Combined Effects Of Elevated CO2 Research Articles

Climate-induced changes in essential oil production and terpene composition in alpine aromatic plants

Alpine regions are biodiversity hotspots for endemic species with unique adaptations to harsh climatic conditions. These adaptations often involve specialized behaviours and metabolism including the production of secondary metabolites that protects plants from environmental stresses. This study examines the impacts of elevated CO2 (eCO2) and combined effects of elevated CO2 and temperature (eCO2+T) on two alpine aromatic herbs, namely Angelica glauca and Nardostachys jatamansi. These species were raised in open-top chambers (OTCs) and treated with elevated CO2 (600 ppm) and temperature (+2.0 °C from control) during 2018 to 2020. The primary (total soluble sugar, starch, total soluble protein, amino acid and proline contents), secondary metabolites (Phenolics, essential oil yield, and components using GC-MS) and antioxidant activities (superoxide dismutase and peroxidase) were measured. Total soluble sugar increased under eCO2, while starch content, total amino acid and total soluble protein initially increased but later declined in response to the treatments. Proline content and antioxidant activities were higher under eCO2 and eCO2+T treatments. Total phenolic content showed both increasing (in A. glauca) and decreasing (in N. jatamansi) responses to eCO2 and eCO2+T treatments. GC–MS analysis showed decreased monoterpenes in CO2 and temperature treatments, but some sesquiterpenes showed mixed responses with both increases and decreases. These findings suggest that changes in climate can alter the composition of secondary metabolites in alpine herbs, potentially affecting their therapeutic properties and suitability for use in herbal medicine. This study provides valuable insights into the species-specific physiological responses of plants to changing climate.

Combined effect of elevated CO2 and Fe deficiency on common bean metabolism and mineral profile

Abstract Aims Elevated atmospheric CO2 (eCO2) and restricted iron (Fe) supply are known to impact plant growth and nutritional quality of food crops. However, studies aimed at understanding how eCO2 will interact with Fe deficiency are scarce. Changes in the nutritional status of the common bean (Phaseolus vulgaris L.) may significantly impact the nutritional status of populations that rely heavily on this crop. Methods To understand the combined effects of eCO2 and Fe deficiency on mechanisms relevant to plant nutrient uptake and accumulation, common bean plants were grown under Fe sufficiency (Fe+, 20 mM Fe-EDDHA) and Fe deficiency (Fe-, 0 mM Fe-EDDHA) combined with eCO2 (800 ppm) or ambient CO2 (aCO2, 400 ppm) in hydroponics until maturity. Results Elevated CO2, besides stimulating photosynthesis and stomatal closure, highly affected plant Fe metabolism: stimulated root ferric chelate reductase (FCR) activity by 6-fold and downregulated the expression of root FRO1 and IRT1 expressions by about 4-fold. In leaves, citrate and oxalate increased, but ferritin expression decreased by 9-fold. Such changes may have determined the differences on mineral accumulation patterns particularly the lower levels of Fe in roots (62%), leaves (38%) and seeds (50%). The combination of Fe deficiency and eCO2 doubled the effect of a single factor on FCR up-regulation, balanced the internal pH of Fe deficient plants, and resulted in the lowest Fe accumulation in all plant parts. Conclusions These results suggest that eCO2 directly affects the Fe uptake mechanism of common bean plants, decreasing plant Fe content.

Combined effects of elevated CO2 and warmer temperature on limitations to photosynthesis and carbon sequestration in yellow birch.

