ecosystem Productivity Simulator),定量化研究2020—2050年CO₂施肥效应对全球叶面积指数(LAI)和总初级生产力(GPP)的影响。研究结果显示2020—2050年,在RCP2.6、RCP4.5和RCP8.5气候情景下,CO₂施肥效应导致的LAI年际变化趋势分别为0.002、0.003和0.005 m^-2m^-2a^-1;三个气候情景下CO₂施肥效应对LAI的影响为CO₂每增加0.1%,LAI平均增加约8.1%—9.2%,由此导致GPP对应增加7.9%—14.6%;由CO₂施...     

太湖生态系统能量闭合特征及其影响因素

地表能量不闭合不仅限制了涡度相关观测数据在陆面模型发展和验证等应用性研究中的价值,还给生态系统CO2源汇特征辨析带来不确定性。基于太湖避风港站2012年涡度相关通量、辐射、气象和水温梯度观测数据,分析了太湖能量闭合的多尺度(小时、日和月)时间变化特征,阐述了大气稳定度、摩擦风速和湖风对太湖能量闭合状况的影响。结果表明:太湖小时尺度的能量闭合度为0.59,且昼夜差异较小;日尺度的能量闭合度为0.73,在内陆水体观测结果中处于中等水平;月平均能量闭合度呈现冬季高、夏季低的季节变化特征;年平均时太湖仍有27%的能量不闭合。因摩擦风速减小,太湖能量闭合度在大气极不稳定条件下要比弱不稳定条件下结果低0.3;对于太湖这类大型浅水湖泊,其能量闭合度全天都受动力湍流交换强度制约,能量闭合度随摩擦风速增大而显著提高;虽然湖风发生使太湖小时尺度的能量闭合度降低了0.1,但其影响在日尺度上并不明显。     

北京永定河沿河沙地杨树人工林光能利用效率

光能利用效率(LUE)是影响生态系统生产力大小和质量的主要因素。以位于北京市大兴区永定河沿河沙地的杨树(欧美107/108,Populus euramericana cv.)人工林生态系统作为研究对象,依托涡度相关观测系统,对该生态系统的LUE进行研究,从而确定LUE在不同时间尺度上的影响因子,并确定最大光能利用利用效率(LUEmax)。结果表明:LUE存在明显的季节变化趋势,4月份生长季开始后LUE迅速升高,到7—8月达到最大,而后逐渐降低;在生长季不同阶段,LUE日动态的影响因子不同:4月份气温(Ta)、蒸散比(EF)和饱和水汽压差(VPD)是影响LUE日动态的主要因子,7、8月份光合有效辐射(PAR)和冠层导度(gc)是主要影响因子,5—6月与9—10月LUE日动态则与土壤水分(VWC)有较大关系;而LUE月动态则与月蒸散比(EFm)和月平均土壤温度(Tsm)有关。由于该人工林各月光能利用最适宜环境条件不同,各月LUEmax也各有差异,该生态系统年LUEmax为0.44 g C/MJ PAR,7、8月LUEmax最大,分别为0.66和0.69 g C/MJ PAR。研究结果表明,在利用光能利用模型进行区域乃至全球初级生产力估算时需要根据研究的不同时间尺度确定LUEmax。     

毛竹林总初级生产力年际变化及其驱动因素——以安吉县为例

森林生态系统碳通量的年际变化及其驱动因素分析是了解森林碳收支动态变化以及预测未来气候变化对森林碳收支影响的重要理论基础,对评估森林应对气候变化的贡献具有重要意义。结合MODIS叶面积指数(LAI)和归一化植被指数(NDVI)产品、MERRA气象数据和通量塔观测数据,采用光能利用率模型模拟2004—2011年安吉县毛竹林生态系统总初级生产力(GPP)空间分布,并分析GPP年际变化及其驱动因素。结果表明:(1)小年毛竹林GPP稍高于大年GPP;(2)2004—2011年安吉县毛竹林年日均GPP呈下降趋势,东部、西部和整个安吉县毛竹林年日均GPP变化速率分别为-0.064、-0.033和-0.045g C m-2W-1,年均温度持续下降是主要驱动因素;(3)LAI年际变化是GPP年际变化的主要驱动因素,主要原因是毛竹林大小年交替规律引起了有效LAI年际间差异;(4)西部GPP年际变化幅度大于东部,环境和生物因素对GPP年际变化的作用方向决定了毛竹林GPP年际变化的幅度。     

Seasonal and interannual variations in carbon dioxide exchange over a cropland in the North China Plain

