Automated measurement of canopy stomatal conductance based on infrared temperature

Decreased water uptake closes stomates, which reduces transpiration and increases leaf temperature. The leaf or canopy temperature has long been used to make an empirical estimate of plant water stress. However, with a few supplemental measurements and application of biophysical principles, infrared measurement of canopy temperature can be used to calculate canopy stomatal conductance (g_C), a physiological variable derived from the energy balance for a plant canopy. Calculation of g_C requires an accurate measurement of canopy temperature and an estimate of plant height, but all of the other measurements are available on automated weather stations. Canopy stomatal conductance provides a field-scale measurement of daily and seasonal stomatal response to prevailing soil water and atmospheric conditions, and facilitates a comparison of models that scale conductance from single leaves (measured with porometers) to canopies. A sensitivity analysis of the input measurements/estimates showed g_C is highly sensitive to small changes in canopy and air temperature, and less sensitive to the other required measurements (relative humidity, net radiation, wind speed, and plant canopy height). The measurement of g_C becomes increasingly sensitive to all of the component factors as the conditions become cloudier, cooler, and more humid. We determined g_C for alfalfa and turfgrass by making the necessary environmental measurements and coupling them with a two-source (plant canopy layer and soil layer) energy balance model. We then compared these g_C values to maximum single leaf values scaled-up to the canopy level (g_CP, defined as potential canopy stomatal conductance herein) for the two crops. For both crops, g_C matched g_CP within approximately 10% after irrigation. The turfgrass g_C measurements were also compared to mean single leaf values measured with a porometer. At mid-day, g_C values were typically about double the single leaf values. Because this approach for determining g_C allows continuous, non-contact measurement, it has considerable potential for coupling with measurements of soil moisture to better understand plant–soil water relations. It also has potential for use in precision drought stress and irrigation scheduling.     

Effects of atmospheric CO2 enrichment on CO2 exchange rates of beech stands in small model ecosystems

CO₂ enrichment experiments were performed during two vegetation periods on young beech stands in four closed mini-greenhouses. The houses were climatized according to the outside microclimate (±0,5 °C,±15 % rel. air humidity, wind speed approximately to outside in the range of 0.5 – 2.5 m s^?1, max. 17 % PAR reduction). The model ecosystems — consisting of 36 young beech (2.5 yr-old) in a soil block of 0.38 m³ and an air volume of 0.64 m³ — were exposed to CO₂ concentrations of the unchanged ambient air (350±34 ppmv, control) and of 700 ppmv (698±10 ppmv). Plant growth parameters were measured non distructively and at the end of the 1^st season samples were taken for weighing the phytomass. CO₂ gas exchange of the stands taken as a whole were continuously measured with two entire mini-greenhouses and, in addition, a compact mini-cuvette system (CMS 400, Walz) was used for measuring dark respiration and CO₂ net assimilation rates of single leaves in both stands. Under the influence of the additional CO₂ supply stem diameter (2 cm above the first lateral roots) was increased by 13.5 %, stem height by 27.4 %, and the number of leaves/tree by 33 % at the end of the 2^nd season. The number of buds was not significantly different and the effect on mean area per leaf was insignificant. Leaf area index was by 1.4 units greater. All dry weights of the main organs were increased after the 1^st season: leaf 60 %, stem 34 %, bud 54 %. Roots <2 mm φ weighed 1.5-fold more and roots > 2 mm φ 1.7-fold more under elevated CO₂. CO₂ gas exchange of two systems was measured. Whole system CO₂ losses during night as well as photosynthetic CO₂ gains during days were greater at 700 ppmv than in the control system. However, if one balances CO₂ gains with CO₂ losses over a period of five days in August both model-ecosystems taken as a whole were sinks for CO₂. During this selected time period of 5 days at the peak of the season the beech stand at 350 ppmv was the greater sink. At 350 ppmv CO₂ (control) the average leaf respiration for 20 °C amounted to 0.31±0.18 and at 700 ppmv to 0.57± 0.42 μmol CO₂ m^?2 s^?1 (n=35/40, t=3.48, α < 0.05), and correlated positively with leaf temperature. At light saturation the mean net assimilation rate was 4.48 μmol m^?2 (leaf area) s^?1 in the control and 6.21 μmol m^?2 s^?1 at the high CO₂ concentration corresponding with an enhancement factor of 1.39 for the selected time period. Results from the whole stand and from single leaf measurements are compared by means of mathematical modelling procedures in order to quantify CO₂ enrichment effects on beech model ecosystems.     

