基于光合产物动态分配的玉米生物量模拟

光合产物分配是作物生长发育及生物量形成的关键环节,也是作物生长模拟的重要内容.本研究依据光合产物分配机理,结合玉米不同生长阶段的光合产物分配特点,构建了玉米光合产物分配模型.与WOFOST模型的CO₂同化模块相结合,实现了对玉米各器官生物量动态的逐日模拟.利用锦州农田生态系统野外观测站5年的春玉米大田试验资料对模拟效果进行了验证.结果表明: 模型能解释总生物量变化的95.4%;对营养器官生物量变化的解释率达87.0%;对叶、根、茎生物量变化的解释率分别达85.3%,67.9%和76.5%;对穗生物量变化的解释率达87.5%.模型可实现玉米各器官的生物量动态的准确模拟.     

玉米农田蒸散过程及其对气候变化的响应模拟

应用基于生理生态学过程的EALCO模型,对玉米农田生态系统的蒸散(ET)过程进行了模拟,在模型检验基础上,使用该模型模拟了玉米农田生态系统ET过程对未来气候变化的响应。结果表明,EALCO模型中能量与水过程的动态耦合机制使模型能够较好地模拟农田蒸散过程,基于涡度相关法的观测值与模型模拟值在小时、日尺度上均吻合较好,模型可以解释67%的日蒸散的变化特征。对土壤蒸发与冠层蒸腾的分别模拟显示,生长季土壤蒸发约占ET的36%。温度的升高会引起ET与冠层蒸腾的增加,同时土壤蒸发减少;ET对降水减少的响应较为敏感,主要表现在土壤蒸发的下降。大气CO2浓度升高对冠层蒸腾影响显著,该情景下冠层蒸腾下降幅度最大。研究所假设的2100年气候情景下,该农田生态系统生长季蒸散将减少,然而相对于降水的减少而言,蒸散的减少量较小,即水分支出项相对增加,因此,发生土壤水分匮乏的可能性加大,这可能会加剧该地区的暖干化趋势,给作物产量及生态环境带来威胁。     

雨养玉米农田生态系统的蒸散特征及其作物系数

基于雨养玉米农田生态系统2007年整个生长季的涡度相关通量资料,对蒸散的日、季动态进行分析.结果表明：玉米农田生态系统蒸散的日、季动态均呈单峰型变化,最大值分别出现在12:00左右和7月.结合修正的Penman-Monteith公式与相应的生态、气象观测要素,对作物系数(K指数)影响因子的分析结果表明,K指数主要受叶面积指数(LAI)、气温(T_a)、净辐射(R_n)以及表层土壤含水量的影响.在此基础上,初步建立了半小时尺度的作物系数(K指数)模型.     

植物光合产物分配及其影响因子研究进展

植物光合产物分配受环境因子和生物因子的共同影响。为增进对植物对全球变化响应的理解, 从植物个体水平与群落/生态系统水平综述了植物光合产物分配的影响因子与影响机理的最新研究进展。植物个体在光照增强及受水分和养分胁迫时, 会将光合产物更多地分配到根系; CO₂浓度升高对植物光合产物分配的影响受土壤氮素的制约, 植物受氮素胁迫时, CO₂浓度升高会促进光合产物更多地分配到根系; 反之, 对植物光合产物分配没有影响。植物群落/生态系统的光合产物分配对环境因子的响应不敏感; 光合产物向根系的分配比例随其生长阶段逐渐降低。功能平衡假说、源汇关系假说和相关生长关系假说分别从环境因子、个体发育和环境因子与个体发育协同作用方面阐述了植物光合产物分配的影响机理。在此基础上,指出了未来拟重点加强的研究方向: 1)生态系统尺度的光合产物向呼吸部分的分配研究; 2)地下净初级生产力(belowground net primary productivity, BNPP)研究; 3)温室和野外条件下及幼苗和成熟林光合产物分配对环境因子响应的比较研究; 4)生态系统尺度的多因子控制试验; 5)整合环境因子和个体发育对植物光合产物分配格局的影响研究。     

春玉米最大叶面积指数的确定方法及其应用

玉米叶面积指数达到最大时光合产物基本停止向营养器官分配,是玉米进入生殖生长阶段的标志.对锦州农田生态系统野外观测站2005-2011年多品种的春玉米大田试验资料分析发现春玉米最大叶面积指数出现于吐丝后2周左右,提出了春玉米叶面积指数达到最大时的积温指标,即播种至叶面积指数最大时的≥10℃有效积温为1085.3℃·d和(或)出苗至叶面积指数最大时的≥10℃有效积温为1010.4℃·d.在此基础上,采用修正的Logistic方程构建了春玉米相对叶面积指数动态普适模型.研究结果为准确模拟春玉米叶片生长及光合产物分配提供了依据.     

