Differential effects of diurnal asymmetric and symmetric warming on yield and water utilization of soybean

Aims Global warming does not mean similar warmer temperatures between daytime and nighttime. Soybean (Glycine max) is a widely planted legume crop around the world and an important food crop in China. The aim of this study was to understand the responses of soybean growth and water utilization to future asymmetric warming, which would provide scientific reference for evaluating the adaptation of soybean to the future climate scenarios.Methods This experiment was carried out in artificial climate chambers, using the method of potted plants, under three temperature conditions; contrast (CON, 26 °C during the day and 16 °C during night), symmetric warming (ETs, elevated temperature of 3 °C both during the day and night), asymmetric warming (ETa, elevated temperature of 2 °C during the day and elevated temperature of 4 °C during night). We investigated the differential effects of diurnal asymmetric and symmetric warming on the yield and water consumption of soybean. Important findings The results revealed that, under the background of 26 °C during the day and 16 °C during night: 1) the effect of ETs on soybean yields showed no significant function that mainly benefit from the increase in the amount of biomass to ease negative influence of decrease in the harvest index. ETa reduced yields of soybean by 38.9% (p < 0.05) due to both significant decrease in harvest index and yield components (pod number per plant, grain number per pod and 100-grain weight). 2) ETs showed no obvious effect on the whole growing stage evapotranspiration (ET) of soybean, while ETa reduced the whole growing stage ET by 14.8% (p < 0.05). 3) The effect of the two warming pattern on water consumption of soybean were not significant. The difference in water consumption was mainly derived from the difference in transpiration (T). ETs and ETa reduced total transpiration by 10.7% (p < 0.05) and 26.1% (p < 0.05), respectively. In conclusion, our results suggest that ETs will underestimate the detrimental effects of real climate warming (ETa) on the growth and yield of soybean, and overestimate the effects on water consumption of soybean.     

昼夜不对称性与对称性升温对大豆产量和水分利用的影响

全球气候变暖并不是白天和夜间的平均变暖, 而是呈现一定的不对称性。大豆(Glycine max)是世界范围内种植较广泛的豆科作物, 也是中国重要的粮食作物。研究大豆的生长与水分利用对不对称性气候变暖的响应, 可为预测未来气候变暖情景下大豆的适应提供科学的参考依据。该实验在人工气候箱中采用盆栽方式进行, 设立对照(CON, 昼26 ℃夜16 ℃)、对称性升温(ETs, 昼夜均升高3 ℃)和不对称性升温(ETa, 昼升高2 ℃, 夜升高4 ℃)三个温度情景, 研究了大豆产量和水分利用对昼夜不对称性与对称性升温的差异性响应。结果表明: 在昼/夜26 ℃/16 ℃的背景下, 1) ETs对大豆产量影响不显著, 主要是因为生物量的增加缓解了收获指数下降对大豆的不利影响; ETa使大豆产量减少38.9%, 是由于大豆的收获指数和产量构成要素(荚数、粒数、百粒重)均显著降低。2) ETs对大豆全生育期蒸散量(ET)的影响不显著, ETa使大豆整个生育期ET减少14.8%。3)两种升温模式对大豆耗水量中蒸发量的影响都不显著, 耗水量的差异主要来自蒸腾量的差异, 其中ETs和ETa分别使大豆全生育期蒸腾量降低10.7%和26.1%。综上所述, 只针对ETs进行研究, 而没有对ETa进行研究的实验会低估真正的气候变暖情景(ETa)对大豆生长和产量的不利影响, 高估其对大豆耗水量的影响。     

Changes in the microbial community structure of bacteria,archaea and fungi in response to elevated CO2 and warming in an Australian native grassland soil

