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Effects of rising atmospheric concentrations of carbon dioxide on plants

By: Daniel R. Taub (
Biology Department, Southwestern University
) © 2010 Nature Education
Effects of Rising Atmospheric Concentrations of Carbon
Dioxide on Plants
Photosynthetic assimilation of CO2 is central to the metabolism of plants. As
atmospheric concentrations of CO2 rise, how will this affect the plants we
depend on?
Atmospheric concentrations of carbon dioxide have been steadily rising, from
approximately 315 ppm (parts per million) in 1959 to a current atmospheric average of
approximately 385 ppm (Keeling
et al.
,2009). Current projections are for concentrations to
continue to rise to as much as 500–1000 ppm by the year 2100 (IPCC 2007).
While a great deal of media and public attention has focused on the effects that such higher
concentrations of CO2 are likely to have on global climate, rising CO2 concentrations are
also likely to have profound direct effects on the growth, physiology, and chemistry of
plants, independent of any effects on climate (Ziska 2008). These effects result from the
central importance of CO 2 to plant metabolism. As photosynthetic organisms, plants take
up atmospheric CO2, chemically reducing the carbon. This represents not only an
acquisition of stored chemical energy for the plant, but also provides the carbon skeletons
for the organic molecules that make up a plants’ structure. Overall, the carbon, hydrogen
and oxygen assimilated into organic molecules by photosynthesis make up ~96% of the
total dry mass of a typical plant (Marschner 1995). Photosynthesis is therefore at the heart
of the nutritional metabolism of plants, and increasing the availability of CO2 for
photosynthesis can have profound effects on plant growth and many aspects of plant
Our knowledge of plant responses to future CO2 concentrations rests on the results of
experiments that have experimentally increased CO2 and then compared the performance
of the experimental plants with those grown under current ambient CO 2 conditions. Such
experiments have been performed in a wide variety of settings, including greenhouses and
chambers of a variety of sizes and designs. However plants grown in chambers may not
experience the effects of increasing CO2 the same way as plants growing in more natural
Citation: Taub, D. (2010) Effects of Rising Atmospheric Concentrations of
Carbon Dioxide on Plants.
Nature Education Knowledge
experience the effects of increasing CO2 the same way as plants growing in more natural
settings. For this reason, techniques of Free-Air Carbon dioxide Enrichment (FACE) have
been developed that allow natural or agricultural ecosystems to be fumigated with elevated
concentrations of CO2 in the field without use of chambers (Figure 1). As these experiments
are the most naturalistic, they should provide the best indication of the responses of plants
to increased CO2 under the real-world conditions of the future. This article therefore
focuses on data from FACE experiments wherever these are available. Whenever possible, to
ensure the generality of conclusions, reference is made to analyses that have incorporated
data from multiple experiments independently conducted at various research facilities.
Figure 1: Free - air carbon dioxide enrichment allows experiments with controlled atmospheric
concentrations of carbon dioxide to be conducted in the field and avoids potential
experimental artifacts from growing plants in enclosed chambers.
Courtesy of David F. Karnosky.
One of the most consistent effects of elevated atmospheric CO2 on plants is an increase in
the rate of photosynthetic carbon fixation by leaves. Across a range of FACE experiments,
with a variety of plant species, growth of plants at elevated CO2 concentrations of 475–600
ppm increases leaf photosynthetic rates by an average of 40% (Ainsworth & Rogers 2007).
Carbon dioxide concentrations are also important in regulating the openness of stomata,
pores through which plants exchange gasses, with the external environment. Open stomata
allow CO2 to diffuse into leaves for photosynthesis, but also provide a pathway for water to
diffuse out of leaves. Plants therefore regulate the degree of stomatal opening (related to a
measure known as stomatal conductance) as a compromise between the goals of
maintaining high rates of photosynthesis and low rates of water loss. As CO2
concentrations increase, plants can maintain high photosynthetic rates with relatively low
stomatal conductance. Across a variety of FACE experiments, growth under elevated CO2
decreases stomatal conductance of water by an average of 22% (Ainsworth & Rogers 2007).
