Elevated CO2 levels enhance the uptake and metabolism of organic nitrogen

The effects of elevated CO₂ (eCO₂) on the relative uptake of inorganic and organic nitrogen (N) are unclear. The uptake of different N sources by pak choi (Brassica chinensis L.) seedlings supplied with a mixture of nitrate, glycine and ammonium was studied using ¹⁵N‐labelling under ambient CO₂ (aCO₂) (350 ppm) or eCO₂ (650 ppm) conditions. ¹⁵N‐labelled short‐term uptake and ¹⁵N‐gas chromatography mass spectrometry (GC–MS) were applied to measure the effects of eCO₂ on glycine uptake and metabolism. Elevated CO₂ increased the shoot biomass by 36% over 15 days, but had little effect on root growth. Over the same period, the N concentrations of shoots and roots were decreased by 30 and 2%, respectively. Elevated CO₂ enhanced the uptake and N contribution of glycine, which accounted for 38–44% and 21–40% of total N uptake in roots and shoots, respectively, while the uptake of nitrate and ammonium was reduced. The increased glycine uptake resulted from the enhanced active uptake and enhanced metabolism in the roots. We conclude that eCO₂ may increase the uptake and contribution of organic N forms to total plant N nutrition. Our findings provide new insights into plant N regulation under eCO₂ conditions.     

Phosphorus supply enhances the response of legumes to elevated CO2 (FACE) in a phosphorus-deficient vertisol

Background & aims

Understanding the mechanism of how phosphorus (P) regulates the response of legumes to elevated CO₂ (eCO₂) is important for developing P management strategies to cope with increasing atmospheric CO₂ concentration. This study aimed to explore this mechanism by investigating interactive effects of CO₂ and P supply on root morphology, nodulation and soil P fractions in the rhizosphere.

Methods

A column experiment was conducted under ambient (350?ppm) (aCO₂) and eCO₂ (550?ppm) in a free air CO₂ enrichment (FACE) system. Chickpea and field pea were grown in a P-deficient Vertisol with P addition of 0–16?mg?P?kg^?1.

Results

Increasing P supply increased plant growth and total P uptake with the increase being greater under eCO₂ than under aCO₂. Elevated CO₂ increased root biomass and length, on average, by 16?% and 14?%, respectively. Nodule biomass increased by 46?% in response to eCO₂ at 16?mg P kg^?1, but was not affected by eCO₂ at no P supply. Total P uptake was correlated with root length while N uptake correlated with nodule number and biomass regardless of CO₂ level. Elevated CO₂ increased the NaOH-extractable organic P by 92?% when 16?mg P kg^?1 was applied.

Conclusion

The increase in P and N uptake and nodule number under eCO₂ resulted from the increased biomass production, rather than from changes in specific root-absorbing capability or specific nodule function. Elevated CO₂ appears to enhance P immobilization in the rhizosphere.     

Short photoperiod attenuates CO2 fertilization effect on shoot biomass in Arabidopsis thaliana

The level of carbon dioxide (CO₂) in the air can affect several traits in plants. Elevated atmospheric CO₂ (eCO₂) can enhance photosynthesis and increase plant productivity, including biomass, although there are inconsistencies regarding the effects of eCO₂ on the plant growth response. The compounding effects of ambient environmental conditions such as light intensity, photoperiod, water availability, and soil nutrient composition can affect the extent to which eCO₂ enhances plant productivity. This study aimed to investigate the growth response of Arabidopsis thaliana to eCO₂ (800 ppm) under short photoperiod (8/16 h, light/dark cycle). Here, we report an attenuated fertilization effect of eCO₂ on the shoot biomass of Arabidopsis plants grown under short photoperiod. The biomass of two-, three-, and four-week-old Arabidopsis plants was increased by 10%, 15%, and 28%, respectively, under eCO₂ compared to the ambient CO₂ (aCO₂, 400 ppm) i.e. control. However, the number of rosette leaves, rosette area, and shoot biomass were similar in mature plants under both CO₂ conditions, despite 40% higher photosynthesis in eCO₂ exposed plants. The levels of chlorophylls and carotenoids were similar in the fully expanded rosette leaves regardless of the level of CO₂. In conclusion, CO₂ enrichment moderately increased Arabidopsis shoot biomass at the juvenile stage, whereas the eCO₂-induced increment in shoot biomass was not apparent in mature plants. A shorter day-length can limit the source-to-sink resource allocation in a plant in age-dependent manner, hence diminishing the eCO₂ fertilization effect on the shoot biomass in Arabidopsis plants grown under short photoperiod.     

