Photosynthetic acclimation to elevated CO2 in wheat cultivars

Wheat (T. aestivum) cvs. Kalyansona and Kundan grown under atmospheric (CA) and elevated CO₂ concentrations (650±50 cm³ m^-3 - CE) in open top chambers were examined for net photosynthetic rate (PN), stomatal limitation (l _s) of P _N, ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, and saccharide content of the leaves. The P _N values of both CA- and CE-grown plants compared at the same CO₂ concentration showed a down regulation under CE at the post-anthesis stage. The negative acclimation of P _N appeared to be due to both stomatal and mesophyll components, and the RuBPC activity got also adjusted. There was a decrease in activation state of RuBPC under CE. In connection with this, an increased accumulation of saccharides in wheat leaf under CE was observed. Kalyansona, owing to its larger sink potential in terms of the number of grains, showed a greater enhancement under CE in both post-ear emergence dry matter production and grain yield. Under CE, this cultivar also showed a lower down regulation of P _N than Kundan. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photosynthetic acclimation to elevated CO2 in wheat cultivars

Wheat (T. aestivum) cvs. Kalyansona and Kundan grown under atmospheric (CA) and elevated CO₂ concentrations (650±50 cm³ m^-3 - CE) in open top chambers were examined for net photosynthetic rate (PN), stomatal limitation (l _s) of P _N, ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, and saccharide content of the leaves. The P _N values of both CA- and CE-grown plants compared at the same CO₂ concentration showed a down regulation under CE at the post-anthesis stage. The negative acclimation of P _N appeared to be due to both stomatal and mesophyll components, and the RuBPC activity got also adjusted. There was a decrease in activation state of RuBPC under CE. In connection with this, an increased accumulation of saccharides in wheat leaf under CE was observed. Kalyansona, owing to its larger sink potential in terms of the number of grains, showed a greater enhancement under CE in both post-ear emergence dry matter production and grain yield. Under CE, this cultivar also showed a lower down regulation of P _N than Kundan.     

Genetic variation in plant below-ground response to elevated CO2 and two herbivore species

Aims

It is unclear how changing atmospheric conditions, including rising carbon dioxide concentration, influence interactions between above and below-ground systems and if intraspecific variation exists in this response.

Methods

We assessed interactive effects of atmospheric CO₂ concentration, above-ground herbivory, and plant genotype on root traits and mycorrhizal associations. Plants from five families of Asclepias syriaca, a perennial forb, were grown under ambient and elevated atmospheric CO₂ concentrations. Foliar herbivory by either lepidopteran caterpillars or phloem-feeding aphids was imposed. Mycorrhizal colonization, below-ground biomass, root biomass, and secondary defensive chemistry in roots were quantified.

Results

We observed substantial genetic variation among A. syriaca families in their mycorrhizal colonization levels in response to elevated CO₂ and herbivory treatments. Elevated CO₂ treatment increased root biomass in all genetic families, whereas foliar herbivory tended to decrease root biomass. Root cardenolide concentration and composition varied greatly among plant families, and elevated CO₂ treatment increased root cardenolides in two of the five plant families. Moreover, herbivores differentially affected the composition of cardenolides expressed below ground.

Conclusions

Increased atmospheric CO₂ has the potential to influence interactions among plants, herbivores and mycorrhizal fungi and intraspecific variation suggests that such interactions can evolve.     