This would be expected to decrease overall plant water use, although the magnitude of the
overall effect of CO2 will depend on how it affects other determinants of plant water use,
such as plant size, morphology, and leaf temperature. Overall, FACE experiments show
decreases in whole plant water use of 5–20% under elevated CO2. This in turn can have
consequences for the hydrological cycle of entire ecosystems, with soil moisture levels and
runoff both increasing under elevated CO2 (Leakey
et al.
Since photosynthesis and stomatal behavior are central to plant carbon and water
metabolism, growth of plants under elevated CO2 leads to a large variety of secondary
effects on plant physiology. The availability of additional photosynthate enables most plants
to grow faster under elevated CO2, with dry matter production in FACE experiments being
increased on average by 17% for the aboveground, and more than 30% for the belowground,
portions of plants (Ainsworth & Long 2005; de Graaff
et al.
2006). This increased growth is
also reflected in the harvestable yield of crops, with wheat, rice and soybean all showing
increases in yield of 12–14% under elevated CO2 in FACE experiments (Ainsworth 2008;
et al.
Elevated CO 2 also leads to changes in the chemical composition of plant tissues. Due to
increased photosynthetic activity, leaf nonstructural carbohydrates (sugars and starches) per
unit leaf area increase on average by 30–40% under FACE elevated CO2 (Ainsworth 2008;
Ainsworth & Long 2005). Leaf nitrogen concentrations in plant tissues typically decrease in
FACE under elevated CO2, with nitrogen per unit leaf mass decreasing on average by 13%
(Ainsworth & Long 2005). This decrease in tissue nitrogen is likely due to several factors:
dilution of nitrogen from increased carbohydrate concentrations; decreased uptake of
minerals from the soil, as stomatal conductance decreases and plants take up less water
(Taub & Wang 2008); and decreases in the rate of assimilation of nitrate into organic
compounds (Bloom
et al.
Protein concentrations in plant tissues are closely tied to plant nitrogen status. Changes in
plant tissue nitrogen are therefore likely to have important effects on species at higher
trophic levels. Performance is typically diminished for insect herbivores feeding on plants
grown in elevated CO 2 (Zvereva & Kozlov 2006). This can lead to increased consumption of
plant tissues as herbivores compensate for decreased food quality (Stiling and Cornelissen
2007). Effects on human nutrition are likely as well. In FACE experiments, protein
concentrations in grains of wheat, rice and barley, and in potato tubers, are decreased by
5–14% under elevated CO2 (Taub
et al.
2008). Crop concentrations of nutritionally important
minerals including calcium, magnesium and phosphorus may also be decreased under
elevated CO2 (Loladze 2002; Taub & Wang 2008).
Effects of Other Environmental Factors on Plant Response to Elevated
The effects of elevated CO2 on plants can vary depending on other environmental factors.
While elevated CO2 makes carbon more available, plants also require other resources
including minerals obtained from the soil. Elevated CO2 does not directly make these
mineral elements more available and, as noted above, may even decrease the uptake of
some elements. The ability of plants to respond to elevated CO 2 with increased
some elements. The ability of plants to respond to elevated CO 2 with increased
photosynthesis and growth may therefore be limited under conditions of low mineral
availability. This effect has been best documented for nitrogen. In FACE experiments, there
is less enhancement of photosynthesis by elevated CO2 under low than high soil N
conditions (Ainsworth & Long 2005; Ainsworth & Rogers 2007). Crop yield in FACE also
appears to be enhanced by elevated CO2 to a lesser extent under low-N than under high-N
(Ainsworth & Long 2005; Ainsworth 2008; Long
et al.
2006). Across studies using all types
of CO2 fumigation technologies, there is a lower enhancement of biomass production by
elevated CO2 under low-nutrient conditions (Poorter & Navas 2003). Crops grown with low
amounts of N fertilization also show a greater decrease in protein concentrations under
elevated CO2 than crops grown with higher N fertilization (Taub
et al.