Monitoring stomatal conductance of Jatropha curcas seedlings under different levels of water shortage with infrared thermography

Model simulations and experimental measurements were used to investigate the applicability of infrared thermography for the estimation of stomatal conductance and drought stress under sub-optimal meteorological conditions. The study focused on the stomatal conductance index I_g, calculated from the leaf temperature and the temperature of a dry and wet reference leaf. The simulations revealed that I_g is influenced by leaf dimension, wind speed and air temperature and not or hardly by leaf angle, albedo, relative humidity or insolation. In addition, I_g was found to be very sensitive to differences in wind speed, air temperature, insolation, leaf dimension and leaf angle between the measured and the reference leaves. In the experimental part, we evaluated if infrared thermography can be used to improve the knowledge on the water use of Jatropha curcas L., a tropical biofuel crop. Thermal images from Jatropha seedlings grown under three different drought treatments were made on a day with very variable insolation and a day with very low insolation. Smaller newly formed leaves and the active control of the leaf angle proved efficient ways of Jatropha to protect leaves under drought stress from overheating. I_g, assessed in four different ways, and four simplified drought stress indices were derived and related to the measured stomatal conductance (g_s) of the seedlings. The strongest correlation with g_s and the highest discriminative power between the different water treatments were achieved when I_g was calculated by taking the average leaf temperature per plant and the temperature of the dry and wet reference leaves of this plant, rather than the average temperature of several reference leaves. Using the difference between the dry reference and the measured leaf (T_dry − T_l) as a simplified index gave similar results, although correlations were weaker. Other simplified thermal indices were not well correlated with leaf stomatal conductance or with water treatment. Recommendations were formulated for the measurement of I_g and (T_dry − T_l).     

节水灌溉水稻叶片胞间CO2浓度及气孔与非气孔限制

为了揭示节水灌溉水稻叶片光合作用的气孔与非气孔限制特征,在研究节水控制灌溉水稻叶片胞间CO2浓度的动态变化规律基础上,进一步探讨了气孔限制与非气孔限制情况。结果表明：水稻叶片胞间CO2浓度呈现v型的日变化规律,在12:00－14:00达到最低值,非气孔限制指标Ci/C与气孔限制值Ls变化规律相反;节水灌溉条件下未出现重度水分亏缺,没有改变胞间CO2浓度与光合作用速率的关系;较低的土壤含水率情况下,控制灌溉水稻的叶片气孔限制值Ls出现增加,非气孔限制没有增加,光合速率没有出现明显降低;气孔限制值增大、光合速率增加的现象表明Ls夸大了叶片光合作用的气孔限制情况。与常规灌溉相比,节水灌溉水稻叶片胞间CO2浓度的变化及其与影响因子间的关系并未发生变化,节水灌溉水稻叶片光合作用的气孔限制有所增加,但光合速率未出现明显降低。     