动态空气动力学参数对玉米田陆-气通量模拟的影响——以BATSle模型为例

基于2006-2008年锦州玉米农田生态系统的通量、气象及生物因子连续观测,利用所建立的考虑玉米不同发育期叶面积指数、冠层高度和风速的地表粗糙度(z0)和零平面位移(d)动态参数化方案对BATS1e陆面模型进行改进,研究空气动力学参数变化对玉米田陆-气通量模拟的影响.结果表明:改进后的拖曳系数(CD)随植被覆盖度增大而增大,更符合实际;感热、潜热和土壤热通量的模拟精度均有不同程度改进,效率系数分别提高0.0569、0.0194和0.0384,生长季累计改进量分别占总辐射的0.9％、1.1％和1.2％;当输入真实的表层土壤湿度后,z0和d动态参数化对感热和潜热的改进作用更大.合理的动态空气动力学参数化方案对陆面过程模拟具有明显改善作用.     

不同空间尺度下的ALMANAC模型验证

ALMANAC模型最早作为EPIC模型的一部分,用于模拟土壤侵蚀导致的土地生产力的下降．它将试验数据的统计过程和作物生长的机理过程结合起来,是一种典型的基于过程模拟的应用型作物生长模型．如能在不同的空间尺度上验证模型的适用性,无疑会大大扩展模型的应用范围．从这一目的出发,利用美国得克萨斯州19个试验田和9个县的玉米和高粱产量资料及其相关的作物、土壤、田问管理等数据,模拟了1998年田间尺度,1989～1998年县级尺度的平均作物产量．模拟结果表明,ALMANAC模型能够很好地模拟两种不同空间尺度的作物产量,其相对误差在田问尺度上分别为8．9％(高粱)和9．4％(玉米),在县级尺度上分别达到2．6％(玉米)和—0．6％(高粱)．该模型在进行产量预测、掌握作物生长动态,指导农业生产管理和土地利用等方面具有很好的应用前景．     

基于遥感和Penman-Monteith模型的内陆河流域不同生态系统蒸散发估算

遥感数据具有很好的时空连续性,它是区域蒸散发通量估算的有效方法。引入了一个简单的具有生物物理基础的Penman-Monteith(P-M)模型,分别利用黑河流域高寒草地阿柔站和干旱区农田盈科站2008—2009年的气象数据和MODIS(Moderate Resolution Imaging Spectroradiometer)叶面积指数(LAI),实现了2008—2009年日蒸散发的估算,并同时实现了对植被蒸腾和土壤蒸发的分别估算。结果表明,利用P-M公式模拟的蒸散发与实测的蒸散发具有较好的一致性,日蒸散发模拟的决定系数(R2)超过0.8。估算的高寒草甸和干旱区农田玉米全年平均的蒸腾分别为0.78 mm/d和1.20 mm/d,分别占总蒸散发的60%和61%,土壤蒸发分别为0.53和0.77 mm/d,占总蒸发的40%和39%。可见两种生态系统的作物蒸腾均强于土壤蒸发,同时农田玉米蒸腾强于高寒草甸蒸腾。研究结果证明了基于遥感的P-M公式可以很好地实现对高寒草地和干旱区农田生态系统蒸散发的估算。通过考虑土壤水分变化对气孔导度的影响,可以提高模型对农田蒸散发的模拟精度。     

生态系统模拟模型的研究进展

从四个方面概述了生态系统模拟模型的发展现状：1)个体及种群,种群动态模型主要模拟在一个生境中单个种的动、植物个体出生或发芽、成长及其死亡过程,还有种内竞争和种间相互作用,主要分析生境中生物之间的相互作用。主要概述了林窗模型和土壤一植物一大气系统模型。2)群落与生态系统,概述了生态系统生产力模型、生物地球化学循环模型及演替模型。主要模拟植物种类在整个生态系统发展过程中的变化,以及植被类型的转变和相关的生物地球化学循环过程的改变,从而反映生物群落对气候变化的响应。3)景观生态系统,景观动态研究包含了时空两个方面的动态变化,一般可分为随机景观模型和基于过程的景观模型。随机模型用于模拟群落格局在演替过程中的动态变化等,基于过程的景观模型深入研究组成景观的各生态系统的空间结构。4)生物圈与地球生态系统,基于过程的陆地生物地球化学模式被用来研究自然生态系统中碳和其它矿物营养物质的潜在通量和蓄积量,较为流行的模式有陆地生态系统模式TEM、CENTURY、法兰克福生物圈模式FBM、Biome-BGC、卡内基-埃姆斯-斯坦福方法CASA等。这些模式己被用于估算自然生态系统对大气CO2加倍及相关气候变化在区域和全球尺度的平衡响应。最后,结合实际工作展望了生态系统模拟模型在各方面的发展方向。     

