Positive Effects Of Elevated CO2 Research Articles

Enhanced photorespiratory and TCA pathways by elevated CO2 to manage ammonium nutrition in tomato leaves

Plants grown under exclusive ammonium (NH4+) nutrition have high carbon (C) demand to sustain proper nitrogen (N) assimilation and energy required for plant growth, generally impaired when compared to nitrate (NO3−) nutrition. Thereby, the increment of the atmospheric carbon dioxide (CO2) concentration, in the context of climate change, will potentially allow plants to better face ammonium nutrition. In this work, tomato (Solanum lycopersicum L.) plants were grown under ammonium or nitrate nutrition in conditions of ambient (aCO2, 400 ppm) or elevated CO2 (eCO2, 800 ppm) atmosphere. Elevated CO2 increased photosynthesis rate and tomato shoot growth regardless of the N source. In the case of NH4+-fed leaves the positive effect of elevated CO2 occurred despite of the high tissue NH4+ accumulation. Under eCO2 ammonium nutrition triggered, among others, the modulation of genes related to C provision pathways (including carbonic anhydrase and glyoxylate cycle), antioxidant response and cell membranes protection. The enhanced photosynthate production at eCO2 facilitated C skeleton provision through the TCA cycle and anaplerotic pathways to promote amino acid synthesis. Moreover, photorespiratory activity was stimulated by eCO2 and contributed to yield serine as additional sink for NH4+ excess. Overall, these changes denote a connection between the respiratory and the photorespiratory pathways linked to ammonium nutrition. This metabolic strategy may allow crops to grow efficiently using ammonium as fertilizer in a future climate change scenario, while mitigating N losses.

Simulation of Maize Biomass and Yield in An Giang, Vietnam, under Climate Variabilities

In this study, the SIMPLECrop model was applied to simulate maize biomass and yield in 2 crop seasons, Autumn - Winter 2020 (AW) and Winter - Spring 2020 - 2021 (WS), in Cho Moi district, An Giang province, Vietnam (10°23'47''N, 105°27'41''E). The research aimed to analyze the effects of climate variabilities, particularly increased temperature, on maize growth and yield. The growth period for the Winter - Spring 2020 - 2021 season was 67 days, which was 1 day longer than the AW season (Autumn - Winter 2020). Four cultivar parameters, namely Tsum, HI, I50A, and I50B, were employed for the calibration process to fine-tune the model. Sensitivity analysis using Morris and FAST methods revealed that RUE and Tbase had the highest sensitivity and significant impact on the SIMPLECrop model. These 2 parameters showed strong interactions and played a crucial role in influencing model outcomes. The evaluation of the model’s performance resulted in RRMSE values ranging from 4.8 to 6.3 % and NSE values between 0.86 and 0.93, indicating good agreement between model predictions and observed data. Regarding the impact of temperature increase, a 5 °C temperature rise led to a reduction in stover biomass ranging from 5.2 % (Autumn - Winter 2020) to 19.3 % (Winter - Spring 2020 - 2021) and a decrease in yield by 11.3 % (Autumn - Winter 2020) and 27.0 % (Winter - Spring 2020 - 2021). Simulating an increase in CO2 concentration alone, varying from 50, 100, 150, 200 to 250 ppm, resulted in increased biomass and yield for maize. The most substantial increases were observed at 250 ppm CO2, with approximately 2.5 % higher biomass and 7.7 to 9.1 % greater yield. However, under more severe heat stress (5 °C increase), the positive effects of elevated CO2 were mitigated, resulting in a reduced increase in biomass and yield, approximately 3 - 5 %. These findings highlight the importance of considering temperature and CO2 interactions when assessing crop responses to climate variability. HIGHLIGHTS The SIMPLECrop model was rigorously validated for maize in An Giang Province, Vietnam. Validation metrics, including RRMSE and NSE, demonstrated good-fit model performance, with RRMSE values ranging from 4.8 to 6.3 % and NSE values between 0.86 and 0.93 for open field conditions. Sensitivity analysis using Morris and FAST methods identified that two parameters, RUE (Radiation Use Efficiency) and Tbase (Base Temperature), consistently exhibited the highest sensitivity within the SIMPLECrop model. These parameters played a pivotal role in influencing model outcomes and understanding maize responses to climate variability. The study examined the combined impact of increased temperature and elevated CO2 on maize. A 5 °C temperature rise led to significant stover biomass reductions, varying from 5.2 % (AW season) to a substantial 19.3 % (WS season), along with yield declines of 11.3 % (AW) and a significant 27.0 % (WS). Elevated CO2, ranging from 50 to 250 ppm, had a positive influence on maize biomass and yield. However, under more intense heat stress (5 °C increase), the favorable CO2 effects diminished. This underscores the necessity of considering temperature and CO2 interactions when analyzing crop responses to climate variability. GRAPHICAL ABSTRACT