Phosphorus application and elevated CO2 enhance drought tolerance in field pea grown in a phosphorus-deficient vertisol

Background and Aims Benefits to crop productivity arising from increasing CO₂ fertilization may be offset by detrimental effects of global climate change, such as an increasing frequency of drought. Phosphorus (P) nutrition plays an important role in crop responses to water stress, but how elevated CO₂ (eCO₂) and P nutrition interact, especially in legumes, is unclear. This study aimed to elucidate whether P supply improves plant drought tolerance under eCO₂.Methods A soil-column experiment was conducted in a free air CO₂ enrichment (SoilFACE) system. Field pea (Pisum sativum) was grown in a P-deficient vertisol, supplied with 15 mg P kg⁻¹ (deficient) or 60 mg P kg⁻¹ (adequate for crop growth) and exposed to ambient CO₂ (aCO₂; 380–400 ppm) or eCO₂ (550–580 ppm). Drought treatments commenced at flowering. Measurements were taken of soil and leaf water content, photosynthesis, stomatal conductance, total soluble sugars and inorganic P content (Pi).Key Results Water-use efficiency was greatest under eCO₂ when the plants were supplied with adequate P compared with other treatments irrespective of drought treatment. Elevated CO₂ decreased stomatal conductance and transpiration rate, and increased the concentration of soluble sugars and relative water contents in leaves. Adequate P supply increased concentrations of soluble sugars and Pi in drought-stressed plants. Adequate P supply but not eCO₂ increased root length distribution in deeper soil layers.Conclusions Phosphorus application and eCO₂ interactively enhanced periodic drought tolerance in field pea as a result of decreased stomatal conductance, deeper rooting and high Pi availability for carbon assimilation in leaves.     

Elevated CO2 temporally enhances phosphorus immobilization in the rhizosphere of wheat and chickpea

Aims

The efficient management of phosphorus (P) in cropping systems remains a challenge due to climate change. We tested how plant species access P pools in soils of varying P status (Olsen-P 3.2–17.6 mg?kg^?1), under elevated atmosphere CO₂ (eCO₂).

Methods

Chickpea (Cicer arietinum L.) and wheat (Triticum aestivum L.) plants were grown in rhizo-boxes containing Vertosol or Calcarosol soil, with two contrasting P fertilizer histories for each soil, and exposed to ambient (380 ppm) or eCO₂ (700 ppm) for 6 weeks.

Results

The NaHCO₃-extractable inorganic P (Pi) in the rhizosphere was depleted by both wheat and chickpea in all soils, but was not significantly affected by CO₂ treatment. However, NaHCO₃-extractable organic P (Po) accumulated, especially under eCO₂ in soils with high P status. The NaOH-extractable Po under eCO₂ accumulated only in the Vertosol with high P status. Crop species did not exhibit different eCO₂-triggered capabilities to access any P pool in either soil, though wheat depleted NaHCO₃-Pi and NaOH-Pi in the rhizosphere more than chickpea. Elevated CO₂ increased microbial biomass C in the rhizosphere by an average of 21 %. Moreover, the size in Po fractions correlated with microbial C but not with rhizosphere pH or phosphatase activity.

Conclusion

Elevated CO₂ increased microbial biomass in the rhizosphere which in turn temporally immobilized P. This P immobilization was greater in soils with high than low P availability.     

Plant productivity is a key driver of soil respiration response to climate change in a nutrient-limited soil.

