Performance and allocation patterns of the perennial herb,Plantago lanceolata,in response to simulated herbivory and elevated CO2 environments

Summary We tested the prediction that plants grown in elevated CO₂ environments are better able to compensate for biomass lost to herbivory than plants grown in ambient CO₂ environments. The herbaceous perennial Plantago lanceolata (Plantaginaceae) was grown in either near ambient (380 ppm) or enriched (700 ppm) CO₂ atmospheres, and then after 4 weeks, plants experienced either 1) no defoliation; 2) every fourth leaf removed by cutting; or 3) every other leaf removed by cutting. Plants were harvested at week 13 (9 weeks after simulated herbivory treatments). Vegetative and reproductive weights were compared, and seeds were counted, weighed, and germinated to assess viability.Plants grown in enriched CO₂ environments had significantly greater shoot weights, leaf areas, and root weights, yet had significantly lower reproductive weights (i.e. stalks + spikes + seeds) and produced fewer seeds, than plants grown in ambient CO₂ environments. Relative biomass allocation patterns further illustrated differences in plants grown in ambient CO₂ environments. Relative biomass allocation patterns further illustrated differences in plant responses to enriched CO₂ atmospheres: enriched CO₂-grown plants only allocated 10% of their carbon resources to reproduction whereas ambient CO₂-grown plants allocated over 20%. Effects of simulated herbivory on plant performance were much less dramatic than those induced by enriched CO₂ atmospheres. Leaf area removal did not reduce shoot weights or reproductive weights of plants in either CO₂ treatment relative to control plants. However, plants from both CO₂ treatments experienced reductions in root weights with leaf area removal, indicating that plants compensated for lost above-ground tissues, and maintained comparable levels of reproductive output and seed viability, at the expense of root growth.     

Elevated CO2 increases water use efficiency by sustaining photosynthesis of water-limited maize and sorghum

Maize and grain sorghum seeds were sown in pots and grown for 39 days in sunlit controlled-environment chambers at 360 (ambient) and 720 (double-ambient, elevated) μmol mol⁻¹ carbon dioxide concentrations [CO₂]. Canopy net photosynthesis (PS) and evapotranspiration (TR) was measured throughout and summarized daily from 08:00 to 17:00 h Eastern Standard Time. Irrigation was withheld from matched pairs of treatments starting on 26 days after sowing (DAS). By 35 DAS, cumulative PS of drought-stress maize, compared to well-watered plants, was 41% lower under ambient [CO₂] but only 13% lower under elevated [CO₂]. In contrast, by 35 DAS, cumulative PS of drought-stress grain sorghum, compared to well-watered plants, was only 9% lower under ambient [CO₂] and 7% lower under elevated [CO₂]. During the 27-35 DAS drought period, water use efficiency (WUE, mol CO₂ Kmol⁻¹ H₂O), was 3.99, 3.88, 5.50, and 8.65 for maize and 3.75, 4.43, 5.26, and 9.94 for grain sorghum, for ambient-[CO₂] well-watered, ambient-[CO₂] stressed, elevated-[CO₂] well-watered and elevated-[CO₂] stressed plants, respectively. Young plants of maize and sorghum used water more efficiently at elevated [CO₂] than at ambient [CO₂], especially under drought. Reductions in biomass by drought for young maize and grain sorghum plants were 42 and 36% at ambient [CO₂], compared to 18 and 14% at elevated [CO₂], respectively. Results of our water stress experiment demonstrated that maintenance of relatively high canopy photosynthetic rates in the face of decreased transpiration rates enhanced WUE in plants grown at elevated [CO₂]. This confirms experimental evidence and conceptual models that suggest that an increase of intercellular [CO₂] (or a sustained intercellular [CO₂]) in the face of decreased stomatal conductance results in relative increases of growth of C₄ plants. In short, drought stress in C₄ crop plants can be ameliorated at elevated [CO₂] as a result of lower stomatal conductance and sustaining intercellular [CO₂]. Furthermore, less water might be required for C₄ crops in future higher CO₂ atmospheres, assuming weather and climate similar to present conditions.     