Effect of elevated CO2 and temperature on crop growth and yield attributes of bell pepper (Capsicum annuum L.)

Investigations were carried out during 2014 and 2015 to study the effect of elevated CO2 and temperature on growth and yield contributing parameters of bell pepper (Capsicum annuum L.) under open top chamber (OTC) at research farm of Department of Environmental Science, Dr Y.S. Parmar UHF, Nauni, Solan, Himachal Pradesh with four treatments [T1(eCO2): OTC with elevated CO2 550±10 ppm; T2(eT & eCO2): elevated temperature by 1°C and elevated CO2 550±10 ppm; T3(aT & aCO2): ambient temperature and CO2 and T4: natural condition] and each treatment had two varieties (California Wonder and Solan Bharpur) of bell pepper which were replicated thrice. Results revealed that bell pepper recorded maximum plant height, leaf area, yield attributes under eCO2 which were significantly higher than all other treatments. However, the harvest duration and days to first harvest was lowest under eCO2. Higherfruit size as well as fruit weight was recorded with eCO2 followed by eT and eCO2, aT and aCO2 and open natural condition. But maximum number of fruits and highest fruit yield was obtained with natural condition which was significantly superior over eCO2 as well as over eT and eCO2 because increase in temperature negated fruit set due to less pollen viability under eCO2 and eT & eCO2 as compared to open. In open natural conditions due to higher pollen viability and more fruit setting as compared to higher CO2 andtemperature conditions, it resulted more yield. Solan Bharpur recorded higher total fruit yield (800.2 g plant-1) than California Wonder (399.1 g plant-1). Elevated CO2 has positive effect on plant growth and yield attributes in both cultivars of bell pepper. However, under interactive effect of elevated CO2 and elevated temperature, rising temperature negated the positive effects of elevated CO2 on crop production.

Delineating the mechanisms of elevated CO2 mediated growth, stress tolerance and phytohormonal regulation in plants.

Global climate change has drastically affected natural ecosystems and crop productivity. Among several factors of global climate change, CO2 is considered to be the dynamic parameter that will regulate the responses of all biological system on earth in the coming decade. A number of experimental studies in the past have demonstrated the positive effects of elevated CO2 on photosynthesis, growth and biomass, biochemical and physiological processes such as increased C:N ratio, secondary metabolite production, as well as phytohormone concentrations. On the other hand, elevated CO2 imparts an adverse effect on the nutritional quality of crop plants and seed quality. Investigations have also revealed effects of elevated CO2 both at cellular and molecular level altering expression of various genes involved in various metabolic processes and stress signaling pathways. Elevated CO2 is known to have mitigating effect on plants in presence of abiotic stresses such as drought, salinity, temperature etc., while contrasting effects in thepresence of different biotic agents i.e. phytopathogens, insects and herbivores. However, a well-defined crosstalk is incited by elevated CO2 both under abiotic and biotic stresses in terms of phytohormones concentration and secondary metabolites production. With this background, the present review attempts to shed light on the major effects of elevated CO2 on plant growth, physiological and molecular responses and will highlight the interactive effects of elevated CO2 with other abiotic and biotic factors. The article will also provide deep insights into the phytohormones modulation under elevated CO2.