The microbial community structure of bacteria, archaea and fungi is described in an Australian native grassland soil after more than 5 years exposure to different atmospheric CO₂ concentrations ([CO₂]) (ambient, + 550 ppm) and temperatures (ambient, + 2°C) under different plant functional types (C ₃ and C ₄ grasses) and at two soil depths (0–5 cm and 5–10 cm). Archaeal community diversity was influenced by elevated [CO₂], while under warming archaeal 16S rRNA gene copy numbers increased for C ₄ plant Themeda triandra and decreased for the C ₃ plant community (P < 0.05). Fungal community diversity resulted in three groups based upon elevated [CO₂], elevated [CO₂] plus warming and ambient [CO₂]. Overall bacterial community diversity was influenced primarily by depth. Specific bacterial taxa changed in richness and relative abundance in response to climate change factors when assessed by a high‐resolution 16S rRNA microarray (PhyloChip). Operational taxonomic unit signal intensities increased under elevated [CO₂] for both Firmicutes and Bacteroidetes, and increased under warming for Actinobacteria and Alphaproteobacteria. For the interaction of elevated [CO₂] and warming there were 103 significant operational taxonomic units (P < 0.01) representing 15 phyla and 30 classes. The majority of these operational taxonomic units increased in abundance for elevated [CO₂] plus warming plots, while abundance declined in warmed or elevated [CO₂] plots. Bacterial abundance (16S rRNA gene copy number) was significantly different for the interaction of elevated [CO₂] and depth (P < 0.05) with decreased abundance under elevated [CO₂] at 5–10 cm, and for Firmicutes under elevated [CO₂] (P < 0.05). Bacteria, archaea and fungi in soil responded differently to elevated [CO₂], warming and their interaction. Taxa identified as significantly climate‐responsive could show differing trends in the direction of response (‘+’ or ‘?’) under elevated CO₂ or warming, which could then not be used to predict their interactive effects supporting the need to investigate interactive effects for climate change. The approach of focusing on specific taxonomic groups provides greater potential for understanding complex microbial community changes in ecosystems under climate change.     

Response of the floating aquatic fern <Emphasis Type="Italic">Azolla filiculoides</Emphasis> to elevated CO<Subscript>2</Subscript>, temperature,and phosphorus levels

Azolla filiculoides is a floating aquatic fern growing in tropical and temperate freshwater ecosystems. As A. filiculoides has symbiotic nitrogen-fixing cyanobacteria (Anabaena azollae) within its leaf cavities, it is cultivated in rice paddies to improve N availability and suppress other wetland weeds. To understand how C assimilation and N accumulation in A. filiculoides respond to elevated atmospheric carbon dioxide concentration (CO₂) in combination with P addition and higher temperatures, we conducted pot experiments during the summer of 2007 and 2008. In 2007, we grew A. filiculoides in pots at two treatment levels of added P fertilizer and at two levels of [CO₂] (380 ppm for ambient and 680 ppm for elevated [CO₂]) in controlled-environment chambers. In 2008, we grew A. filiculoides in four controlled-environment chambers at two [CO₂] levels and two temperature levels (34/26°C (day/night) and 29/21°C). We found that biomass and C assimilation by A. filiculoides were significantly increased by elevated [CO₂], temperature, and P level (all P < 0.01), with a significant interaction between elevated [CO₂] and added P (P < 0.01). Tissue N content was decreased by elevated [CO₂] and increased by higher temperature and P level (all P < 0.01). The acetylene reduction assay showed that the N-fixation activity of A. filiculoides was not significantly different under ambient and elevated [CO₂] but was significantly stimulated by P addition. N-fixation activity decreased at higher temperatures (34/26°C), indicating that 29/21°C was more suitable for A. azollae growth. Therefore, we conclude that the N accumulation potential of A. filiculoides under future climate warming depends primarily on the temperature change and P availability, and C assimilation should be increased by elevated [CO₂].     

Development of gypsy moth larvae feeding on red maple saplings at elevated CO<Subscript>2</Subscript> and temperature