Another environmental factor that interacts with elevated CO2 is atmospheric ozone (O3), a
gaseous toxin. Ground-level O3 concentrations have been increasing worldwide (and are
expected to continue to increase) due to increased emissions of pollutants that react to
produce O3 (Vingarzan 2004). High atmospheric concentrations of ozone can cause damage
to leaves and decreased plant growth and photosynthesis (Feng
et al.
2008; Morgan
et al.
2003). The primary location of O3 injury to plants is the internal tissues of leaves.
Decreased openness of stomata under elevated CO2 can therefore decrease exposure of
sensitive tissues to ozone. Elevated CO2 substantially decreases the negative effects of high
ozone on photosynthesis, growth, and seed yield in both soybeans and rice (Feng
et al.
2008; Morgan
et al.
2003). Across experiments with all plant species, the enhancement of
growth by elevated CO2 is much greater under conditions of ozone stress than otherwise
(Poorter & Navas 2003).
Differences among Plant Functional Types in Response to Rlevated
The preceding discussion has presented the average effects of elevated CO2, but obscures
important patterns of difference in response among plant species. One of the most
important determinants of species differences in response to elevated CO2 is photosynthetic
type. Most plant species (~90%) utilize a photosynthetic process known as C3
photosynthesis. Other species use either of two physiologically distinct processes known as
C4 and CAM photosynthesis (Figure 2). C4 plants include most tropical and sub-tropical
grasses and several important crops, including maize (corn), sugar cane, sorghum, and the
millets. There has therefore been considerably more research on the responses to elevated
CO2 in C4 than in CAM plants.
Figure 2: Each plant species utilizes one of several distinct physiological variants of
photosynthesis mechanisms, including the variants known as C3 and C4
C4 plants use a biochemical pump to concentrate CO2 at the locations within the leaf where
the RUBISCO enzyme mediates incorporation of CO2 by the Calvin-Benson photosynthetic
cycle. Since CO2 concentrations are already high within the bundle sheath cells, increasing
atmospheric CO2 concentrations above current levels has little direct effect on
photosynthetic rates for C4 species. C4 species do respond to elevated CO2 by decreasing
stomatal conductance; this may lead to some indirect enhancement of photosynthesis by
helping avoid water stress under drought conditions (Leakey 2009). In FACE experiments,
stimulation of photosynthesis by elevated CO2 in C4 plants is only about one-third of that
experienced by C3 species. C4 plants also show little or no enhancement of growth (dry
matter production) in these studies (Ainsworth & Long 2005). The very limited data
available also shows no increase in C4 crop yield in FACE studies (Long
et al.
2006). While
there is little FACE data available on effects of elevated CO2 on plant nitrogen and protein
concentrations, data from chamber experiments shows C4 plants to be much less
responsive than C3 plants in this regard (Cotrufo
et al.
1998). The picture that emerges is
that C4 plants are in general relatively unresponsive to elevation of atmospheric CO2 above
current ambient levels.
In contrast to C4 species, another group of plants, legumes (members of the botanical
family Fabaceae) may be especially capable of responding to elevated CO2 with increased
photosynthesis and growth (Rogers
et al.
2009). For most plants, growth under elevated
CO2 can alter the internal balance between carbon (obtained in extra quantities through
enhanced photosynthesis) and nitrogen (either unaffected or taken up in decreased
amounts due to decreased uptake of water). In contrast, most legume species participate in
close mutualistic relationships with bacteria that live in nodules formed on the plant’s roots.
These bacteria are able to "fix" atmospheric nitrogen, chemically reducing it to a form that
can be taken up and used by plants. Under elevated CO2 conditions, legumes may be able
to shunt excess carbon to root nodules where it can serve as a carbon and energy source
for the bacterial symbionts. In effect, legumes may be able to exchange the excess carbon
for nitrogen and thereby maximize the benefits of elevated atmospheric CO2. Many studies
in controlled environments have shown that, compared to other plant species, legumes
show greater enhancement of photosynthesis and growth by elevated CO 2 (Rogers
et al.