Responses of net assimilation rate to elevated atmospheric CO2and temperature at different growth stages in a double rice cropping system

Effects of elevated atmospheric CO2 concentration and temperature on rice dry matter accumulation vary in planting regions and cropping systems. It remains unclear how dry matter productivity responds to factorial combination of elevated CO2 and temperature in the double rice cropping system of China. Field experiments were conducted using open-top chambers (OTC) to simulate different scenarios of elevated CO2 and/or temperature for three rotations of double rice in Jingzhou, Hubei Province. Liangyou 287 and Xiangfengyou 9 were used as rice cultivar for early rice and late rice, respectively. There were five treatments: UC, paddy field without OTC covering; CK, OTC with the similar temperature and CO2 concentration to field environment; ET, OTC with 2 ℃ temperature elevation; EC, OTC with 60 μmol·mol-1 CO2 elevation; ETEC, OTC with simu-ltaneous 2 ℃ temperature elevation and 60 μmol·mol-1 CO2 elevation. We measured aboveground biomass, leaf area index (LAI) and net assimilation rate (NAR) of dry matter under different treatments. Our results showed that elevated CO2 and/or temperature had no significant effects on NAR from transplanting to jointing, increased NAR from jointing to heading, but decreased NAR from heading to maturity (except for EC treatment in early rice). Elevated CO2 and/or temperature promoted leaf area development at all growth stages, with ETEC showing the highest increase in LAI except at maturity. Warming and CO2 enrichment jointly promoted dry matter accumulation at heading, with ETEC increasing aboveground biomass by 10.3%-39.8% and 23.6%-34.4% compared with CK in early rice and late rice, respectively. At maturity of early rice, elevated temperature partly offset the positive effects of elevated CO2 on aboveground biomass, as shown by a reduction of 3.2%-14.1% under ETEC compared with EC. Contrarily at maturity of late rice, co-elevation of CO2 and temperature further increased aboveground biomass, showing a synergistic interaction. Results from regression analysis showed that warming and CO2 enrichment had positive effects on NAR at vegetative stages of double rice, while warming showed negative effects on NAR at reproductive stages. Considering the dissimilarities in growth characteristics, growing periods and ambient temperature, elevated CO2 and temperature might increase dry matter production in the Chinese double rice cropping system.

Stimulation of Growth and Alteration of Hormones by Elevated Carbon Dioxide for Creeping Bentgrass Exposed to Drought

ABSTRACTDrought stress inhibits shoot growth of cool‐season turfgrass species, and elevated CO2 concentration may mitigate the adverse effects of drought through alteration of hormone production. The objective of this study was to determine whether elevated CO2–enhanced drought tolerance in creeping bentgrass (Agrostis stolonifera L.) was associated with the stimulation of tiller and stolon growth and the alteration of stress‐regulating and growth‐regulating hormone accumulation. Creeping bentgrass (cv. Penncross) plants were established for 24 d at ambient (400 μL L−1) or elevated (800 μL L−1) CO2 concentration and subsequently exposed to drought stress for 23 d by withholding irrigation. Drought stress caused significant reduction in leaf relative water content and tiller density, whereas both parameters, as well as stolon length, were maintained at significantly higher values in CO‐treated plants compared with those at ambient CO2 under drought stress. The positive effects of elevated CO2 on the maintenance of leaf hydration and the promotion of tiller density and stolon growth in creeping bentgrass exposed to drought stress could be associated with the suppression of drought‐induced accumulation of abscisic acid and the increase in the endogenous content of isopentenyladenosine, jasmonic acid, and the jasmonic acid precursor 12‐oxo‐phytodienoic acid. These results suggest that the elevated CO2–enhanced growth of tillers and stolons in creeping bentgrass under drought stress could be regulated in part by the adjustment of endogenous hormone levels.

