Correlations among leaf CO2-exchange rates,areas and enzyme activities among soybean cultivars

Soybean (Glycine max (L.) Merr.) genotypes varying in area per nodal unit (usually a trifoliolate) and maturity class were grown in plots at the University of Illinois experimental farm. Leaf CO₂-exchange rates per unit area (CER) were measured under sunlight on intact plants. In addition to previously reported correlations with specific leaf weight and chlorophyll, CER was positively correlated with ribulose bisphosphate carboxylase (RuBPcase) activity, specific activity, and soluble protein, and was negatively correlated with area per leaf unit. The CER: chlorophyll correlation was destroyed by high CER values in 2 chlorophyll-deficient lines. CER values for 27 of the 35 lines tested fell within the range of those for isolines of cultivar Clark varying in leaf characteristics. The CER values were highest for fully expanded leaves during rapid pod fill. These results suggested that photoperiod (maturity) genes and genes for leaf area growth interact with genes controlling photosynthetic CO₂-exchange to produce the major differences in CER values among soybean genotypes.     

Novel<Emphasis Type="Italic"> eceriferum</Emphasis> mutants in<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

We conducted a novel non-visual screen for cuticular wax mutants in Arabidopsis thaliana (L.) Heynh. Using gas chromatography we screened over 1,200 ethyl methane sulfonate (EMS)-mutagenized lines for alterations in the major A. thaliana wild-type stem cuticular chemicals. Five lines showed distinct differences from the wild type and were further analyzed by gas chromatography and scanning electron microscopy. The five mutants were mapped to specific chromosome locations and tested for allelism with other wax mutant loci mapping to the same region. Toward this end, the mapping of the cuticular wax (cer) mutants cer10 to cer20 was conducted to allow more efficient allelism tests with newly identified lines. From these five lines, we have identified three mutants defining novel genes that have been designated CER22, CER23, and CER24. Detailed stem and leaf chemistry has allowed us to place these novel mutants in specific steps of the cuticular wax biosynthetic pathway and to make hypotheses about the function of their gene products.Abbreviations EMS Ethyl methane sulfonate - SEM Scanning electron microscopy - SSLP Simple sequence length polymorphism - WT Wild type     

Photosynthesis and transpiration of the flag leaf in four spring-wheat cultivars

Co₂ exchange and transpiration rates of the flag leaves of four spring wheat (Triticum aestivum L.) cultivars, namely Glenlea, Neepawa, Opal and Kolibri, were compared using infra-red gas-analysis technique. The plants were grown in a controlled environment under an 18-h photoperiod, with day and night temperatures of 20 and 15° C, respectively. The time course of the CO₂-exchange rate (CER) of the flag leaf differed among cultivars. CER began to decrease rapidly some 2 weeks after ear emergence in Glenlea, Neepawa and Kolibri, but only after 4 weeks in Opal. The decline in CER of Glenlea, Neepawa and Opal was continuous throughout the period of grain development whereas in Kolibri CER was maintained at a constant level between the 4th and 6th weeks after ear emergence. The transpiration rates of the flag leaves of the 4 cultivars did not change markedly until 6–7 weeks after ear emergence, indicating that the reduction in CER was not primarily a response to increased stomatal resistance to the diffusion of CO₂. Removing the ear of the main shoot of intact plants failed to depress CER of the subtending flag leaf until 5 weeks after ear removal. Removing the ears of all the tillers of plants in which all but 3 tillers had been removed at ear emergence did not depress CER until 4 weeks after ear emergence, but removal of the ear of the main shoot of plants where all the tillers had been removed at ear emergence reduced the CER of the flag leaf 2 weeks after ear removal. Removal of tillers at ear emergence had a marked effect on the time course of CER and transpiration rates of the flag leaf. Both CER and transpiration rates of a 4-tiller plant were maintained at a higher level throughout ear development as compared to those of a one-tiller plant. The transpiration rate of the flag leaf of Glenlea increased during the later part of the life of the leaf even for one-tiller plants with no ear, indicating that such a stomatal response may be part of the normal course of leaf aging and not a response to a feedback stimulus from the ear.     