Predicted increases in atmospheric CO₂ and global mean temperature may alter important plant-insect associations due to the direct effects of temperature on insect development and the indirect effects of elevated temperature and CO₂ enrichment on phytochemicals important for insect success. We investigated the effects of CO₂ and temperature on the interaction between gypsy moth (Lymantria dispar L.) larvae and red maple (Acer rubrum L.) saplings by bagging first instar larvae within open-top chambers at four CO₂/temperature treatments: (1) ambient temperature, ambient CO₂, (2) ambient temperature, elevated CO₂ (+300 l l^-1 CO₂), (3) elevated temperature (+3.5°C), ambient CO₂, and (4) elevated temperature, elevated CO₂. Larvae were reared to pupation and leaf samples taken biweekly to determine levels of total N, water, non-structural carbohydrates, and an estimate of defensive phenolic compounds in three age classes of foliage: (1) immature, (2) mid-mature and (3) mature. Elevated growth temperature marginally reduced (P <0.1) leaf N and significantly reduced (P <0.05) leaf water across CO₂ treatments in mature leaves, whereas leaves grown at elevated CO₂ concentration had a significant decrease in leaf N and a significant increase in the ratio of starch:N and total non-structural carbohydrates:N. Leaf N and water decreased and starch:N and total non-structural carbohydrates:N ratios increased as leaves aged. Phenolics were unaffected by CO₂ or temperature treatment. There were no interactive effects of CO₂ and temperature on any phytochemical measure. Gypsy moth larvae reached pupation earlier at the elevated temperature (female =8 days, P <0.07; male =7.5 days, P <0.03), whereas mortality and pupal fresh weight of insects were unrelated to either CO₂, temperature or their interaction. Our data show that CO₂ or temperature-induced alterations in leaf constituents had no effect on insect performance; instead, the long-term exposure to a 3.5°C increase in temperature shortened insect development but had no effect on pupal weight. It appears that in some tree-herbivorous insect systems the direct effects of an increased global mean temperature may have greater consequences for altering plant-insect interactions than the indirect effects of an increased temperature or CO₂ concentration on leaf constituents.     

Response of soil biota to elevated atmospheric CO2 in poplar model systems

We tested the hypotheses that increased belowground allocation of carbon by hybrid poplar saplings grown under elevated atmospheric CO₂ would increase mass or turnover of soil biota in bulk but not in rhizosphere soil. Hybrid poplar saplings (Populus×euramericana cv. Eugenei) were grown for 5 months in open-bottom root boxes at the University of Michigan Biological Station in northern, lower Michigan. The experimental design was a randomized-block design with factorial combinations of high or low soil N and ambient (34 Pa) or elevated (69 Pa) CO₂ in five blocks. Rhizosphere microbial biomass carbon was 1.7 times greater in high-than in low-N soil, and did not respond to elevated CO₂. The density of protozoa did not respond to soil N but increased marginally (P < 0.06) under elevated CO₂. Only in high-N soil did arbuscular mycorrhizal fungi and microarthropods respond to CO₂. In high-N soil, arbuscular mycorrhizal root mass was twice as great, and extramatrical hyphae were 11% longer in elevated than in ambient CO₂ treatments. Microarthropod density and activity were determined in situ using minirhizotrons. Microarthropod density did not change in response to elevated CO₂, but in high-N soil, microarthropods were more strongly associated with fine roots under elevated than ambient treatments. Overall, in contrast to the hypotheses, the strongest response to elevated atmospheric CO₂ was in the rhizosphere where (1) unchanged microbial biomass and greater numbers of protozoa (P < 0.06) suggested faster bacterial turnover, (2) arbuscular mycorrhizal root length increased, and (3) the number of microarthropods observed on fine roots rose. Received: 18 March 1997 / Accepted: 5 August 1997     

Contrasting acclimation abilities of two dominant boreal conifers to elevated CO2 and temperature

High latitude forests will experience large changes in temperature and CO₂ concentrations this century. We evaluated the effects of future climate conditions on 2 dominant boreal tree species, Pinus sylvestris L. and Picea abies (L.) H. Karst, exposing seedlings to 3 seasons of ambient (430 ppm) or elevated CO₂ (750 ppm) and ambient temperatures, a + 4 °C warming or a + 8 °C warming. Pinus sylvestris responded positively to warming: seedlings developed a larger canopy, maintained high net CO₂ assimilation rates (A_net), and acclimated dark respiration (R_dark). In contrast, carbon fluxes in Picea abies were negatively impacted by warming: maximum rates of A_net decreased, electron transport was redirected to alternative electron acceptors, and thermal acclimation of R_dark was weak. Elevated CO₂ tended to exacerbate these effects in warm‐grown Picea abies, and by the end of the experiment Picea abies from the +8 °C, high CO₂ treatment produced fewer buds than they had 3 years earlier. Treatments had little effect on leaf and wood anatomy. Our results highlight that species within the same plant functional type may show opposite responses to warming and imply that Picea abies may be particularly vulnerable to warming due to low plasticity in photosynthetic and respiratory metabolism.     