The Impact of Elevated CO2 and High Temperature on the Nutritional Quality of Fruits – A Short Review

Fruits are essential components of modern diet. Fruit nutrients provide important benefits to human in various ways for better health. Phytochemicals in fruit vary in quality and quantity depending mainly on fruit species and cultivar. Additionally, these phytonutrients can also be affected by different environmental factors including atmospheric carbon dioxide (CO2) and temperature. The current changes and the continuous anticipated increase in the CO2 concentrations and temperature in the atmosphere has become a major challenge in crop production. The literature is rich with investigations of individual and combination effects of elevated CO2 and temperature on growth, development and yield of plants, including fruits. The purpose of this review is to evaluate the impacts of elevated CO2 and high temperature individually and interactively on nutritional quality of fruits. According to the reviewed literature, both elevated CO2 and temperature significantly influenced fruit nutrient content and availability. Elevated CO2 is expected to affect positively the fruits nutrient content, while mixed responses found for high temperature. Interaction effects of these factors are the most important since they are predicted to increase concomitantly. With available literature, the combination impact of these factors on fruit nutrients was discussed under three different hypotheses in this review. (1) high temperature may offset the positive effects of elevated CO2, (2) elevated CO2 would compensate for the negative effects of high temperature and (3) interactively, both elevated CO2 and temperature may increase or decrease the phytonutrients in fruits.

Physiological and Proteomic Evidence for the Interactive Effects of Post-Anthesis Heat Stress and Elevated CO2 on Wheat.

Elevated CO2 promotes leaf photosynthesis and improves crop grain yield. However, as a major anthropogenic greenhouse gas, CO2 contributes to more frequent and severe heat stress, which threatens crop productivity. The combined effects of elevated CO2 and heat stress are complex, and the underlying mechanisms are poorly understood. In the present study, the effects of elevated CO2 and high-temperature on foliar physiological traits and the proteome of spring wheat grown under two CO2 concentrations (380 and 550µmolmol-1 ) and two temperature conditions (ambient and post-anthesis heat stress) are examined. Elevated CO2 increases leaf photosynthetic traits, biomass, and grain yield, while heat stress depresses photosynthesis and yield. Temperature-induced impacts on chlorophyll content and grain yield are not significantly different under the two CO2 concentrations. Analysis of the leaf proteome reveals that proteins involved in photosynthesis as well as antioxidant and protein synthesis pathways are significantly downregulated due to the combination of elevated CO2 and heat stress. Correspondingly, plants treated with elevated CO2 and heat stress exhibit decreased green leaf area, photosynthetic rate, antioxidant enzyme activities, and 1000-kernel weight. The present study demonstrates that future post-anthesis heat episodes will diminish the positive effects of elevated CO2 and negatively impact wheat production.

Future changes in rice yields over the Mekong River Delta due to climate change—Alarming or alerting?

The crop simulation model Decision Support System for Agrotechnology Transfer (DSSAT) was applied over the Mekong River Delta (MRD), Southern Vietnam, to assess future (2020–2050) impacts of climate change on rice production. The DSSAT model was driven using observed station data and projected climate data derived through the dynamical downscaling of three global climate models (GCMs) using the Weather Research and Forecasting (WRF) model. The WRF model was simulated at a spatial resolution of 30 km over the study region, and the large-scale driving fields for future climates were taken from the Coupled Model Inter-Comparison Project Phase 3 (CMIP3) global models ECHAM5, CCSM3, and MIROC5 under the A2 emission scenario. Rice growth during two main seasons, namely, the winter-spring (winter) and summer-autumn (summer), were selected to quantify impacts under both irrigated and rain-fed rice cultivation. The results from this climate-crop study suggest that under rain-fed conditions, winter rice yield was likely to experience nearly 24% reduction while summer rice yield was projected to decrease by about 49%. Without irrigation, the annual rice yield was projected to decrease by about 36.5%, and under irrigated conditions, climate change is likely to reduce annual irrigated rice yields by about 1.78%. Winter rice yield was likely to decrease by 4.7% while summer rice yield was projected to marginally increase by about 0.68%. Increasing temperatures and seasonal variations of precipitation are likely to significantly reduce rice yields under rain-fed condition. In addition, (1) a decrease (increase) in the number of rainy days during the dry (wet) season and (2) positive effects of elevated CO2 for rain-fed rice growth under each of the three WRF model realizations would markedly influence rice yields. With Vietnam being one of the largest exporters of rice, these findings have serious implications for the local agricultural sector. This also serves an early warning for the policymakers and stakeholders for effective planning of not only crop production but also water resource management. The findings call for prudent diversification strategy planning by those countries which import rice.