三江平原土壤动物群落多样性对CO2浓度升高的响应

为研究大气CO₂浓度升高条件下土壤动物的响应, 本文采用开顶式气室(OTC)控制大气CO₂浓度, 设置了3个梯度, 分别为低浓度370 ppm背景CO₂ (AC)、中浓度550 ppm CO₂ (EC1)和高浓度700 ppm CO₂ (EC2)。于2017年秋季取样并用改良Tullgren干漏斗法和Baermann湿漏斗分离土壤动物。结果表明: (1)共捕获土壤动物6,268头, 隶属于7纲15目, 优势类群为甲螨亚目, 占捕获量的88.13%; 常见类群为弹尾目和双翅目幼虫, 合计占捕获量的9%。不同CO₂浓度水平下, 优势类群(甲螨亚目)和常见类群(弹尾目、双翅目幼虫)相同, 但是稀有类群存在一定差异。(2) CO₂浓度升高显著增加了甲螨亚目的类群数和个体密度, 显著降低了弹尾目的类群数和个体密度, 对其他土壤动物无显著影响。(3)三江平原不同浓度条件下土壤动物的Shannon-Wiener多样性指数、Pielou均匀度指数均为AC > EC1 > EC2, 而优势度指数为EC2 > EC1 > AC, 丰富度指数为AC > EC2 > EC1。研究表明, 气候变化有可能影响土壤动物的群落结构以及土壤动物的多样性。     

CO2 and malate metabolism in starch-containing and starch-lacking guard-cell protoplasts

Isolated, purified mesophyll and guard-cell protoplasts of Vicia faba L. and Allium cepa L. were exposed to ¹⁴CO₂ in the light and in the dark. The guard-cell protoplasts of Vicia and Allium did not show any labeling in phosphorylated products of the Calvin cycle, thus appearing to lack the ability to reduce CO₂ photosynthetically. In Vicia, high amounts of radioactivity (35%) appeared in starch after 60-s pulses of ¹⁴CO₂ both in the light and in the dark. Presumably, the ¹⁴CO₂ is fixed into the malate via PEP carboxylase and then metabolized into starch as the final product of gluconeogenesis. This is supported by the fact that guard-cell protoplasts exposed to malic acid uniformly labeled with ¹⁴CO₂ showed high amounts of labeled starch after the incubation, whereas cells labeled with [4-¹⁴C]malate had minimal amounts of labeled starch (1/120).In contrast, the starch-deficient Allium, guard-cell protoplasts did not show any significant ¹⁴CO₂ fixation. However, adding PEP to an homogenate stimulated ¹⁴CO₂ uptake, thus supporting the interpretation that the presence of starch as a source of PEP is necessary for incorporating CO₂ and delivering malate. With starch-containing Vicia guard-cell protoplasts, the correlation between changes in volume and the interconversion of malate and starch was demonstrated. It was shown that the rapid gluconeogenic conversion of malate into starch prevents an increase of the volume of the protoplasts, whereas the degradation of starch to malate is accompanied by a swelling of the protoplasts.Abbreviations GCPs guard-cell protoplasts - MCPs mesophyll cell protoplasts - PEP phosphoenolpyruvate - DTT dithiothreitol - 3-PGA 3-phosphoglyceric acid - RiBP ribulose 1,5 bisphosphate - MDH malate dehydrogenase - MES 2-(N-morpholino)ethane sulfonic acid - CAM crassulacean acid metabolism     

Short-term CO2 exchange response to temperature,irradiance, and CO2 concentration in strawberry

Relative importance of short-term environmental interaction and preconditioning to CO₂ exchange response was examined in Fragaria ananasa (strawberry, cv. Quinault). Tests included an orthogonal comparison of 15 to 60-min and 6 to 7-h exposures to different levels of temperature (16 to 32°C), photosynthetically active radiation (PAR, 200 to 800 E m² s^-1), and CO₂ (300 to 600 l/l) on successive days of study. Plants were otherwise maintained at 21°C, 300 E m² s^-1 PAR and 300–360 l/l CO₂ as standard conditions. Treatment was restricted to the mean interval of 14 h daily illumination and the first 3–4 days of each test week over a 12-week cultivation period. CO₂ exchange rates were followed with each step-change in environmental level including ascending/descending temperature/PAR within a test period, initial response at standard conditions on successive days of testing, and measurement at reduced O₂. Response generally supported prior concepts of leaf biochemical modeling in identifying CO₂ fixation as the major site of environmental influence, while overall patterns of whole plant CO₂ exchange suggested additional effects for combined environmental factors and preconditioning. These included a positive interaction between temperature and CO₂ concentration on photosynthesis at high irradiance and a greater contribution by dark respiration at lower PAR than previously indicated. The further importance of estimating whole plant CO₂ exchange from repetitive tests and measurements was evidenced by a high correlation of response to prior treatment both during the daily test period and on consecutive days of testing.Abbreviations C₃ plant a plant in which the product of CO₂ fixation is a 3-carbon acid (3-phosphoglyceric acid) - IRGA intra-red gas analyzer - PAR photosynthetically active radiation - RH relative humidity - RuBisCO ribulose-1,5-bisphosphate carboxylase/oxygenase Reference to a company and/or product named by the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.     