基于个体的中国森林生态系统碳收支模型FORCCHN及模型验证

以植物生理学、森林生态学和土壤环境学的基本原理为基础,建立了基于个体的中国森林生态系统碳收支模型FORCCHN。模型通过两种步长运行:在步长为天时的基本过程包括林分(个体)的光合、呼吸、分配和凋落,以及凋落物和土壤有机物的呼吸和转移;在步长为年时的基本过程包括林分的同化物分配、树高和胸径增长、大凋落物生成。通过对模型样地水平上与全国总量上NPP、NEP的验证,说明该模型在考虑幼龄林基础上,能较好的模拟出中国森林生态系统的碳收支,因此可以用来模拟中国森林生态系统碳收支的过去动态和未来发展趋势。     

Diel patterns of autotrophic and heterotrophic respiration among phenological stages

Improved understanding of the links between aboveground production and allocation of photosynthate to belowground processes and the temporal variation in those links is needed to interpret observations of belowground carbon cycling processes. Here, we show that combining a trenching manipulation with high‐frequency soil respiration measurements in a temperate hardwood forest permitted identification of the temporally variable influence of roots on diel and seasonal patterns of soil respiration. The presence of roots in an untrenched plot caused larger daily amplitude and a 2–3 h delay in peak soil CO₂ efflux relative to a root‐free trenched plot. These effects cannot be explained by differences in soil temperature, and they were significant only when a canopy was present during the growing season. This experiment demonstrated that canopy processes affect soil CO₂ efflux rates and patterns at hourly and seasonal time scales, and it provides evidence that root and microbial processes respond differently to environmental factors.     

Plant carbon allocation drives turnover of old soil organic matter in permafrost tundra soils

Carbon cycle feedbacks from permafrost ecosystems are expected to accelerate global climate change. Shifts in vegetation productivity and composition in permafrost regions could influence soil organic carbon (SOC) turnover rates via rhizosphere (root zone) priming effects (RPEs), but these processes are not currently accounted for in model predictions. We use a radiocarbon (bomb‐¹⁴C) approach to test for RPEs in two Arctic tall shrubs, alder (Alnus viridis (Chaix) DC.) and birch (Betula glandulosa Michx.), and in ericaceous heath tundra vegetation. We compare surface CO₂ efflux rates and ¹⁴C content between intact vegetation and plots in which below‐ground allocation of recent photosynthate was prevented by trenching and removal of above‐ground biomass. We show, for the first time, that recent photosynthate drives mineralization of older (>50 years old) SOC under birch shrubs and ericaceous heath tundra. By contrast, we find no evidence of RPEs in soils under alder. This is the first direct evidence from permafrost systems that vegetation influences SOC turnover through below‐ground C allocation. The vulnerability of SOC to decomposition in permafrost systems may therefore be directly linked to vegetation change, such that expansion of birch shrubs across the Arctic could increase decomposition of older SOC. Our results suggest that carbon cycle models that do not include RPEs risk underestimating the carbon cycle feedbacks associated with changing conditions in tundra regions.     

东北地区春玉米气候适宜度模型

农作物生长是一个连续的动态过程,因而作物生长的最适宜气象指标也是连续变化的.据此,本文提出作物生长日可利用降水量的推算方法和气象指标时间插值算法,构建了日尺度气候适宜度模型,利用东北地区农业气象站的多年玉米观测资料进行检验.结果表明： 模型计算的气候适宜度与株高、百粒重存在显著正相关;在春玉米营养生长期间,气候适宜度与株高的相关系数(R²)在0.58以上;春玉米生殖生长期间,气候适宜度与春玉米百粒重的R²在0.45以上.本文建立的日尺度气候适宜度模型能客观地反映营养生长阶段及生殖生长阶段作物与气候条件的相互作用关系.
     