2009). Decreases in tissue nitrogen concentrations under elevated CO2 are also smaller for
legumes than for other C3 species (Cotrufo
et al.
1988; Jablonski
et al.
2002; Taub
et al.
2008). In FACE experiments, soybeans (a legume) show a greater response to elevated CO2
than wheat and rice in photosynthesis and overall growth, although not in harvestable yield
et al.
Plant Community Interactions under Elevated CO2
A number of experiments have found that some plant species that respond positively to
elevated CO2 when grown alone experience decreased growth under elevated CO2 when
grown in mixed plant communities (Poorter & Navas 2003). This effect likely results
because the direct positive effects of elevated CO2 are outweighed by negative effects due
to stimulation of the growth of competitors. Rising atmospheric concentrations of CO 2 may
therefore lead to changes in the composition of plant communities, as some species reap
more of an advantage from the increased CO2 than do others. In mixed-species
experiments under high fertility conditions, C4 plants decrease as a proportion of the
biomass of plant communities under elevated CO2. Similarly, under low fertility conditions,
legumes increase as a proportion of the biomass of plant communities under elevated CO 2
(Poorter & Navas 2003).
Current evidence suggests that that the concentrations of atmospheric CO 2 predicted for
the year 2100 will have major implications for plant physiology and growth. Under elevated
CO2 most plant species show higher rates of photosynthesis, increased growth, decreased
water use and lowered tissue concentrations of nitrogen and protein. Rising CO2 over the
next century is likely to affect both agricultural production and food quality. The effects of
elevated CO2 are not uniform; some species, particularly those that utilize the C4 variant of
photosynthesis, show less of a response to elevated CO2 than do other types of plants.
Rising CO2 is therefore likely to have complex effects on the growth and composition of
natural plant communities.
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Outline | Keywords
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... Even though there might be contrasting relationships between eCO 2 and plant structure alterations, changes in plant traits are inevitable due to the competition in natural plant communities [5,54]. For example, an increased rate of photosynthesis under eCO 2 results in increased growth in most plant species [55]. However, this positive response may only persist when a plant grows alone because competition due to increased growth might outweigh the positive effects when grown in a community [55,56]. ...
... For example, an increased rate of photosynthesis under eCO 2 results in increased growth in most plant species [55]. However, this positive response may only persist when a plant grows alone because competition due to increased growth might outweigh the positive effects when grown in a community [55,56]. Competition is more affected by structural characteristics than photosynthetic capacity [53]. ...
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Unique plant functional traits (morpho-physio-anatomical) may respond to novel environmental conditions to counterbalance elevated carbon dioxide (eCO2) concentrations. Utilizing CO2, plants produce photoassimilates (carbohydrates). A mechanistic understanding of partitioning and translocation of carbon/photoassimilates into different plant parts and soils under ambient and eCO2 is required. In this study, we examine and present the intrinsic relationship between plant functional traits and eCO2 and seek answers to (i) how do plant functional traits (morpho-physio-anatomical features) affect C storage and partitioning under ambient and eCO2 in different plant parts? (ii) How do plant functional traits influence C transfer to the soil and rhizosphere services? Our study suggests that morpho-physio-anatomical features are interlinked, and under eCO2, plant functional traits influence the quantity of C accumulation inside the plant biomass, its potential translocation to different plant parts, and to the soil. The availability of additional photoassimilates aids in increasing the above- and belowground growth of plants. Moreover, plants may retain a predisposition to build thick leaves due to reduced specific leaf area, thicker palisade tissue, and higher palisade/sponge tissue thickness. eCO2 and soil-available N can alter root anatomy, the release of metabolites, and root respiration, impacting potential carbon transfer to the soil.