Study of CO2 exchange processes,resistances to carbon dioxide and chlorophyll content during leaf ontogenesis in poplar

Net photosynthetic (P _N) and dark respiration (R _D) rate, stomatal (rs′) and internal (ri′) resistances to carbon dioxide were measured by gas exchange methods on leaves of different ages, expressed in leaf plastochron index units (LPI) for a fast growing poplar cultivar Unal 2. Although the optimal leaf age differs slightly for the different gas exchange parameters, leaf ontogeny is reflected in the same way in these different parameters. MaximalP _N and minimalrs′ and ri′ values were found at LPI between 6 and 10. Chlorophyll concentrations were lowest at LPI lower than 10 although an increase in two steps was found, when leaf age increases up to maturity.     

Effect of soil drying on growth,biomass allocation and leaf gas exchange of two annual grass species

Influence of short-term water stress on plant growth and leaf gas exchange was studied simultaneously in a growth chamber experiment using two annual grass species differing in photosynthetic pathway type, plant architecture and phenology:Triticum aestivum L. cv. Katya-A-1 (C₃, a drought resistant wheat cultivar of erect growth) andTragus racemosus (L.) All. (C₄, a prostrate weed of warm semiarid areas). At the leaf level, gas exchange rates declined with decreasing soil water potential for both species in such a way that instantaneous photosynthetic water use efficiency (PWUE, mmol CO₂ assimilated per mol H₂O transpired) increased. At adequate water supply, the C₄ grass showed much lower stomatal conductance and higher PWUE than the C₃ species, but this difference disappeared at severe water stress when leaf gas exchange rates were similarly reduced for both species. However, by using soil water more sparingly, the C₄ species was able to assimilate under non-stressful conditions for a longer time than the C₃ wheat did. At the whole-plant level, decreasing water availability substantially reduced the relative growth rate (RGR) ofT. aestivum, while biomass partitioning changed in favour of root growth, so that the plant could exploit the limiting water resource more efficiently. The change in partitioning preceded the overall reduction of RGR and it was associated with increased biomass allocation to roots and less to leaves, as well as with a decrease in specific leaf area. Water saving byT. racemosus sufficiently postponed water stress effects on plant growth occurring only as a moderate reduction in leaf area enlargement. For unstressed vegetative plants, relative growth rate of the C₄ T. racemosus was only slightly higher than that of the C₃ T. aestivum, though it was achieved at a much lower water cost. The lack of difference in RGR was probably due to growth conditions being relatively suboptimal for the C₄ plant and also to a relatively large investment in stem tissues by the C₄ T. racemosus. Only 10% of the plant biomass was allocated to roots in the C₄ species while this was more than 30% for the C₃ wheat cultivar. These results emphasize the importance of water saving and high WUE of C₄ plants in maintaining growth under moderate water stress in comparison with C₃ species.     

Molecular markers for wheat leaf rust resistance gene Lr41

Leaf rust, caused by Puccinia triticina Eriks., is an important foliar disease of common wheat (Triticum aestivum L.) worldwide. Pyramiding several major rust-resistance genes into one adapted cultivar is one strategy for obtaining more durable resistance. Molecular markers linked to these genes are essential tools for gene pyramiding. The rust-resistance gene Lr41 from T. tauschii has been introgressed into chromosome 2D of several wheat cultivars that are currently under commercial production. To discover molecular markers closely linked to Lr41, a set of near-isogenic lines (NILs) of the hard winter wheat cultivar Century were developed through backcrossing. A population of 95 BC₃F_2:6 NILs were evaluated for leaf rust resistance at both seedling and adult plant stages and analyzed with simple sequence repeat (SSR) markers using bulked segregant analysis. Four markers closely linked to Lr41 were identified on chromosome 2DS; the closest marker, Xbarc124, was about 1 cM from Lr41. Physical mapping using Chinese Spring nullitetrasomic and ditelosomic genetic stocks confirmed that markers linked to Lr41 were on chromosome arm 2DS. Marker analysis in a diverse set of wheat germplasm indicated that primers BARC124, GWM210, and GDM35 amplified polymorphic bands between most resistant and susceptible accessions and can be used for marker-assisted selection in breeding programs.     

Can elevated CO(2) improve salt tolerance in olive trees?