Influence of carbon dioxide enrichment, ozone and nitrogen fertilization on cotton (Gossypium hirsutum L.) leaf and root composition

The objective of this study was to test whether elevated [CO₂], [O₃] and nitrogen (N) fertility altered leaf mass per area (LMPA), non‐structural carbohydrate (TNC), N, lignin (LTGA) and proanthocyanidin (PA) concentrations in cotton (Gossypium hirsutum L.) leaves and roots. Cotton was grown in 14 dm³ pots with either sufficient (0·8 g N dm ^{? 3}) or deficient (0·4 and 0·2 g N dm ^{? 3}) N fertilization, and treated in open‐top chambers with either ambient or elevated ( + 175 and + 350 μ mol mol ^{? 1}) [CO₂] in combination with either charcoal‐filtered air (CF) or non‐filtered air plus 1·5 times ambient [O₃]. At about 50 d after planting, LMPA, starch and PA concentrations in canopy leaves were as much as 51–72% higher in plants treated with elevated [CO₂] compared with plants treated with ambient [CO₂], whereas leaf N concentration was 29% lower in elevated [CO₂]‐treated plants compared with controls. None of the treatments had a major effect on LTGA concentrations on a TNC‐free mass basis. LMPA and starch levels were up to 48% lower in plants treated with elevated [O₃] and ambient [CO₂] compared with CF controls, although the elevated [O₃] effect was diminished when plants were treated concurrently with elevated [CO₂]. On a total mass basis, leaf N and PA concentrations were higher in samples treated with elevated [O₃] in ambient [CO₂], but the difference was much reduced by elevated [CO₂]. On a TNC‐free basis, however, elevated [O₃] had little effect on tissue N and PA concentrations. Fertilization treatments resulted in higher PA and lower N concentrations in tissues from the deficient N fertility treatments. The experiment showed that suppression by elevated [O₃] of LMPA and starch was largely prevented by elevated [CO₂], and that interpretation of [CO₂] and [O₃] effects should include comparisons on a TNC‐free basis. Overall, the experiment indicated that allocation to starch and PA may be related to how environmental factors affect source–sink relationships in plants, although the effects of elevated [O₃] on secondary metabolites differed in this respect.     

Responses of Photosynthetic and Defence Systems to High Temperature Stress in Quercus suber L Seedlings Grown under Elevated CO2

Abstract: Growth in elevated CO₂ led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO₂-grown plants. No down-regulation of photosynthesis was found after six months of growth under elevated CO₂. Photosynthetic rates at 15°C or 35 °C were also higher in elevated than in ambient CO₂-grown plants, when measured at their respective CO₂ growth condition. Stomata of elevated CO₂-grown plants were less responsive to temperature as compared to ambient CO₂ plants. The after effect of a heat-shock treatment (4 h at 45 °C in a chamber with 80% of relative humidity and 800–1000 tmol m^-2 s^-1 photon flux density) on A_max was less in elevated than in ambient CO₂-grown plants. At the photochemical level, the negative effect of the heat-shock treatment was slightly more pronounced in ambient than in elevated CO₂-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO₂-grown plants, in comparison to ambient CO₂ plants, is suggested by the increase in superoxide dismutase activity, after 1 h at 45 °C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO₂-grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO₂-grown plants immediately after 1 h at 45 °C. The observed increase in catalase after 1 h at 45 °C in both ambient and elevated CO₂-grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature.     

Root-zone CO2 and root-zone temperature effects on photosynthesis and nitrogen metabolism of aeroponically grown lettuce (Lactuca sativa L.) in the tropics