Elevated CO2 and warmer temperature occur simultaneously under the current climate change. However, their combined effects on the photosynthetic traits in boreal trees are not well understood. This study investigated the morphological and photosynthetic responses of yellow birch (Betula alleghaniensis Britt.) to a combined treatment of CO2 and temperature (ambient, ACT (400μmolmol-1 CO2 and current temperature) vs elevated, ECT (750μmolmol-1 CO2 and current +4 °C temperature)). It was found that ECT significantly reduced leaf-area based photosynthetic rate (An), maximum Rubisco carboxylation rate (Vcmax), photosynthetic electron transport rate (Jmax), leaf nitrogen concentration, respiration and mesophyll conductance. There were two interesting findings: first, the primary mechanism of photosynthetic limitation shifted from Ribulose-1,5-bisphosphate (RuBP) carboxylation (related to Vcmax) to RuBP regeneration (related to Jmax) in response to ECT, leading to decreased transition point (Ci-t and An-t) from RuBP carboxylation to regeneration; second, the increase in total leaf area in response to ECT more than compensated for the downregulation of leaf-area based photosynthesis, leading to greater biomass in ECT than in ACT. We proposed a new protocol for evaluating photosynthetic limitations by comparing the relative relationship between the transition point (Ci-t and An-t) and the photosynthetic rate at growth CO2 (Ci-g and An-g). Furthermore, we found that Jmax (RuBP regeneration) was the primary limitation to An under ECT.

Daytime warming during early grain filling offsets the CO2 fertilization effect in rice

Increasing concentrations of atmospheric CO2 are projected to have positive effects on crop photosynthesis and yield (CO2 fertilization effect, CFE). High-temperature events, such as heatwaves, during sensitive periods can have significant negative impacts on crop yield and quality; however, the combined effects of elevated CO2 (EC) and short-period elevated temperature (ET) have not been determined in the open field. Here, we show a strong negative interaction between EC and ET obtained from a temperature-free-air controlled enhancement treatment embedded in a season-long free-air CO2 enrichment (FACE) experiment on a japonica rice cultivar, Koshihikari, over three seasons at the Tsukuba FACE facility in Ibaraki, Japan. CFE was 15% at ambient temperature, but it was reduced to 3% by ET, where canopy surface temperature (Tc) was elevated by ∼1.6 °C for 20 d after flowering. Reductions in CFE mainly arose from poor grain setting at Tc above ∼30 °C. High Tc also increased the percentage of chalky grains and substantially decreased the grain appearance quality, although the threshold temperature varied between the seasons. Simultaneous increases in atmospheric CO2 concentration and air temperature are expected to increase daytime canopy temperatures more than air warming alone, thereby affecting grain yield and quality. Crop models without these processes are likely to underestimate the negative impacts of climate change on crop yield and quality. The development of adaptation measures against heat stress, particularly during reproductive and grain-filling periods, needs to be enhanced and accelerated.

Growth, DMS and DMSP production in Emiliania huxleyi under elevated CO2 and UV radiation

The effects of ocean acidification and solar radiation on marine organisms have received increasing attention. Coccolithophores are a major producer of dimethylsulfoniopropionate (DMSP), which is a precursor of dimethylsulfide (DMS), a volatile biogenic active gas related to climate. Here, we investigated the individual and combined effects of elevated CO2 and ultraviolet radiation (UVR) on growth, DMS, and DMSP production of Emiliania huxleyi. Elevated CO2 (1000 μatm, HC) decreased the cell concentration, DMS, and particulate DMSP (DMSPp) concentrations by 17%, 20%, and 13%, respectively, compared with ambient CO2 (400 μatm, LC) in the semi-continuous culture. The addition of UVA to photosynthetically active radiation (PAR) increased cell concentration of E. huxleyi by 16% on day 4, which may be due to the photorepair effects induced by UVA, and the effect was time-dependent. PAR + UVA and PAR + UVA + UVB exposure decreased cellular DMS by 25%–56%, and increased cellular DMSPp by 60%–130% compared with PAR on days 3–4. Cellular DMSPp followed the order: PAR + UVA > PAR + UVA + UVB > PAR, and HC had no significant effects on cellular DMSPp compared with LC in the combined experiment. These results aid our understanding of the effects of ocean acidification and UV radiation on the production of methyl sulfur compounds in the ocean.