Direct emission of methane and nitrous oxide from switchgrass and corn stover: implications for large-scale biomass storage

Little is known about the contributions of biomass feedstock storage to the net greenhouse gas emissions from cellulosic biofuels. Direct emissions of methane and nitrous oxide during decomposition in storage may contribute substantially to the global warming potential of biofuels. In this study, laboratory-scale bales of switchgrass and corn stover were stored under a range of moisture (13.0–32.9%) and temperature (5–35 °C) conditions and monitored for O₂ consumption and CO₂, CH₄, and N₂O production over 8 weeks. Gas concentrations and emissions rates were highly variable within and between experimental groups. Stover bales produced higher CO₂ concentrations (P = 0.0002) and lower O₂ (P < 0.0001) during storage than switchgrass bales. Methane concentrations (1.8–2100 ppm) were inversely correlated with bale moisture (P < 0.05), with emissions rates ranging from 4.4–914.9 μg kg⁻¹ DM day⁻¹. Nitrous oxide concentrations ranged from 0 to 31 ppm, and emissions from switchgrass bales inversely correlated with temperature and moisture (P < 0.0001). Net global warming potential from each treatment (0–2.4 gCO₂e kg⁻¹ DM) suggests that direct emission of methane and nitrous oxide from aerobically stored feedstocks have a small effect on net global warming potential of cellulosic biofuels.     

Large‐scale variations in the vegetation growing season and annual cycle of atmospheric CO2 at high northern latitudes from 1950 to 2011

We combine satellite and ground observations during 1950–2011 to study the long‐term links between multiple climate (air temperature and cryospheric dynamics) and vegetation (greenness and atmospheric CO₂ concentrations) indicators of the growing season of northern ecosystems (>45°N) and their connection with the carbon cycle. During the last three decades, the thermal potential growing season has lengthened by about 10.5 days (P < 0.01, 1982–2011), which is unprecedented in the context of the past 60 years. The overall lengthening has been stronger and more significant in Eurasia (12.6 days, P < 0.01) than North America (6.2 days, P > 0.05). The photosynthetic growing season has closely tracked the pace of warming and extension of the potential growing season in spring, but not in autumn when factors such as light and moisture limitation may constrain photosynthesis. The autumnal extension of the photosynthetic growing season since 1982 appears to be about half that of the thermal potential growing season, yielding a smaller lengthening of the photosynthetic growing season (6.7 days at the circumpolar scale, P < 0.01). Nevertheless, when integrated over the growing season, photosynthetic activity has closely followed the interannual variations and warming trend in cumulative growing season temperatures. This lengthening and intensification of the photosynthetic growing season, manifested principally over Eurasia rather than North America, is associated with a long‐term increase (22.2% since 1972, P < 0.01) in the amplitude of the CO₂ annual cycle at northern latitudes. The springtime extension of the photosynthetic and potential growing seasons has apparently stimulated earlier and stronger net CO₂ uptake by northern ecosystems, while the autumnal extension is associated with an earlier net release of CO₂ to the atmosphere. These contrasting responses may be critical in determining the impact of continued warming on northern terrestrial ecosystems and the carbon cycle.     

Impacts of elevated CO2 and temperature on soil respiration in warm temperate evergreen Quercus glauca stands: an open-top chamber experiment

We conducted an open-top chamber experiment for 3?years to examine the effect of elevated CO₂ and temperature on soil respiration in experimental stands of Quercus glauca, an evergreen tree species common in the warm temperate zone of Japan. Seedlings of Q. glauca were planted in open-top chambers and treated with factorial combinations of ambient and elevated (ambient?×?1.4, ambient?×?1.8) CO₂ concentrations and ambient and elevated (+3°C) air temperatures. Elevated CO₂ significantly increased the total soil respiration rate (P?<?0.001) and the soil respiration rate at 15°C (R ₁₅) (P?<?0.05) but had no significant effect on the temperature coefficient Q ₁₀. Although temperature significantly affected total soil respiration rate (P?<?0.05), neither the R ₁₅ nor the Q ₁₀ of total soil respiration was affected significantly by the air temperature increase. Annual soil respiration rate, estimated from R ₁₅, Q ₁₀, and soil temperature data, tended to increase with elevated CO₂ concentration. These results suggest that soil respiration rate in Japanese warm temperate broad-leaved forests dominated by Q. glauca is sensitive to elevated CO₂ and is likely to increase under future climatic conditions.     