大气CO2浓度倍增和高温对玉米气孔特征及气体交换参数的影响

为深入了解未来大气CO2浓度升高背景下玉米气孔特征及气体交换过程对高温的响应机理,该研究利用人工气候室,探究在大气CO2浓度400 μmol/mol（C400）和800 μmol/mol（C800）下,不同温度处理（昼/夜）25/19 ℃、31/25 ℃和37/31 ℃对玉米气孔特征及气体交换参数的影响机理。结果表明：1）CO2浓度升高对玉米气孔密度的影响并不显著（P > 0.05）,增温却导致玉米不同轴面气孔密度均显著增加（P < 0.001）;不同轴面气孔密度的增加幅度均随温度升高而增大,叶片气孔密度对环境温度升高的响应呈现出非线性变化趋势。2）将环境温度由25/19 ℃增加到37/31 ℃导致C400和C800处理下玉米蒸腾速率（Tr）分别提高57%和84%,且不同轴面的气孔密度均与Tr之间存在较好的线性相关关系（近轴面R2=0.69;远轴面R2=0.71）。3）当温度从25/19 ℃升高到31/25 ℃,2个CO2浓度处理下玉米的Pn分别提高23%和21%,但环境温度提高到37/31 ℃却导致Pn分别降低24%和13%,说明高温环境（37/31 ℃）对光合反应位点造成生理伤害,而高浓度CO2缓解了高温对玉米造成的生理胁迫。同时,37/31 ℃条件下玉米叶片光合系统II（PSII）最大光化学效率（Fv/Fm）显著降低的结果也直接支持了上述结论。研究结果有助于从气孔特征的角度深入了解 CO2 浓度和温度升高对玉米叶片气体交换过程产生的影响,为未来气候变化背景下实现农作物绿色高效提质增产提供理论依据。     

CO2浓度升高、氮和水分对春小麦养分吸收和土壤养分的效应

研究了 2种CO2浓度水平 ,2种土壤水分处理和 5种N肥施用水平对春小麦 (TriticumaestivumL cv DingxiNo. 8654)养分吸收和土壤速效养分的影响。结果表明 ,高CO2浓度 (700 molmol-1)明显降低春小麦对氮(N)的吸收 ,低N时降低更为明显 ,但对磷 (P)、钾 (K)吸收的影响不明显。小麦对N、P、K吸收 ,干旱处理明显比湿润处理低。CO2浓度增高对土壤速效N的影响与土壤水分状况有关。湿润处理 ,CO2浓度增加的处理速效N量比当前CO2浓度的处理低 ;而干旱处理 ,施N 50、100、150mgkg-1时 ,速效N则较高。高CO2 浓度对土壤速效P、K量的影响不明显 ,而低N和水分不足 ,土壤速效P、K量较高     

日光温室二氧化碳施肥技术研究

给出了施与不施二氧化碳（ＣＯ２）温室内二氧化碳浓度的日变化状况,分析了施用二氧化碳对蔬菜生长发育和产量的促进作用,提出了对不同种类蔬菜施用二氧化碳的适宜施放期、一天内适宜施放时间以及适宜施放浓度。     

大气CO2浓度升高对土壤碳库的影响

土壤碳库是输入、输出土壤碳量的平衡:大气CO2浓度升高有可能通过生态系统中的各种生理过程来增加输入土壤的碳量,输入土壤碳量的增加使土壤成为一个潜在的碳汇,有可能缓解大气CO2浓度的升高;但另一方面输入土壤碳量的增加,为微生物的生长提供了能量,从而提高了微生物的活性,因此土壤呼吸增强,土壤碳输出增加.本文综述了大气CO2浓度升高对土壤碳输入、输出的影响以及目前研究中存在的争论,并提出有待进一步研究的领域和方向.     

Effect of CO2 enrichment on carbon and nitrogen interaction in wheat and soybean

Effect of CO₂ enrichment on the carbon-nitrogen balance in whole plant and the acclimation of photosynthesis was studied in wheat (spring wheat) and soybean (A62-1 [nodulated] and A62-2 [non-nodulated]) with a combination of two nitrogen application rates (0 g N land area m^-2 and 30 g N land area m^-2) and two temperature treatments (30/20°C (day/night) and 26/16°C). Results were as follows.