Effects of cadmium on soil nitrification in the rhizosphere of Robinia pseudoacacia L. seedlings under elevated atmospheric CO2 scenarios

The individual impacts of elevated CO2 and heavy metals on soil nitrification have been widely reported. However, studies on the combined effects of elevated CO2 and heavy metals on soil nitrification are still limited. Here, a 135-day growth chamber experiment was conducted to investigate the impacts of elevated CO2 and cadmium (Cd) levels on soil nitrification in the rhizosphere of Robinia pseudoacacia L. seedlings. Elevated CO2 combined with Cd pollution generally stimulated ammonia monooxygenase (AMO), hydroxylamine oxidase (HAO), and nitrite oxidoreductase (NXR) activities. Compared to the control, the abundance of ammonia-oxidizing bacteria (AOB) at day 135 and ammonia-oxidizing archaea (AOA) increased significantly (p < 0.05) and the abundance of AOB at days 45 and 90 and that of the nitrite-oxidizing bacteria (NOB) decreased under elevated CO2 + Cd. Elevated CO2 mostly led to a significant (p < 0.05) decrease in soil nitrification intensity in the rhizosphere of R. pseudoacacia exposed to Cd. The effects of Cd, CO2, and their interaction on HAO and NXR activities were significant (p < 0.01). Soil pH, the C/N ratio, water-soluble organic carbon, water-soluble organic nitrogen (WSON), and total carbon were the dominant factors (p < 0.05) affecting nitrifying enzyme activities and nitrification intensity in rhizosphere soils. Elevated CO2 clearly affected AOA, AOB, and NOB community structures and dominant genera by shaping C/N ratio, pH, and Cd and WSON contents in rhizosphere soils under Cd exposure. Overall, the responses of pH, C/N ratio, WSON, and Cd to elevated CO2 led to changes in rhizosphere soil nitrification under the combination of elevated CO2 and Cd pollution.

Evaluating bloom potential of the green-tide forming alga Ulva ohnoi under ocean acidification and warming

The occurrence of green-tides, whose bloom potential may be increased by various human activities and biogeochemical process, results in enormous economic losses and ecosystem collapse. In this study, we investigated the ecophysiology of the subtropical green-tide forming alga, Ulva ohnoi complex (hereafter: U. ohnoi), under simulated future ocean conditions in order to predict its bloom potential using photosynthesis and growth measurements, and stable isotope analyses. Our mesocosm system included four experimental conditions that simulated the individual and combined effects of elevated CO2 and temperature, namely control (450 μatm CO2 & 20 °C), acidification (900 μatm CO2 & 20 °C), warming (450 μatm CO2 & 25 °C), and greenhouse (900 μatm CO2 & 25 °C). Photosynthetic electron transport rates (rETR) increased significantly under acidification conditions, but net photosynthesis and growth were not affected. In contrast, rETR, net photosynthesis, and growth all decreased significantly under elevated temperature conditions (i.e. both warming and greenhouse). These results represent the imbalance of energy metabolism between electron transport and O2 production that may be expected under ocean acidification conditions. This imbalance appears to be related to carbon and nitrogen assimilation by U. ohnoi. In particular, 13C and 15N discrimination data suggest U. ohnoi prefers CO2 and NH4+ over HCO3− and NO3− as sources of carbon and nitrogen, respectively, and this results in increased N content in the thallus under ocean acidification conditions. Together, our results suggest a trade-off in which the bloom potential of U. ohnoi could increase under ocean acidification due to greater N accumulation and through the saving of energy during carbon and nitrogen metabolism, but that elevated temperatures could decrease U. ohnoi's bloom potential through a decrease in photosynthesis and growth.

