应用近红外光谱预测水稻叶片氮含量

以水稻(Oryza sativa)新鲜叶片和干叶粉末两种状态的样品为研究对象, 基于近红外光谱(NIRS)技术, 应用偏最小二乘法(PLS)、主成分回归(PCR)和逐步多元回归(SMLR), 建立并评价了水稻叶片氮含量(NC)近红外光谱模型。结果表明, 基于PLS建立的模型表现最好, 鲜叶氮含量近红外光谱校正模型校正决定系数R_C²为0.940, 校正标准误差RMSEC为0.226; 干叶粉末氮含量的近红外光谱校正模型R_C²为0.977, RMSEC为0.136。模型的内部交叉验证分析表明, 预测鲜叶氮含量内部验证决定系数R_CV²为0.866, 内部验证标准误差RMSECV为0.243; 预测干叶粉末氮含量R_CV²为0.900, RMSECV为0.202。模型的外部验证分析表明, 预测水稻鲜叶氮含量的外部验证决定系数R_V²大于0.800, 外部验证标准误差RMSEP小于0.500, 预测干叶粉末氮含量的R_V²为0.944, RMSEP为0.142。说明, 近红外光谱分析技术与化学分析方法一致性较好, 且基于干叶粉末建立的近红外光谱预测模型的准确性和精确度较新鲜叶片高。     

湿地植物小叶章对外源氮输入的响应

选取三江平原典型沼泽湿地植物小叶章为对象,通过野外控制试验（2004—2007年）,研究了4个不同氮素输入水平［0（对照,CK）、6（N₆）、12（N₁₂）和24（N₂₄） g·m^-2·a^-1］对小叶章叶片形态、叶绿素和生物量累积等的影响.结果表明：不同氮处理间小叶章叶长和叶宽未出现显著差异,比叶面积在N₁₂处理时最小［（149.54±18.27） cm²·g^-1］,即此氮处理水平下叶片的厚度最大.叶片的叶绿素含量均呈单峰型变化,峰前,随着氮输入量的增大而增大,且N₁₂和N₂₄处理下峰值出现的时间早于N₆和CK处理;峰后,N₂₄处理下叶绿素含量迅速降低,N₆处理则降低缓慢,说明适量的氮输入延缓了叶片衰老.连续的高氮（N₂₄）输入使小叶章的生长发育有所提前,在成熟后叶片出现早衰现象.2005和2007年生长季末,小叶章地上部分生物量均随着外源氮输入量的增加而增大,但是经过4年 (2007年) 连续高氮（N₂₄）处理的小叶章地上部分生物量较输入2年 (2005年) 时降低了53.72％.     

Photosynthetic Oxygen Production Facilitates Translocation of 11C-Labelled Photoassimilates from Tendrils and Leaflets of Pisum sativum L

The translocation profiles of ¹¹C-photoassimilates from eithertendrils or leaflets of the compound leaf of Pisum sativum weresimilar in shape, speed and susceptibility to blockage by chillingand heat girdling. When the feed leaf component was exposedto an anaerobic gas stream consisting of N₂ gas supplementedwith 40 Pa CO₂, the export of previously-fixed ¹¹C-photoassimilatesfrom both leaflets and tendrils continued in the light, butstopped in the dark. However, in the light, translocation of¹¹C-assimilates from the leaflet was rapidly blocked by a flowof pure N₂ (i.e. anoxia). Movement of ¹¹C-assimilates from theleaf of another C₃ plant, sunflower, was similar to that fromthe pea leaflet. In contrast to both laminar leaf components,export from the tendrils was stopped under pure N₂ only in thedark. Taken together the data suggest that photosynthetic O₂production facilitated the movement of ¹¹C-assimilates in theabsence of exogenous O₂. The differences observed between thetendrils and the leaflets exposed to pure N₂ could be attributedto the greater capacity of tendrils to produce and recycle CO₂to support photosynthetic O₂ production in the light. Key words: Pea, ¹¹C-translocation, anoxia, tendril, leaflet     