We compared growth, leaf gas exchange characteristics, water relations, chlorophyll fluorescence, and Na⁺ and Cl⁻ concentration of two cultivars (‘Koroneiki’ and ‘Picual’) of olive (Olea europaea L.) trees in response to high salinity (NaCl 100 mM) and elevated CO₂ (eCO₂) concentration (700 μL L⁻¹). The cultivar ‘Koroneiki’ is considered to be more salt sensitive than the relatively salt-tolerant ‘Picual’. After 3 months of treatment, the 9-month-old cuttings of ‘Koroneiki’ had significantly greater shoot growth, and net CO₂ assimilation (A_CO2) at eCO₂ than at ambient CO₂, but this difference disappeared under salt stress. Growth and A_CO2 of ‘Picual’ did not respond to eCO₂ regardless of salinity treatment. Stomatal conductance (g_s) and leaf transpiration were decreased at eCO₂ such that leaf water use efficiency (WUE) increased in both cultivars regardless of saline treatment. Salt stress increased leaf Na⁺ and Cl⁻ concentration, reduced growth and leaf osmotic potential, but increased leaf turgor compared with non-salinized control plants of both cultivars. Salinity decreased A_CO2, g_s, and WUE, but internal CO₂ concentrations in the mesophyll were not affected. eCO₂ increased the sensitivity of PSII and chlorophyll concentration to salinity. eCO₂ did not affect leaf or root Na⁺ or Cl⁻ concentrations in salt-tolerant ‘Picual’, but eCO₂ decreased leaf and root Na⁺ concentration and root Cl⁻ concentration in the more salt-sensitive ‘Koroneiki’. Na⁺ and Cl⁻ accumulation was associated with the lower water use in ‘Koroneiki’ but not in ‘Picual’. Although eCO₂ increased WUE in salinized leaves and decreased salt ion uptake in the relatively salt-tolerant ‘Koroneiki’, growth of these young olive trees was not affected by eCO₂.     

Salt resistance of chickpea genotypes in solutions salinized with NaCl or Na2SO4

Summary To assess the potential for developing a salt resistant cultivar of chickpea (Cicer arietinum L.) 160 genotypes were screened for percent survival after 9 weeks in greenhouse solution cultures, with 50 mM NaCl or 25 mM Na₂SO₄. All plants grew well in the sulfate treatment but only cv. L-550 survived the chloride treatment. Salt damage appeared and developed slowly. To check these apparent effects of cultivar and kind of anion, three genotypes including cv. L-550 were then grown in solutions with isoosmotic NaCl or Na₂SO₄ at three levels (−0.044, −0.088, and −0.132 MPa), and in a separate experiment cv. L-550 was grown with NaCl and Na₂SO₄ at four levels: 10, 20, 30 and 50 mM Na. Salt composition affected shoot weight less than salt level or cultivar did. Shoot dry weight was only slightly less in chloride treatments than in isoosmotic sulfate, and for the least sensitive cultivar (L-550) this held only at the highest salt level, corresponding to that in the screening trial. Further, sensitivity to sulfate and to chloride was equal when sodium concentrations in shoots were equal, regardless of anion compositions of media. Shoot Na concentration was a useful negative indicator of growth under salt stress regardles of cultivar, and may be a useful tolerance indicator also for other species that neither accumulate nor efficiently exclude Na.     

古林箐秋海棠叶斑结构对叶色的影响

该研究以古林箐秋海棠(Begonia gulinqingensis)为材料,通过分析叶片形态特征、上表皮光学特性、组织结构、叶绿素含量及叶绿素荧光参数(F_v/F_m),探讨了叶片色斑的形成原因。结果表明:(1)古林箐秋海棠叶斑发生频率和数量无明显规律,但发生部位相对稳定,叶斑主要发生在正对叶柄的两条主脉之间。(2)斑区有两种光反射模式,点状反射和多角形反射,栅栏组织细胞呈近等轴的圆形,排列疏松,与上表皮细胞间存在空隙;非斑区只有点状反射模式,栅栏组织细胞为漏斗型,排列紧密,与上表皮细胞间不存在空隙。(3)斑区和非斑区叶绿体均有密集的堆积基粒和丰富的类囊体膜,斑区叶绿素a、b及总叶绿素含量仅比非斑区分别低24.9%、25.2%、25.1%。(4)叶绿素荧光参数(F_v/F_m)值斑区为0.793,非斑区为0.790。虽然斑区叶绿素含量比非斑区略低,但叶绿体结构完整,且叶绿素荧光参数与非斑区无显著差异。斑区上表皮与栅栏组织细胞间的空隙可使光线到达绿色组织时发生二次反射,在叶片表皮细胞边缘形成白色多边形光反射使该区域相对周围正常叶片区域偏白,基于上述结果可推测古林箐秋海棠的淡绿色块斑形成与特殊的叶片结构有关。     