Despite knowledge of the interaction between climate change factors significant uncertainty exists concerning the individual and interactive effects of elevated carbon dioxide (eCO₂) and elevated temperature (eT) on the soil microbiome and function. Here we examine the individual and interactive effects of eCO₂ and eT on tree growth, soil respiration (R_soil), biomass, structural and functional composition of microbial community, nitrogen (N) mineralisation and N availability in a whole tree chamber experiment. Eucalyptus globulus plants were grown from seedling to ca. 10 m tall for 15 months in a nutrient-poor sandy soil under ambient and elevated (+ 240 ppm) atmospheric CO₂ concentrations combined with ambient or elevated temperatures (+ 3 °C) in a full factorial design. Plant growth was strongly stimulated under eCO₂, but eT had little impact on any measured plant property. In contrast, R_soil was not consistently affected by eCO₂ or eT, but correlated strongly with root and leaf biomass. The response of N-mineralisation and nutrient availability to eCO₂ and eT varied across time, and available N correlated strongly with plant height. Further, the C:N ratio of the microbial biomass and leaves were both higher under eCeT treatment. However, these functional measures were not significantly linked to either structural or functional diversity of the soil microbiome. Taken together, these results suggest that in this low-nutrient soil, belowground processes are principally driven by aboveground productivity. Our work provides novel insight into mechanisms underlying above- and belowground response to climate change, and the potential to sequester C in a low-nutrient status soil under future climatic conditions may be limited .     

Root Damage by Insects Reverses the Effects of Elevated Atmospheric CO2 on Eucalypt Seedlings

Predicted increases in atmospheric carbon dioxide (CO₂) are widely anticipated to increase biomass accumulation by accelerating rates of photosynthesis in many plant taxa. Little, however, is known about how soil-borne plant antagonists might modify the effects of elevated CO₂ (eCO₂), with root-feeding insects being particularly understudied. Root damage by insects often reduces rates of photosynthesis by disrupting root function and imposing water deficits. These insects therefore have considerable potential for modifying plant responses to eCO₂. We investigated how root damage by a soil-dwelling insect (Xylotrupes gideon australicus) modified the responses of Eucalyptus globulus to eCO₂. eCO₂ increased plant height when E. globulus were 14 weeks old and continued to do so at an accelerated rate compared to those grown at ambient CO₂ (aCO₂). Plants exposed to root-damaging insects showed a rapid decline in growth rates thereafter. In eCO₂, shoot and root biomass increased by 46 and 35%, respectively, in insect-free plants but these effects were arrested when soil-dwelling insects were present so that plants were the same size as those grown at aCO₂. Specific leaf mass increased by 29% under eCO₂, but at eCO₂ root damage caused it to decline by 16%, similar to values seen in plants at aCO₂ without root damage. Leaf C:N ratio increased by >30% at eCO₂ as a consequence of declining leaf N concentrations, but this change was also moderated by soil insects. Soil insects also reduced leaf water content by 9% at eCO₂, which potentially arose through impaired water uptake by the roots. We hypothesise that this may have impaired photosynthetic activity to the extent that observed plant responses to eCO₂ no longer occurred. In conclusion, soil-dwelling insects could modify plant responses to eCO₂ predicted by climate change plant growth models.     

Indirect effect of elevated CO2 concentration on Bemisia tabaci MEAM1 feeding on Bt soybean plants

The development of herbivore insects is influenced by the quality of their host plants. Elevated CO₂ alters plant metabolism, which may change the nutritional quality of the plant, modifying the life history and feeding behaviour of herbivore insects. Understanding how insect pests respond to increasing CO₂ concentration is essential for predicting the impact of the pest on food security. In this study, we investigated the effects of elevated CO₂ (eCO₂) on the life history and feeding behaviour of the MEAM1 species of Bemisia tabaci on a Bt soybean cultivar. We found that eCO₂ increased the egg to adult development time and reduced the reproductive responses (fecundity and fertility) of B. tabaci. The whitefly B. tabaci that fed on the soybean plants grown under eCO₂ conditions was negatively influenced by several traits related to the host plant resistance, such as the time spent on phloem sap ingestion. Furthermore, we evaluated the changes in the C:N concentration and plant morphology of the Bt plants. The biomass (weight of leaves and stems) of the Bt soybean plants grown under eCO₂ conditions was significantly increased, and the elevated C:N ratio in the phenological stage V6 (i.e. when the plants had six trifoliate leaves developed) was the most pronounced difference in the Bt soybean plants subjected to eCO₂ treatment. Taken together, our results indicate that Bt plants cultivated under eCO₂ inhibit B. tabaci feeding, which can reduce whitefly infestations of the soybean fields.     