Relationship between Leaf Structure and Gas Exchange in Wheat Leaves at Different Insertion Levels

Net photosynthesis rate (P_n), stomatal conductance to CO₂ andresidual conductance to CO₂ were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO₂ and O₂ levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (V_mes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm² of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. P_n per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm^–2 h^–1 and32·32±1·61 mg dm^–2 h^–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in P_n per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in V_mes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin P_n per unit leaf area was studied. Key words: Photosynthesis, structure, wheat     

Some Effects of Yellow Rust (Puccinia striiformis) on 14Carbon Assimilation and Translocation in Wheat

A well-developed infection of Yellow Rust on a leaf of springwheat (Jufy I) caused the assimilation of ¹⁴CO₂ by that leafto decrease to 43.5 per cent of that of an uninfected leaf.Over a period of three hours translocation of ¹⁴C from an infectedleaf was only 0.87 per cent of that from a control leaf. Whencontrol plants were kept in the light for periods up to 16 hoursafter assimilating ¹⁴CO₂ translocation continued at a steadyrate, whereas there was only negligible translocation from infectedleaves after the first few hours. The retention of labelledassimilates in the infected leaf could be partly, but not completely,accounted for by a conversion of assimilates to an alcohol-insolubleform. Rust infection had no effect on the distribution patternof ¹⁴C to other leaves from one which had assimilated ¹⁴CO₂.In contrast to the marked retention of assimilate by an infectedleaf, such a leaf was unable to distort the normal distributionby attracting assimilates from the other leaves.     

Translocation Profiles of [11C] and [13N]-Labelled Metabolites after Assimilation of 11CO2 and [13N]-Labelled Ammonia Gas by Leaves of Helianthus annuus L. and Lupinus albus L.

Tracer amounts of atmospheric [¹³N]-Iabelled ammonia gas, wereabsorbed by leaves of Lupinus albus and Helianthus annuus inboth the light and the dark. Exogenous [¹³N]-ammonia was onlyabsorbed in the dark when the feeding occurred shortly aftera period of illumination and the tissue was not depleted ofits carbohydrate reserves (e.g. starch). Incorporation of the[¹³N]-ammonia appeared to occur via the leaf glutamine synthetase/glutamatesynthase (GS/GOGAT) cycle since 2.0 mol m^–3 MSX, an inhibitorof the GS reduced uptake in both the light and dark. Photosyntheticincorporation of ¹¹CO₂ was not affected by this treatment Therate of movement of [¹³N]-assimilates in the petiole of attachedleaves of Helianthus and Lupinus was similar to that of the¹¹Cl-photo assimilates. Export of both [¹³N] and [¹¹C]-Iabelledassimilates from the leaf and movement in the petiole in boththe light and the dark was inhibited by source leaf anoxia (i.e.nitrogen gas). Translocation was re-established at the samerate when the feed leaf was exposed to gas containing more than2% O₂ which permitted dark respiration to proceed. After aninitial feeding of either ¹¹CO₂ or [¹³N]-ammonia at ambient(21%) O₂ exposure of the source leaf to 2% O2, or 50% O² didnot alter the rates of translocation, indicating that changesin photosynthetic activity in the source leaf due to photorespiratoryactivity need not markedly alter, at least during the shortperiod, the loading and translocation of either [¹¹C ] or [¹³N]-labelledleaf products. Key words: Translocation, CO₂, NH₃, Leaves, Helianthus annuus, Lupinus albus     