The response of plants to elevated CO2

Summary Communities, consisting of six co-occurring, disturbed site annuals, were subjected to CO₂ unenriched (300 ppm) and to CO₂ enriched (450 and 600 ppm) atmospheres at different levels of light and nutrient availability. In general, total community production increased with CO₂ enrichment to 450 ppm, but a further increase in CO₂ to 600 ppm had little or no effect. The response of community production to CO₂ level was not affected by nutrient availability but was affected by light level.Of the six species, four display C₃ metabolism. The proportion of total community production contributed by these species increased as a result of CO₂ enrichment, and was dependent upon both light and nutrient availability. The relative success of some species, particularly in terms of reproduction (total seed biomass), was significantly altered by CO₂ concentration depending on the level of nutrients. There were not only changes in reproductive success (seed biomass) and shoot biomass but also changes in the proportion of biomass allocated to seed.These experiments demonstrate that CO₂ enrichment does affect annual plant communities both in terms of productivity and species composition and that the affect of CO₂ on such system may depend upon other resources such as light and nutrients.     

Involvement of ethylene in the morphological and developmental response of rice to elevated atmospheric CO2 concentrations

We tested the hypothesis that increased carbohydrate flux under elevatedCO₂ regulates accelerated development using rice (Oryzasativa L. cv. Jarrah). Plants were grown either in flooded soil orsolution culture at either 360 or 700 L CO₂L^–1. Total dry mass, shoot elongation rates (SER),tiller appearance rates (TAR) and ethylene release from intact rice seedlingswere measured from 5 to 42 days after planting (DAP). At maturity, shoot andsheath length, tiller number and grain mass were also measured. ElevatedCO₂ had a profound effect on growth, morphology and development andthe effects were more pronounced during the early growth phase. Total aboveground biomass increased at elevated CO₂ and this was accounted for by enhanced tiller number. Grain yield was increased by 56% under elevated CO₂mainly due to increased tiller number and hence panicle number. TAR and SERwereenhanced at elevated CO₂ but SER increased only untill 25 DAP.Elevated CO₂ stimulated a 2-3-fold increase in endogenous andACC-mediated ethylene release but the ACC concentration in the leaves waslittleaffected showing that rates of ACC synthesis matched its oxidation. Inhibitionof ethylene action by 1-aminocyclopropane (1-MCP) had a more pronouncedinhibitory effect on ethylene release in plants that were grown at 700 ascompared to 360 L CO₂ L^–1. Feedingsucrose to intact plants enhanced ethylene synthesis and these results areconsistent with the hypothesis that increased accumulation of sucrose atelevated CO₂ may enhance expression of genes in the ethylenebiosynthetic pathway. We conclude that increase in ethylene release may becentral in promoting accelerated development under elevated CO₂ andthis coincides with the release of auxiliary buds and accelerated rates oftiller appearance hence increased grain yield at elevated CO₂.     

The response of plants to elevated CO2

Summary Four coexisting annual plant species were grown in competition at three levels of CO₂ (300, 600, and 1,200 ppm) and two levels of soil moisture (moist and dry). Plant height was higher at high CO₂ concentrations for the three C₃ species but not for the C₄ species (Amaranthus retroflexus). Total community biomass increased with increasing CO₂ at both soil moisture levels. The contribution of each species to total community biomass was influenced by CO₂ concentration. The effects were especially pronounced for Polygonum pensylvanicum which contributed more to community production as CO₂ and soil moisture increased. Amaranthus behaved in exactly the reverse way; it did best under ambient CO₂ and dry soil moisture conditions. The results suggest that changes in competitive interactions and community structure will occur with the anticipated rise in global CO₂ concentration.     