Elevated carbon dioxide increases soil nitrogen and phosphorus availability in a phosphorus‐limited Eucalyptus woodland

Free‐air CO₂ enrichment (FACE) experiments have demonstrated increased plant productivity in response to elevated (e)CO₂, with the magnitude of responses related to soil nutrient status. Whilst understanding nutrient constraints on productivity responses to eCO₂ is crucial for predicting carbon uptake and storage, very little is known about how eCO₂ affects nutrient cycling in phosphorus (P)‐limited ecosystems. Our study investigates eCO₂ effects on soil N and P dynamics at the EucFACE experiment in Western Sydney over an 18‐month period. Three ambient and three eCO₂ (+150 ppm) FACE rings were installed in a P‐limited, mature Cumberland Plain Eucalyptus woodland. Levels of plant accessible nutrients, evaluated using ion exchange resins, were increased under eCO₂, compared to ambient, for nitrate (+93%), ammonium (+12%) and phosphate (+54%). There was a strong seasonality to responses, particularly for phosphate, resulting in a relatively greater stimulation in available P, compared to N, under eCO₂ in spring and summer. eCO₂ was also associated with faster nutrient turnover rates in the first six months of the experiment, with higher N (+175%) and P (+211%) mineralization rates compared to ambient rings, although this difference did not persist. Seasonally dependant effects of eCO₂ were seen for concentrations of dissolved organic carbon in soil solution (+31%), and there was also a reduction in bulk soil pH (‐0.18 units) observed under eCO₂. These results demonstrate that CO₂ fertilization increases nutrient availability – particularly for phosphate – in P‐limited soils, likely via increased plant belowground investment in labile carbon and associated enhancement of microbial turnover of organic matter and mobilization of chemically bound P. Early evidence suggests that there is the potential for the observed increases in P availability to support increased ecosystem C‐accumulation under future predicted CO₂ concentrations.     

Nitrogen input mediates the effect of free-air CO2 enrichment on mycorrhizal fungal abundance

Plots containing Lolium perenne L., Trifolium repens L. or a mixture of both plant species were exposed to elevated atmospheric CO₂ (eCO₂) for 10 consecutive seasons using free‐air CO₂ enrichment technology at ETH Zürich, Switzerland. The CO₂ treatment was crossed with a two‐level nitrogen (N) fertilization treatment. In the tenth year, soil samples were collected on three occasions through the growing season to assess the impact of eCO₂ and N fertilization on mycorrhizal fungal abundance. Soil moisture content, which varied with harvest date, was linked to the vegetation type and was higher under eCO₂. Root weight density was affected by vegetation type: lower for clover, higher for grass. Root weight density was stimulated by eCO₂ and decreased by high N fertilization. The percent root length colonized by mycorrhizal fungi was lowest in the clover plots and highest in the grass plots. High N significantly decreased root length colonized. There was no overall effect of eCO₂ on root length colonized; however, there was a significant eCO₂× N interaction: eCO₂ increased root length colonized at high N, but decreased root length colonized at low N. Extraradical mycorrhizal hyphal density was linked to soil moisture content. Extraradical mycorrhizal hyphal density was not affected by eCO₂ or high N individually, but as for root length colonized, there was a significant eCO₂× N interaction: eCO₂ increased extraradical mycorrhizal hyphal density at low N but not at high N. These environmental effects on root colonization and external mycorrhizal hyphae were independent of soil moisture content and root weight density. This field study demonstrated a significant mediating effect of N fertilization on the response of arbuscular mycorrhizal fungi to eCO₂ irrespective of any change in root biomass.     