N rate and transport under variable cropping history and fertilizer rate on loamy sand and clay loam soils: II. Performance of LEACHMN using different calibration scenarios

Testing of existing agronomic models is needed to ensure their validity and applicability to different soils, cropping systems and environments. Data collected from a 3-year field experiment of maize (zea mays L.) on a loamy sand and a clay loam soil were used to validate the research version of the LEACHMN model for water flow and N fate and transport. Three calibration scenarios with increasing levels of generalization for transformation rate coefficients were used based on: (i) each year, treatment and soil type (ii) 3-year average values for each treatment and soil type, and (iii) average over years and soil types. Model accuracy was tested using both graphical and statistical methods including 1:1 scale plot, root mean square error and normalized root mean square error, and correlation coefficient values. The model accurately predicted drainage water flow rate and volume under both sites. Calibrated N transformation rate constants for each treatment, year and soil type provided satisfactory predictions of growing season cumulative NO₃–N leaching losses, and accurate predictions of growing season cumulative maize N uptake at both sites. The use of 3-year average rate constant values for each site resulted in fairly satisfactory predictions of NO₃–N leaching losses on the clay loam site, but inaccurate predictions on the loamy sand site. The model provided accurate predictions of cumulative maize N uptake for both sites. Using the rate constant values averaged over years and soil types resulted mostly in inaccurate predictions. Use of year and soil type-specific N rate coefficients results in accurate LEACHMN predictions of N leaching and maize N uptake. When rate coefficients are generalized over years for each soil type, satisfactory model predictions may be expected when N dynamics are not strongly affected by yearly variations in organic N inputs.     

Growth and transpiration of maize and winter wheat in response to water deficits in pots and plots

Pots used for experiments conducted on plants grown in them create rooting environments that are affected by limited soil volume, which can affect various physiological processes, including transpiration, and plant growth. However, the applicability of results from pot experiments to the field has received limited attention. The objective of this study was to compare the growth and transpiration of maize (Zea mays L.) and winter wheat (Triticum aestivum L.) when grown in pots and field plots under various constant water deficits. The experiments were conducted under similar environmental conditions for both pots and plots. Transpirational responses at both transient (RTTr) and daily (RDTr) time scales to a decreasing fraction of available soil water (FASW) were analyzed. For a comparable FASW, there was a significant reduction in shoot dry weight and total transpiration for plants in pots compared to those in plots. A parabolic relationship between shoot dry weight and total transpiration existed and was not influenced by soil volume or crop type. The plot experiment data for both crops was consistent with pot data for the response of RDTr and RTTr to changes in FASW, which was represented by a linear-plateau function. However, the threshold values were significantly different for the two time scales. The threshold values and slopes of the linear-plateau function for maize and wheat were not significantly different in the response of RTTr to FASW, but were significantly different in the response of RDTr to FASW. Therefore, the transpirational responses of the selected maize and winter wheat hybrids to soil drought were different at the daily and transient time scales.     

Effects of Warming and Nitrogen Addition on Plant Photosynthate Partitioning in an Alpine Meadow on the Tibetan Plateau

Quantifying plant carbon (C) allocation among different pools is critical for understanding and predicting how C turnover responds to global climate change in terrestrial ecosystems. A field experiment with increasing warming and nitrogen (N) was established to investigate interactive effects on plant C allocation in alpine meadows. Open-top chambers (OTCs) were used to simulate warming. In OTCs, daytime air and soil temperature at 5 cm depth increased by 2.0 and 1.6 °C, respectively, compared with ambient conditions, but soil moisture at 5 cm depth decreased by 4.95% (v/v) from 2012 to 2014. Warming reduced aboveground biomass by 38, 36, and 43% in 2012, 2013, and 2014, respectively, and increased belowground biomass by 64% and 29% in 2013 and 2014, respectively, and the root-to-shoot ratio was significantly increased. Specifically, warming increased the proportion of plant roots in the deep layers (10–20 cm). Both N addition and its combination with warming substantially enhanced belowground biomass. Pulse-labeling experiments for ¹³C revealed that warming reduced the translocation of assimilated C to shoots by 8.8% (38.7% in warming, and 47.5% in the control [CK]), and increased the allocation to root by 12.2% (55.5% in warming, and 43.3% in CK) after 28 days labeling. However, N addition increased the proportion of assimilated C allocated to shoots by 6.5% (54.0% in N addition, and 47.5% in CK), whereas warming combined with N addition reduced this proportion by 10.9%. A decline in soil water content in the surface layer may be the main cause of plants allocating more newly fixed photosynthate to roots. Therefore, plants promoted root growth to draw water from deeper soil layers (10–20 cm). We concluded that climate warming will change the allocation patterns of plant photosynthates by affecting soil water availability, whereas N addition will increase plant photosynthates aboveground in alpine meadows and thus will significantly affect C turnover under future climate change scenarios.