In China, croplands account for a relatively large form of vegetation cover. Quantifying carbon dioxide exchange and understanding the environmental controls on carbon fluxes over croplands are critical in understanding regional carbon budgets and ecosystem behaviors. In this study, the net ecosystem exchange (NEE) at a winter wheat/summer maize rotation cropping site, representative of the main cropping system in the North China Plain, was continuously measured using the eddy covariance technique from 2005 to 2009. In order to interpret the abiotic factors regulating NEE, NEE was partitioned into gross primary production (GPP) and ecosystem respiration (R_eco). Daytime R_eco was extrapolated from the relationship between nighttime NEE and soil temperature under high turbulent conditions. GPP was then estimated by subtracting daytime NEE from the daytime estimates of R_eco. Results show that the seasonal patterns of the temperature responses of R_eco and light‐response parameters are closely related to the crop phenology. Daily R_eco was highly dependent on both daily GPP and air temperature. Interannual variability showed that GPP and R_eco were mainly controlled by temperature. Water availability also exerted a limit on R_eco. The annual NEE was ?585 and ?533 g C m^?2 for two seasons of 2006–2007 and 2007–2008, respectively, and the wheat field absorbed more carbon than the maize field. Thus, we concluded that this cropland was a strong carbon sink. However, when the grain harvest was taken into account, the wheat field was diminished into a weak carbon sink, whereas the maize field was converted into a weak carbon source. The observations showed that severe drought occurring during winter did not reduce wheat yield (or integrated NEE) when sufficient irrigation was carried out during spring.     

Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

In this study we examined ecosystem respiration (R_ECO) data from 104 sites belonging to FLUXNET, the global network of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability of R_ECO: temporally and between sites as affected by climate, vegetation structure and plant functional type (PFT) (evergreen needleleaf, grasslands, etc.). We demonstrated that a model using only climate drivers as predictors of R_ECO failed to describe part of the temporal variability in the data and that the dependency on gross primary production (GPP) needed to be included as an additional driver of R_ECO. The maximum seasonal leaf area index (LAI_MAX) had an additional effect that explained the spatial variability of reference respiration (the respiration at reference temperature T_ref=15 °C, without stimulation introduced by photosynthetic activity and without water limitations), with a statistically significant linear relationship (r²=0.52, P<0.001, n=104) even within each PFT. Besides LAI_MAX, we found that reference respiration may be explained partially by total soil carbon content (SoilC). For undisturbed temperate and boreal forests a negative control of total nitrogen deposition (N_depo) on reference respiration was also identified. We developed a new semiempirical model incorporating abiotic factors (climate), recent productivity (daily GPP), general site productivity and canopy structure (LAI_MAX) which performed well in predicting the spatio‐temporal variability of R_ECO, explaining >70% of the variance for most vegetation types. Exceptions include tropical and Mediterranean broadleaf forests and deciduous broadleaf forests. Part of the variability in respiration that could not be described by our model may be attributed to a series of factors, including phenology in deciduous broadleaf forests and management practices in grasslands and croplands.     

华北低丘山地人工林生态系统净碳交换与气象因子的关系

植树造林使我国森林碳储量显著增加,人工林潜在的碳汇功能不容忽视.基于涡度相关技术,对华北低丘山地30年生栓皮栎-刺槐-侧柏人工混交林生态系统进行了连续2a的碳通量观测,以探讨净碳交换(NEE)与气象因子的关系.结果表明:在主要生长季(4～9月份),夜间日平均NEE(生态系统呼吸)随气温升高呈指数增长(P<0.01).2006年和2007年生态系统呼吸的温度敏感系数(Q_(10))分别为1.92和1.86.气温在10℃以下时,NEE日总量较小.气温超过10℃后,人工林以净吸收大气CO_2为主,且日吸收量随温度升高迅速增加.白天净碳吸收量随光合有效辐射(PAR)增加而增大(P<0.01),可由直角双曲线方程描述;不过,当饱和差(VPD)小于1.0 kPa时,二者呈线性相关(P<0.01).2006年和2007年主要生长季(4～9月份)的平均表观初始光能利用率(α)分别为0.032和0.019,平均最大光合速率(P_(max))分别为0.96mg · m~(-2) · s~(-1)和1.10 mg · m~(-2) · s~(-1).α和P_(max)都存在季节变化.在月尺度,P_(max)与VPD和PAR呈明显的负相关关系(分别为P<0.01和P<0.05),但与气温相关性不显著;α与对应的PAR、气温和VPD均无明显相关关系.     

Net ecosystem production of a Douglas-fir stand for 3 years following clearcut harvesting