Elevated carbon dioxide concentrations indirectly affect plant fitness by altering plant tolerance to herbivory

Global environmental changes, such as rising atmospheric CO₂ concentrations, have a wide range of direct effects on plant physiology, growth, and fecundity. These environmental changes also can affect plants indirectly by altering interactions with other species. Therefore, the effects of global changes on a particular species may depend on the presence and abundance of other community members. We experimentally manipulated atmospheric CO₂ concentration and amounts of herbivore damage (natural insect folivory and clipping to simulate browsing) to examine: (1) how herbivores mediate the effects of elevated CO₂ (eCO₂) on the growth and fitness of Arabidopsis thaliana; and (2) how predicted changes in CO₂ concentration affect plant resistance to herbivores, which influences the amount of damage plants receive, and plant tolerance of herbivory, or the fitness consequences of damage. We found no evidence that CO₂ altered resistance, but plants grown in eCO₂ were less tolerant of herbivory—clipping reduced aboveground biomass and fruit production by 13 and 22%, respectively, when plants were reared under eCO₂, but plants fully compensated for clipping in ambient CO₂ (aCO₂) environments. Costs of tolerance in the form of reduced fitness of undamaged plants were detected in eCO₂ but not aCO₂ environments. Increased costs could reduce selection on tolerance in eCO₂ environments, potentially resulting in even larger fitness effects of clipping in predicted future eCO₂ conditions. Thus, environmental perturbations can indirectly affect both the ecology and evolution of plant populations by altering both the intensity of species interactions as well as the fitness consequences of those interactions.     

Elevated CO2 Modifies N Acquisition of Medicago truncatula by Enhancing N Fixation and Reducing Nitrate Uptake from Soil

The effects of elevated CO₂ (750 ppm vs. 390 ppm) were evaluated on nitrogen (N) acquisition and assimilation by three Medicago truncatula genotypes, including two N-fixing-deficient mutants (dnf1-1 and dnf1-2) and their wild-type (Jemalong). The proportion of N acquisition from atmosphere and soil were quantified by ¹⁵N stable isotope, and N transportation and assimilation-related genes and enzymes were determined by qPCR and biochemical analysis. Elevated CO₂ decreased nitrate uptake from soil in all three plant genotypes by down-regulating nitrate reductase (NR), nitrate transporter NRT1.1 and NR activity. Jemalong plant, however, produced more nodules, up-regulated N-fixation-related genes and enhanced percentage of N derived from fixation (%Ndf) to increase foliar N concentration and N content in whole plant (Ntotal Yield) to satisfy the requirement of larger biomass under elevated CO₂. In contrast, both dnf1 mutants deficient in N fixation consequently decreased activity of glutamine synthetase/glutamate synthase (GS/GOGAT) and N concentration under elevated CO₂. Our results suggest that elevated CO₂ is likely to modify N acquisition of M. truncatula by simultaneously increasing N fixation and reducing nitrate uptake from soil. We propose that elevated CO₂ causes legumes to rely more on N fixation than on N uptake from soil to satisfy N requirements.     

A Microbial Link between Elevated CO2 and Methane Emissions that is Plant Species-Specific

Rising atmospheric CO₂ levels alter the physiology of many plant species, but little is known of changes to root dynamics that may impact soil microbial mediation of greenhouse gas emissions from wetlands. We grew co-occurring wetland plant species that included an invasive reed canary grass (Phalaris arundinacea L.) and a native woolgrass (Scirpus cyperinus L.) in a controlled greenhouse facility under ambient (380 ppm) and elevated atmospheric CO₂ (700 ppm). We hypothesized that elevated atmospheric CO₂ would increase the abundance of both archaeal methanogen and bacterial methanotroph populations through stimulation of plant root and shoot biomass. We found that methane levels emitted from S. cyperinus shoots increased 1.5-fold under elevated CO₂, while no changes in methane levels were detected from P. arundincea. The increase in methane emissions was not explained by enhanced root or shoot growth of S. cyperinus. Principal components analysis of the total phospholipid fatty acid (PLFA) recovered from microbial cell membranes revealed that elevated CO₂ levels shifted the composition of the microbial community under S. cyperinus, while no changes were detected under P. arundinacea. More detailed analysis of microbial abundance showed no impact of elevated CO₂ on a fatty acid indicative of methanotrophic bacteria (18:2ω6c), and no changes were detected in the terminal restriction fragment length polymorphism (T-RFLP) relative abundance profiles of acetate-utilizing archaeal methanogens. Plant carbon depleted in ¹³C was traced into the PLFAs of soil microorganisms as a measure of the plant contribution to microbial PLFA. The relative contribution of plant-derived carbon to PLFA carbon was larger in S. cyperinus compared with P. arundinacea in four PLFAs (i14:0, i15:0, a15:0, and 18:1ω9t). The δ¹³C isotopic values indicate that the contribution of plant-derived carbon to microbial lipids could differ in rhizospheres of CO₂-responsive plant species, such as S. cyperinus in this study. The results from this study show that the CO₂–methane link found in S. cyperinus can occur without a corresponding change in methanogen and methanotroph relative abundances, but PLFA analysis indicated shifts in the community profile of bacteria and fungi that were unique to rhizospheres under elevated CO₂.     