Structure and enzyme expression in photosynthetic organs of the atypical C4 grass Arundinella hirta

In its leaf blade, Arundinella hirta has unusual Kranz cells that lie distant from the veins (distinctive cells; DCs), in addition to the usual Kranz units composed of concentric layers of mesophyll cells (MCs) and bundle sheath cells (BSCs; usual Kranz cells) surrounding the veins. We examined whether chlorophyllous organs other than leaf blades—namely, the leaf sheath, stem, scale leaf, and constituents of the spike—also have this unique anatomy and the C₄ pattern of expression of photosynthetic enzymes. All the organs developed DCs to varying degrees, as well as BSCs. The stem, rachilla, and pedicel had C₄-type anatomy with frequent occurrence of DCs, as in the leaf blade. The leaf sheath, glume, and scale leaf had a modified C₄ anatomy with MCs more than two cells distant from the Kranz cells; DCs were relatively rare. An immunocytochemical study of C₃ and C₄ enzymes revealed that all the organs exhibited essentially the same C₄ pattern of expression as in the leaf blade. In the scale leaf, however, intense expression of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) occurred in the MCs as well as in the BSCs and DCs. In the leaf sheath, the distant MCs also expressed Rubisco. In Arundinella hirta, it seems that the ratio of MC to Kranz cell volumes, and the distance from the Kranz cells, but not from the veins, affects the cellular expression of photosynthetic enzymes. We suggest that the main role of DCs is to keep a constant quantitative balance between the MCs and Kranz cells, which is a prerequisite for effective C₄ pathway operation.     

Photoperiodism and Crassulacean acid metabolism

Measurements of net CO₂ exchange, malate accumulation, properties and capacity of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in leaves of different ages of two short-day dependent Crassulacean acid metabolism (CAM) plants (Kalanchoe blossfeldiana v. Poelln. Tom thumb and K. velutina Welw.) show that, in both species: a) young leaves from plants grown under long days display a CO₂ exchange pattern typical of C₃ plants; b) leaf aging promotes CAM under long-day conditions; c) short-day treatment induces CAM in young leaves to a higher degree than aging under long days; d) at least in K. blossfeldiana, the PEPC form developed with leaf aging under long days and the enzyme form synthetized de novo in young leaves grown under short days were shown to have similar properties. Short days also promote CAM in older leaves though at a lesser extent than in young leaves: The result is that this photoperiodic treatment increases the general level of CAM performance by the whole plant. The physiological meaning of the control of PEPC capacity by photoperiodism could be to afford a precisely timed seasonal increase in CAM potentiality, enabling the plant to immediately optimize its response to the onset of drought periods.Abbreviations CAM Crassulacean acid metabolism - PEP phosphoenolpyruvate - PEPC phosphoenolpyruvate carboxylase (EC 4.1.1.31) - LD long day - SD short day     

The Nir1 locus in barley is tightly linked to the nitrite reductase apoprotein gene Nii

pBNiR1, a cDNA clone encoding part of the barley nitrite reductase apoprotein, was isolated from a barley (cv. Maris Mink) leaf cDNA library using the 1.85 kb insert of the maize nitrite reductase cDNA clone pCIB808 as a heterologous probe. The cDNA insert of pBNiR1 is 503 by in length. The nucleotide coding sequence could be aligned with the 3 end of other higher plant nitrite reductase apoprotein cDNA sequences but diverges in the 3 untranslated region. The whole-plant barley mutant STA3999, previously isolated from the cultivar Tweed, accumulates nitrite after nitrate treatment in the light, has very much lowered levels of nitrite reductase activity and lacks detectable nitrite reductase cross-reacting material due to a recessive mutation in a single nuclear gene which we have designated Nir1. STA3999 has the characteristics expected of a nitrite reductase apoprotein gene mutant. Here we have used pB-NiR1 in RFLP analysis to determine whether the mutation carried by STA3999 is linked to the nitrite reductase apoprotein gene locus Nii. An RFLP was identified between the wild-type barley cultivars Tweed (major hybridising band of 11.5 kb) and Golden Promise (major hybridising band of 7.5 kb) when DraI-digested DNA was probed with the insert from the partial barley nitrite reductase cDNA clone, pBNiR1. DraI-digested DNA from the mutant STA3999 also exhibited a major hybridising band of 11.5 kb after hybridisation with the insert from pBNiR1. F₁ progeny derived from the cross between the cultivar Golden Promise and the homozygous nir1 mutant STA3999 were heterozygous for these bands as anticipated. Co-segregation of the Tweed RFLP band of 11.5 kb and the mutant phenotype (leaf nitrite accumulation after nitrate treatment/loss of detectable nitrite reductase cross-reacting material at M_r 63000) was scored in an F₂ population of 312 plants derived from the cross between the cultivar Golden Promise and the homozygous mutant STA3999. The Tweed RFLP band of 11.5 kb and the mutant phenotype showed strict co-segregation (in approximately one quarter (84) of the 312 F₂ plants examined). Only those F₂ individuals heterozygous for the RFLP pattern gave rise to F₃ progeny which segregated for the mutant phenotype. We conclude that the nir1locus and the nitrite reductase apoprotein gene Nii are very tightly linked.     