Effects of elevated root-zone (RZ) CO₂ concentration (RZ [CO₂]) and RZ temperature (RZT) on photosynthesis, productivity, nitrate (NO₃ ^?), total reduced nitrogen (TRN), total leaf soluble and Rubisco proteins were studied in aeroponically grown lettuce plants in a tropical greenhouse. Three weeks after transplanting, four different RZ [CO₂] concentrations (ambient, 360 ppm, and elevated concentrations of 2,000; 10,000; and 50,000 ppm) were imposed on plants at 20°C-RZT or ambient(A)-RZT (24–38°C). Elevated RZ [CO₂] resulted in significantly higher light-saturated net photosynthetic rate, but lower light-saturated stomatal conductance. Higher elevated RZ [CO₂] also protected plants from both chronic and dynamic photoinhibition (measured by chlorophyll fluorescence Fv/Fm ratio) and reduced leaf water loss. Under each RZ [CO₂], all these variables were significantly higher in 20°C-RZT plants than in A-RZT plants. All plants accumulated more biomass at elevated RZ [CO₂] than at ambient RZ [CO₂]. Greater increases of biomass in roots than in shoots were manifested by lower shoot/root ratios at elevated RZ [CO₂]. Although the total biomass was higher at 20°C-RZT, the increase in biomass under elevated RZ [CO₂] was greater at A-RZT. Shoot NO₃ ^? and TRN concentrations, total leaf soluble and Rubisco protein concentrations were higher in all elevated RZ [CO₂] plants than in plants under ambient RZ [CO₂] at both RZTs. Under each RZ [CO₂], total leaf soluble and Rubisco protein concentrations were significantly higher at 20°C-RZT than at A-RZT. Our results demonstrated that increased P _Nmax and productivity under elevated [CO₂] was partially due to the alleviation of midday water loss, both dynamic and chronic photoinhibition as well as higher turnover of Calvin cycle with higher Rubisco proteins.     

CO2 enrichment predisposes foliage of a eucalypt to freezing injury and reduces spring growth

Seedlings of Eucalyptus pauciflora, were grown in open-top chambers fumigated with ambient and elevated [CO₂], and were divided into two populations using 10% light transmittance screens. The aim was to separate the effects of timing of light interception, temperature and [CO₂] on plant growth. The orientation of the screens exposed plants to a similar total irradiance, but incident during either cold mornings (east-facing) or warm afternoons (west-facing). Following the first autumn freezing event elevated CO₂-grown plants had 10 times more necrotic leaf area than ambient CO₂ plants. West-facing plants had significantly greater (25% more) leaf damage and lower photochemical efficiency (F_v/F_m) in comparison with east-facing plants. Following a late spring freezing event east-facing elevated CO₂ plants suffered a greater sustained loss in F_v/F_m than west-facing elevated CO₂- and ambient CO₂-grown plants. Stomatal conductance was lower under elevated CO₂ than ambient CO₂ except during late spring, with the highest leaf temperatures occurring in west-facing plants under elevated CO₂. These higher leaf temperatures apparently interfered with cold acclimation thereby enhancing frost damage and reducing the ability to take advantage of optimal growing conditions under elevated CO₂.     

Wheat genotypes differing in aluminum tolerance differ in their growth response to CO2 enrichment in acid soils

Aluminum (Al) toxicity is a major factor limiting plant growth in acid soils. Elevated atmospheric CO₂ [CO₂] enhances plant growth. However, there is no report on the effect of elevated [CO₂] on growth of plant genotypes differing in Al tolerance grown in acid soils. We investigated the effect of short‐term elevated [CO₂] on growth of Al‐tolerant (ET8) and Al‐sensitive (ES8) wheat plants and malate exudation from root apices by growing them in acid soils under ambient [CO₂] and elevated [CO₂] using open‐top chambers. Exposure of ET8 plants to elevated [CO₂] enhanced root biomass only. In contrast, shoot biomass of ES8 was enhanced by elevated [CO₂]. Given that exudation of malate to detoxify apoplastic Al is a mechanism for Al tolerance in wheat plants, ET8 plants exuded greater amounts of malate from root apices than ES8 plants under both ambient and elevated [CO₂]. These results indicate that elevated [CO₂] has no effect on malate exudation in both ET8 and ES8 plants. These novel findings have important implications for our understanding how plants respond to elevated [CO₂] grown in unfavorable edaphic conditions in general and in acid soils in particular.     