The impact of elevated CO2 and water deficit stress on growth and photosynthesis of juvenile cacao (Theobroma cacao L.).

Atmospheric CO2 concentration continues to rise and is predicted to reach approximately 700 ppm by 2100. Some predictions suggest that the dry season in West Africa could be extended with climate change. This study examined the effects of elevated CO2 concentration and water deficit on growth and photosynthesis of juvenile cacao. Light-saturated photosynthesis (Pmax), quantum efficiency, and intrinsic water-use efficiency increased significantly in response to elevated CO2, as did a range of growth and development responses (e.g. leaf area and leaf number), but the magnitude of the increase was dependent on the water treatment. Stomatal index was significantly greater in the elevated CO2 treatment; an atypical response which may be a reflection of the environment in which cacao evolved. This study shows a positive effect of elevated CO2 on juvenile cacao which may help to alleviate some of the negative impacts of water deficit stress.

Elevated CO2 and nitrogen addition accelerate net carbon gain in a brackish marsh

Wetlands have an inordinate influence on the global greenhouse gas budget, but how global changes may alter wetland contribution to future greenhouse gas fluxes is poorly understood. We determined the greenhouse gas balance of a tidal marsh exposed to nine years of experimental carbon dioxide (CO2) and nitrogen (N) manipulation. We estimated net carbon (C) gain rates by measuring changes in plant and soil C pools over nine years. In wetland soils that accrete primarily through organic matter inputs, long-term measurements of soil elevation, along with soil C density, provide a robust estimate of net soil C gain. We used net soil C gain along with methane and nitrous oxide fluxes to determine the radiative forcing of the marsh under elevated CO2 and N addition. Nearly all plots exhibited a net gain of C over the study period (up to 203 g C m−2 year−1), and C gain rates were greater with N and CO2 addition. Treatment effects on C gain and methane emissions dominated trends in radiative forcing while nitrous oxide fluxes in all treatments were negligible. Though these soils experience salinities that typically suppress methane emissions, our results suggest that elevated CO2 can stimulate methane emissions, overcoming positive effects of elevated CO2 on C gain, converting brackish marshes that are typically net greenhouse gas sinks into sources. Adding resources, either CO2 or N, will likely increase “blue carbon” accumulation rates in tidal marshes, but importantly, each resource can have distinct influences on the direction of total greenhouse forcing.

Long-term and realistic global change manipulations had low impact on diversity of soil biota in temperate heathland

In a dry heathland ecosystem we manipulated temperature (warming), precipitation (drought) and atmospheric concentration of CO2 in a full-factorial experiment in order to investigate changes in below-ground biodiversity as a result of future climate change. We investigated the responses in community diversity of nematodes, enchytraeids, collembolans and oribatid mites at two and eight years of manipulations. We used a structural equation modelling (SEM) approach analyzing the three manipulations, soil moisture and temperature, and seven soil biological and chemical variables. The analysis revealed a persistent and positive effect of elevated CO2 on litter C:N ratio. After two years of treatment, the fungi to bacteria ratio was increased by warming, and the diversities within oribatid mites, collembolans and nematode groups were all affected by elevated CO2 mediated through increased litter C:N ratio. After eight years of treatment, however, the CO2-increased litter C:N ratio did not influence the diversity in any of the four fauna groups. The number of significant correlations between treatments, food source quality, and soil biota diversities was reduced from six to three after two and eight years, respectively. These results suggest a remarkable resilience within the soil biota against global climate change treatments in the long term.

Low CO2 Sensitivity of Microzooplankton Communities in the Gullmar Fjord, Skagerrak: Evidence from a Long-Term Mesocosm Study.