THE DISTRIBUTION PATTERN OF CARBON-14 ASSIMILATED BY A SINGLE LEAF IN TOBACCO PLANT

When ¹⁴CO₂ was administered to a fully expanded leaf (12th leaf)of tobacco plant at the stage just before flower budding, about30% of ¹⁴C assimilated was translocated to other organs after3 hours. After 21 hours, 20{small tilde}30% of the radioactivitywas translocated to the roots, about 20% to upper stem, 10%to lower stem, and 10% to the 17th leaf located directly abovethe 12th leaf. The amount of ¹⁴C translocated to other leaveswas small after 31 hours. When ¹⁴CO₂ was applied to the 17th leaf, radioactivity in otherorgans was negligible. Judging from the time course of ¹⁴C-incorporation into organicsubstances, it was inferred that sucrose imported into the rootsfrom the 12th leaf was converted into compounds of cationicfraction and sugar esters. ¹⁴C imported into the 17th leaf was mostly incorporated into80% ethanol-soluble fraction, especially into sucrose. On theother hand, ¹⁴C fixed photosynthetically by the 17th leaf wasmostly recovered in starch and protein fraction after 8 hoursof ¹⁴CO₂ assimilation. ¹A part of this paper was presented at the Japanese Societyof Plant Physiologists, in April, 1965. ²Present address: Central Research Institute, Japan MonopolyCorporation, Shinagawa-ku, Tokyo.     

Comparative Studies of Leaf Tissue 4: III. EFFECTS OF WALL-DEGRADING ENZYMES AND OSMOTIC STRESS

Commercially available cell wall-degrading enzymes frequentlyused for protoplast isolation inhibited CO₂ fixation and photosyntheticO₂ evolution, and stimulated dark respiration by leaf tissueand isolated mesophyll protoplasts of Nicotiana tabacum L. andAntirrhinum majus L. They also depolarized the membrane potentialof cells of leaf tissue, inhibited uptake of ⁸⁶Rb by tobaccoleaf tissue and isolated mesophyll protoplasts, and stimulated³⁶CI uptake by tobacco leaf tissue. Where studied, these effectswere found to be reversible. The depolarization effect on Antirrhinumleaf cells occurred even when the enzyme preparations had beendenatured, dialysed, or desalted, and the effect was greatestin those fractions of the enzyme preparation which showed thehighest cellulase activity. Plasmolysis of tobacco leaf tissue inhibited photosyntheticO₂ evolution, CO₂ fixation, and ⁸⁶Rb uptake to levels belowthose exhibited by isolated protoplasts in media of the samecomposition and osmolarity. The implications of these resultsfor work with leaf tissue and isolated protoplasts are discussed.     

Effects of nitrogen on Pinus palustris foliar respiratory responses to elevated atmospheric CO2 concentration

Indirect effects of atmospheric CO₂ concentration [CO₂], onlongleaf pine (Pinus palustris Mill.) foliage respiration werestudied by growing trees in a factorial arrangement of low andhigh [CO₂] (369 and 729µmol CO₂ mol^–1) and low andhigh N (40 and 400 kg ha^–1 yr^–1). Direct effectsof [CO₂] on leaf respiration were tested by measuring respirationrates of foliage from all treatments at two CO₂ levels (360and 720µmol CO₂mol^–1) at the time of measurement.Elevated CO₂ did not directly or indirectly affect leaf respirationwhen expressed on a leaf area or mass basis, but a significantincrease in respiration per unit leaf N was observed in treesgrown in elevated [CO₂] (indirect response to elevated [CO₂]).The lack of a [CO₂] effect on respiration, when analysed onan area or mass basis, may have resulted from combined effectsof [CO₂] on factors that increase respiration (e.g. greateravailability of non-structural carbohydrates stimulating growthand carbon export from leaves) and on factors that decreaserespiration (e.g. lower N concentration leading to lower constructioncosts and maintenance requirements). Thus, [CO₂] affected factorsthat influence respiration, but in opposing ways. Key words: Pinus palustris, elevated CO₂, nitrogen, foliar, respiration     