Seasonal changes and vertical distribution of root standing biomass of graminoids and shrubs at a Siberian tundra site

Background &; aims

Elevated atmospheric CO₂ (eCO₂) can affect soil-plant systems via stimulating plant growth, rhizosphere activity and the decomposition of added (crop residues) or existing (priming) soil organic carbon (C). Increases in C inputs via root exudation, rhizodeposition and root turnover are likely to alter the decomposition of crop residues but will ultimately depend on the N content of the residues and the soil.

Methods

Two soil column experiments were conducted under ambient CO₂ (aCO₂, 390 ppm) and eCO₂ (700 ppm) in a glasshouse using dual-labelled (¹³C/¹⁵N) residues of wheat (Triticum aestivum cv. Yitpi) and field pea (Pisum sativum L. cv. PBA Twilight). The effects of eCO₂ and soil N status on wheat rhizosphere activity and residue decomposition and also N recovery from crop residues with different N status (C/N ratio 19.4–115.4) by different plant treatments (wheat, wheat + 25 mg N kg^?1 and field pea).

Results

Total belowground CO₂ efflux was enhanced under eCO₂ despite no increases in root biomass. Plants decreased residue decomposition, indicating a negative rhizosphere effect. For wheat, eCO₂ reduced the negative rhizosphere effect, resulting in greater rates of decomposition and recovery of N from field pea residues, but only when N fertiliser was added. For field pea, eCO₂ enhanced the negative rhizosphere effect resulting in lower decomposition rates and N recovery from field pea residue.

Conclusions

The effect of eCO₂ on N utilisation varied with the type of residue, enhancing N utilisation of wheat but repressing that of field pea residues, which in turn could alter the amount of N supplied to subsequent crops. Furthermore, reduced decomposition of residues under eCO₂ may slow the formation of new soil C and have implications for long-term soil fertility.

     

Plant phenolics mediated bottom-up effects of elevated CO2 on Acyrthosiphon pisum and its parasitoid Aphidius avenae

Elevated concentrations of atmospheric CO2 can alter plant secondary metabolites,which play important roles in the interactions among plants,herbivorous insects and natural enemies.However,few studies have examined the cascading effects of host plant secondary metabolites on tri-trophic interactions under elevated CO2(eCO2).In this study,we determined the effects of eCO2 on the growth and foliar phenolics of Medicago truncatula and the cascading effects on two color genotypes oiAcyrthosiphon pisum(pink vs.green)and their parasitoid Aphidius avenae in the field open-top chambers.Our results showed that eCO2 increased photosynthetic rate,nodule number,yield and the total phenolic content of M.truncatula.eCO2 had contrasting effects on two genotypes of A.pisum;the green genotype demonstrated increased population abundance,fecundity,growth and feeding efficiency,while the pink genotype showed decreased fitness and these were closely associated with the foliar genstein content.Furthermore,eCO2 decreased the parasitic rate of A.avenae independent of aphid genotypes.eCO2 prolonged the emergence time and reduced the emergence rate and percentage of females when associated with the green genotype,but little difference,except for increased percentage of females,was observed in A.avenae under eCO2 when associated with the pink genotype,indicating that parasitoids can perceive and discriminate the qualities of aphid hosts.We concluded that eCO2 altered plant phenolics and thus the performance of aphids and parasitoids.Our results indicate that plant phenolics vary by different abiotic and biotic stimuli and could potentially deliver the cascading effects of eCO2 to the higher trophic levels.Our results also suggest that the green genotype is expected to perform better in future eCO2 because of decreased plant resistance after its infestation and decreased parasitic rate.     