Effects of Elevated CO2 and Temperature on Biomass Growth and Allocation in a Boreal Bioenergy Crop (Phalaris arundinacea L.) from Young and Old Cultivations

An auto-controlled climate system was used to study how a boreal bioenergy crop (reed canary grass, Phalaris arundinacea L., hereafter RCG) responded to a warming climate and elevated CO₂. Over one growing season (April–September of 2009), RCG from young and old cultivations (3 years [3-year] and 10 years [10-year]) was grown in closed chambers under ambient conditions (CON), elevated CO₂ (EC, approximately 700 μmol?mol^?1), elevated temperature (ET, ambient + approximately 3 °C) and elevated temperature and CO₂ (ETC). The treatments were replicated four times. Throughout the growing season, the above-ground (leaf and stem biomass) and below-ground biomasses were measured six times, representing various developmental stages (early stages: the first three stages, and late stages: the last three stages). Compared to the growth observed under CON, EC enhanced RCG biomass growth over the whole growing season (p?<?0.05), whereas ET increased RCG biomass growth in early stages but decreased growth in late stages, regardless of the cultivation age. However, the negative effect of ET later in the growing season was partially mitigated by CO₂ enrichment. Compared to CON plants, the final total biomass was 18 % higher for 3-year plants and 8 % higher for 10-year plants grown under EC. In comparison, for 3-year and 10-year plants, the biomass was 5 and 3 % lower under ET and 7 and 4 % greater under ETC, respectively. Under EC, the below-ground growth contributed more to the total biomass growth compared to the above-ground portion. The opposite situation was observed under ET and ETC. The climate-related changes in biomass growth were smaller in the old cultivation than in the young cultivation due to the lower net assimilation rate and lower specific leaf area in the old cultivation plants.     

Seed germination and seedling physiology of Larix kaempferi and Pinus densiflora in seedbeds with charcoal and elevated CO2

We investigated the effect of ectomycorrhizal colonization, charcoal and CO₂ levels on the germination of seeds of Larix kaempferi and Pinus densiflora, and also their subsequent physiological activity and growth. The seeds were sown in brown forest soil or brown forest soil mixed with charcoal, at ambient CO₂ (360 μmol mol⁻¹) or elevated CO₂ (720 μmol mol⁻¹), with or without ectomycorrhiza. The proportions of both conifer seeds that germinated in forest soil mixed with charcoal were significantly greater than for seeds sown in forest soil grown at each CO₂ level (P < 0.05; t-test). However, the ectomycorrhizal colonization rate of each species grown in brown forest soil mixed with charcoal was significantly lower than in forest soil at each CO₂ treatment [CO₂] (P < 0.01; t-test). The phosphorus concentrations in needles of each seedling colonized with ectomycorrhiza and grown in forest soil were greater than in nonectomycorrhizal seedlings at each CO₂ level, especially for L. kaempferi seedlings (P < 0.05; t-test), but the concentrations in seedlings grown in brown forest soil mixed with charcoal were not increased at any CO₂ level. Moreover, the maximum net photosynthetic rate of each seedling for light and CO₂ saturation (P _max) increased when the seedlings were grown with ectomycorrhiza at 720 μmol mol⁻¹ [CO₂]. Ectomycorrhizal colonization led to an increase in the stem diameter of each species grown in each soil treatment at each CO₂ level. However, charcoal slowed the initial growth of both species of seedling, constraining ectomycorrhizal development. These results indicate that charcoal strongly assists seed germination and physiological activity.     

Reduced diurnal temperature range does not change warming impacts on ecosystem carbon balance of Mediterranean grassland mesocosms