准噶尔荒漠早春短命植物的光合特性及生物量分配特点

准噶尔荒漠分布的早春短命植物不仅具有十分独特的生物学特点,而且在荒漠植物群落演替、物种多样性维持及土壤改良与防治水土流失等方面具有重要的生态学价值。该文运用Li-6400开放式气体交换光合作用测定系统,对分布于准噶尔荒漠的16种早春短命植物生长盛期的净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)等特征进行了测定,并对其中7种植物与生长相关的生物量分配特征进行了分析。结果表明:1)16种植物的最大P_n、 最大T_r及WUE分别为8.07~35.96 μmol CO₂·m^-2·s^-1、3.16~29.64 mmol H₂O·m^-2·s^-1、0.54~4.26 μmol CO₂·mmol^-1H₂O;种间最大P_n与最大气孔导度(Stomatal conductance, G_s)之间存在正相关关系,其相关系数为0.77(p<0.05),线性回归斜率为26.36 μmol·mmol^-1;从光合速率对胞间CO₂浓度及光量子通量密度的响应曲线来看,这类植物的表观CO₂补偿点均在4~5 Pa之间(28~30 ℃),表观羧化效率为0.64~1.86 μmol CO₂·m^-2·s^-1·Pa^-1,表观量子效率为0.05~0.06。2)从生物量分配来看,所测植物的个体生物量为0.05~0.39 g;单株总叶面积为 3.24~51.40 cm²;单位叶面积干重为0.40~0.77 g·m^-2,根在总生物量中所占比例为5.72%~19.43%,单株叶面积比在2.92~9.00 m²·kg^-1之间。种间根所占生物量的比与对应的WUE之间的比较分析结果表明,二者之间存在显著的正相关关系,其相关系数r为0.93(p<0.01)。这些结果表明,所观测的早春短命植物具有典型的C₃植物特征,相比其它类型的荒漠植物具有较高的单位叶面积P_n、高T_r及低WUE,并且在生长发育过程中表现出很低的根/地上生物量比、较高的叶面积比和单位叶面积干重,说明它们具有相对高的生长速率,这与其生长发育节律相一致,反映了它们与准噶尔荒漠环境相适应的特点。     

Stomatal Responses of Variegated Leaves to CO2 Enrichment

The responses of stomatal density and stomatal index of fivespecies of ornamental plants with variegated leaves grown attwo mole fractions of atmospheric CO₂ (350 and 700 µmolmol^-1) were measured. The use of variegated leaves allowed anypotential effects of mesophyll photosynthetic capacity to beuncoupled from the responses of stomatal density to changesin atmospheric CO₂ concentration. There was a decrease in stomataldensity and stomatal index with CO₂ enrichment on both white(unpigmented) and green (pigmented) leaf areas. A similar responseof stomatal density and index was also observed on areas ofleaves with pigmentation other than green indicating that anydifferences in metabolic processes associated with colouredleaves are not influencing the responses of stomatal densityto CO₂ concentrations. Therefore the carboxylation capacityof mesophyll tissue has no direct influence on stomatal densityand index responses as suggested previously (Friend and Woodward1990 Advances in Ecological Research 20: 59-124), instead theresponses were related to leaf structure. The stomatal characteristics(density and index) of homobaric variegated leaves showed agreater sensitivity to CO₂ on green portions, whereas heterobaricleaves showed a greater sensitivity on white areas. These resultsprovide evidence that leaf structure may play an important rolein determining the magnitude of stomatal density and index responsesto CO₂ concentrations.Copyright 1995, 1999 Academic Press Leaf structure, photosynthesis, stomatal conductance, CO₂, stomatal density, stomatal index     

Compartmental analysis of 35SO2-4exchange kinetics in roots and leaves of a tropical legume Macroptilium atropurpureum cv. Siratro

Compartmental analysis of ³⁵SO^2-₄ tracer exchange kinetics hasbeen used to estimate unidirectional fluxes and compartmentcontents in excised root and leaf tissue of the tropical legume,Macroptilium atropurpureum. In excised root tissue only 5% ofthe sulphate taken up across the plasmalemma was reduced toorganic forms whereas in excised leaf tissue approximately 20%was reduced. It was necessary, therefore, to incorporate themetabolism of sulphate during the course of the experiment intothe compartmental models. In root tissue, wash-out data was fitted by three exponentials,assumed to correspond to exchange in the extracellular spaces,cytoplasm and vacuole, but in leaf tissue two large, slowlyexchanging compartments have been postulated in order to achievea fit to the data. It is likely that differences in leaf cellpopulations cause the ‘anomalous’ tracer exchangekinetics and the justification of this assumption is discussed. The fluxes of sulphate at the plasmalemma were greater thanthe corresponding fluxes at the tonoplast in both roots andleaves. The flux of SO^2-₄ from the cytoplasm to the externalsolution did not appear to limit the loss of SO^2-₄ from thevacuole. At an external SO^2-₄concentration of 0.25 mol m^-3 therate constants for exchange in the vacuole were two orders ofmagnitude greater in roots than in the slowest exchanging leafcell population. It is possible, therefore, that the slow lossof SO^2-₄ from leaf cell vacuoles may limit the redistributionof sulphate during S-stress. Key words: Compartmental analysis, sulphate, deficiency, Macroptilium atropurpureum     