Ocean acidification is considered as a crucial stressor for marine communities. In this study, we tested the effects of the IPCC RPC6.0 end-of-century acidification scenario on a natural plankton community in the Gullmar Fjord, Sweden, during a long-term mesocosm experiment from a spring bloom to a mid-summer situation. The focus of this study was on microzooplankton and its interactions with phytoplankton and mesozooplankton. The microzooplankton community was dominated by ciliates, especially small Strombidium sp., with the exception of the last days when heterotrophic dinoflagellates increased in abundance. We did not observe any effects of high CO2 on the community composition and diversity of microzooplankton. While ciliate abundance, biomass and growth rate were not affected by elevated CO2, we observed a positive effect of elevated CO2 on dinoflagellate abundances. Additionally, growth rates of dinoflagellates were significantly higher in the high CO2 treatments. Given the higher Chlorophyll a content measured under high CO2, our results point at mainly indirect effects of CO2 on microzooplankton caused by changes in phytoplankton standing stocks, in this case most likely an increase in small-sized phytoplankton of <8 μm. Overall, the results from the present study covering the most important part of the growing season indicate that coastal microzooplankton communities are rather robust towards realistic acidification scenarios.

Elevated CO2 and warming shift the functional composition of soil nematode communities in a semiarid grassland

Climate change can alter soil communities and functions, but the consequences are uncertain for most ecosystems. We assessed the impacts of climate change on soil nematodes in a semiarid grassland using a 7-year, factorial manipulation of temperature and [CO2]. Elevated CO2 and warming decreased the abundance of plant-feeding nematodes and nematodes with intermediate to high values on the colonizer-persister scale (cp3-5), including predators and omnivores. Thus, under futuristic climate conditions, nematode communities were even more dominated by r-strategists (cp1-2) that feed on bacteria and fungi. These results indicate that climate change could alter soil functioning in semiarid grasslands. For example, the lower abundance of plant-feeding nematodes could facilitate positive effects of elevated CO2 and warming on plant productivity. The effects of elevated CO2 and warming on nematode functional composition were typically less than additive, highlighting the need for multi-factor studies.

Adaptability of Indocalamus decorus to climate change based on physiological and biochemical responses to elevated carbon dioxide and ozone

Carbon dioxide (CO2) and ozone (O3) are important greenhouse gases that contribute to global climate change. The effects of elevated CO2 and/or O3 on plants remain unclear. Plant responses to mixtures of the two gases at high concentrations are likely to be complex. Previous studies have shown that the ability to tolerate elevated levels of the two gases varies among plant species; physiological adaptability in the face of changing atmospheric composition also differs among taxa. However, the effects of mixtures of the two greenhouse gases on the growth and physiology of bamboo are largely unexplored, even though bamboos are important vegetation elements throughout tropical and subtropical regions of the planet. In this study, we used open-topped chambers (OTCs) to double the concentrations of atmospheric CO2 and O3, and examined changes in membrane lipid peroxidation, photosynthetic physiology, and antioxidase activities in Indocalamus decorus leaves. After 103 days of treatment, elevated O3 depressed net photosynthetic rate (Pn) without changing stomatal function, but caused no significant oxidative damage in the leaves. High levels of antioxidase activities were maintained in the leaves, indicating that this species had a strong tolerance to elevated O3. Decreases in reactive oxygen content and antioxidase activity in the leaves highlighted the significant positive effects of elevated CO2 on photosynthesis in I. decorus. When a mixture of both gases was supplied at high concentrations, we detected no oxidative damage, although photosynthetic capacity was reduced. Negative effects of O3 were very marked during the early part of the treatment period, but the effects of CO2 were positive. CO2 mitigated the oxidative damage caused by O3 and promoted the growth of I. decorus. Thus, I. decorus tolerated the two greenhouse gases, and was able to adapt to elevated CO2 and O3 levels. These findings contribute to the current knowledge base on the response of bamboo to global climate change.