Combined effects of elevated CO2 and temperature on multitrophic interactions involving a parasitoid of plant virus vectors

Atmospheric concentration of carbon dioxide (CO2) is predicted to double by late twenty-first century, likely increasing global temperature by 2.2 °C. Elevated CO2 (eCO2) and temperature (eT) affect agricultural crops as well as pests and their natural enemies. Changes in any part of multitrophic systems due to environmental factors can affect pest infestation and disease dynamics, as well as the effectiveness of biological control programs. Our study evaluated the effects of eCO2 and eT combined on the performance of the parasitoid Aphidius colemani Vierick (Hymenoptera: Braconidae) when its aphid host Rhopalosiphum padi L. (Hemiptera: Aphididae) was exposed to non-infected or Barley yellow dwarf virus (BYDV–PAV) infected wheat (Triticum aestivum L., Poaceae). Using controlled environment chambers, plant physiology and parasitoid performance were examined under ambient (aCO2a aCO2 = 400 ppm, aT = 20 °C) and elevated (eCO2e eCO2 = 800 ppm, eT = 22 °C) conditions. Virus infection reduced plant biomass and chlorophyll content more pronouncedly under eCO2&eT. Developmental time from oviposition to adult emergence of A. colemani significantly decreased under eCO2&eT, on virus-infected and non-infected plants. However, parasitism rate, sex ratio and pupal survivorship remained unchanged under eCO2&eT, regardless of virus infection. Therefore, we incline to suggest that the biocontrol of R. padi by A. colemani will continue being effective in a future climate with similar conditions as studied here. This study provides empirical data on a particular tritrophic system (plant-pest-parasitoid) affected by plant virus and eCO2&eT, essential to complement scientific knowledge about the impact of climate change on complex interactions of agro-ecosystems.

Effects of climate change factors on marine macroalgae: A review.

Marine macroalgae, the main primary producers in coastal waters, play important roles in the fishery industry and global carbon cycles. With progressive ocean global changes, however, they are increasingly exposed to enhanced levels of multiple environmental drivers, such as ocean acidification, warming, heatwaves, UV radiation and deoxygenation. While most macroalgae have developed physiological strategies against variations of these drivers, their eco-physiological responses to each or combinations of the drivers differ spatiotemporally and species-specifically. Many freshwater macroalgae are tolerant of pH drop and its diel fluctuations and capable of acclimating to changes in carbonate chemistry. However, calcifying species, such as coralline algae, are very sensitive to acidification of seawater, which reduces their calcification, and additionally, temperature rise and UV further decrease their physiological performance. Except for these calcifying species, both economically important and harmful macroalgae can benefit from elevated CO2 concentrations and moderate temperature rise, which might be responsible for increasing events of harmful macroalgal blooms including green macroalgal blooms caused by Ulva spp. and golden tides caused by Sargassum spp. Upper intertidal macroalgae, especially those tolerant of dehydration during low tide, increase their photosynthesis under elevated CO2 concentrations during the initial dehydration period, however, these species might be endangered by heatwaves, which can expose them to high temperature levels above their thermal windows' upper limit. On the other hand, since macroalgae are distributed in shallow waters, they are inevitably exposed to solar UV radiation. The effects of UV radiation, depending on weather conditions and species, can be harmful as well as beneficial to many species. Moderate levels of UV-A (315-400nm) can enhance photosynthesis of green, brown and red algae, while UV-B (280-315nm) mainly show inhibitory impacts. Although little has been documented on the combined effects of elevated CO2, temperature or heatwaves with UV radiation, exposures to heatwaves during midday under high levels of UV radiation can be detrimental to most species, especially to their microscopic stages which are less tolerant of climate change induced stress. In parallel, reduced availability of dissolved O2 in coastal water along with eutrophication might favour the macroalgae's carboxylation process by suppressing their oxygenation or photorespiration. In this review, we analyse effects of climate change-relevant drivers individually and/or jointly on different macroalgal groups and different life cycle stages based on the literatures surveyed, and provide perspectives for future studies.