An Analysis of Some Effects of Humidity on Photosynthesis by a Tomato Canopy under Winter Light Conditions and a Range of Carbon Dioxide Concentrations

The rates of net photosynthesis by closed canopies of tomatoplants were measured at three CO₂ concentrations and three humiditiesover a range of natural light flux densities. The data havebeen analysed using a model of canopy photosynthesis which allowsfor variation in leaf area index and other leaf and canopy characteristics.The model also deals explicitly with the effects of CO₂ concentration,leaf conductance, and photorespiration on the leaf photochemicalefficiency, . The leaves were found to have a photochemicalefficiency in the absence of photorespiration, _m, of 12?6 ?10^–9 kg (CO₂) J^–1. At a CO₂ concentration of 0?73 ? 10^–3 kg m^–3 (400vpm) the leaf photochemical efficiency, , and canopy light utilizationefficiency, _c, were 18 per cent greater at a vapour pressuredeficit of 0?5 kPa than at 1?0 kPa. At a CO₂ concentration of2?2 ? 10^–3 kg m^–3 (1200 vpm) they were only 5 percent greater.     

Effect of leaf age on light and dark 14CO2 fixation in a CAM plant, Bryophyllum calycinum

Leaves of different ages from B. calycinum were exposed to ¹⁴CO₂in light during day and night. The labelling pattern on thechromatogram differed with leaf age. Young leaves had similarpatterns to those of C3 plants during both day and night. Matureleaves showed high incorporation of ¹⁴C into C4 acids, especiallyat night. In contrast, no significant difference with leaf agewas observed in the pattern of dark ¹⁴CO₂ fixation products.Study of the enzyme activity and the content of titratable acidat each leaf age suggested that high incorporation of ¹⁴C inC4 acids during the night was due to the simultaneous absorptionof CO₂ by both enzymes RuDPcarboxylase and PEPcarboxylase. (Received November 24, 1977; )     

Carbon Dioxide Effects on Carbohydrate Status and Partitioning in Rice

The atmospheric carbon dioxide (CO₂) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO₂ concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO₂ concentrations of 160, 250, 330, 500, 660, and 900µmolCO₂ mol¹ air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO₂ concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO₂ concentration but tended to level off above 500µmolmol^–1 CO₂. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol^–1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO₂ concentration. At maturity, increasing CO₂ concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO₂concentrations below 330µmol mol^–1 than for treatmentsat concentrations above ambient Increasing CO₂ concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO₂ enrichment, starch, sucrose     

Changes in the Rate of Photosynthesis during Grain Filling and the Enzymatic Activities Associated with the Photosynthetic Carbon Metabolism in Rice Panicles