The response of plants to elevated CO2

Tree saplings, two groups of three species from each of two deciduous tree communities, were grown in competition at three CO₂ concentrations and two light levels. After one growing season, biomass was measured to assess the effect of CO₂ on community structure, and nitrogen and phosphorus concentrations were measured for leaves, stems, and roots of all trees. Gas-exchange measurements were made on the same species grown under the same CO₂ concentrations.Photosynthetic capacity (rate of photosynthesis at saturating CO₂ and light) tended to decline as CO₂ concentration increased, but differences were not statistically significant. Stomatal conductance declined significantly as CO₂ increased. Nitrogen and phosphorus concentrations generally declined as CO₂ increased, but there were some unexpected patterns in roots and stems. CO₂ concentration did not significantly affect the overall growth of either community after one season, but the relative biomass of each species changed in a complex way, depending on CO₂ light level, and community.     

Influence of elevated CO(2) on the sensitivity of two soybean cultivars to sulphur dioxide

Two cultivars of soybean (Glycine max cv. Bragg and PK 472) were subjected to elevated concentrations of CO(2) (600 &mgr;l l(-1)) and/or SO(2) (0.06 &mgr;l l(-1)), for 8 h from germination to grain maturity in open top chambers under field conditions to assess the modification in response to SO(2) exposure resulting form CO(2) enrichment. Exposure to SO(2) alone resulted in reductions in plant growth, biomass and yield, as well as declines in foliar starch and protein content in both the cultivars of soybean. Elevated CO(2) stimulated plant growth, yield and enhanced foliar starch content, photosynthesis and WUE in both the cultivars. In plants exposed to the combination of elevated CO(2)+SO(2), the adverse influence of SO(2) was mitigated by CO(2) enrichment. This effect was considered to result from the provision of extra carbon sources required for repair and detoxification processes and a reduction in SO(2) uptake through reduction in stomatal conductance. PK 472 exhibited greater sensitivity to SO(2) than Bragg. PK 472 also showed greater stimulation of yield under CO(2)+SO(2) treatment than Bragg.     

Soil microbial response in tallgrass prairie to elevated CO2

Terrestrial responses to increasing atmospheric CO₂ are important to the global carbon budget. Increased plant production under elevated CO₂ is expected to increase soil C which may induce N limitations. The objectives of this study were to determine the effects of increased CO₂ on 1) the amount of carbon and nitrogen stored in soil organic matter and microbial biomass and 2) soil microbial activity. A tallgrass prairie ecosystem was exposed to ambient and twice-ambient CO₂ concentrations in open-top chambers in the field from 1989 to 1992 and compared to unchambered ambient CO₂ during the entire growing season. During 1990 and 1991, N fertilizer was included as a treatment. The soil microbial response to CO₂ was measured during 1991 and 1992. Soil organic C and N were not significantly affected by enriched atmospheric CO₂. The response of microbial biomass to CO₂ enrichment was dependent upon soil water conditions. In 1991, a dry year, CO₂ enrichment significantly increased microbial biomass C and N. In 1992, a wet year, microbial biomass C and N were unaffected by the CO₂ treatments. Added N increased microbial C and N under CO₂ enrichment. Microbial activity was consistently greater under CO₂ enrichment because of better soil water conditions. Added N stimulated microbial activity under CO₂ enrichment. Increased microbial N with CO₂ enrichment may indicate plant production could be limited by N availability. The soil system also could compensate for the limited N by increasing the labile pool to support increased plant production with elevated atmospheric CO₂. Longer-term studies are needed to determine how tallgrass prairie will respond to increased C input.     

