Photosynthesis in intact leaves of C3 plants: Physics,physiology and rate limitations

The instantaneous rate of photosynthetic CO₂ assimilation in C₃ plants has generally been studied in model systems such as isolated chloroplasts and algae. From these studies and from theoretical analyses of gas exchange behavior it is now possible to study the biochemistry of photosynthesis in intact leaves using a combination of methods, most of which are nondestructive. The limitations to the rate of photosynthesis can be divided among three general classes: (1) the supply or utilization of CO₂, (2) the supply or utilization of light, and (3) the supply or utilization of phosphate. The first limitation is most readily studied by determining how the CO₂ assimilation rate varies with the partial pressure of CO₂ inside the leaf. The second limitation can be studied by determining the quantum requirement of photosynthesis. The third limitation is most easily detected as a loss of O₂ sensitivity of photosynthesis. Measurement of fluorescence from intact leaves can give additional information about the various limitations. These methods are all non-destructive and so can be observed repeatedly as the environment of a leaf is changed. In addition, leaves can be quick-frozen and metabolite concentrations then measured to give more information about the limitations to intact leaf photosynthesis rates. In this review the physics and biochemistry of photosynthesis in intact C₃ leaves, and the interface between physiology and photosynthesis—triose phosphate utilization—are discussed.     

Light Fluctuations and Photosynthesis

The effects of fluctuating light on photosynthesis are examined.A simple model of leaf photosynthesis is used so that the analysiscan be presented in explicit terms, the time-dependent problemis solved, and the response of photosynthesis to step changesin light-flux density is calculated. The presence of light fluctuationscan cause a discrepancy between measurements and estimates ofphotosynthesis; the relevant factors are the response time ofthe device used for measuring light-flux density, the responsetime of the photosynthetic system in the leaf, and the steady-statelight response curve with the degree of non-linearity and thevalue of the light-flux density for maximum photosynthesis beingespecially important. Some general methods for estimating practicallythe effects of light fluctuations on photosynthesis are described.The use of the methods of time-series analysis in such problemsis discussed.     

New applications of photoacoustics to the study of photosynthesis

Photoacoustic methods offer unique capabilities for photosynthesis research. Phenomena that are readily observed by photoacoustics include the storage of energy by electron transport, oxygen evolution by leaf tissue at microsecond time resolution, and the conformational changes of photosystems caused by charge separation. Despite these capabilities, photoacoustic methods have not been widely exploited in photosynthesis research. One factor that has contributed to their slow adoption is uncertainty in the interpretation of photoacoustic signals. Careful experimentation is resolving this uncertainty, however, and technical refinements of photoacoustic methods continue to be made. This review provides an overview of the application of photoacoustics to the study of photosynthesis with an emphasis on the resolution of uncertainties in the interpretation of photoacoustic signals. Recent developments in photoacoustic technology are also presented, including a microphotoacoustic spectrometer, gas permeable photoacoustic cells, the use of photoacoustics to monitor phytoplankton populations, and the use of photoacoustics to study protein dynamics. This revised version was published online in June 2006 with corrections to the Cover Date.     

Future CO2 concentrations, though not warmer temperatures, enhance wheat photosynthesis temperature responses

The temperature dependence of C3 photosynthesis is known to vary according to the growth environment. Atmospheric CO2 concentration and temperature are predicted to increase with climate change. To test whether long-term growth in elevated CO2 and temperature modifies photosynthesis temperature response, wheat (Triticum aestivum L.) was grown in ambient CO2 (370 micromol mol(-1)) and elevated CO2 (700 micromol mol(-1)) combined with ambient temperatures and 4 degrees C warmer ones, using temperature gradient chambers in the field. Flag leaf photosynthesis was measured at temperatures ranging from 20 to 35 degrees C and varying CO2 concentrations between ear emergence and anthesis. The maximum rate of carboxylation was determined in vitro in the first year of the experiment and from the photosynthesis-intercellular CO2 response in the second year. With measurement CO2 concentrations of 330 micromol mol(-1) or lower, growth temperature had no effect on flag leaf photosynthesis in plants grown in ambient CO2, while it increased photosynthesis in elevated growth CO2. However, warmer growth temperatures did not modify the response of photosynthesis to measurement temperatures from 20 to 35 degrees C. A central finding of this study was that the increase with temperature in photosynthesis and the photosynthesis temperature optimum were significantly higher in plants grown in elevated rather than ambient CO2. In association with this, growth in elevated CO2 increased the temperature response (activation energy) of the maximum rate of carboxylation. The results provide field evidence that growth under CO2 enrichment enhances the response of Rubisco activity to temperature in wheat.     