Combined effects of elevated CO2, N fertilizer and water deficit stress on diazotrophic community in sub-humid tropical paddy soil

Elevated carbon dioxide (eCO2), higher dose of recommended nitrogen (HDN), and water deficit stress (WDS) are three important factors which influence individually on diazotrophic community in paddy soil, thereby affecting crop yield and its nitrogen use efficiency. However, the combined effects of eCO2, HDN, and WDS on soil diazotrophic community remains inadequate particularly in rice. Hence, the present study was conducted in CO2-maintained open-top chamber to assess the diazotrophic community under combined influence of eCO2 (550 ± 20 μmol mol−1 as compared to ambient CO2i.e. 400 ± 10 μmol mol−1) and HDN (120 kg N ha−1, 50% higher than recommended dose of N for rice i.e. 80 kg N ha−1, in sub-humid tropical region of eastern India) with and without WDS (−60 kPa) at two growth stages of rice (tillering, TI and panicle initiation, PI) and correlated with soil carbon (C) pools and enzyme activities. The results indicated that soil organic C, readily mineralizable C, microbial biomass C, acid and alkaline phosphatase activities were significantly (p < 0.05) increased under combined influence of eCO2 and HDN at both TI and PI stages of rice without WDS. The results also showed that abundance of nifH varied from ambient CO2 (aCO2) to eCO2 and found higher in aCO2 under recommended dose of nitrogen (RDN) without WDS, whereas under eCO2, nifH copy number was found higher under HDN at both TI and PI stages of rice without WDS. Biplot analysis revealed that abundance of nifH and nitrifiers were highly correlated under aCO2 coupled with RDN without WDS. Illumina MiSeq®-based targeted nifH metagenome showed that eCO2 encouraged the relative abundance of Proteobacteria and Cyanobacteria, whereas suppressed the other diazotrophic phyla like Actinobacteria, Firmicutes, and Chlorobi, but the reverse trend was observed in HDN treatments. Heatmap analysis revealed a unique differentiation of Rhizobiales and Pseudomonadales under eCO2 coupled with RDN without WDS. Moreover, three-way interactions of eCO2, HDN, and WDS also showed significant (p < 0.05) difference of soil C pools and enzymatic activities at both growth stages of rice. Overall, the present study showed that diazotrophic community in paddy soil was significantly (p < 0.05) altered by the additive effects of eCO2, HDN, and WDS.

Subtle bacterioplankton community responses to elevated CO2 and warming in the oligotrophic South Pacific gyre.

Bacterioplankton play a critical role in primary production, carbon cycling, and nutrient cycling in the oligotrophic ocean. To investigate the effect of elevated CO2 and warming on the composition and function of bacterioplankton communities in oligotrophic waters, we performed two trace-metal clean deck board incubation experiments during the New Zealand GEOTRACES transect of the South Pacific gyre (SPG). High-throughput amplicon sequencing of the 16S rRNA gene revealed that bacterioplankton community composition was distinct between the fringe and ultra-oligotrophic centre of the SPG and changed consistently in response to elevated CO2 at the ultra-oligotrophic centre but not at the mesotrophic fringe of the SPG. The combined effects of elevated CO2 and warming resulted in a high degree of heterogeneity between replicate communities. Community-level protein synthesis rates (3 H-Leucine incorporation) and bacterioplankton abundance were not affected by elevated CO2 alone or in combination with warming at the fringe or ultra-oligotrophic centre of the SPG. These data suggest bacterioplankton community responses to elevated CO2 may be modulated by nutrient regimes in open ocean ecosystems and highlight the need for further investigation in expanding oligotrophic subtropical gyres.