Daily minimum temperature (T_min) has increased faster than daily maximum temperature (T_max) in many parts of the world, leading to decreases in diurnal temperature range (DTR). Projections suggest that these trends are likely to continue in many regions, particularly in northern latitudes and in arid regions. Despite wide speculation that asymmetric warming has different impacts on plant and ecosystem production than equal‐night‐and‐day warming, there has been little direct comparison of these scenarios. Reduced DTR has also been widely misinterpreted as a result of night‐only warming, when in fact T_min occurs near dawn, indicating higher morning as well as night temperatures. We report on the first experiment to examine ecosystem‐scale impacts of faster increases in T_min than in T_max, using precise temperature controls to create realistic diurnal temperature profiles with gradual day–night temperature transitions and elevated early morning as well as night temperatures. Studying a constructed grassland ecosystem containing species native to Oregon, USA, we found that the ecosystem lost more carbon at elevated than ambient temperatures, but remained unaffected by the 3 °C difference in DTR between symmetric warming (constantly ambient + 3.5 °C) and asymmetric warming (dawn T_min = ambient + 5 °C, afternoon T_max = ambient + 2 °C). Reducing DTR had no apparent effect on photosynthesis, probably because temperatures were most different in the morning and late afternoon when light was low. Respiration was also similar in both warming treatments, because respiration temperature sensitivity was not sufficient to respond to the limited temperature differences between asymmetric and symmetric warming. We concluded that changes in daily mean temperatures, rather than changes in T_min/T_max, were sufficient for predicting ecosystem carbon fluxes in this reconstructed Mediterranean grassland system.     

Rising sea level,temperature, and precipitation impact plant and ecosystem responses to elevated CO2 on a Chesapeake Bay wetland: review of a 28‐year study

An ongoing field study of the effects of elevated atmospheric CO₂ on a brackish wetland on Chesapeake Bay, started in 1987, is unique as the longest continually running investigation of the effects of elevated CO₂ on an ecosystem. Since the beginning of the study, atmospheric CO₂ increased 18%, sea level rose 20 cm, and growing season temperature varied with approximately the same range as predicted for global warming in the 21st century. This review looks back at this study for clues about how the effects of rising sea level, temperature, and precipitation interact with high atmospheric CO₂ to alter the physiology of C3 and C4 photosynthetic species, carbon assimilation, evapotranspiration, plant and ecosystem nitrogen, and distribution of plant communities in this brackish wetland. Rising sea level caused a shift to higher elevations in the Scirpus olneyi C3 populations on the wetland, displacing the Spartina patens C4 populations. Elevated CO₂ stimulated carbon assimilation in the Scirpus C3 species measured by increased shoot and root density and biomass, net ecosystem production, dissolved organic and inorganic carbon, and methane production. But elevated CO₂ also decreased biomass of the grass, S. patens C4. The elevated CO₂ treatment reduced tissue nitrogen concentration in shoots, roots, and total canopy nitrogen, which was associated with reduced ecosystem respiration. Net ecosystem production was mediated by precipitation through soil salinity: high salinity reduced the CO₂ effect on net ecosystem production, which was zero in years of severe drought. The elevated CO₂ stimulation of shoot density in the Scirpus C3 species was sustained throughout the 28 years of the study. Results from this study suggest that rising CO₂ can add substantial amounts of carbon to ecosystems through stimulation of carbon assimilation, increased root exudates to supply nitrogen fixation, reduced dark respiration, and improved water and nitrogen use efficiency.     

Effects of ocean acidification increase embryonic sensitivity to thermal extremes in Atlantic cod,Gadus morhua

Thermal tolerance windows serve as a powerful tool for estimating the vulnerability of marine species and their life stages to increasing temperature means and extremes. However, it remains uncertain to which extent additional drivers, such as ocean acidification, modify organismal responses to temperature. This study investigated the effects of CO₂‐driven ocean acidification on embryonic thermal sensitivity and performance in Atlantic cod, Gadus morhua, from the Kattegat. Fertilized eggs were exposed to factorial combinations of two PCO₂ conditions (400 μatm vs. 1100 μatm) and five temperature treatments (0, 3, 6, 9 and 12 °C), which allow identifying both lower and upper thermal tolerance thresholds. We quantified hatching success, oxygen consumption (MO₂) and mitochondrial functioning of embryos as well as larval morphometrics at hatch and the abundance of acid–base‐relevant ionocytes on the yolk sac epithelium of newly hatched larvae. Hatching success was high under ambient spawning conditions (3–6 °C), but decreased towards both cold and warm temperature extremes. Elevated PCO₂ caused a significant decrease in hatching success, particularly at cold (3 and 0 °C) and warm (12 °C) temperatures. Warming imposed limitations to MO₂ and mitochondrial capacities. Elevated PCO₂ stimulated MO₂ at cold and intermediate temperatures, but exacerbated warming‐induced constraints on MO₂, indicating a synergistic interaction with temperature. Mitochondrial functioning was not affected by PCO₂. Increased MO₂ in response to elevated PCO₂ was paralleled by reduced larval size at hatch. Finally, ionocyte abundance decreased with increasing temperature, but did not differ between PCO₂ treatments. Our results demonstrate increased thermal sensitivity of cod embryos under future PCO₂ conditions and suggest that acclimation to elevated PCO₂ requires reallocation of limited resources at the expense of embryonic growth. We conclude that ocean acidification constrains the thermal performance window of embryos, which has important implication for the susceptibility of cod to projected climate change.     