To investigate the variations in annual and seasonal net ecosystem production (F_NEP) during the development of a young forest, 3 years of continuous eddy covariance measurements of carbon dioxide (CO₂) fluxes were collected following clearcut harvesting and replanting of a coastal Douglas‐fir stand on the east coast of Vancouver Island, BC, Canada. The impact of changing weather and stand structure on F_NEP was examined by developing relationships between F_NEP and variables such as light, temperature, soil moisture, and leaf area index (LAI). In all 3 years, the stand was a large source of CO₂ (620, 520, and 600 g C m^?2 yr^?1 in the first, second, and third years, respectively). During this period, the growth of pioneer and understory species resulted in an increase in maximum growing season LAI from 0.2 in the year the seedlings were planted to 2.5 in the third year. The associated increase in annual gross ecosystem production (P=F_NEP?R_e, where R_e is ecosystem respiration) from 220 g C m^?2 yr^?1 in the first year to 640 g C m^?2 yr^?1 in the third year was exceeded by an increase in annual R_e from 840 to 1240 g C m^?2 yr^?1. Seasonal and interannual variations in daytime F_NEP and P were well described by variations in photosynthetically active radiation, temperature, and changes in LAI. Night‐time measurements of R_e exponentially increased with 2 cm soil temperature with an average Q₁₀ of 2 (relative increase in R_e for a 10°C increase in temperature) and R₁₀ (R_e at 10°C) that increased from 2.1 in the first year to 2.5 in the second year to 3.2 μmol m^?2 s^?1 in the third year. Although the re‐establishment of vegetation in this stand had a major impact on both P and R_e, interannual variations in weather also affected annual F_NEP. Drought, in the summer of the third year, resulted in early senescence and reduced both P and R_e. This resulted in more C being lost from the stand in the third year after harvesting than in the second year.     

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.     

华北平原冬小麦农田生态系统通量贡献区

利用2013—2014年涡度相关系统观测的华北平原冬小麦农田生态系统通量数据,结合通量贡献区模型FSAM,分析华北平原冬小麦农田生态系统通量贡献区的时空分布特点,对比研究不同大气稳定层结条件和生长期内通量贡献区的分布差异.结果表明: 在主风风向上,冬小麦整个生育期内大气稳定条件下的通量贡献区范围大于不稳定条件下的贡献区范围.在0°～90°主风风向上,生长初期稳定条件下通量贡献区范围比不稳定条件下大17.8 m左右,生长末期稳定条件下的通量贡献区范围比不稳定条件下大11 m左右.生长初期的通量贡献最大值点位置比生长末期距观测点位置远15 m(大气稳定条件)和12.4 m(大气不稳定条件);通量贡献最大值点在稳定条件下比不稳定条件下距观测点位置远5 m(生长初期)和2.4 m(生长末期).在非主风风向上,当风向为90°～180°时,生长初期和生长末期不同大气条件下的最大通量值分别位于距观测点的67.8、53.4和47.0、30.8 m.当风向为270°～360°时,生长初期和生长末期不同大气条件下的最大通量值位于距观测点的58.8、42和41.1、33.1 m.在整个生育期尺度上,观测塔的通量信息主要来自东北、西南和东南方向,其所占比例分别为35.4%、32.5%和19.4%.冬小麦整个生育期内通量贡献区的主要变化发生在观测点东北方向16.0～173.8 m和西南方向14.7～209 m,通量信息全部来源于农田生态系统.两个典型日期的通量贡献区日变化特征明显,通量贡献区范围随大气稳定条件和风向改变而发生变化.夜晚通量信息全部来源于农田生态系统,白天少部分通量信息来源于居民区和果园.本文的定量化结果可为农田生态系统通量贡献区的研究提供依据.     

Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables

Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO₂ based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ∼29°N to ∼64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.     

Canopy photosynthesis of six major arable crops is enhanced under diffuse light due to canopy architecture

Diffuse radiation generally increases photosynthetic rates if total radiation is kept constant. Different hypotheses have been proposed to explain this enhancement of photosynthesis, but conclusive results over a wide range of diffuse conditions or about the effect of canopy architecture are lacking. Here, we show the response of canopy photosynthesis to different fractions of diffuse light conditions for five major arable crops (pea, potato, wheat, barley, rapeseed) and cover crops characterized by different canopy architecture. We used 13 years of flux and microclimate measurements over a field with a typical 4 year crop rotation scheme in Switzerland. We investigated the effect of diffuse light on photosynthesis over a gradient of diffuse light fractions ranging from 100% diffuse (overcast sky) to 11% diffuse light (clear‐sky conditions). Gross primary productivity (GPP) increased with diffuse fraction and thus was greater under diffuse than direct light conditions if the absolute photon flux density per unit surface area was kept constant. Mean leaf tilt angle (MTA) and canopy height were found to be the best predictors of the diffuse versus direct radiation effect on photosynthesis. Climatic factors, such as the drought index and growing degree days (GDD), had a significant influence on initial quantum yield under direct but not diffuse light conditions, which depended primarily on MTA. The maximum photosynthetic rate at 2,000 µmol m^?2 s^?1 photosynthetically active radiation under direct conditions strongly depended on GDD, MTA, leaf area index (LAI) and the interaction between MTA and LAI, while under diffuse conditions, this parameter depended mostly on MTA and only to a minor extent on canopy height and their interaction. The strongest photosynthesis enhancement under diffuse light was found for wheat, barley and rapeseed, whereas the lowest was for pea. Thus, we suggest that measuring canopy architecture and diffuse radiation will greatly improve GPP estimates of global cropping systems.