Photosynthesis is known to occur in rice panicles, but littlehas been reported about the photosynthetic or biochemical characteristicsof such panicles. The estimated gross amount of photo-syntheticallyassimilated CO₂ in a panicle is 30% of that in a flag leaf.This result and the good light-intercepting characteristicsof the panicle in the canopy suggest that photosynthesis inthe panicle may contribute significantly to grain filling. Therice panicle is composed of spikelets and of rachis-branchesincluding rachis which have estimated gross rates of photosynthesisduring the 30-day period after anthesis of 130 to 180 and 50to 100 µmol CO₂.(mg Chl)^–1.h^–1, respectively.The corresponding rate for the flag leaf is 180 to 230 µmolCO₂.(mg Chl)^–.h^–. On the basis of Chl, spikeletshave a high photosynthetic capability which is similar to thatof the flag leaf. The activities of ribulose-l,5-bisphosphate carboxylase (RuBPCase),phosphoenolpyruvate carboxylase (PEPCase), and pyruvate.P_i dikinase(PPDK) in spikelets were 129, 220, and 87 µmol.(mg Chl)^–.h^–,respectively. The activities of PEPCase and PPDK in spikeletswere considerably higher than those in the flag leaf or rachis-branches.Oxygen-insensitive photosynthesis was found only in spikelets.The K_m of NaHCO₃ for photosynthesis by slices of spikelets inan aqueous solution (0.6 mM) was considerably lower than thatfor slices of flag leaf (4.2 mM). All these results indicatethat spikelets have different photosynthetic characteristicsfrom those of the flag leaf and rachis-branches. The possibilityof C₃–C₄ intermediate photosynthesis or C₄-like photosynthesisin spikelets is discussed. ⁴Present address: Department of Biochemistry, Faculty of Science,Saitama University, Urawa, 338 Japan (Received February 14, 1990; Accepted June 12, 1990)     

Effects of CO2 and Photosynthetic Photon Flux on Yield, Gas Exchange and Growth Rate of Lactuca Sativa L. 'Waldmann's Green'

Knight, S. L. and Mitchell, C. A. 1988. Effects of CO₂ and photosyntheticphoton flux on yield, gas exchange and growth rate of Lactucasativa L. ‘Waldmann’s Green'.—J. exp. Bot.39: 317–328. Enrichment of CO₂ to 46 mmol m^–3 (1 000 mm³ dm^–3)at a moderate photosynthetic photon flux (PPF) of 450 µmolm^–2 s^–1 stimulated fresh and dry weight gain oflettuce leaves 39% to 75% relative to plants at 16 mmol m^–3CO₂ (350 mm³ dm^–3). Relative growth rate (RGR) was stimulatedonly during the first several days of exponential growth. ElevatingCO₂ above 46 mmol m^–3 at moderate PPF had no further benefit.However, high PPF of 880–900 µmol m^–2 s^–1gave further, substantial increases in growth, RGR, net assimilationrate (NAR) and photosynthetic rate (Pn), but a decrease in leafarea ratio (LAR), at 46 or 69 mmol m^–3 (1000 or 1500 mm³dm^–3) CO², the differences being greater at the higherCO₂ level. Enrichment of CO₂ to a supraoptimal level of 92 mmolm^–3 (2000 mm³ dm^–3) at high PPF increased leaf areaand LAR, decreased specific leaf weight, NAR and Pn and hadno effect on leaf, stem and root dry weight or RGR relativeto plants grown at 69 mmol m^–3 CO₂ after 8 d of treatment.The results of the study indicate that leaf lettuce growth ismost responsive to a combination of high PPF and CO₂ enrichmentto 69 mmol m^–3 for several days at the onset of exponentialgrowth, after which optimizing resources might be conserved. Key words: Photosynthesis, relative growth rate, CO₂ enrichment     

C3 and CAM Photosynthetic Characteristics of the Submerged Aquatic Macrophyte Littorella uniflora: Regulation of Leaf Internal CO2 Supply in Response to Variation in Rooting Substrate Inorganic Carbon Concentration