Aphid and host‐plant genotype × genotype interactions under elevated CO2

1. Elevated CO₂ can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO₂ and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype‐specific responses to elevated CO₂. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype‐specific effects and possible host plant‐by‐insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO₂ (ambient, 700, and 1000 ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700 ppm CO₂ concentration, but increased in the 1000 ppm concentration relative to ambient. The effect of CO₂ on aphid density was dependent on host plant genotype; the density of aphids in high CO₂ decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO₂ was found, nor did we find significant genotype‐by‐genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO₂ for some plant genotypes. The likely impact of genotype‐specific responses on future changes in the genetic structure of plant and insect populations is discussed.     

Nitrogen application is required to realize wheat yield stimulation by elevated CO2 but will not remove the CO2‐induced reduction in grain protein concentration

Elevated CO₂ (eCO₂) generally promotes increased grain yield (GY) and decreased grain protein concentration (GPC), but the extent to which these effects depend on the magnitude of fertilization remains unclear. We collected data on the eCO₂ responses of GY, GPC and grain protein yield and their relationships with nitrogen (N) application rates across experimental data covering 11 field grown wheat (Triticum aestivum) cultivars studied in eight countries on four continents. The eCO₂‐induced stimulation of GY increased with N application rates up to ~200 kg/ha. At higher N application, stimulation of GY by eCO₂ stagnated or even declined. This was valid both when the yield stimulation was expressed as the total effect and using per ppm CO₂ scaling. GPC was decreased by on average 7% under eCO₂ and the magnitude of this effect did not depend on N application rate. The net effect of responses on GY and protein concentration was that eCO₂ typically increased and decreased grain protein yield at N application rates below and above ~100 kg/ha respectively. We conclude that a negative effect on wheat GPC seems inevitable under eCO₂ and that substantial N application rates may be required to sustain wheat protein yields in a world with rising CO₂.     

Nitric oxide enhances development of lateral roots in tomato (Solanum lycopersicum L.) under elevated carbon dioxide

Elevated carbon dioxide (CO₂) has been shown to enhance the growth and development of plants, especially of roots. Amongst them, lateral roots play an important role in nutrient uptake, and thus alleviate the nutrient limitation to plant growth under elevated CO₂. This paper examined the mechanism underlying CO₂ elevation-induced lateral root formation in tomato. The endogenous nitric oxide (NO) in roots was detected by the specific probe 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate (DAF-FM DA). We suggest that CO₂ elevation-induced NO accumulation was important for lateral root formation. Elevated CO₂ significantly increased the activity of nitric oxide synthase in roots, but not nitrate reductase activity. Moreover, the pharmacological evidence showed that nitric oxide synthase rather than nitrate reductase was responsible for CO₂ elevation-induced NO accumulation. Elevated CO₂ enhanced the activity of nitric oxide synthase and promoted production of NO, which was involved in lateral root formation in tomato under elevated CO₂.     

Fungal Communities Respond to Long-Term CO2 Elevation by Community Reassembly

Fungal communities play a major role as decomposers in the Earth''s ecosystems. Their community-level responses to elevated CO₂ (eCO₂), one of the major global change factors impacting ecosystems, are not well understood. Using 28S rRNA gene amplicon sequencing and co-occurrence ecological network approaches, we analyzed the response of soil fungal communities in the BioCON (biodiversity, CO₂, and N deposition) experimental site in Minnesota, USA, in which a grassland ecosystem has been exposed to eCO₂ for 12 years. Long-term eCO₂ did not significantly change the overall fungal community structure and species richness, but significantly increased community evenness and diversity. The relative abundances of 119 operational taxonomic units (OTU; ∼27% of the total captured sequences) were changed significantly. Significantly changed OTU under eCO₂ were associated with decreased overall relative abundance of Ascomycota, but increased relative abundance of Basidiomycota. Co-occurrence ecological network analysis indicated that eCO₂ increased fungal community network complexity, as evidenced by higher intermodular and intramodular connectivity and shorter geodesic distance. In contrast, decreased connections for dominant fungal species were observed in the eCO₂ network. Community reassembly of unrelated fungal species into highly connected dense modules was observed. Such changes in the co-occurrence network topology were significantly associated with altered soil and plant properties under eCO₂, especially with increased plant biomass and NH₄⁺ availability. This study provided novel insights into how eCO₂ shapes soil fungal communities in grassland ecosystems.