Is Cassava (Manihot esculenta Crantz) a Climate “Smart” Crop? A Review in the Context of Bridging Future Food Demand Gap

Climate change and its impact on agriculture are one of the ongoing research areas, and the major task among agricultural managers is to meet the food demand in the future in the context of the production gap of major food grain crops. Literature analysis is carried out to understand the climate resilience of cassava, one of the major tuber crops and is considered to bridge the food demand gap in the near future. Systematic analysis of literature includes influence of changing environmental parameters such as temperature, solar radiation, photoperiod, air humidity, soil water deficit, salinity, elevated ozone and CO2, combined effects of elevated CO2 with temperature, water deficit and salinity to the growth and yield of cassava along with its resilience to biotic stresses and its climate suitability. Studies indicate cassava can tolerate a temperature level of up to 40 °C, and thereafter the rate of photosynthesis decreases. Cassava can be cultivated in regions with variations in solar radiation without much compromise in its yield in the context of global dimming of sunshine duration. The resilience to water stress and air humidity variations are adapted by reducing stomatal conductance without influencing the rate of photosynthesis. Cassava has also an inbuilt mechanism to cope with water scarcity by leaf drooping. Already established cassava can tolerate a salinity level of up to 150 mM and the younger ones can tolerate up to a level of 40 mM. Studies also indicate a strong positive influence of elevated CO2 of up to 700 ppm on the rate of photosynthesis and yield of cassava. Elevated CO2 enhances the resilience of cassava to water stress and salinity. Similarly, the combined effect of elevated CO2 and higher temperatures also increases the yield attributes of cassava. These all indicate the resilience of cassava to the changing climate and it ensures as an insurance crop as well as food security crop in the near future. Studies show its resilience to biotic stresses as well. Climate suitability studies also show its suitability in the present locations in the near future as well as its adaptation to other areas. However, the research gap is identified in areas of influence of elevated ozone on growth characteristics of cassava. This study also recommends identifying the extent of tolerance level of cassava to the influence of the combined effect of salinity and elevated CO2. Further, researchers need to concentrate on developing biotic as well as abiotic stress-tolerant genes in cassava varieties to increase its production irrespective of the changing climatic conditions.

Do elevated CO2 and temperature affect organic nitrogen fractions and enzyme activities in soil under rice crop?

A study was conducted to quantify the effect of elevated carbon dioxide (CO2) and temperature on soil organic nitrogen (N) fractions and enzyme activities in rice rhizosphere. Rice crop was grown inside the open top chambers in the ICAR-Indian Agricultural Research Institute. The N was applied in four different doses. Grain yield and aboveground N uptake by rice significantly reduced under elevated temperature. However, elevated CO2 along with elevated temperature was able to compensate this loss. Principal component analysis clearly indicated that microbial biomass carbon, microbial biomass N, amino acid N, total hydrolysable N, ammonia N and serine–threonine N contributed significantly to rice grain yield. Combined effect of elevated CO2 and elevated temperature decreased the total hydrolysable N, especially for lower N doses. The N-acetyl-glucosaminidase and leucine aminopeptidase enzyme activities were negatively correlated with the organic N pools. Higher activities of these enzymes under limited N supply may accelerate the decomposition of organic N in soil. When N was applied in super-optimal dose, plant N demand was met thereby causing lesser depletion of total hydrolysable N. Better nitrogen management will alleviate faster depletion of native soil N under future scenario of climate change and thus might cause N sequestration in soil.

Combined effect of elevated CO2 and temperature on growth, biomass and secondary metabolite of Hypericum perforatum L. in a western Himalayan region