Growth,loss, and vertical distribution of Pinus radiata fine roots growing at ambient and elevated CO2 concentration

Increased below-ground carbon allocation in forest ecosystems is a likely consequence of rising atmospheric CO₂ concentration. If this results in changes to fine root growth, turnover and distribution long-term soil carbon cycling and storage could be altered. Bi-weekly measurements were made to determine the dynamics and distribution of fine roots (< 1 mm diameter) for Pinus radiata trees growing at ambient (350 μmol mol^–1) and elevated (650 μmol mol^–1) CO₂ concentration in large open-top chambers. Measurements were made using minirhizotrons installed horizontally at depths of 0.1, 0.3, 0.5 and 0.9 m. During the first year, at a depth of 0.3 m, the increase in relative growth rate of roots occurred 6 weeks earlier in the elevated CO₂ treatment and the maximum rate was reached 10 weeks earlier than for trees in the ambient treatment. After 2 years, cumulative fine root growth (P_t) was 36% greater for trees growing at elevated CO₂ than at ambient CO₂ concentration, although this difference was not significant. A model of root growth driven by daily soil temperature accounted for between 43 and 99% of root growth variability. Total root loss (L_t) was 9% in the ambient and 14% in the elevated CO₂ treatment, although this difference was not significant. Root loss was greatest at 0.3 m. In the first year, 62% of fine roots grown between mid-summer and late-autumn disappeared within a year in the elevated CO₂ treatment, but only 18% in the ambient CO₂ treatment (P < 0.01). An exponential model relating L_t to time accounted for between 74 and 99% of the variability. Root cohort half-lives were 951 d for the ambient and 333 d for the elevated treatment. Root length density decreased exponentially with depth in both treatments, but relatively more fine roots grown in the elevated CO₂ treatment tended to occur deeper in the soil profile.     

Effects of elevated pCO2 on the metabolism of a temperate rhodolith Lithothamnion corallioides grown under different temperatures

Coralline algae are considered among the most sensitive species to near future ocean acidification. We tested the effects of elevated pCO₂ on the metabolism of the free‐living coralline alga Lithothamnion corallioides (“maerl”) and the interactions with changes in temperature. Specimens were collected in North Brittany (France) and grown for 3 months at pCO₂ of 380 (ambient pCO₂), 550, 750, and 1000 μatm (elevated pCO₂) and at successive temperatures of 10°C (ambient temperature in winter), 16°C (ambient temperature in summer), and 19°C (ambient temperature in summer +3°C). At each temperature, gross primary production, respiration (oxygen flux), and calcification (alkalinity flux) rates were assessed in the light and dark. Pigments were determined by HPLC. Chl a, carotene, and zeaxanthin were the three major pigments found in L. corallioides thalli. Elevated pCO₂ did not affect pigment content while temperature slightly decreased zeaxanthin and carotene content at 10°C. Gross production was not affected by temperature but was significantly affected by pCO₂ with an increase between 380 and 550 μatm. Light, dark, and diel (24 h) calcification rates strongly decreased with increasing pCO₂ regardless of the temperature. Although elevated pCO₂ only slightly affected gross production in L. corallioides, diel net calcification was reduced by up to 80% under the 1,000 μatm treatment. Our findings suggested that near future levels of CO₂ will have profound consequences for carbon and carbonate budgets in rhodolith beds and for the sustainability of these habitats.     