... It is still unclear which physiological processes are most sensitive to waterlogging and impact growth. For example, controlled experiments have shown that elevated CO 2 increases the rate of photosynthesis and reduces water loss through transpiration due to regulation of stomatal opening (Taub, 2010). From these experiments, CSMs were improved to simulate altered photosynthetic and transpiration rates due to CO 2 . ...
... Increasing atmospheric CO 2 concentration due to climate change favors growth of C3 plants, such as wheat and barley. Elevated CO 2 increases the rate of photosynthetic carbon dioxide uptake by leaves and reduces water loss via transpiration due to the regulation of stomatal opening (Taub, 2010). However, waterlogging limits root water conductivity, causing stomatal closure and reducing CO 2 concentration within the leaves, antagonizing CO 2 effects on crops (Else et al., 2001;Jitsuyama, 2017). ...
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... Elevated CO2 concentrations, and consequently reduced photorespiration, have been shown to reduce nitrate assimilation, also threatening food quality by depleting crop protein concentrations (Bloom, 2009). Therefore, future atmospheric CO2 concentrations predicted for 2100 point to major implications for plant physiology (Taub, 2010), including higher rates of photosynthesis and therefore, increased plant growth (Dusenge et al., 2019), stomatal closure and decreased water use, but lowered tissue concentrations of nitrogen and protein (Taub & Wang, 2008). ...
... concentration of CO2 enables plants to grow faster due to increased photosynthetic activity, which seems to be the perfect situation to increase biomass of harvestable crops (Long et al., 2006;Ainsworth, 2008). Nevertheless, inhibition of photorespiration also leads to changes in the chemical composition of plants, such as an increase in sugar and starch concentrations and a decrease in nitrogen assimilation (Ainsworth, 2008;Bloom et al., 2010), which are likely to affect both agricultural production and food quality (Taub, 2010). ...
Hydrogen sulfide is a signaling molecule in plants that regulates essential biological processes through protein persulfidation. However, little is known about sulfide-mediated regulation in relation to photorespiration. Here, we performed label-free quantitative proteomic analysis and observed a high impact on protein persulfidation levels when plants grown under nonphotorespiratory conditions were transferred to air, with 98.7% of the identified proteins being more persulfidated under suppressed photorespiration. Interestingly, a higher level of ROS was detected under nonphotorespiratory conditions. Analysis of the effect of sulfide on aspects associated with non- or photorespiratory growth conditions has demonstrated that protects plants grown under suppressed photorespiration. Thus, sulfide amends the imbalance of carbon/nitrogen and restores ATP levels to concentrations like those of air-grown plants; balances the high level of ROS in plants under nonphotorespiratory conditions to reach a cellular redox state similar to that in air-grown plants; and regulates stomatal closure, to decrease the high guard cell ROS levels and induce stomatal aperture. In this way, sulfide signals the CO2 -dependent stomata movement, in the opposite direction of the established ABA-dependent movement. Our findings suggest that the high persulfidation level under suppressed photorespiration reveals an essential role of sulfide signaling under these conditions.
... With carbon and hydrogen constituting approximately 96% of the dry mass of plants [6], plants ability to assimilate more CO2 is anticipated to have profound effect on the metabolism and growth of plants [6]. Consequently, the rate of photosynthesis by plants was also found to have increased in the presence of increased CO2 [7]. While most studies have investigated the merits of excess CO2 to plant growth [8], not much has been discussed about its effect on the pH of plants. ...
... We understand that the chambered method of plant exposure to increased CO2 levels may not mimic the exposure of plants to increased CO2 in a more natural setting. Nevertheless, our result is significant and we welcome fellow scientists with the capability to use Free-Air Carbon dioxide Enrichment (FACE) technique [7] of plant exposure to increase CO2 to monitor plant pH to replicate our data. ...