Rising carbon dioxide [CO2] levels and air temperature influence overall growth and production pattern of crop plants, and thus they help in understanding the functional relationship between the environment and crop performance. The present experiment was conducted to study the simultaneous effect of elevated CO2 (550 ± 50 μmol mol−1) and air temperature (2.5 ± 0.5 °C above ambient) on Hypericum perforatum growth, biomass and carbon-based plant secondary metabolite concentrations at free air CO2 enrichment (FACE) and free air temperature increase (FATI) facilities of CSIR-Institute of Himalayan Bioresource Technology, Palampur, India during 2016-2017. Experiment was laid out in factorial CRD (completely randomized design) with five replications. Results showed that the growth and biomass were significantly affected by elevated CO2 and temperature. Plant height at 140 days after exposure (DAE) and 280 DAE was 8.49% and 6.90% higher in FACE + FATI as compared to ambient, respectively. Total dry biomass was 35.70% and 55.20% higher in FACE + FATI as compared to ambient at 140 DAE and 280 DAE, respectively. Application of vermicompost recorded 8.50% higher biomass and 20.65% higher hypericin content as compared to control. Hypericin concentration reduced significantly by 22.00% in elevated CO2, while under combined effect of elevated CO2 and temperature it reduced by 19.30% when compared to ambient. Phenological stages i.e. bud and flower formations were advanced by 4 and 5 days, respectively, under FACE as compared to ambient.

Modulation of Morpho-Physiological Responses in Populus deltoides by Elevated Carbon Dioxide and Temperature

AbstractRising atmospheric carbon dioxide (CO2) and temperature alter gene-expression arrays commensurate with physio-morphological changes, resulting in issues of adaptation, growth patterns, and productivity of terrestrial vegetation. An experiment was conducted to investigate the adaptive response of Populus deltoides clone G48 to the combined effect of elevated CO2 and temperature inside open-top chambers. The elevated CO2 and temperature acted as environmental cues to help express upregulated/downregulated genes involved in important metabolic pathways. As a result, P. deltoides exposed to the elevated CO2 and temperature developed adaptation to undo the effect by enhancing gaseous exchange, transpiration, and carbon assimilation and partitioning as observed on 180 days after treatment. The elevated conditions significantly enhanced stomatal density and size on adaxial/abaxial leaf surfaces, chlorophyll b that augmented photosynthesis, stomatal conductance, transpiration, and internal CO2, but decreased instantaneous and intrinsic water-use efficiency. These stimulated biomass accumulation in root, stem, and leaves. Hence, the elevated conditions of CO2 and temperature operate at the gene-expression level that acts pleiotropically for reinforcement of photosynthetic apparatus, morphological amendment for accelerated gaseous exchange, and finally growth and biomass improvement, supporting adaptive plasticity of clonal planting stock of the species to future climatic change and global warming.

Direct and indirect effects of elevated CO2 and nitrogen addition on soil microbial communities in the rhizosphere of Bothriochloa ischaemum

Elevated CO2 and nitrogen (N) addition both affect soil microbial communities, which significantly influence soil processes and plant growth. Here, we evaluated the combined effects of elevated CO2 and N addition on the soil–microbe–plant system of the Chinese Loess Plateau. A pot cultivation experiment with two CO2 treatment levels (400 and 800 μmol mol−1) and three N addition levels (0, 2.5, and 5 g N m−2 year−1) was conducted in climate-controlled chambers to evaluate the effects of elevated CO2 and N addition on microbial community structure in the rhizosphere of Bothriochloa ischaemum using phospholipid fatty acid (PLFA) profiles and associated soil and plant properties. Structural equation modeling (SEM) was used to identify the direct and indirect effects of the experimental treatments on the structure of microbial communities. Elevated CO2 and N addition both increased total and fungal PLFAs. N addition alone increased bacterial, Gram-positive, and Gram-negative PLFAs. However, elevated CO2 interacting with N addition had no significant effects on the microbial community. The SEM indicated that N addition directly affected the soil microbial community structure. Elevated CO2 and N addition both indirectly affected the microbial communities by affecting plant and soil variables. N addition exerted a stronger total effect than elevated CO2. The results highlighted the importance of comprehensively studying soil–microbe–plant systems to deeply reveal how characteristics of terrestrial ecosystems may respond under global change.