Down-regulation of Rubisco activity under combined increases of CO<Subscript>2</Subscript> and temperature minimized by changes in Rubisco k<Subscript>cat</Subscript> in wheat

Increases in growth temperature have been observed to affect photosynthesis differently under long-term exposure to ambient- and twice ambient-air CO₂ concentrations. This study investigates the causes of this interaction in wheat (Triticum aestivum L.) grown in the field over two consecutive years under temperature gradient chambers in ambient (370 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric CO₂ concentrations and at ambient or ambient +4°C temperatures, with either a low or a high nitrogen supply. The photosynthesis-internal CO₂ response curves and the activity, activation state, k_cat and amount of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) were measured, as well as the soluble protein concentration in flag leaves at ear emergence and 8–15 days after anthesis. A high nitrogen supply increased V_cmax, the Rubisco amount and activity and soluble protein contents, but did not significantly change the Rubisco k_cat. Both elevated CO₂ and above ambient temperatures had negative effects on V_cmax and Rubisco activity, but at elevated CO₂, an increase in temperature did not decrease V_cmax or Rubisco activity in relation to ambient temperature. The amounts of Rubisco and soluble protein decreased with elevated CO₂ and temperature. The negative impact of elevated CO₂ on Rubisco properties was somewhat counteracted at elevated temperatures by an increase in k_cat. This effect can diminish the detrimental effects on photosynthesis of combined increases of CO₂ and temperature.     

Elevated CO2 and temperature alter development and food utilization of Spodoptera litura fed on resistant soybean

Effects of elevated atmospheric CO₂ (elevated CO₂ vs. ambient CO₂) and temperature (+0.67–0.79°C vs. ambient temperature) on the developmental life cycle of Spodoptera litura and the food utilization of the fourth‐instar larvae fed on soybean (resistant cultivar Lamar vs. susceptible landrace JLNMH) grown in open‐top chambers were studied from 2013 to 2015. The results indicated that: (i) compared with ambient CO₂, elevated CO₂ significantly prolonged the duration of larva and pupa, and adult longevity; significantly decreased the pupation rate, pupal weight, fecundity, the relative growth rate (RGR), efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD); and increased the relative consumption rate (RCR) and approximate digestibility (AD). (ii) Compared with ambient temperature, elevated temperature significantly shortened the duration of larva and pupa; significantly decreased the pupal weight; and increased the RGR, RCR, ECD and ECI. (iii) Compared with the susceptible soybean accession JLNMH, the resistant soybean cultivar Lamar significantly prolonged the duration of larva and pupa; significantly decreased the pupation rate, pupal weight, adult longevity, fecundity and RGR, RCR and AD; and increased the indexes of ECD. (iv) At elevated temperature, S. litura fed on resistant vs. susceptible cultivars showed opposite trends in the RGR, RCR, AD, ECD and ECI. In addition, elevated temperature under elevated CO₂ significantly decreased the RGR (2014), ECD (2013 & 2014) and ECI (2013) and increased the AD (2013 & 2014) compared with other treatment combinations when S. litura fed on Lamar. Future climatic change of temperature and CO₂ concentration would likely affect growth and food utilization of S. litura, with increased food intake, but the reduced fecundity may compensate for the increased food consumption, resulting in no significant reduction in insect‐induced yield loss in soybean production. Nevertheless, use of insect resistant soybean cultivars will aid in ecological management of S. litura and reduce the insecticide load in soybean production.     

Increased temperature mitigates the effects of ocean acidification on the calcification of juvenile Pocillopora damicornis,but at a cost

This study tested the interactive effects of increased seawater temperature and CO₂ partial pressure (pCO₂) on the photochemistry, bleaching, and early growth of the reef coral Pocillopora damicornis. New recruits were maintained at ambient or high temperature (29 or 30.8 °C) and pCO₂ (~ 500 and ~ 1100 μatm) in a full-factorial experiment for 3 weeks. Neither a sharp decline in photochemical efficiency (Fv/Fm) nor evident bleaching was observed at high temperature and/or high pCO₂. Furthermore, elevated temperature greatly promoted lateral growth and calcification, while polyp budding exhibited temperature-dependent responses to pCO₂. High pCO₂ depressed calcification by 28% at ambient temperature, but did not impact calcification at 30.8 °C. Interestingly, elevated temperature in concert with high pCO₂ significantly retarded the budding process. These results suggest that increased temperature can mitigate the adverse effects of acidification on the calcification of juvenile P. damicornis, but at a substantial cost to asexual budding.