1. Carbon (dry matter)-nitrogen balance of whole plant throughout growth was remarkably different between wheat and soybean, as follows: 1) in wheat, the relationship between the amount of dry matter (DMt) and amount of nitrogen absorbed (Nt) in whole plant was expressed by an exponential regression, in which the regression coefficient was affected by only the nitrogen application rate, and not by CO₂ and temperature treatments, and 2) in soybean the DMt-Nt relationship was basically expressed by a linear regression, in which the regression coefficient was only slightly affected by the nitrogen treatment (at 0N, DMt-Nt balance finally converged to a linear regression). Thus, carbon-nitrogen interaction in wheat was strongly affected by the underground environment (nitrogen nutrition), but not by the above ground environment (CO₂ enrichment and temperature), while that in soybean was less affected by both under and above ground environments.

2. The photosynthetic response curve to CO₂ concentration in wheat and soybean was less affected by the CO₂ enrichment treatment, while that in wheat and soybean (A62-2) was affected by the nitrogen treatment, indicating that nitrogen nutrition is a more important factor for the regulation of photosynthesis regardless of the CO₂ enrichment.

3. Carbon isotope discrimination (..:1) in soybean was similar to that in wheat under ambient CO₂, while lower than that in wheat under CO₂ enrichment, suggesting that the carbon metabolism is considerably different between wheat and soybean under the CO₂ enrichment conditions.     

大气CO_2浓度富集对华北平原农田土壤可溶性碳含量的影响

<正>由温室气体排放导致的气候变化是当前全球关注的热点问题之一[1]。化石燃料燃烧、水泥生产、土地利用变化等人类活动向大气中排放大量CO2,进而引起全球变暖和地球系统碳循环过程的显著变化。研究表明,大气CO2浓度已由1870年的280μmol mol-1增加至2005年的379μmol mol-1,目前仍以1.9μmol mol-1a-1的速率急剧攀升;同期地表温度平均增加了0.74℃(变幅0.56~0.92℃)[2]。根据《中国应对气候变化国家方案》     

CO2施肥对黄瓜幼苗矿质营养吸收与分配的影响

以土培和砂培黄瓜幼苗为试材,研究CO2施肥对植株矿质营养吸收和分配的影响。结果表明:每天上午以1100±100μl/L CO2浓度施肥3 h或上、下午各施肥3 h明显降低植株各部位多数矿质元素的含量,CO2施肥时间延长,降幅增大。CO2施肥增强了黄瓜对矿质元素的吸收能力,使单株吸收总量显著增加,且施肥时间越长,吸收数量越多。因此,在CO2施肥的同时应增加矿质营养的供给。     

Carbon dynamics in subtropical forest soil: effects of atmospheric carbon dioxide enrichment and nitrogen addition

Purpose  

The levels of atmospheric carbon dioxide concentration ([CO₂]) are rapidly increasing. Understanding carbon (C) dynamics in soil is important for assessing the soil C sequestration potential under elevated [CO₂]. Nitrogen (N) is often regarded as a limiting factor in the soil C sequestration under future CO₂ enrichment environment. However, few studies have been carried out to examine what would happen in the subtropical or tropical areas where the ambient N deposition is high. In this study, we used open-top chambers to study the effect of elevated atmospheric [CO₂] alone and together with N addition on the soil C dynamics in the first 4 years of the treatments applied in southern China.     