Field Studies of Photosynthesis as Affected by Water Stress, Temperature, and Light in Birch

This study continues the investigations previously conducted as laboratory experiments. The results from the present study confirm our earlier observations made on alder seedlings concerning the effect of water stress, temperature and light on the net uptake of CO₂. A variable that we could call the physiological water stress is proposed as a measure of the intrinsic factor of photosynthesis during and after drought. A physiological water stress builds up and discharges slowly and interacts strongly with temperature. Our model for the effects of physiological water stress, temperature, and light intensity explains satisfactorily the net uptake of CO₂ in birch in the field. Thus, our earlier results concerning the effects of physiological water stress on photosynthesis are not artifacts generated by the unnatural laboratory environment.     

华北平原玉米田生态系统光合作用特征及影响因素

采用涡度相关法对华北平原夏玉米田进行了连续4a(2003-2006年)的碳通量观测,结果表明:夏玉米田生态系统初始量子效率(α)、最大光合速率(P_max)、暗呼吸速率(R_d)和总初级生产力(GPP)随作物生长发育而变化。在夏玉米生育前期和后期,α、P_max、R_d和GPP都比较小,其最大值出现在抽穗期/灌浆期。2003-2006年,夏玉米生长季平均α、P_max、R_d的范围分别为0.054-0.124 μmol/μmol、1.72-2.93 mg CO₂ · m^-2 · s^-1、0.23-0.38 mg CO₂ · m^-2 · s^-1。α、P_max和R_d均随叶面积指数(LAI)增加呈指数增长。2003-2006年夏玉米生长季GPP总量分别为806.2、741.5、703.0、817.4 g C/m²,年际差异较大。玉米田生态系统GPP随温度升高呈指数增长。在玉米营养生长阶段,GPP随LAI增加而增大,两者之间的关系可用直角双曲线方程来表示;生殖生长阶段,GPP随LAI降低而下降.相同LAI下,生殖生长阶段的GPP明显低于营养生长阶段。     

Can we measure terrestrial photosynthesis from space directly,using spectral reflectance and fluorescence?

Attempts to estimate photosynthetic rate or gross primary productivity from remotely sensed absorbed solar radiation depend on knowledge of the light use efficiency (LUE). Early models assumed LUE to be constant, but now most researchers try to adjust it for variations in temperature and moisture stress. However, more exact methods are now required. Hyperspectral remote sensing offers the possibility of sensing the changes in the xanthophyll cycle, which is closely coupled to photosynthesis. Several studies have shown that an index (the photochemical reflectance index) based on the reflectance at 531 nm is strongly correlated with the LUE over hours, days and months. A second hyperspectral approach relies on the remote detection of fluorescence, which is a directly related to the efficiency of photosynthesis. We discuss the state of the art of the two approaches. Both have been demonstrated to be effective, but we specify seven conditions required before the methods can become operational.     

Diurnal stratification, photosynthesis and nitrogenfixation in a shallow, equatorial Lake (Lake George, Uganda)

From a series of experiments and measurements covering one 24-h period in Lake George the diurnal patterns of photosynthesis, nitrogen-fixation and stratification are described. The thermal cycle shows three distinct phases of isothermy, intense stratification and mixing. During stratification the surface water temperature reached 36°C, whereas the bottom temperature remained at 25°C. The phytoplankton are evenly distributed at dawn, sink out during the day and tend towards an even redistribution as thermal stratification breaks down. Depth-time profiles of oxygen concentration and pH values showed that intense photosynthetic and respiratory activity occurred. The shortness of the predominant limnological cycle is thought to be instrumental in restricting species fluctuations. Changes of total CO2 concentration in situ within the euphotic zone indicated that 2.25 g C/m².12 h were photosynthetically fixed during daytime. From changes of in situ oxygen concentration, gross photosynthesis was estimated to be 12 g O₂/m².12 h and net particulate production over 24 h as zero. Photosynthetic activity was also measured with the i^C and oxygen techniques by enclosing algal samples in light and dark bottles. The patterns of activity recorded by the two methods were similar, although quantitatively the oxygen method gave rather higher values than did the method. Daily gross photosynthesis was estimated as 15.56 g O₂/m².12 h and 4.5 gC/m².12 h. These figures are compatible with one another and with the production estimates calculated from Tailing's model of integral daily photosynthesis. The balance between respiration and photosynthesis is described as a function of the underwater light climate and the relative rate of respiration. Both the experimental and theoretical approaches suggest that the column 24-h net particulate production is an extremely small percentage of gross photosynthesis. Nitrogen-fixation was measured using both the ¹⁵N₂ and the acetylene reduction techniques. The day-long incubation of the ¹⁵N₂ experiment showed that 11 mg N/m².day were fixed. The series of shorter acetylene reduction experiments gave a value of 58 mg N/m².day. The acetylene technique showed relatively high nitro-genase activity at very low light intensities. The ¹⁵N₂ results indicated little N2-fixation at low light intensities. The differences between the two techniques are discussed. Gross photosynthesis estimates calculated from seven different methods run simultaneously are compared. The figures show reasonable agreement, but since the gaseous environment in the euphotic zone is particularly suitable for photo respiration the values are not considered reliable estimates of phytoplankton photosynthesis.     