In vitro response of strawberry cultivars and regenerants to Colletotrichum acutatum

Diseases affecting strawberry (Fragaria × ananassa Duch.) have been of major concern in recent years because of their widespread occurrence and potential for yield loss. Anthracnose, caused by the fungus Colletotrichum acutatum, is one of the most serious diseases of strawberry worldwide. Tissue-culture induced (somaclonal) variation provides one strategy for generating disease-resistant genotypes. As part of a program to generate strawberry germplasm resistant to anthracnose, an in vitro screening system was used to evaluate several commercial cultivars, Chandler, Delmarvel, Honeoye, Latestar, Pelican and Sweet Charlie propagated in vitro, and shoots regenerated from leaf explants of these cultivars for resistance to C.␣acutatum isolate Goff (highly virulent). Regenerants with increased levels of resistance were identified from all of the cultivars. The greatest increases in disease resistance were observed for regenerants from leaf explants of cultivars Pelican and Chandler that exhibited 17.5- and 6.2-fold increases in resistance, respectively. The highest levels of anthracnose resistance (2 to 6% leaf necrosis) were exhibited by regenerants from explants of cultivars Pelican and Sweet Charlie. These studies suggest that generating somaclonal variation may be a viable approach to obtaining strawberry plants with increased levels of anthracnose resistance.     

Growth response of Equisetum fluviatile to elevated CO2 and temperature

In contrast to crop plants and terrestrial herbaceous plants, aquatic plants have raised only modest interest among scientists working on climate change. However, climate change studies on emergent macrophytes can be justified with their crucial role in the ecosystem functioning of aquatic habitats. Here we present the results of a three-year study on the growth response of Equisetum fluviatile, a prominent littoral species of boreal lakes, to elevated CO₂ (doubled to 600–700 ppm) and temperature (increased 2.5–3 °C). Our findings reveal that temperature effects on this species were far more distinct than the effects of CO₂, and no interactions of temperature and CO₂ were observed. Temperature increase had a positive effect on the emergence of shoots and shoot length growth as well as on the maximum length of shoots. Maximum biomass was also positively affected by temperature. The enhancing effects of temperature were carried over to the next growing season. CO₂ enrichment also affected the maximum length of shoots, but the effect was negative. In addition, some response to CO₂ in fertility was observed, but again the effect of temperature was more obvious. Exposure to CO₂ enrichment seemed to have some positive effects on the belowground biomass of E. fluviatile, although this response was not very clear. Thus, we speculate that in the future climate this species will grow faster and the littoral stands will produce more shoot biomass.     

Carbon fluxes acclimate more strongly to elevated growth temperatures than to elevated CO2 concentrations in a northern conifer

Increasing temperatures and atmospheric CO₂ concentrations will affect tree carbon fluxes, generating potential feedbacks between forests and the global climate system. We studied how elevated temperatures and CO₂ impacted leaf carbon dynamics in Norway spruce (Picea abies), a dominant northern forest species, to improve predictions of future photosynthetic and respiratory fluxes from high‐latitude conifers. Seedlings were grown under ambient (AC, c. 435 μmol mol^?1) or elevated (EC, 750 μmol mol^?1) CO₂ concentrations at ambient, +4 °C, or +8 °C growing temperatures. Photosynthetic rates (A_sat) were high in +4 °C/EC seedlings and lowest in +8 °C spruce, implying that moderate, but not extreme, climate change may stimulate carbon uptake. A_sat, dark respiration (R_dark), and light respiration (R_light) rates acclimated to temperature, but not CO₂: the thermal optimum of A_sat increased, and R_dark and R_light were suppressed under warming. In all treatments, the Q₁₀ of R_light (the relative increase in respiration for a 10 °C increase in leaf temperature) was 35% higher than the Q₁₀ of R_dark, so the ratio of R_light to R_dark increased with rising leaf temperature. However, across all treatments and a range of 10–40 °C leaf temperatures, a consistent relationship between R_light and R_dark was found, which could be used to model R_light in future climates. Acclimation reduced daily modeled respiratory losses from warm‐grown seedlings by 22–56%. When R_light was modeled as a constant fraction of R_dark, modeled daily respiratory losses were 11–65% greater than when using measured values of R_light. Our findings highlight the impact of acclimation to future climates on predictions of carbon uptake and losses in northern trees, in particular the need to model daytime respiratory losses from direct measurements of R_light or appropriate relationships with R_dark.