纤维素降解菌对农业有机废弃物发酵进行CO2施肥的作用

采用室内培养和大棚试验相结合,对分离的3种纤维素降解菌在有机废弃物发酵释放CO2中的作用及其对增加大棚CO2浓度的效果进行了研究。结果表明,分离获得的三种菌均能明显促进有机废弃物发酵CO2的释放,其中菌A和菌C的效果优于菌B;3种菌混合接种时效果最佳。在大棚栽培条件下,昼间CO2浓度大部分时间低于300μL/L,处于亏缺状态;采用棚中不接种直接发酵也可大幅提高大棚的CO2浓度,但释放的时间只有9 d左右;采用3种菌混合接种的方法棚内全天维持CO2浓度800μL/L以上的时间可达14 d以上。     

增施CO2气肥对温室流场影响的数值模拟及验证

CO2气体是温室作物光合作用的重要原料之一。为掌握温室CO2气肥增施性能,以温室CO2气肥增施为研究对象,采用计算流体力学（computational fluid dynamics,CFD）技术建立二维紊流数值计算模型。基于FLUENT软件,结合SIMPLE算法,采用有孔介质模型、模型、离心坐标（discrete ordinates,DO）模型,添加组分传输模型,对气肥喷射高度、气肥增施流量等因素对CO2增施性能进行数值模拟,得到温室内CO2浓度变化和分布规律。研究结果表明：气肥增施过程对作物区的温度场影响较小,温室的作物区域最大温度与最小温度差值不超过0.5℃,作物区域的气流流场以及温度场分布较为均匀;由于CO2的沉积效应,温室下部区域的CO2浓度相对较高;气肥喷射高度越高,CO2扩散的范围越大,沉积在作物区的CO2相对越少,CO2的浓度也相对较低;气肥增施流量越大,作物区域的CO2浓度上升越快。试验结果表明,CO2浓度模拟值与试验值差异不大于5 %,模拟结果与试验结果较吻合,证明了模型的正确性。该研究对掌握温室CO2气肥增施性能的流场变化规律,开展温室气肥增施装备的优化设计具有一定的参考价值。     

土壤微生物生物量和呼吸强度对大气CO2浓度升高的响应

随着全球环境变化对陆地生态系统的影响逐渐成为公众和科学界关注的热点,CO2作为一种重要的温室气体受到格外重视.大气CO2浓度升高将直接影响陆地植物的光合作用[1].植物的光合产物约有20% ～ 50%被运送到地下,通过根系分泌及死亡输入土壤[2],因此大气CO2浓度升高将会间接影响土壤生态系统.长期以来,关于大气CO2浓度升高对农作物地上部分的研究较多,但关于大气CO2浓度升高对土壤特别是土壤微生物的影响的研究报道较少.     

水分对日光温室独本菊生长动态影响的模拟

光合作用与干物质生产是观赏植物外观品质形成的基础。水分是影响植物光合作用与干物质生产的重要因子。为定量研究水分对日光温室独本菊光合作用与干物质生产的影响,本研究以秋菊品种‘神马’(Chrysanthemum morifolium.L‘Shenma’)为试验材料,于2006年8月～2007年6月在北京日光温室内进行了不同定植期和不同水分处理的栽培试验,以生理辐热积为发育尺度,定量分析了基质水势对独本菊叶面积指数、光合速率和干物质生产动态的影响,建立了基质水势对独本菊叶面积指数、光合速率和干物质生产影响的模拟模型,并用与建立模型相独立的数据对模型进行了检验。结果表明,模型对日光温室独本菊叶面积指数、叶片最大总光合速率和植株总干重的预测结果较好,叶面积指数、叶片最大总光合速率和植株总干重的模拟值与实测值之间基于1︰1线的决定系数分别为0.94,0.90,0.94,相对预测误差分别为11.95%、3.13%、11.14%。本研究建立的模型可以为日光温室秋菊品种‘神马’的水分管理提供理论依据和决策支持。     