Combined effects of elevated carbon dioxide and temperature on phytoplankton-zooplankton link: A multi-influence of climate change on freshwater planktonic communities

It is essential to understand the combined effects of elevated CO2 and temperature on phytoplankton-zooplankton link when attempting to predict climate change responses of freshwater ecosystems. Phytoplankton species differ in stoichiometric and fatty acids composition, and this may result in phytoplankton-mediated effect on zooplankton at elevated CO2 and temperature. Beyond the isolated analysis of CO2 or temperature effect, few studies have assessed zooplankton growth under the phytoplankton-mediated effects of elevated CO2 and temperature. In this study, three algal species (green alga, diatom, cyanobacteria) were fed on zooplankton Daphnia magna, under the conditions of CO2 concentrations of ambient (390 ppm) and elevated (1000 ppm) levels and temperatures at 20, 25 and 30 °C. Elevated CO2 increased the algal biomass, while it reduced the phosphorus (P) and ω3 polyunsaturated fatty acids (ω3 PUFAs) to carbon (C) ratios. Elevated temperature decreased the P/C ratios in all algal cultures and ω3 PUFAs/C ratios in the diatom and the cyanobacteria cultures. Phytoplankton-mediated effect of elevated CO2 reduced the growth of zooplankton fed on the green and the mixed three algae culture. The stimulation of zooplankton fed on the diatom and the cyanobacteria by elevated temperature can be offset by decreasing food P and ω3 PUFAs contents. The combined effects of elevated CO2 and temperature on the growth of daphnids were mainly mediated by ω3 PUFAs/C ratios in the phytoplankton. Rising temperature as a combined direct and indirectly phytoplankton-mediated effect on zooplankton may be able to ameliorate the negative effects of elevated CO2. The results indicated that the combined effects of increased CO2 and temperature increased the fatty acid content of the green alga but not the other algae. This study highlighted that climate change with simultaneously increasing temperature and CO2 may entangle the carbon transfer in freshwater planktonic communities.

The Pressure Is On - Epiphyte Water-Relations Altered Under Elevated CO2.

Vascular epiphytes are a major biomass component of forests across the globe and they contribute to 9% of global vascular plant diversity. To improve our understanding of the whole-plant response of epiphytes to future climate change, we investigated for the first time both individual and combined effects of elevated CO2 (560 ppm) and light on the physiology and growth of two epiphyte species [Tillandsia brachycaulos (CAM) and Phlebodium aureum (C3)] grown for 272 days under controlled conditions. We found that under elevated CO2 the difference in water loss between the light (650 μmol m-2s-1) and shade (130 μmol m-2s-1) treatment was strongly reduced. Stomatal conductance (gs) decreased under elevated CO2, resulting in an approximate 40–45% reduction in water loss over a 24 h day/night period under high light and high CO2 conditions. Under lower light conditions water loss was reduced by approximately 20% for the CAM bromeliad under elevated CO2 and increased by approximately 126% for the C3 fern. Diurnal changes in leaf turgor and water loss rates correlated strong positively under ambient CO2 (400 ppm) and high light conditions. Future predicted increases in atmospheric CO2 are likely to alter plant water-relations in epiphytes, thus reducing the canopy cooling potential of epiphytes to future increases in temperature.

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.

Independent and combined effects of elevated CO2 and post-anthesis heat stress on protein quantity and quality in spring wheat grains.

Spring wheat plants were grown under two CO2 concentrations (380 and 550 μmol mol-1) and two temperature treatments (ambient and post-anthesis heat stress) to investigate the effects of elevated CO2 and heat stress on grain protein quality. Contents of protein components, glutenin macropolymers (GMP) and amino acids in grains decreased due to elevated CO2, while increased by high temperature. The combination of elevated CO2 and heat stress increased the contents of total protein and albumin, but decreased the contents of gliadin and glutenin, while the content and particle size distribution of GMP as well as the contents of amino acids were not significantly affected. Furthermore, we found that the content and particle size distribution of GMP were not only determined by the contents of proteins and high-molecular-weight glutenin subunits, but also related to the contents of amino acids containing disulfide bonds, which favor the formation of large insoluble polymers.