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The concept of bioremediation is quickly becoming the norm in the resolution of environmental issues. The steady increase in carbon dioxide (CO2) levels, as documented by NASA [1], inspired scientists to engineer plants to absorb excess CO2 from the atmosphere. Here, we have explored the consequences of the uptake of excess CO2 by select plants. Carbon dioxide dissolves in H2O to produce H2CO3, which dissociates to yield H+ ions. We hypothesized that increased CO2 absorption results in decrease in pH of plant sap. Three plants (Byophyllum pinnatum, Romaine Lettuce and Nevada Lettuce), exposed to increased CO2 concentrations (15%), demonstrated a consistent increase in pH towards alkalinity compared to control plants. Based on the outcome being opposite of what we have hypothesized, our results suggest Byophyllum pinnatum, Romaine lettuce and Nevada lettuce, all have a unique homeostatic system to prevent over-absorption of CO2 in a CO2-rich environment.
... The increased CO2 would likely to affect agricultural production and food quality with comparatively less effect on photosynthesis in C4 plants. In general, increased CO2 results in increased growth, higher photosynthesis, lower stomatal conductance, decreased water consumption, and lowering tissue protein contents in plants (Taub, 2010;Gamage et al., 2018). In the context of cell culturing, CO2 via bicarbonate buffer plays a crucial role in pH maintenance and cellular integrity; where CO2 inhibition causes acidification of medium (Dubey et al., 2021). ...
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... Consequently, the quality of food declines and that in turn affects utilization of food. Taub (2010) documents that protein concentration in some important crops declines as CO 2 increases in the atmosphere. The concentrations of other minerals such as calcium and magnesium may also fall with increased CO 2 . ...
Frequent occurrences of extreme weather events such as droughts, floods, cyclones, and hailstorms—arguably caused by climate change—are likely to increase food insecurity across the globe, especially in developing countries. They pose formidable challenges to achieving the United Nations Development Program’s (UNDP) Sustainable Development Goal (SDG) of ending hunger and ensuring access by all to safe, nutritious, and sufficient food all year round by 2030. Using household survey data for eight states of India’s Northeast Region (NER) obtained from the India Human Development Survey for 2011–12, this chapter empirically analyzes the incidence, intensity, and inequality of food insecurity among the households in the region, which is known for its remoteness and relative economic destitution. Applying econometric techniques to household data and village-level weather data, it further investigates the impact of the extreme weather events on food insecurity after controlling for several demographic and socio-economic factors. The results of this exercise indicate that extreme weather events interact with household income to significantly increase the likelihood of food insecurity in the short as well as long run, although they do not have statistically significant impacts on their own. Further, there is some evidence of floods and hailstorms increasing the likelihood of food insecurity through their interactions with the household income in the long run. Similarly, the results suggest that droughts and floods increase the probability of food insecurity through their interactions with the distance to the market and household income in the short run. These results are robust to the inclusion of additional control variables and the use of alternative functional assumption of the regression model.KeywordsExtreme weather eventsFood insecurityNortheast region (NER)Sustainable Development Goals (SDGs)India Human Development Survey
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O estudo tem por objetivos: estimar e analisar as mudanças espaço-temporais da Eficiência do Uso da Água (Water Use Efficiency - WUE) no MATOPIBA e avaliar a influência de fatores climáticos e do uso e ocupação do solo na variação do WUE. No estudo serão utilizados os produtos MOD17A2 (GPP) e MOD16A2 (ET) derivados do sensor MODIS (Moderate Resolution Imaging Spectroradiometer) obtidos no United States Geological Survey (USGS), com resolução espacial 1 km x 1km, para as computo da WUE anual no período entre 2001 e 2019. Em relação a avaliação do uso da terra será realizado com as imagens do MAPBIOMAS, com resolução de 30m x 30m. Já os dados de precipitação serão provenientes do Climate Hazard Group InfraRed Precipitation with Station data (CHIRPS) com resolução espacial de 5,6 km por 5,6 km. As realizações dos cálculos matemáticos serão executadas nos softwares ambiente R versão 3.6-3 e Quantum GIS versão 3.4-6. Os resultados apontam que os maiores (menores) valores de WUE ocorrem em regiões agrícolas e áreas de vegetação nativa amazônica (áreas de superfícies não vegetadas). Este padrão da WUE está associado à crescente expansão agrícola sobre as regiões (Oeste Baiano e na porção Piauí), motivados principalmente pelo plantio de soja. Além disso, constatou-se que as anomalias positivas (negativas) da WUE ocorrem em anos secos (chuvosos). Concluindo assim que, áreas agrícolas são propensas aos maiores valores da WUE devido ao manejo cultural auxiliando no desenvolvimento das culturas agrícolas. As respostas da vegetação aos eventos secos e chuvosos foram mais sensíveis em áreas agrícolas que em áreas de vegetação nativa.