C4 photosynthetic carbon metabolism in the leaves of aromatic tropical grasses — I. Leaf anatomy,CO2 compensation point and CO2 assimilation

A few species of Cymbopogon and Vetiveria are potentially important tropical grasses producing essential oils. In the present study, we report on the leaf anatomy and photosynthetic carbon assimilation in five species of Cymbopogon and Vetiveria zizanioides. Kranz-type leaf anatomy with a centrifugal distribution of chloroplasts and exclusive localization of starch in the bundle sheath cells were common among the test plants. Besides the Kranz leaf anatomy, these grasses displayed other typical C₄ characteristics including a low (0–5 µl/l) CO₂ compensation point, lack of light saturation of CO₂ uptake at high photon flux densities, high temperature (35°C) optimum of net photosynthesis, high rates of net photosynthesis (55–67 mg CO₂ dm^-2 leaf area h^-1), little or no response of net photosynthesis to atmospheric levels of O₂ and high leaf ¹³C/¹²C ratios. The biochemical studies with ¹⁴CO₂ indicated that the leaves of the above plant species synthesize predominantly malate during short term (5 s) photosynthesis. In pulse-chase experiments it was shown that the synthesis of 3-phosphoglycerate proceeds at the expense of malate, the major first formed product of photosynthesis in these plant species.     

Growth under UV-B radiation increases tolerance to high-light stress in pea and bean plants

Pea (Pisum sativum L.) and bean (Phaseolus vulgaris L.) plants were exposed to enhanced levels of UV-B radiation in a growth chamber. Leaf discs of UV-B treated and control plants were exposed to high-light (HL) stress (PAR: 1200 mol m^–2 s^–1) to study whether pre-treatment with UV-B affected the photoprotective mechanisms of the plants against photoinhibition. At regular time intervals leaf discs were taken to perform chlorophyll a fluorescence and oxygen evolution measurements to assess damage to the photosystems. Also, after 1 h of HL treatment the concentration of xanthophyll cycle pigments was determined. A significantly slower decline of maximum quantum efficiency of PSII (F _v/F _m), together with a slower decline of oxygen evolution during HL stress was observed in leaf discs of UV-B treated plants compared to controls in both plant species. This indicated an increased tolerance to HL stress in UV-B treated plants. The total pool of xanthophyll cycle pigments was increased in UV-B treated pea plants compared to controls, but in bean no significant differences were found between treatments. However, in bean plants thiol concentrations were significantly enhanced by UV-B treatment, and UV-absorbing compounds increased in both species, indicating a higher antioxidant capacity. An increased leaf thickness, together with increases in antioxidant capacity could have contributed to the higher protection against photoinhibition in UV-B treated plants.     

Comparison of soil tests and leaf analysis as methods of diagnosing Zn deficiency in British Columbia apple orchards

Soil Zn extracted by 0.25M MgCl₂ or DTPA as an index of Zn availability was compared to Zn or P:Zn concentration in leaves for 40 commercial apple orchards in southern British Columbia. Sampled trees included a wide range of ages and cultivar/rootstock combinations. Leaves were sampled from the midportion of current season's shoots at four times; May–June 1984, July 1984, May 1985 and July 1985. At the same time the severity of the four Zn deficiency symptoms, rosetting, blind bud, little leaf and chlorosis was assessed. Little relationship was found between soil and leaf Zn measures, except in July 1984, when both terminal leaf Zn and P:Zn concentrations varied directly with 0.25M MgCl₂ extractable soil Zn. Soil Zn extracted by 0.25M MgCl₂ was more closely related to severity of deficiency symptoms on the trees at all four samples dates than was DTPA-soil Zn or leaf Zn concentration. Blindbud was the most useful indicator of deficiency in samples collected in May whereas chlorosis was the most useful one in July.     