Acclimation of peanut (Arachis hypogaea L.) leaf photosynthesis to elevated growth CO2 and temperature

Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO₂ concentrations ([CO₂]) of 360 μmol mol⁻¹ (ambient) and 720 μmol mol⁻¹ (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO₂] and temperature, and to assess whether elevated [CO₂] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO₂] had higher midday photosynthetic CO₂ exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO₂]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO₂]. Declines in Rubisco under elevated growth [CO₂] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO₂], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO₂] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO₂] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO₂] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO₂]. Under elevated [CO₂], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO₂] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO₂]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO₂] and temperature as predicted for this century.     

Photosynthetic acclimation and photosynthate partitioning in soybean leaves in response to carbon dioxide enrichment

Photosynthetic rates and photosynthate partitioning were studied in three-week-old soybean [Glycine max (L.) Merr. cv. Williams] plants exposed to either ambient (35 Pa) or elevated (70 Pa) CO₂ in controlled environment chambers. Ambient CO₂-grown plants also were given a single 24 h treatment with 70 Pa CO₂ 1 d prior to sampling. Photosynthetic rates of ambient CO₂-grown plants initially increased 36% when the measurement CO₂ was doubled from 35 to 70 Pa. Photosynthetic rates of the third trifoliolate leaf, both after 1 and 21 d of elevated CO₂ treatment, were 30 to 45% below those of ambient CO₂-grown plants when measured at 35 Pa CO₂. These reduced photosynthetic rates were not due to increased stomatal resistance and were observed for 2 to 8 h after plants given 1 d of CO₂ enrichment were returned to ambient CO₂. Initial and total ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities, percent activation, Rubisco protein, soluble protein and leaf chlorophyll content were similar in all CO₂ treatments. Quantum yields of photosynthesis, determined at limiting irradiances and at 35 Pa CO₂, were 0.049±0.003 and 0.038±0.005 mol CO₂ fixed per mol quanta for ambient and elevated CO₂-grown plants, respectively (p<0.05). Leaf starch and sucrose levels were greater in plants grown at 70 than at 35 Pa CO₂. Starch accumulation rates during the day were greater in ambient CO₂-grown plants than in plants exposed to elevated CO₂ for either 1 or 21 d. However, the percentage of C partitioned to starch relative to total C fixed was unaffected by 1 d of CO₂ enrichment. The above results showed that both photosynthetic and starch accumulation rates of soybean leaflets measured at 35 Pa CO₂ were temporarily reduced after 1 and 21 d of CO₂ enrichment. The biochemical mechanism affecting these responses was not identified.Abbreviations SLW- specific leaf weight (g m^–2) - Rubisco- ribulose 1,5-bisphosphate carboxylase/oxygenase - Rul- 5bisP, ribulose 1,5 bisphosphate - DAP- days after planting - SAR- starch accumulation rate - C_i- intercellular CO₂ concentration     

Elevated CO2 decreases seed germination in Arabidopsis thaliana

The impact of elevated [CO₂] on seed germination was studied in different genotypes of Arabidopsis thaliana from natural populations. Two generations of seeds were studied: the maternal generation was produced in the greenhouse (present-day conditions), the offspring generation was produced in two chambers where the CO₂ concentration was either the present atmospheric concentration (about 350 ppm) or elevated (700 ppm). The seeds were tested for proportion of germinated seeds and mean germination time in both chambers to study the impact of elevated [CO₂] during seed production and germination. Elevated [CO₂] during maturation of seeds on the mother-plants decreased the proportion of germinated seeds, while elevated [CO₂] during germination had no effect on the proportion of germinated seeds. However, when seeds were both produced and germinated under elevated [CO₂] (situation expected by the end of next century), germination was slow and low. Moreover, the effect of the [CO₂] treatment differs among genotypes of Arabidopsis: there is a strong treatment × genotype interaction. This means that there is ample genetic variance for a selective response modiying the effects of high levels of [CO₂] in natural populations of Arabidopsis thaliana. The outcome at the community level will depend on what seeds are available, when they germinate and the resulting competition following germination.     