A field experiment with elevated atmospheric CO2-mediated changes to C4 crop-herbivore interactions.

The effects of elevated CO2 (E-CO2) on maize and Asian corn borer (ACB), Ostrinia furnacalis, in open-top chambers were studied. The plants were infested with ACB and exposed to ambient and elevated (550 and 750 μl/l) CO2. E-CO2 increased the plant height and kernel number per ear. The plants had lower nitrogen contents and higher TNC: N ratios under E-CO2 than at ambient CO2. The response of plant height to E-CO2 was significantly dampened in plants with ACB infestation. However, the weight gain of the survivors declined in plants grown under E-CO2. Moreover, the plant damage caused by ACB was not different among the treatments. Overwintering larvae developed under E-CO2 had a lower supercooling point than those developed under ambient CO2. The results indicated that there was a positive effect of E-CO2 on the accumulation of maize biomass, i.e., the “air-fertilizer” effect, which led to a nutritional deficiency in the plants. The fitness-related parameters of ACB were adversely affected by the CO2-mediated decreased in plant nutritional quality, and ACB might alter its food consumption to compensate for these changes. Larval damage to maize under E-CO2 appears to be offset by this “air-fertilizer” effect, with reductions in larval fitness.

Long-term responses of plant growth, soil microbial communities and soil enzyme activities to elevated CO2 and neighbouring plants

Tree neighbourhoods can complicate the prediction of plant belowground responses to elevated CO2. We studied the effects of elevated CO2 on the root traits, soil microbial communities, and microbial extracellular enzyme activities in the rhizospheres of Abies faxoniana saplings grown alone or with different neighbouring species. A. faxoniana (alone), A. faxoniana grown with dwarf bamboo (Fargesia rufa), and A. faxoniana grown with biocrusts were exposed to ambient or to CO2-enriched air (ambient+350μmolmol−1) for six years. The CO2×neighbourhood interaction significantly affected A. faxoniana saplings growth, soil microbial communities, and soil enzyme activities. Elevated CO2 had relatively little effect on plant and microbial biomass and phospholipid fatty acid (PLFA) profiles in saplings grown alone. However, increased ectomycorrhizal colonization was observed in the roots of these saplings. Results suggested that the growth of saplings grown with biocrusts under elevated CO2 conditions was obtained by the enhanced soil microbial characteristics, whereas the positive effects of elevated CO2 on ectomycorrhizal fungi colonization in saplings grown alone could not delay or alleviate the progressive nitrogen (N) limitation as is evidenced by similar plant biomass under elevated and ambient CO2 treatments. In contrast, elevated CO2 significantly decreased the growth of A. faxoniana in the presence of dwarf bamboo, and this reduction was accompanied by decreased soil and leaf N concentrations, microbial biomass carbon (C) and N, labile C, and total PLFA. We propose that the depletion of the C pool and the reduction in the soil microbial metabolic activities in saplings grown with dwarf bamboo may limit the rates of decomposition to release nutrients from organic matter for plant growth. These results suggest that neighbouring plants have belowground feedback that potentially contributes to plant performance. On the other hand, the results of the present study also showed that the responses of soil organic C to elevated CO2 are different in the presence and absence of neighbours and dependent on neighbour identity. Only mesocosms with biocrust had a tendency to maintain more soil organic C by increased soil microbial community abundance. Our results also highlight the value of studying elevated CO2 effects on aboveground–belowground associations to improve the prediction of subalpine ecosystem functioning under climate changes.