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The effects of elevated carbon dioxide on plant–herbivore interactions have been summarized in a number of narrative reviews and metaanalyses, while accompanying elevation of temperature has not received sufficient attention. The goal of our study is to search, by means of metaanalysis, for a general pattern in responses of herbivores, and plant characteristics important for herbivores, to simultaneous experimental increase of carbon dioxide and temperature (ECET) in comparison with both ambient conditions and responses to elevated CO2 (EC) and temperature (ET) applied separately. Our database includes 42 papers describing studies of 31 plant species and seven herbivore species. Nitrogen concentration and C/N ratio in plants decreased under both EC and ECET treatments, whereas ET had no significant effect. Concentrations of nonstructural carbohydrates and phenolics increased in EC, decreased in ET and did not change in ECET treatments, whereas terpenes did not respond to EC but increased in both ET and ECET; leaf toughness increased in both EC and ECET. Responses of defensive secondary compounds to treatments differed between woody and green tissues as well as between gymnosperm and angiosperm plants. Insect herbivore performance was adversely affected by EC, favoured by ET, and not modified by ECET. Our analysis allowed to distinguish three types of relationships between CO2 and temperature elevation: (1) responses to EC do not depend on temperature (nitrogen, C/N, leaf toughness, phenolics in angiosperm leaves), (2) responses to EC are mitigated by ET (sugars and starch, terpenes in needles of gymnosperms, insect performance) and (3) effects emerge only under ECET (nitrogen in gymnosperms, and phenolics and terpenes in woody tissues). This result indicates that conclusions of CO2 elevation studies cannot be directly extrapolated to a more realistic climate change scenario. The predicted negative effects of CO2 elevation on herbivores are likely to be mitigated by temperature increase.
Summary • Reproductive traits are key characteristics for predicting the response of communities and ecosystems to global change. • We used meta-analysis to integrate data on eight reproductive traits from 159 CO2 enrichment papers that provided information on 79 species. • Across all species, CO2 enrichment (500–800 µl l−1) resulted in more flowers (+19%), more fruits (+18%), more seeds (+16%), greater individual seed mass (+4%), greater total seed mass (+25%), and lower seed nitrogen concentration, (N) (−14%). Crops and undomesticated (wild) species did not differ in total mass response to elevated CO2 (+31%), but crops allocated more mass to reproduction and produced more fruits (+28% vs +4%) and seeds (+21% vs +4%) than did wild species when grown at high CO2. Seed [N] was not affected by high CO2 concentrations in legumes, but declined significantly in most nonlegumes. • Our results provide robust estimates of average plant reproductive responses to CO2 enrichment and demonstrate important differences among individual taxa and among functional groups. In particular, crops were more responsive to elevated CO2 than were wild species. These differences and the substantial decline in seed [N] in many species have broad implications for the functioning of future natural and agro-ecosystems.