Nitrogen assimilation and transpiration: key processes conditioning responsiveness of wheat to elevated [CO2] and temperature

Although climate scenarios have predicted an increase in [CO₂] and temperature conditions, to date few experiments have focused on the interaction of [CO₂] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO₂. The main goal of this study was to analyze the effect of interacting [CO₂] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated [CO₂] and temperature conditions. For this purpose, wheat plants were exposed to elevated [CO₂] (400 vs 700 µmol mol^?1) and temperature (ambient vs ambient + 4°C) in CO₂ gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated [CO₂] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated [CO₂] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated [CO₂] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity.     

Effect of elevated carbon-dioxide on plant growth,physiology, yield and seed quality of chickpea (Cicer arietinum L.) in Indo-Gangetic plains

In the present scenario of climate change with constantly increasing CO₂ concentration, there is a risk of altered crop performance in terms of growth, yield, grain nutritional value and seed quality. Therefore, an experiment was conducted in open top chamber (OTCs) during 2017–18 and 2018–19 to assess the effect of elevated atmospheric carbondioxide (e[CO₂]) (600 ppm) on chickpea (cv. JG 14) crop growth, biomass accumulation, physiological function, seed yield and its quality in terms of germination and vigour. The e[CO₂] treatment increased the plant height, leaf and stem biomass over ambient CO₂ (a[CO₂]) treatment. The e[CO₂] increased seed yield by 11–18% which was attributed to an increase in the number of pods (6–10%) and seeds plant⁻¹ (8–9%) over a[CO₂]. However, e[CO₂] reduced the seed protein (7%), total phenol (13%) and thiobarbituric acid reactive substances (12%) and increased the starch (21%) and water uptake rate as compared to seeds harvested from a[CO₂] environment. Exposing chickpea plant to e[CO₂] treatment had no impact on germination and vigour of the harvested seeds. Also, the physical attributes, total soluble sugar and antioxidant enzymes activities of harvested seeds were comparable in a[CO₂] and e[CO₂] treatment. Hence, the experimental findings depict that e[CO₂] upto 600 ppm could add to the growth and productivity of chickpea in a sub-tropical climate with an implication on its nutritional quality of the produce.     

Elevated CO2 alleviates negative effects of salinity on broccoli (Brassica oleracea L. var Italica) plants by modulating water balance through aquaporins abundance

In the global change scenario, increased CO₂ may favour water use efficiency (WUE) by plants. By contrast, in arid and semiarid areas, salinity may reduce water uptake from soils. However, an elevated WUE does not ensure a reduced water uptake and upon salinity this fact may constitute an advantage for plant tolerance. In this work, we aimed to determine the combined effects of enhanced [CO₂] and salinity on the plant water status, in relation to the regulation of PIP aquaporins, in the root and leaf tissues of broccoli plants (Brassica oleracea L. var Italica), under these two environmental factors. Thus, different salinity concentrations (0, 60 and 90 mM NaCl) were applied under ambient (380 ppm) and elevated (800 ppm) [CO₂]. Under non-salinised conditions, stomatal conductance (G_s) and transpiration rate (E) decreased with rising [CO₂] whereas water potential (Ψ_ω) was maintained stable, which caused a reduction in the root hydraulic conductance (L₀). In addition, PIP1 and PIP2 abundance in the roots was decreased compared to ambient [CO₂]. Under salinity, the greater stomatal closure observed at elevated [CO₂] – compared to that at ambient [CO₂] – caused a greater reduction in G_s and E and allowed plants to maintain their water balance. In addition, a lower decrease in L₀ under salt stress was observed at elevated [CO₂], when comparing with the decrease at ambient [CO₂]. Modifications in PIP1 and PIP2 abundance or their functionality in the roots is discussed. In fact, an improved water status of the broccoli plants treated with 90 mM NaCl and elevated [CO₂], evidenced by a higher Ψ_ω, was observed together with higher photosynthetic rate and water use efficiency. These factors conferred on the salinised broccoli plants greater leaf area and biomass at elevated [CO₂], in comparison with ambient [CO₂]. We can conclude that, under elevated [CO₂] and salt stress, the water flow is influenced by the tight control of the aquaporins in the roots and leaves of broccoli plants and that increased PIP1 and PIP2 abundance in these organs provides a mechanism of tolerance that maintains the plant water status.     