A Manometric Technique for Determination of Apparent Photosynthesis of Lolium

A manometric technique for measuring photosynthesis of detachedleaves of Lolium is described. Results are compared with infra-redgas analysis data and ¹⁴CO₂ assimilation by attached leavesfrom similar plant material. All three methods gave similarcomparative estimates of apparent photosynthesis.     

Effects of prolonged restriction in water supply on photosynthesis, shoot development and storage root yield in sweet potato

Besides the paucity of information on the effects of drought stress on photosynthesis and yield in sweet potato [ Ipomoea batatas (L.) Lam.], available reports are also contradictory. The aim of this study was to shed light on the effects of long-term restricted water supply on shoot development, photosynthesis and storage root yield in field-grown sweet potato. Experiments were conducted under a rainout shelter where effects of restricted water supply were assessed in two varieties (Resisto and A15). Large decreases in stomatal conductance occurred in both varieties after 5 weeks of treatment. However, continued measurements revealed a large varietal difference in persistence of this response and effects on CO₂ assimilation. Although restricted water supply decreased leaf relative water content similarly in both varieties, the negative effects on stomatal conductance disappeared with time in A15 (indicating high drought acclimation capacity) but not in Resisto, thus leading to inhibition of CO₂ assimilation in Resisto. Chlorophyll a fluorescence measurements, and the relationship between stomatal conductance, intercellular CO₂ concentration and CO₂ assimilation rate, indicated that drought stress inhibited photosynthesis primarily through stomatal closure. Although yield loss was considerably larger in Resisto, it was also reduced by up to 60% in A15, even though photosynthesis, expressed on a leaf area basis, was not inhibited in this variety. In A15 yield loss appears to be closely associated with decreased aboveground biomass accumulation, whereas in Resisto, combined effects on biomass accumulation and photosynthesis per unit leaf area are indicated, suggesting that research aimed at improving drought tolerance in sweet potato should consider both these factors.     

P515的测量原理、方法和应用

光谱技术已广泛应用于光合研究领域,如光吸收信号P515和P700氧化还原动力学以及叶绿素荧光等,可快速、准确地检测植物的光合活性。P515信号广泛存在于高等植物和藻类中,是类囊体膜上的色素分子吸收光能后,其吸收光谱发生位移造成。利用光诱导的P515快速和慢速动力学,可检测PSI和PSII反应中心的比值、ATP合酶的质子...     

Introduction to optical methods in photosynthesis

Optical spectroscopy is widely used to study structure and function of photosynthetic systems. Due to the large variety of different methods, these studies have contributed a lot to the identification of the cofactors involved in the primary reactions of photosynthesis and to the elucidation of the kinetics of the light-induced energy and electron transfer reactions. Within other aspects of photosynthesis research as e.g. photoinhibition, these techniques play an important role as well. In this brief introduction, I will focus on the basic principles of the different methods and the information obtained by applying these various techniques. In the reviews that follow, under the section “Optical Methods”, these methods are discussed in detail.     

A new principle photosynthesis capacity biosensor based on quantitative measurement of delayed fluorescence in vivo