First, we report the results of the longest-known field study (9 years) to examine the effects of elevated carbon dioxide (CO2) on leaf miner densities in a scrub-oak community at Kennedy Space Center, Florida. Here, the densities of all leaf miner species (6) on all host species (3) were lower in every year in elevated CO2 than they were in ambient CO2. Second, meta-analyses were used to review the effects of elevated CO2 on both plants (n=59 studies) and herbivores (n=75 studies). The log of the response ratio was chosen as the metric to calculate effect sizes. Results showed that elevated CO2 significantly decreased herbivore abundance (−21.6%), increased relative consumption rates (+16.5%), development time (+3.87%) and total consumption (+9.2%), and significantly decreased relative growth rate (−8.3%), conversion efficiency (−19.9%) and pupal weight (−5.03%). No significant differences were observed among herbivore guilds. Host plants growing under enriched CO2 environments exhibited significantly larger biomass (+38.4%), increased C/N ratio (+26.57%), and decreased nitrogen concentration (−16.4%), as well as increased concentrations of tannins (+29.9%) and other phenolics. Effects of changes on plant primary and secondary chemistry due to elevated CO2 and consequences for herbivore growth and development are discussed.
Meta-analysis techniques were used to examine the effect of elevated atmospheric carbon dioxide [CO2] on the protein concentrations of major food crops, incorporating 228 experimental observations on barley, rice, wheat, soybean and potato. Each crop had lower protein concentrations when grown at elevated (540–958 μmol mol−1) compared with ambient (315–400 μmol mol−1) CO2. For wheat, barley and rice, the reduction in grain protein concentration was ∼10–15% of the value at ambient CO2. For potato, the reduction in tuber protein concentration was 14%. For soybean, there was a much smaller, although statistically significant reduction of protein concentration of 1.4%. The magnitude of the CO2 effect on wheat grains was smaller under high soil N conditions than under low soil N. Protein concentrations in potato tubers were reduced more for plants grown at high than at low concentrations of ozone. For soybean, the ozone effect was the reverse, as elevated CO2 increased the protein concentration of soybean grown at high ozone concentrations. The magnitude of the CO2 effect also varied depending on experimental methodology. For both wheat and soybean, studies performed in open-top chambers produced a larger CO2 effect than those performed using other types of experimental facilities. There was also indication of a possible pot artifact as, for both wheat and soybean, studies performed in open-top chambers showed a significantly greater CO2 effect when plants were rooted in pots rather than in the ground. Studies on wheat also showed a greater CO2 effect when protein concentration was measured in whole grains rather than flour. While the magnitude of the effect of elevated CO2 varied depending on the experimental procedures, a reduction in protein concentration was consistently found for most crops. These findings suggest that the increasing CO2 concentrations of the 21st century are likely to decrease the protein concentration of many human plant foods.
Surface ozone concentrations ([O3]) during the growing season in much of the northern temperate zone reach mean peak daily concentrations of 60 p.p.b. Concentrations are predicted to continue to rise over much of the globe during the next 50 years. Although these low levels of ozone may not induce visible symptoms on most vegetation, they can result in substantial losses of production and reproductive output. Establishing the vulnerability of vegetation to rising background ozone is complicated by marked differences in findings between individual studies. Ozone effects are influenced by exposure dynamics, nutrient and moisture conditions, and the species and cultivars that are investigated. Meta-analytic techniques provide an objective means to quantitatively summarize treatment responses. Soybean has been the subject of many studies of ozone effects. It is both the most widely planted dicotyledonous crop and a model for other C3 annual plants. Meta-analytic techniques were used to quantitatively summarize the response of soybean to an average, chronic ozone exposure of 70 p.p.b., from 53 peer-reviewed studies. At maturity, the average shoot biomass was decreased 34% and seed yield was 24% lower. Even in studies where [O3] was < 60 p.p.b., there was a significant decrease in biomass and seed production. At low [O3], decreased production corresponded to a decrease in leaf photosynthesis, but in higher [O3] the larger loss in production was associated with decreases in both leaf photosynthesis and leaf area. The impact of ozone increased with developmental stage, with little effect on vegetative growth and the greatest effect evident at completion of seed filling. Other stress treatments, including UV-B and drought, did not alter the ozone response. Elevated carbon dioxide significantly decreased ozone-induced losses, which may be explained by a significant decrease in stomatal conductance.