Chilling and freezing stress in live oaks (Quercus section Virentes): intra- and inter-specific variation in PS II sensitivity corresponds to latitude of origin

Sensitivity to cold and freezing differs between populations within two species of live oaks (Quercus section Virentes Nixon) corresponding to the climates from which they originate. Two populations of Quercus virginiana (originating from North Carolina and north central Florida) and two populations of the sister species, Q. oleoides, (originating from Belize and Costa Rica) were grown under controlled climate regimes simulating tropical and temperate conditions. Three experiments were conducted in order to test for differentiation in cold and freezing tolerance between the two species and between the two populations within each species. In the first experiment, divergences in response to cold were tested for by examining photosystem II (PS II) photosynthetic yield (ΔF/F _m′) and non-photochemical quenching (NPQ) of plants in both growing conditions after short-term exposure to three temperatures (6, 15 and 30°C) under moderate light (400 μmol m⁻² s⁻¹). Without cold acclimation (tropical treatment), the North Carolina population showed the highest photosynthetic yield in response to chilling temperatures (6°C). Both ecotypes of both species showed maximum ΔF/F _m′ and minimum NPQ at their daytime growth temperatures (30°C and 15°C for the tropical and temperate treatments, respectively). Under the temperate treatment where plants were allowed to acclimate to cold, the Q. virginiana populations showed greater NPQ under chilling temperatures than Q. oleoides populations, suggesting enhanced mechanisms of photoprotective energy dissipation in the more temperate species. In the second and third experiments, inter- and intra-specific differentiation in response to freezing was tested for by examining dark-adapted F _v/F _m before and after overnight freezing cycles. Without cold acclimation, the extent of post-freezing declines in F _v/F _m were dependent on the minimum freezing temperature (0, −2, −5 or −10°C) for both populations in both species. The most marked declines in F _v/F _m occurred after freezing at −10°C, measured 24 h after freezing. These declines were continuous and irreversible over the time period. The North Carolina population, however, which represents the northern range limit of Q. virginiana, showed significantly less decline in F _v/F _m than the north central Florida population, which in turn showed a lower decline in Fv/F _m than the two Q. oleoides populations from Belize and Costa Rica. In contrast, after exposure to three months of chilling temperatures (temperate treatment), the two Q. virginiana populations showed no decline in F _v/F _m after freezing at −10°C, while the two Q. oleoides populations showed declines in F _v/F _m reaching 0.2 and 0.1 for Costa Rica and Belize, respectively. Under warm growth conditions, the two species showed different F ₀ dynamics directly after freezing. The two Q. oleoides populations showed an initial rise in F ₀ 30 min after freezing, followed by a subsequent decrease, while the Q. virginiana populations showed a continuous decrease in F ₀ after freezing. The North Carolina population of Q. virginiana showed a tendency toward deciduousness in response to winter temperatures, dropping 58% of its leaves over the three month winter period compared to only 6% in the tropical treatment. In contrast, the Florida population dropped 38% of its leaves during winter. The two populations of the tropical Q. oleoides showed no change in leaf drop during the 3-months winter (10% and 12%) relative to their leaf drop over the same timecourse in the tropical treatment. These results indicate important ecotypic differences in sensitivity to freezing and cold stress between the two populations of Q. virginiana as well as between the two species, corresponding to their climates of origin.     