Dry matter and nitrogen accumulation and partitioning in rice (Oryza sativa L.) exposed to experimental warming with elevated CO2

Effects of elevated CO₂ concentration ([CO₂]) and air temperature (T_air) on accumulation and intra-plant partitioning of dry matter (DM) and nitrogen in paddy rice were investigated by performing a pot experiment in six natural sunlit temperature gradient chambers (TGCs) with or without CO₂ fumigation. Rice (Oryza sativa L.) plants were grown in TGCs for a whole season under two levels of [CO₂] (ambient, 380 ppm; elevated, 622 ppm) and two daily T_air regimes (ambient, 25.2°C; elevated, 27.3°C) in split-plot design with triplication. The effects of elevated [CO₂] and T_air on DM were most dramatic for grain and shoot with a significant (P?<?0.05) interaction between [CO₂] and T_air. Overall, total grain DM increased with elevated [CO₂] by 69.6% in ambient T_air but decreased with elevated T_air by 33.8% in ambient [CO₂] due to warming-induced floral sterility. Meanwhile, shoot DM significantly increased with elevated T_air by 20.8% in ambient [CO₂] and by 46.6% in elevated [CO₂]. Although no [CO₂]?×?T_air interaction was detected, the greatest total DM was achieved by co-elevation of [CO₂] and T_air (by 42.8% relative to the ambient conditions) via enhanced shoot and root DM accumulation, but not grain. This was attributed largely both to increase in tiller number and to accumulation of photosynthate in the shoot and root due to inhibition of photosynthate allocation to grain caused by warming-induced floral sterility. Distribution of N (both soil N and fertilizer ¹⁵N) among rice parts in responding to climatic variables entirely followed the pattern of DM. Our findings demonstrate that the projected warming is likely to induce a significant reduction in grain yield of rice by inhibiting DM (i.e., photosynthates) allocation to grain, though this may partially be mitigated by elevated [CO₂].     

Responses of Senna reticulata,a legume tree from the Amazonian floodplains,to elevated atmospheric CO2 concentration and waterlogging

Key message

The Amazonian tree Senna reticulata showed an increase in photosynthesis and starch content under elevated [CO ₂ ] that led an increment in biomass after 90 days. Elevated [CO ₂ ] was also capable of reducing the negative effect of waterlogging.

Abstract

Tree species from the Amazonian floodplains have to cope with low oxygen availability due to annual pulses of inundation that can last up to 7 months. Species capable of adapting to flooding and/or waterlogged conditions usually partition their storage to favor starch and allocate it to roots, where carbohydrates are used to maintain respiration rates during waterlogging. In spite of climate change, virtually nothing is known about how elevated atmospheric CO₂ concentration ([CO₂]) will affect plants when combined with waterlogging. In this work, we used open top chambers to evaluate the effect of elevated [CO₂] during a period of terrestrial phase and in subsequent combination with waterlogged conditions to determine if the surplus carbon provided by elevated [CO₂] may improve the waterlogging tolerance of the fast-growing Amazonian legume tree Senna reticulata. During the terrestrial phase, photosynthesis was ca. 28 % higher after 30, 45 and 120 days of elevated [CO₂], and starch content in the leaves was, on average, 49 % higher than with ambient [CO₂]. Total biomass was inversely correlated to the starch content of leaves, indicating that starch might be the main carbohydrate source for biomass production during the terrestrial phase. This response was more pronounced under elevated [CO₂], resulting in 30 % more biomass in comparison to ambient [CO₂] plants. After 135 days at elevated [CO₂] an inversion has been observed in total biomass accumulation, in which ambient [CO₂] presented a greater increment in total biomass in comparison to elevated [CO₂], indicating negative effects on growth after long-term CO₂ exposure. However, plants with elevated [CO₂]/waterlogged displayed a greater increment in biomass in comparison with ambient [CO₂]/waterlogged that, unlike during the terrestrial phase, was unrelated to starch reserves. We conclude that S. reticulata displays mechanisms that make this species capable of responding positively to elevated [CO₂] during the first pulse of growth. This response capacity is also associated with a “buffering effect” that prevents the plants from decreasing their biomass under waterlogged conditions.     