Delayed fluorescence (DF) is an excellent marker for evaluating plant photosynthesis. Compared with common methods for measuring the photosynthesis rate based on consumption of CO₂, DF technique can quantify the plant photosynthesis capacity more accurately and faster under its physiological status with less interference from the environment. We previously reported a method for measuring photosynthesis using DF of chloroplast [Wang, C.L., Xing, D., Chen, Q., 2004. Biosens. Bioelectron. 20, 454–459]. In the study, a novel fast and portable photosynthesis capacity biosensor system was developed, which was composed of light-emitting diode lattice as excitation light source, Channel Photomultiplier DC-Module to achieve DF, single-chip microcomputer as control center, hermetic dark sample chamber, battery power supply and CO₂, humidity and temperature controller. Compared with our previous work, the system was portable and can directly measure plant photosynthesis capacity in vivo in less than 10 s. A database in the software to carry out data acquisition and processing was developed to translate maximal DF intensity to net photosynthesis rate (Pn). In addition, local-control and remote-control mode can be chosen in the system. To demonstrate the utility of the system, it was applied to evaluate maximum Pn of four different plant species samples (Queen Rape Myrtle (var. rubra), soybean (Lu Hei No. 1), maize (Jin Dan No. 39) and rice (Jing Dao No. 21)) in field. The results were compared with that using commercial photosynthesis system LI-6400 and the uncertainty was less than ±5%. The new principle of photosynthesis measurement is a challenge and breakthrough to conventional method of gas exchange and may be a potential technique of next generation photosynthesis measurement.     

苜蓿国际发展态势分析

苜蓿是草食动物的优质饲草, 被誉为“牧草之王”。发展苜蓿产业对提升我国草食畜牧业具有重要意义。该研究采用定性调研与定量分析相结合的方法, 从创新链角度, 研究了全球苜蓿科技产出、代表性国家苜蓿产业格局和全球苜蓿市场贸易等状况及我国苜蓿产业存在的问题, 旨在为我国苜蓿产业发展提供参考。分析发现, 美国是全球最重要的苜蓿生产国, 在苜蓿基础研究、技术开发、品种培育和商业化种植等方面均具有很强的优势, 引领了全球苜蓿产业的发展。欧美等跨国企业掌控着全球苜蓿产业链的各个关键环节, 是苜蓿产品的主要出口市场, 而亚洲苜蓿产品消费缺口最大。近10年来, 我国在苜蓿科技领域表现活跃, 科技成果产出呈快速增长趋势, 但在成果数量和影响力方面与欧美国家差距明显, 且苜蓿育种进程缓慢, 优质苜蓿产品对外依存度仍然较高。综合来看, 我国应持续加大苜蓿的研发力度和科技投入, 推进苜蓿产业化发展, 提升苜蓿产品的自给率, 保障草食畜牧业健康、稳定发展。     

P700氧化还原动力学的测量方法及原理

P700氧化还原动力学技术可快速且无损地检测植物光系统I (PSI)的活性, 是光合研究领域中广泛使用的一种技术。该文系统归纳了P700氧化还原动力学的主要测量方法, 详细阐述其原理并探讨该技术的局限性, 旨在为深入研究光合作用机理提供技术支持。     

Effect of desiccation on the photosynthesis of seaweeds from the intertidal zone in Honshu, Japan

Intertidal seaweeds are periodically exposed during low tide and thus experience extreme levels of desiccation. The physiological activity of seaweeds changes during this water loss process. This study examined how desiccation affects the photosynthesis and respiration of seaweeds from different intertidal levels, and whether the ability to retain photosynthesis and respiration rates during desiccation varies among these species. Photosynthesis and respiration rates of 12 species of seaweeds were measured under various levels of desiccation, using an infrared CO₂ gas analyzer. High levels of drought negatively affected photosynthesis, while most species showed initial rises in photosynthetic rates. The ability to retain photosynthesis and respiration activities under desiccation conditions varied among species. These physiological responses were not related to the intertidal level at which these species occur, but to their ability to prevent water loss. The species with lower rates of water loss had slower declines in the rate of photosynthesis and respiration.     

Ecophysiological studies on Sonoran Desert plants,VI. Seasonal photosynthesis and production of Machaeranthera gracilis,a winter ephemeral*

Abstract. A comparative study of two chromosomal races of the winter-active ephemeral Machaeranthera gracilis showed that the seasonal magnitudes of photosynthesis were only slightly greater for a progeny desert race than for an ancestral foothills race. Maximum observed photosynthetic capacity and the seasonal reduction in foliar photosynthesis occurred earlier in the year for the desert race. The relative growth rate was higher in this race up until the time of its peak seasonal biomass. A ratio of harvested net production to estimated gross primary production decreased until anthesis. Photosynthesis contributing to net growth continued into periods with moderate environmental stress. The continuation of growth by the desert race was enhanced by maintenance of a higher root-shoot ratio, as well as greater relative stem growth. During reproduction, foliar CO₂ assimilation could not solely provide the measured dry matter accumulation, suggesting the importance of assimilate contribution by photosynthetic stems. Seasonal increases in the enthalpy content of whole plants and plant organs occurred for both races, indicating the absence of significant translocation during reproduction and the potential for stem photosynthesis.     