The relationships between CO₂ concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO₂ supply around the roots. Free CO₂ in sediment-interstitial-waterranged from 1–01 mol m^–3 (Esthwaite), 0.79 mol m^–3(peat), 0.32 mol m^–3 (silt) and 0–17 mol m^–3(sand), with plants maintained under PAR of 40 µmol m^–2s^–1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO₂ had larger leaf fresh weight (0–69 g) andtotal surface area (223 cm² g^–1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm²g^–1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO₂ concentration[CO₂], was highest in the sand-grown plants (2–69 molm^–3, corresponding to 6.5% CO₂ in air) and lowest inthe Esthwaite plants (1–08 mol m^–3). Expressionof CAM in transplants was also greatest in the low CO₂ regime,with H⁺ (measured as dawn-dusk titratable acidity) of 50µmolg^– fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO₂]₁ and would makea major contribution to daytime CO₂ fixation in vivo. A range of leaf sections (0–2, 1–0, 5–0 and17–0 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO₂ evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO₂ and 1–0mol m^–3 exogenous CO₂ was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O₂ g^–1 fr. wt. h^–1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO₂ g^–1 fr. wt. h^–1) with a K_0.5 of 80 mmol m^–3.In terms of light response, saturation of photosynthesis intissue slices occurred at 850–1000 µmol m^–2s^–1 although light compensation points (6–11 µmolm^–2s^–1) and chlorophyll a: b ratios (1.3) were low.While CO₂ and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO₂ supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO₂ concentrating mechanisms interact inintact plants to maintain saturating CO₂ levels within leaflacunae, although the responses of the various components ofCO₂ supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO₂ concentration, crassulacean acid metabolism, root inorganic carbon supply, CO₂ concentrating mechanism     

Green Light Drives CO2 Fixation Deep within Leaves

Maximal ^l4CO₂-fixation in spinach occurs in the middle of thepalisade mesophyll [Nishio et al. (1993) Plant Cell 5: 953],however, ninety percent of the blue and red light is attenuatedin the upper twenty percent of a spinach leaf [Cui et al. (1991)Plant Cell Environ. 14: 493]. In this report, we showed thatgreen light drives ¹⁴CO₂-fixation deep within spinach leavescompared to red and blue light. Blue light caused fixation mainlyin the palisade mesophyll of the leaf, whereas red light drovefixation slightly deeper into the leaf than did blue light.¹⁴CO₂-fixation measured under green light resulted in less fixationin the upper epidermal layer (guard cells) and upper most palisademesophyll compared to red and blue light, but led to more fixationdeeper in the leaf than that caused by either red or blue light.Saturating white, red, or green light resulted in similar maximal¹⁴CO₂-fixation rates, whereas under the highest irradiance ofblue light given, carbon fixation was not saturated, but itasymptotically approached the maximal ¹⁴CO₂-fixation rates attainedunder the other types of light. The importance of green lightin photosynthesis is discussed. ¹Supported in part by grants from Competitive Research GrantsOffice, U.S. Department of Agriculture (Nos. 91-37100-6672 and93-37100-8855).     

Effects of Nitrogen Fertilizer on the Distribution of Photosynthate during Grain Growth of Spring Wheat

The distribution of photosynthate labelled with ¹⁴C was studiedin spring wheat grown with different amounts of nitrogen fertilizerin the three years 1972–4, after exposing the flag leafor the leaf below the flag leaf to ¹⁴CO₂ at 6–10 or 19–26days after anthesis. The movement of ¹⁴C to ears was unaffectedby nitrogen fertilizer except after early exposure in 1973,when nitrogen increased the retention of ¹⁴C in stems at maturity The concentration of sugar in the top part of the shoot at theend of the day was unaffected by nitrogen in 1973, but at 22days after anthesis in 1974 the concentration of sucrose inthe glumes and rachis, and in the flag leaf lamina was increasedby nitrogen. Loss of sugar by translocation and respirationduring the night may explain why this increase in concentrationwas not reflected in the ¹⁴C distribution 24 h after supplying¹⁴C. The proportion of the total ¹⁴C content of the shoot that wasin the ear at maturity ranged from 68 to 95 per cent dependingon when and to which leaf the ¹⁴CO₂ was supplied. Less than5 per cent remained in the leaf exposed to ¹⁴CO₂. The proportionof the final ear weight contributed by the leaf below the flagleaf was about half that contributed by the flag leaf. In 1974 about 24 per cent of the ¹⁴C absorbed by the flag leaf,and 56 per cent of that absorbed by the second leaf, was lostby maturity, presumably by respiration. Most loss occurred inthe first 24 h.