Effects of elevated CO2 on five plant-aphid interactions

We investigated interactions between five species of phloem-feeding aphids (Homoptera: Aphididae) and their host plants at elevated CO₂; Acyrthosiphon pisum (Harris) on Vicia faba L., Aphis nerii Boyer de Fonscolombe on Asclepias syriaca L., Aphis oenotherae Oestlund on Oenothera biennis L., Aulacorthum solani (Kaltenbach) on Nicotiana sylvestris Speg. & Comes and Myzus persicae (Sulzer) on Solanum dulcamara L. Host plants grown at elevated CO₂ generally had greater biomass, leaf area and C:N ratios than those grown at ambient CO₂, while plants with aphids had lower biomass and leaf area than those without aphids.The responses of aphid populations to elevated CO₂ were species-specific with one species increasing (M. persicae), one decreasing (A. pisum), and the other three being unaffected. CO₂ treatment did not affect the proportion of alate individuals produced. In general, aphid abundance was not significantly related to foliar nitrogen concentration.We performed separate analyses to test whether either aphid presence or aphid abundance modified the response of host plants to elevated CO₂. In terms of aphid presence, only three of the potential 15 interactions (five aphid species x three plant traits) were significant; A. solani slightly modified the response of the plant biomass to elevated CO₂ and M. persicae affected the response of leaf area and allocation. In terms of aphid abundance, only two of the potential 15 interactions were significant with A. nerii modifying the plant response to CO₂ in terms of total leaf area and allocation.We conclude that, in contrast to other insect groups such as leaf chewers, populations of most phloem-feeders may not be negatively affected by increased CO₂ concentrations in the future. The reasons for this difference include the possibility that aphids may be able to compensate for changes in host plant quality by altering feeding behaviour or by synthesizing amino acids. In addition, there is little evidence that aphid herbivory, even at high levels, will substantially modify the response of plants to elevated CO₂.     

No heat-stimulated germination found in herbaceous species from burned subtropical grassland

The inverse relationship between numbers of stomata (stomatal frequency) on tree leaves and ambient CO₂ concentration is increasingly applied for reconstructing past atmospheric CO₂ levels. The abundance of leaf remains of Quercus robur in Holocene peat and lake deposits in Europe makes this species potentially suitable for high-resolution stomatal frequency analysis. In order to quantify the CO₂ responsiveness of the species, the behavior of the stomatal index for Q. robur during the current anthropogenic CO₂ increase is determined on the basis of buried, herbarium and modern leaf material from the Netherlands. The stomatal index (SI), expressing the ratio of the number of stomata in a given area divided by the total number of stomata and other epidermal cells in that same area, is used in order to minimize influences on stomatal frequency of environmental conditions other than CO₂. The sigmoid SI response pattern recorded for Q. robur resembles that of the closely related species Q. petraea, although there is a difference in the timing of the response limitation of the two species to increasing atmospheric CO₂. For calibration purposes only the linear phase of the sigmoidal response curve is taken into consideration in the presented CO₂ response model, which allows confident combination of Q. robur and Q. petraea over the interval from 290 to 325 ppmv CO₂. The model is conservative in reconstructing past CO₂ mixing ratios outside the range of monitored response. As a result of the observed SI response limit, the model predicts CO₂ levels below 325 ppmv with a mean error of 10.2 ppmv, whereas higher CO₂ levels are underestimated.     

Seasonal variations in apparent photosynthesis among plant stands of different soybean cultivars

The CO₂- and H₂O-exchange rates between soybean canopies and the atmosphere were measured in three mobile chambers (4 m³). Each chamber stopped at 8 or 9 plots (3.1-m² ground area) every 25 min. Diurnal and seasonal CO₂-exchange rates (CER) of 13 soybean (Glycine max (L.) Merr.) cultivars are summarized here. The oldest two cultivars, released in 1927 and 1932, had the lowest CER values. The CER usually decreased in the afternoon (23.4 vs 27.8 mol CO₂ m^-2 s^-1 at 1.6 mmol photons m^-2 s^-1), except shortly after rainfall. During a drought, these reductions occurred earlier in the day and were more pronounced. We present evidence for a nonstomatal component of the CO₂ flux-reaction system causing CER reductions during a water stress. Daytime CER values were not correlated with temperature (24–34° C), but nighttime values were (15–25° C, r=0.85,* n=41).     

Gibberellic-acid causes flowering in the short-day plants Panicum miliaceum L., P. miliare lamk., and Setaria italica (L.) P. Beauv.

Treatment with gibberellic acid (GA₃) causes formation of flowers in Panicum ciliaceum and Panicum miliare, two short-day plants, under long days (continuous light), and hastens the emergence of ears in Setaria italica, a quantitative short-day plant, under both inductive and non-inductive photoperiods. The GA₃-induced inflorescences, however, remain short and bear only few spikelets; in the two Panicum species, the spikelets also remain sterile.