Isoprene Emission from Velvet Bean Leaves (Interactions among Nitrogen Availability,Growth Photon Flux Density,and Leaf Development)

Although isoprene synthesis is closely coupled to photosynthesis, both via ATP requirements and carbon substrate availability, control of isoprene emission is not always closely linked to photosynthetic processes. In this study we grew velvet bean (Mucuna sp.) under different levels of photon flux density (PFD) and nitrogen availability in an effort to understand better the degree to which these two processes are linked. As has been observed in past studies, we found that during early leaf ontogeny the onset of positive rates of net photosynthesis precedes that of isoprene emission by 3 to 4 d. Other studies have shown that this lag is correlated with the induction of isoprene synthase activity, indicating that overall control of the process is under control of that enzyme. During leaf senescence, photosynthesis rate and isoprene emission rate declined in parallel, suggesting similar controls over the two processes. This coordinated decline was accelerated when plants were grown with high PFD and high nitrogen availability. The latter effect included declines in the photon yield of photosynthesis, suggesting that an unexplained stress arose during growth under these conditions, triggering a premature decline in photosynthesis and isoprene emission rate. In mature leaves, growth PFD and nitrogen nutrition affected photosynthesis and isoprene emission in qualitatively similar, but quantitatively different, ways. This resulted in a significant shift in the percentage of fixed carbon that was re-emitted as isoprene. In the case of increasing growth PFD, isoprene emission rate was more strongly affected than photosynthesis rate, and more carbon was lost as isoprene. In the case of increasing nitrogen, photosynthesis rate increased more than isoprene emission rate, and leaves containing high amounts of nitrogen lost a lower percentage of their assimilated carbon as isoprene. Taken together, our results demonstrate that, although the general correlation between isoprene emission rate and photosynthesis rate is consistently expressed, there is evidence that both processes are capable of independent responses to plant growth environment.     

A new principle photosynthesis capacity biosensor based on quantitative measurement of delayed fluorescence in vivo

Delayed fluorescence (DF) is an excellent marker for evaluating plant photosynthesis. Compared with common methods for measuring the photosynthesis rate based on consumption of CO₂, DF technique can quantify the plant photosynthesis capacity more accurately and faster under its physiological status with less interference from the environment. We previously reported a method for measuring photosynthesis using DF of chloroplast [Wang, C.L., Xing, D., Chen, Q., 2004. Biosens. Bioelectron. 20, 454–459]. In the study, a novel fast and portable photosynthesis capacity biosensor system was developed, which was composed of light-emitting diode lattice as excitation light source, Channel Photomultiplier DC-Module to achieve DF, single-chip microcomputer as control center, hermetic dark sample chamber, battery power supply and CO₂, humidity and temperature controller. Compared with our previous work, the system was portable and can directly measure plant photosynthesis capacity in vivo in less than 10 s. A database in the software to carry out data acquisition and processing was developed to translate maximal DF intensity to net photosynthesis rate (Pn). In addition, local-control and remote-control mode can be chosen in the system. To demonstrate the utility of the system, it was applied to evaluate maximum Pn of four different plant species samples (Queen Rape Myrtle (var. rubra), soybean (Lu Hei No. 1), maize (Jin Dan No. 39) and rice (Jing Dao No. 21)) in field. The results were compared with that using commercial photosynthesis system LI-6400 and the uncertainty was less than ±5%. The new principle of photosynthesis measurement is a challenge and breakthrough to conventional method of gas exchange and may be a potential technique of next generation photosynthesis measurement.     

Specific leaf area relates to the differences in leaf construction cost,photosynthesis, nitrogen allocation,and use efficiencies between invasive and noninvasive alien congeners

Comparisons between invasive and native species may not characterize the traits of invasive species, as native species might be invasive elsewhere if they were introduced. In this study, invasive Oxalis corymbosa and Peperomia pellucida were compared with their respective noninvasive alien congeners. We hypothesized that the invasive species have higher specific leaf (SLA) than their respective noninvasive alien congeners, and analyzed the physiological and ecological consequences of the higher SLA. Higher SLA was indeed the most important trait for the two invaders, which was associated with their lower leaf construction cost, higher nitrogen (N) allocation to photosynthesis and photosynthetic N use efficiency (PNUE). The higher N allocation to photosynthesis of the invaders in turn increased their PNUE, N content in photosynthesis, biochemical capacity for photosynthesis, and therefore light-saturated photosynthetic rate. The above resource capture-, use- and growth-related traits may facilitate the two invaders' invasion, while further comparative studies on a wider range of invasive and noninvasive congeners are needed to understand the generality of this pattern and to fully assess the competitive advantages afforded by these traits.