Atmospheric carbon dioxide and fertilizer nitrogen effects on radiation interception by rice 1

In order to predict the potential impacts of global change, it is important to understand the impact of increasing global atmospheric [CO₂] on the growth and yield of crop plants. The objectives of this study were to determine the interaction of N fertilization rates and atmospheric [CO₂] on radiation interception and radiation-use efficiency of rice (Oryza sativa L. cv. IR72) grown under tropical field conditions. Rice plants were grown inside open top chambers in a lowland rice field at the International Rice Research Institute in the Philippines at ambient (about 350 μmol mol^-1) or elevated (about 600 μmol mol^-1 during the 1993 wet season and 700 μmol mol^-1 during the 1994 dry season) in combination with three levels of applied N (0, 50 or 100 kg N ha^-1 in the wet season; 0, 90 or 200 kg N ha-1 in the dry season). Light interception was not directly affected by [CO₂], but elevated [CO₂] indirectly increased light interception through increasing total absorbed N. Plant N requirement for radiation interception was similar for rice grown under ambient [CO₂] or elevated [CO₂] treatments. The conversion efficiency of intercepted radiation to dry matter, radiation-use efficiency (RUE), was about 35% greater at elevated [CO₂] than at ambient [CO₂]. The relationship between leaf N and RUE was curvilinear. At ambient [CO₂], RUE was fairly stable across levels of leaf N, but leaf N less than about 2.5% resulted in lower RUE for plants grown with elevated [CO₂] than for plant grown at ambient [CO₂]. Decreased leaf N with increased [CO₂], therefore decreased RUE of rice plants grown at elevated [CO₂]. When predicting responses of rice to elevated [CO₂], RUE should be adjusted with a decrease in leaf N. This revised version was published online in June 2006 with corrections to the Cover Date.     

ABA and BAP improve the accumulation of carbohydrates and alter carbon allocation in potato plants at elevated CO2

Elevated CO₂ interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO₂ concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO₂ levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO₂ concentration and plant growth regulators (PGRs) on potato (Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants (cvs. Agria and Fontane) to combined application of CO₂ levels (400 vs. 800 µmol mol⁻¹) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO₂ levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO₂. In Agria, the ratio of leaf intercellular to ambient air CO₂ concentrations [C_i:C_a] was declined in elevated-CO₂-grown plants, which indicated the stomata would become more conservative at higher CO₂ levels. On the other hand, the increased C_i:C_a in Fontane showed a stomatal acclimation to higher CO₂ concentration. The higher leaf dark respiration of the elevated CO₂-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO₂ and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO₂ on tuber yield and productivity of the potato plants.     

Profiles of isoprene emission and photosynthetic parameters in hybrid poplars exposed to free‐air CO2 enrichment†

Poplar (Populus × euroamericana) saplings were grown in the field to study the changes of photosynthesis and isoprene emission with leaf ontogeny in response to free air carbon dioxide enrichment (FACE) and soil nutrient availability. Plants growing in elevated [CO₂] produced more leaves than those in ambient [CO₂]. The rate of leaf expansion was measured by comparing leaves along the plant profile. Leaf expansion and nitrogen concentration per unit of leaf area was similar between nutrient treatment, and this led to similar source–sink functional balance. Consequently, soil nutrient availability did not cause downward acclimation of photosynthetic capacity in elevated [CO₂] and did not affect isoprene synthesis. Photosynthesis assessed in growth [CO₂] was higher in plants growing in elevated than in ambient [CO₂]. After normalizing for the different number of leaves over the profile, maximal photosynthesis was reached and started to decline earlier in elevated than in ambient [CO₂]. This may indicate a [CO₂]‐driven acceleration of leaf maturity and senescence. Isoprene emission was adversely affected by elevated [CO₂]. When measured on the different leaves of the profile, isoprene peak emission was higher and was reached earlier in ambient than in elevated [CO₂]. However, a larger number of leaves was emitting isoprene in plant growing in elevated [CO₂]. When integrating over the plant profile, emissions in the two [CO₂] levels were not different. Normalization as for photosynthesis showed that profiles of isoprene emission were remarkably similar in the two [CO₂] levels, with peak emissions at the centre of the profile. Only the rate of increase of the emission of young leaves may have been faster in elevated than in ambient [CO₂]. Our results indicate that elevated [CO₂] may overall have a limited effect on isoprene emission from young seedlings and that plants generally regulate the emission to reach the maximum at the centre of the leaf profile, irrespective of the total leaf number. In comparison with leaf expansion and photosynthesis, isoprene showed marked and repeatable differences among leaves of the profile and may therefore be a useful trait to accurately monitor changes of leaf ontogeny as a consequence of elevated [CO₂].     