     

The effects of clonal integration on morphological plasticity and placement of daughter ramets in black locust (Robinia pseudoacacia)

We studied the field response of Robinia pseudoacacia L. to light, total soil nitrogen, available soil phosphorus and soil pH. Results indicated that there was very strong clonal integration between mother and daughter ramets. Mother ramets can provide nitrogen and phosphorus to daughter ramets sufficient for their continued growth through strong clonal integration, but cannot provide enough photosynthate. With clonal integration, soil nitrogen and phosphorus availability had no effect on biomass allocation to roots, number of ramets and length of connection roots. Biomass allocation to roots increased markedly and responded to nitrogen and phosphorus availability, when the connections were severed. Light had a significant effect on the percent of biomass allocation to leaves and number of ramets, but no effect on the length of connection roots. Daughter ramets allocated more resources to leaves, and clones placed more daughter ramets in high light patches than in low light patches. Soil pH had a significant effect on ramet number and connection root length. Clones concentrated in alkaline patches and escaped from acid patches through selective placement of daughter ramets and changing the length of connection roots. We suggest that the clonal integration may be very strong and provide sufficient soil resources to daughter ramets, then affect the daughter ramets’ morphology and placement, if the size of a specific ramet is significantly larger than the other ramets in an arbor clone.     

干旱条件下夏玉米地-气温差的影响因素及其模拟

地-气温差指标表征作物水分亏缺状况已经被广泛研究,但地-气温差随作物生育进程的变化特征及其影响因子的观测研究仍较少,制约着地-气温差的准确模拟.基于夏玉米2014年三叶期和2015年拔节期的5个灌溉水分控制试验资料的研究表明: 随着夏玉米生育进程的推进,土壤水分的变化显著影响了夏玉米农田的地-气温差,土壤水分亏缺越严重,地-气温差越高.在整个水分处理期间,归一化植被指数是地-气温差的主要影响因子且两者呈显著的线性关系,但不同生育期地-气温差还受其他因子的影响:三叶期后受冠层吸收光合有效辐射比影响且呈显著的线性关系,三叶期至拔节期则受土壤相对湿度和空气相对湿度的影响且呈显著的线性关系.在此基础上,基于2014年试验资料建立了夏玉米全生育期地-气温差模拟模型、营养生长期地-气温差模拟模型和生殖生长期地-气温差模拟模型,并利用2015年夏玉米拔节期5个灌溉水分控制试验资料进行了模型验证,结果表明,夏玉米全生育期地-气温差模型可以解释2015年地-气温差变异的63%,但地-气温差分生育期模拟模型,即营养生长期地-气温差模拟模型和生殖生长期地-气温差模拟模型综合的模拟结果则可解释2015年地-气温差变异的79%.研究结果为基于地-气温差的作物干旱指标定量评估作物干旱提供了依据.     

Net primary productivity mapped for Canada at 1-km resolution

Aim To map net primary productivity (NPP) over the Canadian landmass at 1‐km resolution. Location Canada. Methods A simulation model, the Boreal Ecosystem Productivity Simulator (BEPS), has been developed. The model uses a sunlit and shaded leaf separation strategy and a daily integration scheme in order to implement an instantaneous leaf‐level photosynthesis model over large areas. Two key driving variables, leaf area index (every 10 days) and land cover type (annual), are derived from satellite measurements of the Advanced Very High Resolution Radiometer (AVHRR). Other spatially explicit input data are also prepared, including daily meteorological data (radiation, precipitation, temperature, and humidity), available soil water holding capacity (AWC) and forest biomass. The model outputs are compared with ground plot data to ensure that no significant systematic biases are created. Results The simulation results show that Canada’s annual net primary production was 1.22 Gt C year^?1 in 1994, 78% attributed to forests, mainly the boreal forest, without considering the contribution of the understorey. The NPP averaged over the entire landmass was ~140 g C m^?2 year^?1 in 1994. Geographically, NPP varied greatly among ecozones and provinces/territories. The seasonality of NPP is characterized by strong summer photosynthesis capacities and a short growing season in northern ecosystems. Conclusions This study is the first attempt to simulate Canada‐wide NPP with a process‐based model at 1‐km resolution and using a daily step. The statistics of NPP are therefore expected to be more accurate than previous analyses at coarser spatial or temporal resolutions. The use of remote sensing data makes such simulations possible. BEPS is capable of integrating the effects of climate, vegetation, and soil on plant growth at a regional scale. BEPS and its parameterization scheme and products can be a basis for future studies of the carbon cycle in mid‐high latitude ecosystems.