CO2浓度升高和磷素亏缺对黑麦草气孔特征及气体交换参数的影响

为深入理解未来大气CO2浓度升高背景下草地生态系统结构与功能响应土壤磷亏缺的潜在机理,该研究利用可精准控制CO2浓度的大型人工气候室,探讨了正常CO2浓度400 μmol/mol、升高CO2浓度800 μmol/mol和磷素供应水平（0.004、0.012、0.02、0.06、0.1和0.5 mmol/L）对黑麦草气孔特征及其气体交换过程的影响。结果表明,CO2浓度升高使供磷水平0.1和0.5 mmol/L的气孔密度增加约35%（P=0.012）和25%（P<0.001）,但却减小气孔开度13%（P=0.002）和12%（P=0.005）,且导致供磷水平为0.06 mmol/L的黑麦草气孔分布更加规则。同时,CO2浓度升高还导致供磷水平0.1和0.5 mmol/L的净光合速率显著增加8.6%（P=0.002）和15.8%（P<0.001）,从而提高黑麦草的水分利用效率。另外,不同供磷水平明显改变了植株生物量及其分配,且高浓度CO2对较高磷水平时地上生长产生更强的施肥效应。研究结果将为深入理解草地生态系统对大气CO2浓度升高和土壤磷素亏缺的响应机理提供理论依据和数据支撑。     

Quantifying soil water effects on nitrogen mineralization from soil organic matter and from fresh crop residues

A loamy sand was incubated with and without addition of carrot leaves at six different water contents ranging from 6% to 20% (g 100 g^-1 dry soil) and N mineralization was monitored during 98 days. We calculated zero- and first-order rates for mineralization in the unamended soil and first-order rates for N mineralization in the residue-amended soil. Although N mineralization was strongly affected by soil moisture, rates were still important at 6% water content (corresponding to permanent wilting point), particularly in the residue-amended soil. Soil water content was recalculated as soil water tension and as percent water-filled pore space (%WFPS) and a parabolic, a logistic and a Gaussian-type function were fitted to the relation between N mineralization rates and water content, %WFPS or pF. Water potential was a less suitable parameter than either %WFPS or water content to describe the soil water influence on N mineralization, because N mineralization rates were extremely sensitive to changes in the water potential in the range of pF values between 1.5 and 2.5. In the residue-amended soil the Gaussian model yielded an optimum %WFPS of 56% for N mineralization, which is slightly lower than optimum values cited in literature. N mineralization in the unamended soil was more influenced by soil water than N mineralization from fresh crop residues. This could be explained by less water limitation of the microbial population decomposing the residues, due to the water content of the residues. The effect of the water contained in the residues was most pronounced in the lowest water content treatments. The water retention curves of both undisturbed and repacked soil were determined and suggested that extrapolation of results obtained during laboratory incubations, using disturbed soil, to field conditions will be difficult unless soil bulk density effects are accounted for, as is the case with the use of %WFPS.     

大气CO2和O3升高对菜地土壤酶活性和微生物量的影响

利用OTC平台和青菜盆栽实验,探索[CO2]、[O3]或[CO2+O3]升高条件下,土壤理化性质、微生物量和土壤酶活性的变化,以期获得未来大气CO2或/和O3升高对土壤微生态系统的风险性。结果表明,[CO2]升高不同程度地提高了土壤的可溶性有机碳（DOC）、可溶性有机氮（DON）、总磷（TP）、总碳（TC）、铵态氮（AN）、硝态氮（NN）含量和含水量（SWC）,进而不同程度地提高了土壤微生物量碳（MBC）、微生物量氮（MBN）含量以及土壤蛋白酶（PRA）、蔗糖酶（SA）、脲酶（UA）、多酚氧化酶（POA）、酸性磷酸酶（APA）和中性磷酸酶（NPA）活性。相反,[O3]升高不同程度降低了土壤DOC、TP、TK、TC、TN、AN、NN、SWC、MBC和MBN含量,提高了MBC/MBN比值,在不同程度上降低了土壤PRA、SA、UA、POA、APA和NPA酶活性。而[CO2+O3]在一定程度上消减了[O3]对土壤微生物量和酶活性的抑制作用,也降低了[CO2]升高对土壤微生物量和酶活性的刺激效应。因此,土壤微生物量和土壤酶活性的变化可用于评价未来大气CO2或/和O3升高对菜地土壤微生态环境的影响。