Enhanced isoprene emission capacity and altered light responsiveness in aspen grown under elevated atmospheric CO2 concentration

Controversial evidence of CO₂‐responsiveness of isoprene emission has been reported in the literature with the response ranging from inhibition to enhancement, but the reasons for such differences are not understood. We studied isoprene emission characteristics of hybrid aspen (Populus tremula x P. tremuloides) grown under ambient (380 μmol mol^?1) and elevated (780 μmol mol^?1) [CO₂] to test the hypothesis that growth [CO₂] effects on isoprene emission are driven by modifications in substrate pool size, reflecting altered light use efficiency for isoprene synthesis. A novel in vivo method for estimation of the pool size of the immediate isoprene precursor, dimethylallyldiphosphate (DMADP) and the activity of isoprene synthase was used. Growth at elevated [CO₂] resulted in greater leaf thickness, more advanced development of mesophyll and moderately increased photosynthetic capacity due to morphological “upregulation”, but isoprene emission rate under growth light and temperature was not significantly different among ambient‐ and elevated‐[CO₂]‐grown plants independent of whether measured at 380 μmol mol^?1 or 780 μmol mol^?1 CO₂. However, DMADP pool size was significantly less in elevated‐[CO₂]‐grown plants, but this was compensated by increased isoprene synthase activity. Analysis of CO₂ and light response curves of isoprene emission demonstrated that the [CO₂] for maximum isoprene emission was shifted to lower [CO₂] in elevated‐[CO₂]‐grown plants. The light‐saturated isoprene emission rate (I_max,Q) was greater, but the quantum efficiency at given I_max,Q was less in elevated‐[CO₂]‐grown plants, especially at higher CO₂ measurement concentration, reflecting stronger DMADP limitation at lower light and higher [CO₂]. These results collectively demonstrate important shifts in light and CO₂‐responsiveness of isoprene emission in elevated‐[CO₂]‐acclimated plants that need consideration in modeling isoprene emissions in future climates.     

How is the relationship between the C4 cereal Sorghum bicolor and the C3 root hemi-parasites Striga hermonthica and Striga asiatica affected by elevated CO2?

The C₄ cereal Sorghum bicolor was grown under either ambient (350 μmol mol^?1) or elevated (700 μmol mol^?1) [CO₂] in either the presence or absence of the C₃ obligate root hemi-parasites Striga hermonthica or S. asiatica. Both uninfected and infected sorghum plants were taller and had greater biomass, photosynthetic rates, water-use efficiencies and leaf areas under elevated compared with ambient [CO₂]. There was no evidence of any downregula-tion of photosynthesis in sorghum grown at elevated [CO₂]. Biomass of infected sorghum was lower under both ambient and elevated [CO₂], and although infected plants were larger under elevated [CO₂] the relative impact of infection on host biomass was either the same (S. asiatica) or only slightly less (S. hermonthica) than under ambient [CO₂]. In contrast, biomass of S. hermonthica and S. asiatica per host was lower under elevated than ambient [CO₂], although rates of photosynthesis were higher at elevated [CO₂] and parasite stomatal conductance was not responsive to [CO₂]. Parasites emerged above-ground and flowered earlier under ambient compared with elevated [CO₂]. It appears that the mechanism(s) by which the parasites affect host growth is (are) relatively insensitive to increased atmospheric [CO₂], although the parasites themselves were adversely affected by growth at elevated [CO₂].