Cellular and Molecular Mechanisms for Elevated CO2–Regulation of Plant Growth and Stress Adaptation

ABSTRACTIncreases in atmospheric CO2 concentration have exerted significant impacts on plant growth. Numerous studies have reported positive effects of elevated CO2 on plant growth and adaptation to various environmental stresses in many plant species. The mechanisms by which CO2 enrichment regulates plant growth and stress adaptation are not completely understood. There have been some recent exciting advances in elucidating the cellular, metabolic, and molecular basis for increased growth under elevated CO2. At the cellular level, cell growth involving both cell division and cell expansion is stimulated by increasing CO2, which has been associated with increased photosynthetic activities and carbohydrate availability, and also with the expression of genes controlling cell division, cycling, and cell expansion. Proteomic profiling studies identified CO2–regulated proteins mainly involved in photosynthesis, carbon metabolism, energy pathways, molecular chaperones, and antioxidant proteins. Transcriptomic analyses identified several hundreds of genes responsive to elevated CO2 levels, which play roles in cell wall loosening, photosynthesis, respiration, water use, and protein synthesis, as well as stress defense. This paper reviews recent progress in the mechanistic understanding of CO2 regulation of plant growth and stress adaptation at the cellular, metabolic, and molecular levels, and addresses research gaps and future research perspective areas.

Long-term Wood Production in Water-Limited Forests: Evaluating Potential CO2 Fertilization Along with Historical Confounding Factors

Increased aridity may have severe effects on productivity of dry forests. However, it remains unclear to what degree the positive effects of elevated CO2 (both increased carboxylation rates and enhanced water-use efficiency) may offset the negative effects of drought and climate warming. In forest ecosystems, it is particularly challenging to evaluate CO2 effects on productivity because the impacts of climate variability, competition, and management, combine to have longlasting effects on stand-level productivity. Here we address this problem using a unique long-term database containing repeated inventories of wood biomass for every decade from 1912 to 2002 in a pine forest (Pinus pinaster Ait.) in central Spain (≈7,500 ha.). The approach is based upon a combination of statistical analyses of long-term historical management data and mechanistic modeling which allows us to evaluate the effects of potential CO2 fertilization, climate, and stand structure on woody net primary production (W-NPP). We found a significant negative effect of drought on W-NPP during the first half of the twentieth century that diminishes at the turn of the century. Simulations with a process-based ecosystem model, ORCHIDEE, suggest that wood production under conditions that included CO2 fertilization produced a more highly correlated long-term W-NPP than simulations keeping CO2 values in preindustrial levels. Interestingly, however, the CO2 effect was only apparent when accounting for confounding factors such as competition and management legacies. Identifying CO2 fertilization on forest growth is a critical issue, and requires partitioning CO2 effects from confounding factors that have jointly shaped stand dynamics and carbon balance during the twentieth century.

Effects of ambient and elevated CO2 on growth, chlorophyll fluorescence, photosynthetic pigments, antioxidants, and secondary metabolites of Catharanthus roseus (L.) G Don. grown under three different soil N levels.

Catharanthus roseus L. plants were grown under ambient (375 ± 30 ppm) and elevated (560 ± 25 ppm) concentrations of atmospheric CO2 at different rates of N supply (without supplemental N, 0 kg N ha(-1); recommended N, 50 kg N ha(-1); and double recommended N, 100 kg N ha(-1)) in open top chambers under field condition. Elevated CO2 significantly increased photosynthetic pigments, photosynthetic efficiency, and organic carbon content in leaves at recommended (RN) and double recommended N (DRN), while significantly decreased total nitrogen content in without supplemental N (WSN). Activities of superoxide dismutase, catalase, and ascorbate peroxidase were declined, while glutathione reductase, peroxidase, and phenylalanine-ammonia lyase were stimulated under elevated CO2. However, the responses of the above enzymes were modified with different rates of N supply. Elevated CO2 significantly reduced superoxide production rate, hydrogen peroxide, and malondialdehyde contents in RN and DRN. Compared with ambient, total alkaloids content increased maximally at recommended level of N, while total phenolics in WSN under elevated CO2. Elevated CO2 stimulated growth of plants by increasing plant height and numbers of branches and leaves, and the magnitude of increment were maximum in DRN. The study suggests that elevated CO2 has positively affected plants by increasing growth and alkaloids production and reducing the level of oxidative stress. However, the positive effects of elevated CO2 were comparatively lesser in plants grown under limited N availability than in moderate and higher N availability. Furthermore, the excess N supply in DRN has stimulated the growth but not the alkaloids production under elevated CO2.